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Birder LA, Wolf-Johnston AS, Zabbarova I, Ikeda Y, Robertson AM, Cardozo R, Azari F, Kanai AJ, Kuchel GA, Jackson EK. Hypoxanthine Induces Signs of Bladder Aging With Voiding Dysfunction and Lower Urinary Tract Remodeling. J Gerontol A Biol Sci Med Sci 2024; 79:glad171. [PMID: 37463319 PMCID: PMC11083631 DOI: 10.1093/gerona/glad171] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2023] [Indexed: 07/20/2023] Open
Abstract
BACKGROUND Lower urinary tract syndrome (LUTS) is a group of urinary tract symptoms and signs that can include urinary incontinence. Advancing age is a major risk factor for LUTS; however, the underlying biochemical mechanisms of age-related LUTS remain unknown. Hypoxanthine (HX) is a purine metabolite associated with generation of tissue-damaging reactive oxygen species (ROS). This study tested the hypothesis that exposure of the adult bladder to HX-ROS over time damages key LUT elements, mimicking qualitatively some of the changes observed with aging. METHODS Adult 3-month-old female Fischer 344 rats were treated with vehicle or HX (10 mg/kg/day; 3 weeks) administered in drinking water. Targeted purine metabolomics and molecular approaches were used to assess purine metabolites and biomarkers for oxidative stress and cellular damage. Biomechanical approaches assessed LUT structure and measurements of LUT function (using custom-metabolic cages and cystometry) were also employed. RESULTS HX exposure increased biomarkers indicative of oxidative stress, pathophysiological ROS production, and depletion of cellular energy with declines in NAD+ levels. Moreover, HX treatment caused bladder remodeling and decreased the intercontraction interval and leak point pressure (surrogate measure to assess stress urinary incontinence). CONCLUSIONS These studies provide evidence that in adult rats chronic exposure to HX causes changes in voiding behavior and in bladder structure resembling alterations observed with aging. These results suggest that increased levels of uro-damaging HX were associated with ROS/oxidative stress-associated cellular damage, which may be central to age-associated development of LUTS, opening up potential opportunities for geroscience-guided interventions.
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Affiliation(s)
- Lori A Birder
- Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - Amanda S Wolf-Johnston
- Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - Irina Zabbarova
- Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - Youko Ikeda
- Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - Anne M Robertson
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Ricardo Cardozo
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Fatemeh Azari
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Anthony J Kanai
- Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - George A Kuchel
- UConn Center on Aging, University of Connecticut, Farmington, Connecticut, USA
| | - Edwin K Jackson
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
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2
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Tobe Y, Robertson AM, Ramezanpour M, Cebral JR, Watkins SC, Charbel FT, Amin-Hanjani S, Yu AK, Cheng BC, Woo HH. Comapping Cellular Content and Extracellular Matrix with Hemodynamics in Intact Arterial Tissues Using Scanning Immunofluorescent Multiphoton Microscopy. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2024; 30:342-358. [PMID: 38525887 PMCID: PMC11057816 DOI: 10.1093/mam/ozae025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2023] [Revised: 03/01/2024] [Accepted: 03/04/2024] [Indexed: 03/26/2024]
Abstract
Deviation of blood flow from an optimal range is known to be associated with the initiation and progression of vascular pathologies. Important open questions remain about how the abnormal flow drives specific wall changes in pathologies such as cerebral aneurysms where the flow is highly heterogeneous and complex. This knowledge gap precludes the clinical use of readily available flow data to predict outcomes and improve treatment of these diseases. As both flow and the pathological wall changes are spatially heterogeneous, a crucial requirement for progress in this area is a methodology for acquiring and comapping local vascular wall biology data with local hemodynamic data. Here, we developed an imaging pipeline to address this pressing need. A protocol that employs scanning multiphoton microscopy was developed to obtain three-dimensional (3D) datasets for smooth muscle actin, collagen, and elastin in intact vascular specimens. A cluster analysis was introduced to objectively categorize the smooth muscle cells (SMC) across the vascular specimen based on SMC actin density. Finally, direct quantitative comparison of local flow and wall biology in 3D intact specimens was achieved by comapping both heterogeneous SMC data and wall thickness to patient-specific hemodynamic results.
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Affiliation(s)
- Yasutaka Tobe
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA 15261, USA
| | - Anne M Robertson
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA 15261, USA
| | - Mehdi Ramezanpour
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA 15261, USA
| | - Juan R Cebral
- Department of Bioengineering, George Mason University, Fairfax, VA 22030, USA
| | - Simon C Watkins
- Department of Cell Biology, University of Pittsburgh, PA 15261, USA
| | - Fady T Charbel
- Department of Neurosurgery, University of Illinois at Chicago, Chicago, IL 60612, USA
| | - Sepideh Amin-Hanjani
- Department of Neurological Surgery, University Hospital Cleveland Medical Center, Cleveland, OH 44106, USA
| | - Alexander K Yu
- Department of Neurological Surgery, Allegheny Health Network, Pittsburgh, PA 15212, USA
| | - Boyle C Cheng
- Neuroscience and Orthopedic Institutes, Allegheny Health Network, Pittsburgh, PA 15212, USA
| | - Henry H Woo
- Department of Neurosurgery, Donald and Barbara Zucker School of Medicine at Hofstra Northwell, Manhasset, NY 11549, USA
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3
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Lee PY, Fryc G, Gnalian J, Wang B, Hua Y, Waxman S, Zhong F, Yang B, Sigal IA. Direct measurements of collagen fiber recruitment in the posterior pole of the eye. Acta Biomater 2024; 173:135-147. [PMID: 37967694 PMCID: PMC10843755 DOI: 10.1016/j.actbio.2023.11.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2023] [Revised: 11/07/2023] [Accepted: 11/09/2023] [Indexed: 11/17/2023]
Abstract
Collagen is the main load-bearing component of the peripapillary sclera (PPS) and lamina cribrosa (LC) in the eye. Whilst it has been shown that uncrimping and recruitment of the PPS and LC collagen fibers underlies the macro-scale nonlinear stiffening of both tissues with increased intraocular pressure (IOP), the uncrimping and recruitment as a function of local stretch have not been directly measured. This knowledge is crucial to understanding their functions in bearing loads and maintaining tissue integrity. In this project we measured local stretch-induced collagen fiber bundle uncrimping and recruitment curves of the PPS and LC. Thin coronal samples of PPS and LC of sheep eyes were mounted and stretched biaxially quasi-statically using a custom system. At each step, we imaged the PPS and LC with instant polarized light microscopy and quantified pixel-level (1.5 μm/pixel) collagen fiber orientations. We used digital image correlation to measure the local stretch and quantified collagen crimp by the circular standard deviation of fiber orientations, or waviness. Local stretch-recruitment curves of PPS and LC approximated sigmoid functions. PPS recruited more fibers than the LC at the low levels of stretch. At 10% stretch the curves crossed with 75% bundles recruited. The PPS had higher uncrimping rate and waviness remaining after recruitment than the LC: 0.9º vs. 0.6º and 3.1º vs. 2.7º. Altogether our findings support describing fiber recruitment of both PPS and LC with sigmoid curves, with the PPS recruiting faster and at lower stretch than the LC, consistent with a stiffer tissue. STATEMENT OF SIGNIFICANCE: Peripapillary sclera (PPS) and lamina cribrosa (LC) collagen recruitment behaviors are central to the nonlinear mechanical behavior of the posterior pole of the eye. How PPS and LC collagen fibers recruit under stretch is crucial to develop constitutive models of the tissues but remains unclear. We used image-based stretch testing to characterize PPS and LC collagen fiber bundle recruitment under local stretch. We found that fiber-level stretch-recruitment curves of PPS and LC approximated sigmoid functions. PPS recruited more fibers at a low stretch, but at 10% bundle stretch the two curves crossed with 75% bundles recruited. We also found that PPS and LC fibers had different uncrimping rates and non-zero waviness's when recruited.
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Affiliation(s)
- Po-Yi Lee
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA, USA
| | - Gosia Fryc
- Department of Chemistry, Dietrich School of Arts and Sciences, University of Pittsburgh, Pittsburgh, PA, USA
| | - John Gnalian
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Bingrui Wang
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Yi Hua
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA; Department of Biomedical Engineering, University of Mississippi, University, MS, USA; Department of Mechanical Engineering, University of Mississippi, University, MS, USA
| | - Susannah Waxman
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Fuqiang Zhong
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Bin Yang
- Department of Engineering, Rangos School of Health Sciences, Duquesne University, Pittsburgh, PA, USA
| | - Ian A Sigal
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA, USA.
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4
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Mohammadkhah M, Klinge S. Review paper: The importance of consideration of collagen cross-links in computational models of collagen-based tissues. J Mech Behav Biomed Mater 2023; 148:106203. [PMID: 37879165 DOI: 10.1016/j.jmbbm.2023.106203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2023] [Revised: 09/25/2023] [Accepted: 10/17/2023] [Indexed: 10/27/2023]
Abstract
Collagen as the main protein in Extra Cellular Matrix (ECM) is the main load-bearing component of fibrous tissues. Nanostructure and architecture of collagen fibrils play an important role in mechanical behavior of these tissues. Extensive experimental and theoretical studies have so far been performed to capture these properties, but none of the current models realistically represent the complexity of network mechanics because still less is known about the collagen's inner structure and its effect on the mechanical properties of tissues. The goal of this review article is to emphasize the significance of cross-links in computational modeling of different collagen-based tissues, and to reveal the need for continuum models to consider cross-links properties to better reflect the mechanical behavior observed in experiments. In addition, this study outlines the limitations of current investigations and provides potential suggestions for the future work.
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Affiliation(s)
- Melika Mohammadkhah
- Technische Universität Berlin, Institute of Mechanics, Chair of Structural Mechanics and Analysis, Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany.
| | - Sandra Klinge
- Technische Universität Berlin, Institute of Mechanics, Chair of Structural Mechanics and Analysis, Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany
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5
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Wang X, Carpenter HJ, Ghayesh MH, Kotousov A, Zander AC, Amabili M, Psaltis PJ. A review on the biomechanical behaviour of the aorta. J Mech Behav Biomed Mater 2023; 144:105922. [PMID: 37320894 DOI: 10.1016/j.jmbbm.2023.105922] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Revised: 05/14/2023] [Accepted: 05/20/2023] [Indexed: 06/17/2023]
Abstract
Large aortic aneurysm and acute and chronic aortic dissection are pathologies of the aorta requiring surgery. Recent advances in medical intervention have improved patient outcomes; however, a clear understanding of the mechanisms leading to aortic failure and, hence, a better understanding of failure risk, is still missing. Biomechanical analysis of the aorta could provide insights into the development and progression of aortic abnormalities, giving clinicians a powerful tool in risk stratification. The complexity of the aortic system presents significant challenges for a biomechanical study and requires various approaches to analyse the aorta. To address this, here we present a holistic review of the biomechanical studies of the aorta by categorising articles into four broad approaches, namely theoretical, in vivo, experimental and combined investigations. Experimental studies that focus on identifying mechanical properties of the aortic tissue are also included. By reviewing the literature and discussing drawbacks, limitations and future challenges in each area, we hope to present a more complete picture of the state-of-the-art of aortic biomechanics to stimulate research on critical topics. Combining experimental modalities and computational approaches could lead to more comprehensive results in risk prediction for the aortic system.
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Affiliation(s)
- Xiaochen Wang
- School of Electrical and Mechanical Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia.
| | - Harry J Carpenter
- School of Electrical and Mechanical Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Mergen H Ghayesh
- School of Electrical and Mechanical Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia.
| | - Andrei Kotousov
- School of Electrical and Mechanical Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Anthony C Zander
- School of Electrical and Mechanical Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Marco Amabili
- Department of Mechanical Engineering, McGill University, Montreal H3A 0C3, Canada
| | - Peter J Psaltis
- Adelaide Medical School, The University of Adelaide, Adelaide, South Australia 5005, Australia; Department of Cardiology, Central Adelaide Local Health Network, Adelaide, South Australia 5000, Australia; Vascular Research Centre, Heart Health Theme, South Australian Health & Medical Research Institute (SAHMRI), Adelaide, South Australia 5000, Australia
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6
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Lee PY, Fryc G, Gnalian J, Hua Y, Waxman S, Zhong F, Yang B, Sigal IA. Direct measurements of collagen fiber recruitment in the posterior pole of the eye. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.05.07.539784. [PMID: 37215028 PMCID: PMC10197604 DOI: 10.1101/2023.05.07.539784] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Collagen is the main load-bearing component of the peripapillary sclera (PPS) and lamina cribrosa (LC) in the eye. Whilst it has been shown that uncrimping and recruitment of the PPS and LC collagen fibers underlies the macro-scale nonlinear stiffening of both tissues with increased intraocular pressure (IOP), the uncrimping and recruitment as a function of local stretch have not been directly measured. This knowledge is crucial for the development of constitutive models associating micro and macro scales. In this project we measured local stretch-induced collagen fiber bundle uncrimping and recruitment curves of the PPS and LC. Thin coronal samples of PPS and LC of sheep eyes were mounted and stretched biaxially quasi-statically using a custom system. At each step, we imaged the PPS and LC with instant polarized light microscopy and quantified pixel-level (1.5 μm/pixel) collagen fiber orientations. We used digital image correlation to measure the local stretch and quantified collagen crimp by the circular standard deviation of fiber orientations, or waviness. Local stretch-recruitment curves of PPS and LC approximated sigmoid functions. PPS recruited more fibers than the LC at the low levels of stretch. At 10% stretch the curves crossed with 75% bundles recruited. The PPS had higher uncrimping rate and waviness remaining after recruitment than the LC: 0.9° vs. 0.6° and 3.1° vs. 2.7°. Altogether our findings support describing fiber recruitment of both PPS and LC with sigmoid curves, with the PPS recruiting faster and at lower stretch than the LC, consistent with a stiffer tissue.
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Affiliation(s)
- Po-Yi Lee
- Department of Ophthalmology, University of Pittsburgh School of Medicine
- Department of Bioengineering, Swanson School of Engineering
| | - Gosia Fryc
- Department of Chemistry, Dietrich School of Arts and Sciences University of Pittsburgh, Pittsburgh, PA
| | - John Gnalian
- Department of Ophthalmology, University of Pittsburgh School of Medicine
| | - Yi Hua
- Department of Ophthalmology, University of Pittsburgh School of Medicine
- Department of Biomedical Engineering, University of Mississippi, University, MS
- Department of Mechanical Engineering, University of Mississippi, University, MS
| | - Susannah Waxman
- Department of Ophthalmology, University of Pittsburgh School of Medicine
| | - Fuqiang Zhong
- Department of Ophthalmology, University of Pittsburgh School of Medicine
| | - Bin Yang
- Department of Engineering, Rangos School of Health Sciences, Duquesne University, Pittsburgh, PA
| | - Ian A Sigal
- Department of Ophthalmology, University of Pittsburgh School of Medicine
- Department of Bioengineering, Swanson School of Engineering
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7
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Foong TY, Hua Y, Amini R, Sigal IA. Who bears the load? IOP-induced collagen fiber recruitment over the corneoscleral shell. Exp Eye Res 2023; 230:109446. [PMID: 36935071 PMCID: PMC10133210 DOI: 10.1016/j.exer.2023.109446] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2022] [Revised: 02/25/2023] [Accepted: 03/16/2023] [Indexed: 03/19/2023]
Abstract
Collagen is the main load-bearing component of cornea and sclera. When stretched, both of these tissues exhibit a behavior known as collagen fiber recruitment. In recruitment, as the tissues stretch the constitutive collagen fibers lose their natural waviness, progressively straightening. Recruited, straight, fibers bear substantially more mechanical load than non-recruited, wavy, fibers. As such, the process of recruitment underlies the well-established nonlinear macroscopic behavior of the corneoscleral shell. Recruitment has an interesting implication: when recruitment is incomplete, only a fraction of the collagen fibers is actually contributing to bear the loads, with the rest remaining "in reserve". In other words, at a given intraocular pressure (IOP), it is possible that not all the collagen fibers of the cornea and sclera are actually contributing to bear the loads. To the best of our knowledge, the fraction of corneoscleral shell fibers recruited and contributing to bear the load of IOP has not been reported. Our goal was to obtain regionally-resolved estimates of the fraction of corneoscleral collagen fibers recruited and in reserve. We developed a fiber-based microstructural constitutive model that could account for collagen fiber undulations or crimp via their tortuosity. We used experimentally-measured collagen fiber crimp tortuosity distributions in human eyes to derive region-specific nonlinear hyperelastic mechanical properties. We then built a three-dimensional axisymmetric model of the globe, assigning region-specific mechanical properties and regional anisotropy. The model was used to simulate the IOP-induced shell deformation. The model-predicted tissue stretch was then used to quantify collagen recruitment within each shell region. The calculations showed that, at low IOPs, collagen fibers in the posterior equator were recruited the fastest, such that at a physiologic IOP of 15 mmHg, over 90% of fibers were recruited, compared with only a third in the cornea and the peripapillary sclera. The differences in recruitment between regions, in turn, mean that at a physiologic IOP the posterior equator had a fiber reserve of only 10%, whereas the cornea and peripapillary sclera had two thirds. At an elevated IOP of 50 mmHg, collagen fibers in the limbus and the anterior/posterior equator were almost fully recruited, compared with 90% in the cornea and the posterior sclera, and 70% in the peripapillary sclera and the equator. That even at such an elevated IOP not all the fibers were recruited suggests that there are likely other conditions that challenge the corneoscleral tissues even more than IOP. The fraction of fibers recruited may have other potential implications. For example, fibers that are not bearing loads may be more susceptible to enzymatic digestion or remodeling. Similarly, it may be possible to control tissue stiffness through the fraction of recruited fibers without the need to add or remove collagen.
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Affiliation(s)
- Tian Yong Foong
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States; Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States
| | - Yi Hua
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States; Department of Biomedical Engineering, University of Mississippi, MS, United States; Department of Mechanical Engineering, University of Mississippi, MS, United States
| | - Rouzbeh Amini
- Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA, United States; Department of Bioengineering, Northeastern University, Boston, MA, United States
| | - Ian A Sigal
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States; Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States; McGowan Institute for Regenerative Medicine, University of Pittsburgh Medical Center and University of Pittsburgh, Pittsburgh, PA, United States.
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8
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Jan NJ, Lee PY, Wallace J, Iasella M, Gogola A, Wang B, Sigal IA. Stretch-Induced Uncrimping of Equatorial Sclera Collagen Bundles. J Biomech Eng 2023; 145:054503. [PMID: 36459150 PMCID: PMC9791674 DOI: 10.1115/1.4056354] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Revised: 11/20/2022] [Accepted: 11/21/2022] [Indexed: 12/03/2022]
Abstract
Stretch-induced collagen uncrimping underlies the nonlinear mechanical behavior of the sclera according to what is often called the process of recruitment. We recently reported experimental measurements of sclera collagen crimp and pressure-induced uncrimping. Our studies, however, were cross-sectional, providing statistical descriptions of crimp with no information on the effects of stretch on specific collagen bundles. Data on bundle-specific uncrimping is necessary to better understand the effects of macroscale input on the collagen microscale and tissue failure. Our goal in this project was to measure bundle-specific stretch-induced collagen uncrimping of sclera. Three goat eyes were cryosectioned sagittally (30 μm). Samples of equatorial sclera were isolated, mounted to a custom uni-axial stretcher and imaged with polarized light microscopy at various levels of clamp-to-clamp stretch until failure. At each stretch level, local strain was measured using image tracking techniques. The level of collagen crimping was determined from the bundle waviness, defined as the circular standard deviation of fiber orientation along a bundle. Eye-specific recruitment curves were then computed using eye-specific waviness at maximum stretch before sample failure to define fibers as recruited. Nonlinear mixed effect models were used to determine the associations of waviness to local strain and recruitment to clamp-to-clamp stretch. Waviness decreased exponentially with local strain (p < 0.001), whereas bundle recruitment followed a sigmoidal curve with clamp-to-clamp stretch (p < 0.001). Individual bundle responses to stretch varied substantially, but recruitment curves were similar across sections and eyes. In conclusion, uni-axial stretch caused measurable bundle-specific uncrimping, with the sigmoidal recruitment pattern characteristic of fiber-reinforced soft tissues.
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Affiliation(s)
- Ning-Jiun Jan
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15213
| | - Po-Yi Lee
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15213
| | - Jacob Wallace
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15213
| | - Michael Iasella
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15213
| | - Alexandra Gogola
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213
| | - Bingrui Wang
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213
| | - Ian A. Sigal
- Department of Ophthalmology, Laboratory of Ocular Biomechanics, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15213
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9
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He X, Lu J. Modeling planar response of vascular tissues using quadratic functions of effective strain. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2023; 39:e3653. [PMID: 36164831 DOI: 10.1002/cnm.3653] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Revised: 05/13/2022] [Accepted: 09/24/2022] [Indexed: 05/12/2023]
Abstract
Simulation-based studies of the cardiovascular structure such as aorta have become increasingly popular for many biomedical problems such as predictions of aneurysm rupture. A critical step in these simulations is the development of constitutive models that accurately describe the tissue's mechanical behavior. In this work, we present a new constitutive model, which explicitly accounts for the gradual recruitment of collagen fibers. The recruitment is considered using an effective stretch, which is a continuum-scale kinematic variable measuring the uncrimped stretch of the tissue in an average sense. The strain energy of a fiber bundle is described by a quadratic function of the effective strain. Constitutive models formulated in this manner are applied to describe the responses of ascending thoracic aortic aneurysm and porcine thoracic aorta tissues. The heterogeneous properties of the ATAA tissue are extracted from bulge inflation test data, and then used in finite element analysis to simulate the inflation test. The descriptive and predictive capabilities are further assessed using planar testing data of porcine thoracic aortic tissues. It is found that the constitutive model can accurately describe the stress-strain relations. In particular, the finite element simulation replicates the displacement, strain, and stress distributions with excellent fidelity.
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Affiliation(s)
- Xuehuan He
- Department of Mechanical Engineering, The University of Iowa, Iowa City, Iowa, USA
| | - Jia Lu
- Department of Mechanical Engineering, The University of Iowa, Iowa City, Iowa, USA
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10
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Gasser TC, Miller C, Polzer S, Roy J. A quarter of a century biomechanical rupture risk assessment of abdominal aortic aneurysms. Achievements, clinical relevance, and ongoing developments. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2023; 39:e3587. [PMID: 35347895 DOI: 10.1002/cnm.3587] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2021] [Revised: 01/28/2022] [Accepted: 03/03/2022] [Indexed: 05/12/2023]
Abstract
Abdominal aortic aneurysm (AAA) disease, the local enlargement of the infrarenal aorta, is a serious condition that causes many deaths, especially in men exceeding 65 years of age. Over the past quarter of a century, computational biomechanical models have been developed towards the assessment of AAA risk of rupture, technology that is now on the verge of being integrated within the clinical decision-making process. The modeling of AAA requires a holistic understanding of the clinical problem, in order to set appropriate modeling assumptions and to draw sound conclusions from the simulation results. In this article we summarize and critically discuss the proposed modeling approaches and report the outcome of clinical validation studies for a number of biomechanics-based rupture risk indices. Whilst most of the aspects concerning computational mechanics have already been settled, it is the exploration of the failure properties of the AAA wall and the acquisition of robust input data for simulations that has the greatest potential for the further improvement of this technology.
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Affiliation(s)
- T Christian Gasser
- Department of Engineering Mechanics, KTH Royal Institute of Technology, Stockholm, Sweden
- Faculty of Health Sciences, University of Southern Denmark, Odense, Denmark
| | - Christopher Miller
- Department of Engineering Mechanics, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Stanislav Polzer
- Department of Applied Mechanics, VSB-Technical University of Ostrava, Ostrava-Poruba, Czech Republic
| | - Joy Roy
- Department of Molecular Medicine and Surgery, Karolinska Institutet, Stockholm, Sweden
- Department of Vascular Surgery, Karolinska University Hospital, Stockholm, Sweden
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11
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Sigaeva T, Zhang Y. A novel constitutive model considering the role of elastic lamellae' structural heterogeneity in homogenizing transmural stress distribution in arteries. J R Soc Interface 2023; 20:20220837. [PMID: 37042193 PMCID: PMC10091191 DOI: 10.1098/rsif.2022.0837] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2022] [Accepted: 03/21/2023] [Indexed: 04/13/2023] Open
Abstract
Understanding how the homeostatic stress state can be reached in arterial tissues can provide new insights into vascular physiology. Even though the function of maintaining homeostasis is often linked to the concentric layers of medial elastic lamellae, how the lamellae are capable of evenly distributing the stress transmurally remains to be understood. The recent microstructural study by Yu et al. (2018 J. R. Soc. Interface 15, 20180492) revealed that, circumferentially, lamellar layers closer to the lumen are wavier than the ones further away from it and, thus, experience more unfolding when subjected to blood pressure. Motivated by this peculiar finding, the current study, for the first time, proposes a novel approach to model elastic lamellae and such structural heterogeneity using the extensible worm-like chain model. When implemented into the material description of the conventional two-layer artery model, in which adventitial collagen is modelled using the inextensible worm-like chain model, it is demonstrated that structural heterogeneity in elastic lamellae plays an important role in dictating transmural stress distribution and, therefore, the homeostasis of the arterial wall.
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Affiliation(s)
- Taisiya Sigaeva
- Department of Systems Design Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1
| | - Yanhang Zhang
- Department of Mechanical Engineering, Boston University, Boston, MA 02215, USA
- Department of Biomedical Engineering, Boston University, Boston, MA 02215, USA
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12
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Cheng F, Watton PN, Pederzani G, Kurobe M, Takaoka EI, Chapple C, Birder L, Yoshimura N, Robertson AM. A constrained mixture-micturition-growth (CMMG) model of the urinary bladder: Application to partial bladder outlet obstruction (BOO). J Mech Behav Biomed Mater 2022; 134:105337. [PMID: 35863296 PMCID: PMC9835014 DOI: 10.1016/j.jmbbm.2022.105337] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2021] [Revised: 04/13/2022] [Accepted: 06/24/2022] [Indexed: 01/14/2023]
Abstract
We present a constrained mixture-micturition-growth (CMMG) model for the bladder. It simulates bladder mechanics, voiding function (micturition) and tissue adaptations in response to altered biomechanical conditions. The CMMG model is calibrated with both in vivo and in vitro data from healthy male rat urinary bladders (cystometry, bioimaging of wall structure, mechanical testing) and applied to simulate the growth and remodeling (G&R) response to partial bladder outlet obstruction (BOO). The bladder wall is represented as a multi-layered, anisotropic, nonlinear constrained mixture. A short time scale micturition component of the CMMG model accounts for the active and passive mechanics of voiding. Over a second, longer time scale, G&R algorithms for the evolution of both cellular and extracellular constituents act to maintain/restore bladder (homeostatic) functionality. The CMMG model is applied to a spherical membrane model of the BOO bladder utilizing temporal data from an experimental male rodent model to parameterize and then verify the model. Consistent with the experimental studies of BOO, the model predicts: an initial loss of voiding capacity followed by hypertrophy of SMC to restore voiding function; bladder enlargement; collagen remodeling to maintain its role as a protective sheath; and increased voiding duration with lower average flow rate. This CMMG model enables a mechanistic approach for investigating the bladder's structure-function relationship and its adaption in pathological conditions. While the approach is illustrated with a conceptual spherical bladder model, it provides the basis for application of the CMMG model to anatomical geometries. Such a mechanistic approach has promise as an in silico tool for the rational development of new surgical and pharmacological treatments for bladder diseases such as BOO.
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Affiliation(s)
- Fangzhou Cheng
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, United States
| | - Paul N Watton
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, United States; Department of Computer Science & Insigneo Institute for in silico Medicine, University of Sheffield, Sheffield, United Kingdom.
| | - Giulia Pederzani
- Department of Computer Science & Insigneo Institute for in silico Medicine, University of Sheffield, Sheffield, United Kingdom
| | - Masahiro Kurobe
- Department of Urology, University of Pittsburgh, Pittsburgh, United States
| | - Ei-Ichiro Takaoka
- Department of Urology, University of Pittsburgh, Pittsburgh, United States
| | - Chris Chapple
- Sheffield Teaching Hospitals NHS Foundation Trust, Sheffield, United Kingdom
| | - Lori Birder
- Sheffield Teaching Hospitals NHS Foundation Trust, Sheffield, United Kingdom; Department of Medicine, University of Pittsburgh, United States
| | - Naoki Yoshimura
- Department of Urology, University of Pittsburgh, Pittsburgh, United States
| | - Anne M Robertson
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, United States
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13
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Pineda-Castillo SA, Aparicio-Ruiz S, Burns MM, Laurence DW, Bradshaw E, Gu T, Holzapfel GA, Lee CH. Linking the region-specific tissue microstructure to the biaxial mechanical properties of the porcine left anterior descending artery. Acta Biomater 2022; 150:295-309. [PMID: 35905825 PMCID: PMC10230544 DOI: 10.1016/j.actbio.2022.07.036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Revised: 07/14/2022] [Accepted: 07/20/2022] [Indexed: 11/16/2022]
Abstract
Coronary atherosclerosis is the main cause of death worldwide. Advancing the understanding of coronary microstructure-based mechanics is fundamental for the development of therapeutic tools and surgical procedures. Although the passive biaxial properties of the coronary arteries have been extensively explored, their regional differences and the relationship between tissue microstructure and mechanics have not been fully characterized. In this study, we characterized the passive biaxial mechanical properties and microstructural properties of the proximal, medial, and distal regions of the porcine left anterior descending artery (LADA). We also attempted to relate the biaxial stress-stretch response of the LADA and its respective birefringent responses to the polarized light for obtaining information about the load-dependent microstructural variations. We found that the LADA extensibility is reduced in the proximal-to-distal direction and that the medial region exhibits more heterogeneous mechanical behavior than the other two regions. We have also observed highly dynamic microstructural behavior where fiber families realign themselves depending on loading. In addition, we found that the microstructure of the distal region exhibited highly aligned fibers along the longitudinal axis of the artery. To verify this microstructural feature, we imaged the LADA specimens with multi-photon microscopy and observed that the adventitia microstructure transitioned from a random fiber network in the proximal region to highly aligned fibers in the distal region. Our findings could offer new perspectives for understanding coronary mechanics and aid in the development of tissue-engineered vascular grafts, which are currently limited due to their mismatch with native tissue in terms of mechanical properties and microstructural features. STATEMENT OF SIGNIFICANCE: The tissue biomechanics of coronary arteries is fundamental for the development of revascularization techniques such as coronary artery bypass. These therapeutics require a deep understanding of arterial mechanics, microstructure, and mechanobiology to prevent graft failure and reoperation. The present study characterizes the unique regional mechanical and microstructural properties of the porcine left anterior descending artery using biaxial testing, polarized-light imaging, and confocal microscopy. This comprehensive characterization provides an improved understanding of the collagen/elastin architecture in response to mechanical loads using a region-specific approach. The unique tissue properties obtained from this study will provide guidance for the selection of anastomotic sites in coronary artery bypass grafting and for the design of tissue-engineered vascular grafts.
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Affiliation(s)
- Sergio A Pineda-Castillo
- Biomechanics and Biomaterials Design Lab, School of Aerospace and Mechanical Engineering, The University of Oklahoma, USA; Stephenson School of Biomedical Engineering, The University of Oklahoma, USA
| | - Santiago Aparicio-Ruiz
- Biomechanics and Biomaterials Design Lab, School of Aerospace and Mechanical Engineering, The University of Oklahoma, USA
| | - Madison M Burns
- Biomechanics and Biomaterials Design Lab, School of Aerospace and Mechanical Engineering, The University of Oklahoma, USA
| | - Devin W Laurence
- Biomechanics and Biomaterials Design Lab, School of Aerospace and Mechanical Engineering, The University of Oklahoma, USA
| | - Elizabeth Bradshaw
- Biomechanics and Biomaterials Design Lab, School of Aerospace and Mechanical Engineering, The University of Oklahoma, USA
| | - Tingting Gu
- Samuel Roberts Noble Microscopy Laboratory, The University of Oklahoma, USA
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Austria; Department of Structural Engineering, Norwegian University of Science and Technology, Norway
| | - Chung-Hao Lee
- Biomechanics and Biomaterials Design Lab, School of Aerospace and Mechanical Engineering, The University of Oklahoma, USA.
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14
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Linka K, Cavinato C, Humphrey JD, Cyron CJ. Predicting and understanding arterial elasticity from key microstructural features by bidirectional deep learning. Acta Biomater 2022; 147:63-72. [PMID: 35643194 DOI: 10.1016/j.actbio.2022.05.039] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2022] [Revised: 05/19/2022] [Accepted: 05/19/2022] [Indexed: 01/15/2023]
Abstract
Microstructural features and mechanical properties are closely related in all soft biological tissues. Both yet exhibit considerable inter-individual differences and are affected by factors such as aging and disease and its progression. Histological analysis, modern in situ imaging, and biomechanical testing have deepened our understanding of these complex interrelations, yet two key questions remain: (1) Given the specific microstructure, can one predict the macroscopic mechanical properties without mechanical testing? (2) Can one quantify individual contributions of the different microstructural features to the macroscopic mechanical properties in an automated, systematic and largely unbiased way? Here we propose a bidirectional deep learning architecture to address these two questions. Our architecture uses data from standard histological analyses, two-photon microscopy and biaxial biomechanical testing. Its capabilities are demonstrated by predicting with high accuracy (R2=0.92) the evolving mechanical properties of the murine aorta during maturation and aging. Moreover, our architecture reveals that the extracellular matrix composition and organization are the most prominent factors governing the macroscopic mechanical properties of the tissues studied herein. STATEMENT OF SIGNIFICANCE: .
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Affiliation(s)
- Kevin Linka
- Institute for Continuum and Material Mechanics, Hamburg University of Technology, Hamburg, Germany
| | - Cristina Cavinato
- Department of Biomedical Engineering, Yale University, New Haven, CT, USA
| | - Jay D Humphrey
- Department of Biomedical Engineering, Yale University, New Haven, CT, USA; Vascular Biology and Therapeutics Program, Yale School of Medicine, New Haven, CT, USA
| | - Christian J Cyron
- Institute for Continuum and Material Mechanics, Hamburg University of Technology, Hamburg, Germany; Institute of Material Systems Modeling, Helmholtz-Zentrum Hereon, Geesthacht, Germany.
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15
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Salinas SD, Farra YM, Amini Khoiy K, Houston J, Lee CH, Bellini C, Amini R. The role of elastin on the mechanical properties of the anterior leaflet in porcine tricuspid valves. PLoS One 2022; 17:e0267131. [PMID: 35560311 PMCID: PMC9106221 DOI: 10.1371/journal.pone.0267131] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Accepted: 04/02/2022] [Indexed: 11/19/2022] Open
Abstract
Elastin is present in the extracellular matrix (ECM) of connective tissues, and its mechanical properties are well documented. In Marfan syndrome, however, the inability to properly code for the protein fibrillin-1 prematurely leads to the degradation and loss of elastin fiber integrity in the ECM. In this study, the role of elastin in the ECM of the anterior leaflet of the tricuspid valve was investigated by examining the biomechanical behavior of porcine leaflets before and after the application of the enzyme elastase. Five loading protocols were applied to the leaflet specimens in two groups (elastase-treated and control samples). The mechanical response following elastase application yielded a significantly stiffer material in both the radial and circumferential directions. At a physiological level of stress (85 kPa), the elastase group had an average strain of 26.21% and 6.32% in the radial and circumferential directions, respectively, at baseline prior to elastase application. Following elastase treatment, the average strain was 5.28% and 0.97% in the radial and circumferential directions, respectively. No statistically significant change was found in the control group following sham treatment with phosphate-buffered saline (PBS). Two-photon microscopy images confirmed that after the removal of elastin, the collagen fibers displayed a loss of undulation. With a significant reduction in radial compliance, the ability to withstand physiological loads may be compromised. As such, an extracellular matrix that is structurally deficient in elastin may hinder normal tricuspid valve function.
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Affiliation(s)
- Samuel D. Salinas
- Department of Bioengineering, Northeastern University, Boston, MA, United States of America
- Department of Biomedical Engineering, The University of Akron, Akron, OH, United States of America
| | - Yasmeen M. Farra
- Department of Bioengineering, Northeastern University, Boston, MA, United States of America
| | - Keyvan Amini Khoiy
- Department of Biomedical Engineering, The University of Akron, Akron, OH, United States of America
| | - James Houston
- Department of Psychology, Middle Tennessee State University, Murfreesboro, TN, United States of America
| | - Chung-Hao Lee
- School of Aerospace and Mechanical Engineering, The University of Oklahoma, Norman, OK, United States of America
| | - Chiara Bellini
- Department of Biomedical Engineering, The University of Akron, Akron, OH, United States of America
| | - Rouzbeh Amini
- Department of Bioengineering, Northeastern University, Boston, MA, United States of America
- Department of Biomedical Engineering, The University of Akron, Akron, OH, United States of America
- Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA, United States of America
- * E-mail:
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16
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Tuttle TG, Lujan HL, Tykocki NR, DiCarlo SE, Roccabianca S. Remodeling of extracellular matrix in the urinary bladder of paraplegic rats results in increased compliance and delayed fiber recruitment 16 weeks after spinal cord injury. Acta Biomater 2022; 141:280-289. [PMID: 35032719 PMCID: PMC8898290 DOI: 10.1016/j.actbio.2022.01.015] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Revised: 12/17/2021] [Accepted: 01/07/2022] [Indexed: 01/21/2023]
Abstract
The ability of the urinary bladder to maintain low intravesical pressures while storing urine is key in ensuring proper organ function and highlights the key role that tissue mechanics plays in the lower urinary tract. Loss of supraspinal neuronal connections to the bladder after spinal cord injury can lead to remodeling of the structure of the bladder wall, which may alter its mechanical characteristics. In this study, we investigate if the morphology and mechanical properties of the bladder extracellular matrix are altered in rats 16 weeks after spinal cord injury as compared to animals who underwent sham surgery. We measured and quantified the changes in bladder geometry and mechanical behavior using histological analysis, tensile testing, and constitutive modeling. Our results suggest bladder compliance is increased in paraplegic animals 16 weeks post-injury. Furthermore, constitutive modeling showed that increased distensibility was driven by an increase in collagen fiber waviness, which altered the distribution of fiber recruitment during loading. STATEMENT OF SIGNIFICANCE: The ability of the urinary bladder to store urine under low pressure is key in ensuring proper organ function. This highlights the important role that mechanics plays in the lower urinary tract. Loss of control of neurologic connection to the bladder from spinal cord injury can lead to changes of the structure of the bladder wall, resulting in altered mechanical characteristics. We found that the bladder wall's microstructure in rats 16 weeks after spinal cord injury is more compliant than in healthy animals. This is significant since it is the longest time post-injury analyzed, to date. Understanding the extreme remodeling capabilities of the bladder in pathological conditions is key to inform new possible therapies.
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Affiliation(s)
- Tyler G Tuttle
- Michigan State University, Department of Mechanical Engineering, 428 S. Shaw Lane, Rm 2555, East Lansing, MI 48824, United States
| | - Heidi L Lujan
- Michigan State University, Department of Physiology, 567 Wilson Rd., Rm 2201, East Lansing, MI 48824, United States
| | - Nathan R Tykocki
- Michigan State University, Department of Pharmacology and Toxicology, 1355 Bogue St., B436 Life Science Building, East Lansing, MI 48824, United States
| | - Stephen E DiCarlo
- Michigan State University, Department of Physiology, 567 Wilson Rd., Rm 2201, East Lansing, MI 48824, United States
| | - Sara Roccabianca
- Michigan State University, Department of Mechanical Engineering, 428 S. Shaw Lane, Rm 2555, East Lansing, MI 48824, United States.
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17
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Experimental Investigation of the Anisotropic Mechanical Response of the Porcine Thoracic Aorta. Ann Biomed Eng 2022; 50:452-466. [PMID: 35226280 DOI: 10.1007/s10439-022-02931-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Accepted: 02/10/2022] [Indexed: 12/25/2022]
Abstract
Knowledge of the mechanical properties of blood vessels and determining appropriate constitutive relations are essential in developing methodologies for accurate prognosis of vascular diseases. We examine the directional variation of the mechanical properties of the porcine thoracic aorta by performing uniaxial extension tests on dumbbell-shaped specimens cut at five different orientations with respect to the circumferential direction of the aorta. Specimens in all the orientations considered exhibit a nonlinear constitutive response that is typical of collagenous soft tissues. Shear strain under uniaxial extension demonstrates clearly discernible anisotropy of the mechanical response of the porcine aorta, and samples oriented at 45[Formula: see text] and 60[Formula: see text] with respect to the circumferential direction show a peculiar crescent-shaped shear strain-nominal stretch response not displayed by axial and circumferential specimens. Failure stress indicates decreasing tensile strength of the porcine aortic wall from the circumferential direction to the longitudinal direction. Furthermore, we determine the material parameters for the four-fiber-family and Gasser-Holzapfel-Ogden models from the mechanical response data of the circumferential and longitudinal specimens. It is shown how the material parameters derived from the uniaxial tests on circumferential and longitudinal specimens are insufficient to characterize the response of off-axis specimens.
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18
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Computational and experimental comparison on the effects of flow-induced compression on the permeability of collagen gels. J Mech Behav Biomed Mater 2022; 128:105107. [DOI: 10.1016/j.jmbbm.2022.105107] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Revised: 01/14/2022] [Accepted: 01/29/2022] [Indexed: 11/23/2022]
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19
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Lee PY, Yang B, Hua Y, Waxman S, Zhu Z, Ji F, Sigal IA. Real-time imaging of optic nerve head collagen microstructure and biomechanics using instant polarized light microscopy. Exp Eye Res 2022; 217:108967. [PMID: 35114213 PMCID: PMC8957577 DOI: 10.1016/j.exer.2022.108967] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2021] [Revised: 11/04/2021] [Accepted: 01/25/2022] [Indexed: 01/09/2023]
Abstract
Current tools lack the temporal or spatial resolution necessary to image many important aspects of the architecture and dynamics of the optic nerve head (ONH). We evaluated the potential of instant polarized light microscopy (IPOL) to overcome these limitations by leveraging the ability to capture collagen fiber orientation and density in a single image. Coronal sections through the ONH of fresh normal sheep eyes were imaged using IPOL while they were stretched using custom uniaxial or biaxial micro-stretch devices. IPOL allows identifying ONH collagen architectural details, such as fiber interweaving and crimp, and has high temporal resolution, limited only by the frame rate of the camera. Local collagen fiber orientations and deformations were quantified using color analysis and image tracking techniques. We quantified stretch-induced collagen uncrimping of lamina cribrosa (LC) and peripapillary sclera (PPS), and changes in LC pore size (area) and shape (convexity and aspect ratio). The simultaneous high spatial and temporal resolutions of IPOL revealed complex ONH biomechanics: i) stretch-induced local deformation of the PPS was nonlinear and nonaffine. ii) under load the crimped collagen fibers in the PPS and LC straightened, without torsion and with only small rotations. iii) stretch-induced LC pore deformation was anisotropic and heterogeneous among pores. Overall, with stretch the pores were became larger, more convex, and more circular. We have demonstrated that IPOL reveals details of collagen morphology and mechanics under dynamic loading previously out of reach. IPOL can detect stretch-induced collagen uncrimping and other elements of the tissue nonlinear mechanical behavior. IPOL showed changes in pore morphology and collagen architecture that will help improve understanding of how LC tissue responds to load.
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Affiliation(s)
- Po-Yi Lee
- Department of Bioengineering, Swanson School of Engineering, United States; Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Bin Yang
- Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States; Department of Engineering, Rangos School of Health Sciences, Duquesne University, Pittsburgh, PA, United States
| | - Yi Hua
- Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Susannah Waxman
- Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Ziyi Zhu
- Department of Bioengineering, Swanson School of Engineering, United States; Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Fengting Ji
- Department of Bioengineering, Swanson School of Engineering, United States; Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Ian A Sigal
- Department of Bioengineering, Swanson School of Engineering, United States; Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States.
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20
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Tuttle TG, Morhardt DR, Poli AA, Park JM, Arruda EM, Roccabianca S. Investigation of Fiber-Driven Mechanical Behavior of Human and Porcine Bladder Tissue Tested Under Identical Conditions. J Biomech Eng 2021; 143:1111616. [PMID: 34159357 DOI: 10.1115/1.4051525] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Indexed: 11/08/2022]
Abstract
The urinary bladder is a highly dynamic organ that undergoes large deformations several times per day. Mechanical characteristics of the tissue are crucial in determining the function and dysfunction of the organ. Yet, literature reporting on the mechanical properties of human bladder tissue is scarce and, at times, contradictory. In this study, we focused on mechanically testing tissue from both human and pig bladders using identical protocols to validate the use of pigs as a model for the human bladder. Furthermore, we tested the effect of two treatments on tissue mechanical properties. Namely, elastase to digest elastin fibers, and oxybutynin to reduce smooth muscle cell spasticity. Additionally, mechanical properties based on the anatomical direction of testing were evaluated. We implemented two different material models to aid in the interpretation of the experimental results. We found that human tissue behaves similarly to pig tissue at high deformations (collagen-dominated behavior) while we detected differences between the species at low deformations (amorphous matrix-dominated behavior). Our results also suggest that elastin could play a role in determining the behavior of the fiber network. Finally, we confirmed the anisotropy of the tissue, which reached higher stresses in the transverse direction when compared to the longitudinal direction.
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Affiliation(s)
- Tyler G Tuttle
- Mechanical Engineering Department, Michigan State University, 474 S. Shaw Lane, East Lansing, MI 48824
| | - Duncan R Morhardt
- Department of Urology, Boston Children's Hospital, 300 Longwood Avenue, Boston, MA 02115
| | - Andrea A Poli
- Mechanical Engineering Department, University of Michigan, 2350 Hayward Street, Ann Arbor, MI 48109
| | - John M Park
- Department of Urology, Michigan Medicine, 1500 E. Medical Drive, Ann Arbor, MI 48019
| | - Ellen M Arruda
- Mechanical Engineering Department, University of Michigan, 2350 Hayward Street, Ann Arbor, MI 48109
| | - Sara Roccabianca
- Mechanical Engineering Department, Michigan State University, 474 S. Shaw Lane, East Lansing, MI 48824
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21
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Lu J, He X. Incorporating fiber recruitment in hyperelastic modeling of vascular tissues by means of kinematic average. Biomech Model Mechanobiol 2021; 20:1833-1850. [PMID: 34173928 DOI: 10.1007/s10237-021-01479-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2021] [Accepted: 06/08/2021] [Indexed: 12/26/2022]
Abstract
We present a framework for considering the gradual recruitment of collagen fibers in hyperelastic constitutive modeling. An effective stretch, which is a response variable representing the true stretch at the tissue-scale, is introduced. Properties of the effective stretch are discussed in detail. The effective stretch and strain invariants derived from it are used in selected hyperelastic constitutive models to describe the tissue response. This construction is investigated in conjunction with Holzapfel-Gasser-Ogden family strain energy functions. The ensuing models are validated against a large body of uniaxial and bi-axial stress-strain response data from human aortic aneurysm tissues. Both the descriptive and the predictive capabilities are examined. The former is evaluated by the quality of constitutive fitting, and the latter is assessed using finite element simulation. The models significantly improve the quality of fitting, and reproduce the experiment displacement, stress, and strain distributions with high fidelity in the finite element simulation.
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Affiliation(s)
- Jia Lu
- Department of Mechanical Engineering, and Iowa Technology Institute, The University of Iowa, Iowa City, IA, 52242, USA.
| | - Xuehuan He
- Department of Mechanical Engineering, and Iowa Technology Institute, The University of Iowa, Iowa City, IA, 52242, USA
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22
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Pybus HJ, Tatler AL, Edgar LT, O'Dea RD, Brook BS. Reduced biomechanical models for precision-cut lung-slice stretching experiments. J Math Biol 2021; 82:35. [PMID: 33721103 PMCID: PMC7960642 DOI: 10.1007/s00285-021-01578-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2020] [Revised: 08/25/2020] [Accepted: 02/14/2021] [Indexed: 01/25/2023]
Abstract
Precision-cut lung-slices (PCLS), in which viable airways embedded within lung parenchyma are stretched or induced to contract, are a widely used ex vivo assay to investigate bronchoconstriction and, more recently, mechanical activation of pro-remodelling cytokines in asthmatic airways. We develop a nonlinear fibre-reinforced biomechanical model accounting for smooth muscle contraction and extracellular matrix strain-stiffening. Through numerical simulation, we describe the stresses and contractile responses of an airway within a PCLS of finite thickness, exposing the importance of smooth muscle contraction on the local stress state within the airway. We then consider two simplifying limits of the model (a membrane representation and an asymptotic reduction in the thin-PCLS-limit), that permit analytical progress. Comparison against numerical solution of the full problem shows that the asymptotic reduction successfully captures the key elements of the full model behaviour. The more tractable reduced model that we develop is suitable to be employed in investigations to elucidate the time-dependent feedback mechanisms linking airway mechanics and cytokine activation in asthma.
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Affiliation(s)
- Hannah J Pybus
- School of Mathematical Sciences, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
| | - Amanda L Tatler
- Respiratory Medicine, NIHR Biomedical Research Centre, University of Nottingham, Nottingham, UK
| | - Lowell T Edgar
- Usher Institute of Population Health Sciences and Informatics, University of Edinburgh, Edinburgh, UK
| | - Reuben D O'Dea
- School of Mathematical Sciences, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
| | - Bindi S Brook
- School of Mathematical Sciences, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
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23
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Subramaniam DR, Gutmark E, Andersen N, Nielsen D, Mortensen K, Gravholt C, Backeljauw P, Gutmark-Little I. Influence of Material Model and Aortic Root Motion in Finite Element Analysis of Two Exemplary Cases of Proximal Aortic Dissection. J Biomech Eng 2021; 143:1086152. [PMID: 32793953 DOI: 10.1115/1.4048084] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2020] [Indexed: 01/25/2023]
Abstract
The risk of type-A dissection is increased in subjects with connective tissue disorders and dilatation of the proximal aorta. The location and extents of vessel wall tears in these patients could be potentially missed during prospective imaging studies. The objective of this study is to estimate the distribution of systolic wall stress in two exemplary cases of proximal dissection using finite element analysis (FEA) and evaluate the sensitivity of the distribution to the choice of anisotropic material model and root motion. FEA was performed for predissection aortas, without prior knowledge of the origin and extents of vessel wall tear. The stress distribution was evaluated along the wall tear in the postdissection aortas. The stress distribution was compared for the Fung and Holzapfel models with and without root motion. For the subject with spiral dissection, peak stress coincided with the origin of the tear in the sinotubular junction. For the case with root dissection, maximum stress was obtained at the distal end of the tear. The FEA predicted tear pressure was 20% higher for the subject with root dissection as compared to the case with spiral dissection. The predicted tear pressure was higher (9-11%) for root motions up to 10 mm. The Holzapfel model predicted a tear pressure that was lower (8-15%) than the Fung model. The FEA results showed that both material response and root motion could potentially influence the predicted dissection pressure of the proximal aorta at least for conditions tested in this study.
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Affiliation(s)
| | - Ephraim Gutmark
- Department of Aerospace Engineering and Engineering Mechanics, University of Cincinnati, Cincinnati, OH 45221-0070
| | - Niels Andersen
- Department of Cardiology, Aalborg University Hospital, Aalborg 9100, Denmark
| | - Dorte Nielsen
- Department of Cardiology, Aarhus University Hospital, Aarhus 8200, Denmark
| | - Kristian Mortensen
- Cardiorespiratory Unit, Great Ormond Street Hospital for Children, London WC1N 3JH, UK
| | - Claus Gravholt
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus 8200, Denmark
| | - Philippe Backeljauw
- Division of Endocrinology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229
| | - Iris Gutmark-Little
- Division of Endocrinology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229
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Sang C, Kallmes DF, Kadirvel R, Durka MJ, Ding YH, Dai D, Watkins SC, Robertson AM. Adaptive Remodeling in the Elastase-induced Rabbit Aneurysms. EXPERIMENTAL MECHANICS 2021; 61:263-283. [PMID: 33814553 PMCID: PMC8011419 DOI: 10.1007/s11340-020-00671-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2020] [Accepted: 09/29/2020] [Indexed: 05/11/2023]
Abstract
BACKGROUND Rupture of brain aneurysms is associated with high fatality and morbidity rates. Through remodeling of the collagen matrix, many aneurysms can remain unruptured for decades, despite an enlarging and evolving geometry. OBJECTIVE Our objective was to explore this adaptive remodeling for the first time in an elastase induced aneurysm model in rabbits. METHODS Saccular aneurysms were created in 22 New Zealand white rabbits and remodeling was assessed in tissue harvested 2, 4, 8 and 12 weeks after creation. RESULTS The intramural principal stress ratio doubled after aneurysm creation due to increased longitudinal loads, triggering a remodeling response. A distinct wall layer with multi-directional collagen fibers developed between the media and adventitia as early as 2 weeks, and in all cases by 4 weeks with an average thickness of 50.6 ± 14.3 μm. Collagen fibers in this layer were multi-directional (AI = 0.56 ± 0.15) with low tortuosity (1.08 ± 0.02) compared with adjacent circumferentially aligned medial fibers (AI = 0.78 ± 0.12) and highly tortuous adventitial fibers (1.22 ± 0.03). A second phase of remodeling replaced circumferentially aligned fibers in the inner media with longitudinal fibers. A structurally motivated constitutive model with both remodeling modes was introduced along with methodology for determining material parameters from mechanical testing and multiphoton imaging. CONCLUSIONS A new mechanism was identified by which aneurysm walls can rapidly adapt to changes in load, ensuring the structural integrity of the aneurysm until a slower process of medial reorganization occurs. The rabbit model can be used to evaluate therapies to increase aneurysm wall stability.
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Affiliation(s)
- C Sang
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, 3700 O'Hara Street, Pittsburgh, PA 15261
| | - D F Kallmes
- Department of Radiology, Mayo Clinic, Rochester, MN
| | - R Kadirvel
- Department of Radiology, Mayo Clinic, Rochester, MN
| | - M J Durka
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, 3700 O'Hara Street, Pittsburgh, PA 15261
| | - Y-H Ding
- Department of Radiology, Mayo Clinic, Rochester, MN
| | - D Dai
- Department of Radiology, Mayo Clinic, Rochester, MN
| | - S C Watkins
- Center for Biological Imaging, University of Pittsburgh, Pittsburgh, PA
| | - A M Robertson
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, 3700 O'Hara Street, Pittsburgh, PA 15261
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Fortunato RN, Robertson AM, Sang C, Duan X, Maiti S. Effect of macro-calcification on the failure mechanics of intracranial aneurysmal wall tissue. EXPERIMENTAL MECHANICS 2021; 61:5-18. [PMID: 33776069 PMCID: PMC7992055 DOI: 10.1007/s11340-020-00657-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2020] [Revised: 07/16/2020] [Accepted: 08/05/2020] [Indexed: 06/12/2023]
Abstract
BACKGROUND Calcification was recently found to be present in the majority of cerebral aneurysms, though how calcification and the presence or absence of co-localized lipid pools affect failure properties is still unknown. OBJECTIVE The primary objective is to quantify the biomechanical effect of a macro-calcification with surrounding Near-Calcification Region (NCR) of varying mechanical properties on tissue failure behavior. METHODS We utilized a structurally informed finite element model to simulate pre-failure and failure behavior of a human cerebral tissue specimen modeled as a composite containing a macro-calcification and surrounding NCR, embedded in a fiber matrix composite. Data from multiple imaging modalities was combined to quantify the collagen organization and calcification geometry. An idealized parametric model utilizing the calibrated model was used to explore the impact of NCR properties on tissue failure. RESULTS Compared to tissue without calcification, peak stress was reduced by 82% and 49% for low modulus (representing lipid pool) and high modulus (simulating increase in calcification size) of the NCR, respectively. Failure process strongly depended on NCR properties with lipid pools blunting the onset of complete failure. When the NCR was calcified, the sample was able to sustain larger overall stress, however the failure process was abrupt with nearly simultaneous failure of the loaded fibers. CONCLUSIONS Failure of calcified vascular tissue is strongly influenced by the ultrastructure in the vicinity of the calcification. Computational modeling of failure in fibrous soft tissues can be used to understand how pathological changes impact the tissue failure process, with potentially important clinical implications.
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Affiliation(s)
- R. N. Fortunato
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh Pittsburgh, USA
| | - A. M. Robertson
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh Pittsburgh, USA
- Department of Bioengineering, University of Pittsburgh Pittsburgh, USA
| | - C. Sang
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh Pittsburgh, USA
| | - X. Duan
- Intelligent Automation Group, PNC Bank, University of Pittsburgh Pittsburgh, USA
| | - S. Maiti
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh Pittsburgh, USA
- Department of Bioengineering, University of Pittsburgh Pittsburgh, USA
- Department of Chemical and Petroleum Engineering, University of Pittsburgh Pittsburgh, USA
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Fu J, Wang M, De Vlaminck I, Wang Y. Thick PCL Fibers Improving Host Remodeling of PGS-PCL Composite Grafts Implanted in Rat Common Carotid Arteries. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2020; 16:e2004133. [PMID: 33251720 DOI: 10.1002/smll.202004133] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2020] [Revised: 10/01/2020] [Indexed: 06/12/2023]
Abstract
Vasculopathy and the consequential ischemia are major medical challenges. Grafting is an effective treatment to vascular occlusion. However, autologous grafting, despite scarcity, is the only choice for small diameter blood vessels. Synthetic grafts can fill the gap if they can work satisfactorily in arterial circulation. Electrospun polycaprolactone (PCL) sheathed porous poly(glycerol sebacate) (PGS) vascular grafts have good performances in arterial circulation in abdominal aortas and carotid arteries in rats. However, a major issue associated with the graft remodeling in vivo is limited neo-tissue formation inside PCL sheaths. Small pores of PCL sheaths inhibit cell infiltration and migration. To increase porosity of PCL sheaths of PGS-PCL composite grafts, diameters of electrospun PCL fibers are increased. The thick PCL fibers encourage cell migration and elicit a higher degree of CD206+ cells. In addition, some of the CD206+ cells co-express vascular cell markers in the thick-fiber grafts. The thick-fiber grafts also show improved mechanical properties and a higher elastin and collagen content. The data demonstrate the feasibility of improving graft vascular remodeling by increasing PCL fiber diameters and the critical role of CD206+ cells during graft vascular remodeling.
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Affiliation(s)
- Jiayin Fu
- Department of Cardiology, the First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, 310003, China
| | - Michael Wang
- Nancy E. and Peter C. Meinig School of Biomedical Engineering, Cornell University, Ithaca, New York, 14853, USA
| | - Iwijn De Vlaminck
- Nancy E. and Peter C. Meinig School of Biomedical Engineering, Cornell University, Ithaca, New York, 14853, USA
| | - Yadong Wang
- Nancy E. and Peter C. Meinig School of Biomedical Engineering, Cornell University, Ithaca, New York, 14853, USA
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Teixeira FS, Neufeld E, Kuster N, Watton PN. Modeling intracranial aneurysm stability and growth: an integrative mechanobiological framework for clinical cases. Biomech Model Mechanobiol 2020; 19:2413-2431. [PMID: 32533497 PMCID: PMC7603456 DOI: 10.1007/s10237-020-01351-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2019] [Accepted: 05/12/2020] [Indexed: 11/03/2022]
Abstract
We present a novel patient-specific fluid-solid-growth framework to model the mechanobiological state of clinically detected intracranial aneurysms (IAs) and their evolution. The artery and IA sac are modeled as thick-walled, non-linear elastic fiber-reinforced composites. We represent the undulation distribution of collagen fibers: the adventitia of the healthy artery is modeled as a protective sheath whereas the aneurysm sac is modeled to bear load within physiological range of pressures. Initially, we assume the detected IA is stable and then consider two flow-related mechanisms to drive enlargement: (1) low wall shear stress; (2) dysfunctional endothelium which is associated with regions of high oscillatory flow. Localized collagen degradation and remodelling gives rise to formation of secondary blebs on the aneurysm dome. Restabilization of blebs is achieved by remodelling of the homeostatic collagen fiber stretch distribution. This integrative mechanobiological modelling workflow provides a step towards a personalized risk-assessment and treatment of clinically detected IAs.
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Affiliation(s)
| | - Esra Neufeld
- IT’IS Foundation & ETH Zürich, Zürich, Switzerland
| | - Niels Kuster
- IT’IS Foundation & ETH Zürich, Zürich, Switzerland
| | - Paul N. Watton
- Department of Computer Science, Insigneo Institute for in silico Medicine, University of Sheffield, Sheffield, UK
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, USA
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Birder LA, Wolf-Johnston A, Wein AJ, Cheng F, Grove-Sullivan M, Kanai AJ, Watson AM, Stoltz D, Watkins SC, Robertson AM, Newman D, Dmochowski RR, Jackson EK. Purine nucleoside phosphorylase inhibition ameliorates age-associated lower urinary tract dysfunctions. JCI Insight 2020; 5:140109. [PMID: 32910805 PMCID: PMC7605521 DOI: 10.1172/jci.insight.140109] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2020] [Accepted: 09/04/2020] [Indexed: 12/29/2022] Open
Abstract
In the aging population, lower urinary tract (LUT) dysfunction is common and often leads to storage and voiding difficulties classified into overlapping symptom syndromes. Despite prevalence and consequences of these syndromes, LUT disorders continue to be undertreated simply because there are few therapeutic options. LUT function and structure were assessed in aged (>25 months) male and female Fischer 344 rats randomized to oral treatment with a purine nucleoside phosphorylase (PNPase inhibitor) 8-aminoguanine (8-AG) or vehicle for 6 weeks. The bladders of aged rats exhibited multiple abnormalities: tactile insensitivity, vascular remodeling, reduced collagen-fiber tortuosity, increased bladder stiffness, abnormal smooth muscle morphology, swelling of mitochondria, and increases in urodamaging purine metabolites. Treatment of aged rats with 8-AG restored all evaluated histological, ultrastructural, and physiological abnormalities toward that of a younger state. 8-AG is an effective treatment that ameliorates key age-related structural and physiologic bladder abnormalities. Because PNPase inhibition blocks metabolism of inosine to hypoxanthine and guanosine to guanine, likely uroprotective effects of 8-AG are mediated by increased bladder levels of uroprotective inosine and guanosine and reductions in urodamaging hypoxanthine and xanthine. These findings demonstrate that 8-AG has translational potential for treating age-associated LUT dysfunctions and resultant syndromes in humans.
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Affiliation(s)
- Lori A Birder
- Department of Medicine, Renal-Electrolyte Division, and.,Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | | | - Alan J Wein
- Division of Urology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Fangzhou Cheng
- Department of Mechanical Engineering and Materials Science, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Mara Grove-Sullivan
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - Anthony J Kanai
- Department of Medicine, Renal-Electrolyte Division, and.,Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - Alan M Watson
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - Donna Stoltz
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - Simon C Watkins
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - Anne M Robertson
- Department of Mechanical Engineering and Materials Science, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Diane Newman
- Division of Urology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Roger R Dmochowski
- Department of Urology, Vanderbilt Medical Center, Nashville, Tennessee, USA
| | - Edwin K Jackson
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
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29
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Fu J, Ding X, Stowell CET, Wu YL, Wang Y. Slow degrading poly(glycerol sebacate) derivatives improve vascular graft remodeling in a rat carotid artery interposition model. Biomaterials 2020; 257:120251. [PMID: 32738658 PMCID: PMC8422746 DOI: 10.1016/j.biomaterials.2020.120251] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2020] [Revised: 07/14/2020] [Accepted: 07/19/2020] [Indexed: 01/22/2023]
Abstract
Porous synthetic grafts made of poly (glycerol sebacate) (PGS) can transform into autologous vascular conduits in vivo upon degradation of PGS. A long-held doctrine in tissue engineering is the necessity to match degradation of the scaffolds to tissue regeneration. Here, we tested the impact of degradation of PGS and its derivative in an interposition model of rat common carotid artery (CCA). Previous work indicates a complete degradation of PGS within approximately 2 weeks, likely at the fast end of the spectrum. Thus, the derivation of PGS focuses on delay degradation by conjugating the free hydroxy groups in PGS with a long chain carboxylic acid: palmitic acid, one of the most common lipid components. We evaluated two of the resultant palmitate-PGS (PPGS) in this study: one containing 9% palmitate (9-PPGS) and the other16% palmitate (16-PPGS). 16-PPGS grafts had the highest patency. Ultrasound imaging showed that the lumens of 16-PPGS grafts were similar to CCA and smaller than 9-PPGS and PGS grafts 12 weeks post-operation. Immunohistological and histological examination showed an endothelialized lumens in all three types of grafts within 4 weeks. Inflammatory responses to 16-PPGS grafts were limited to the adventitial space in contrast to a more diffusive infiltration in 9-PPGS and PGS grafts in week 4. Examination of calponin+ and αSMA+ cells revealed that 16-PPGS grafts remodeled into a distinctive bi-layered wall, while the walls of 9-PPGS grafts and PGS grafts only had one thick layer of smooth muscle-like cells. Correspondingly, the expression of collagen III and elastin displayed an identical layered structure in the remodeled 16-PPGS grafts, in contrast to a more spread distribution in 9-PPGS and PGS grafts. All the three types of grafts exhibited the same collagen content and burst pressure after 12 weeks of host remodeling. However, the compliance and elastin content of 16-PPGS grafts in week 12 were closest to those of CCA. Overall, placing the degradation of PGS derived elastomer to a window of 4-12 weeks results in vascular conduits closer to arteries in a rat carotid artery interposition model over a 12-week observation period.
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Affiliation(s)
- Jiayin Fu
- Nancy E. and Peter C. Meining School of Biomedical Engineering, Ithaca, NY, 14853, USA
| | - Xiaochu Ding
- Nancy E. and Peter C. Meining School of Biomedical Engineering, Ithaca, NY, 14853, USA
| | - Chelsea E T Stowell
- Nancy E. and Peter C. Meining School of Biomedical Engineering, Ithaca, NY, 14853, USA
| | - Yen-Lin Wu
- Nancy E. and Peter C. Meining School of Biomedical Engineering, Ithaca, NY, 14853, USA
| | - Yadong Wang
- Nancy E. and Peter C. Meining School of Biomedical Engineering, Ithaca, NY, 14853, USA.
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30
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Barrett JM, Callaghan JP. A one-dimensional collagen-based biomechanical model of passive soft tissue with viscoelasticity and failure. J Theor Biol 2020; 509:110488. [PMID: 32931772 DOI: 10.1016/j.jtbi.2020.110488] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2020] [Revised: 08/31/2020] [Accepted: 09/04/2020] [Indexed: 12/28/2022]
Abstract
INTRODUCTION Strains and sprains of soft tissues, including tendons and ligaments, are frequently occurring injuries. Musculoskeletal models show great promise in prediction and prevention of these injuries. However, these models rarely account for the viscoelastic properties of ligaments and tendons, much less their failure properties. The purpose of this project was to develop, simplify, and analyze a collagen-distribution model to address these limitations. MODEL DEVELOPMENT A distribution-moment approximation was applied to an existing partial differential equation model to reduce its computational complexity. The resulting model was equipped with a Voigt model in series, which endowed it with viscoelastic properties in addition to failure properties. RESULTS The model was able to reproduce the characteristic toe, linear, and failure regions ubiquitous throughout in-vitro tests on tissue specimens. In addition, it was able to reproduce a tri-phasic creep test consisting of an initial deformation, a steady-state, and failure. Stress-relaxation and hysteresis were also reproducible by the model. DISCUSSION AND CONCLUSION The ability to reproduce so many characteristics of biological tissues suggests more bio-fidelity was achieved by the reduced model was other currently available models. Future work to further improve its bio-fidelity is proposed for specific tendons and ligaments.
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Affiliation(s)
- Jeff M Barrett
- University of Waterloo, Department of Kinesiology, Waterloo, Ontario, Canada
| | - Jack P Callaghan
- University of Waterloo, Department of Kinesiology, Waterloo, Ontario, Canada.
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31
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Frösen J, Cebral J, Robertson AM, Aoki T. Flow-induced, inflammation-mediated arterial wall remodeling in the formation and progression of intracranial aneurysms. Neurosurg Focus 2020; 47:E21. [PMID: 31261126 DOI: 10.3171/2019.5.focus19234] [Citation(s) in RCA: 147] [Impact Index Per Article: 36.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2019] [Accepted: 05/01/2019] [Indexed: 01/09/2023]
Abstract
OBJECTIVE Unruptured intracranial aneurysms (UIAs) are relatively common lesions that may cause devastating intracranial hemorrhage, thus producing considerable suffering and anxiety in those affected by the disease or an increased likelihood of developing it. Advances in the knowledge of the pathobiology behind intracranial aneurysm (IA) formation, progression, and rupture have led to preclinical testing of drug therapies that would prevent IA formation or progression. In parallel, novel biologically based diagnostic tools to estimate rupture risk are approaching clinical use. Arterial wall remodeling, triggered by flow and intramural stresses and mediated by inflammation, is relevant to both. METHODS This review discusses the basis of flow-driven vessel remodeling and translates that knowledge to the observations made on the mechanisms of IA initiation and progression on studies using animal models of induced IA formation, study of human IA tissue samples, and study of patient-derived computational fluid dynamics models. RESULTS Blood flow conditions leading to high wall shear stress (WSS) activate proinflammatory signaling in endothelial cells that recruits macrophages to the site exposed to high WSS, especially through macrophage chemoattractant protein 1 (MCP1). This macrophage infiltration leads to protease expression, which disrupts the internal elastic lamina and collagen matrix, leading to focal outward bulging of the wall and IA initiation. For the IA to grow, collagen remodeling and smooth muscle cell (SMC) proliferation are essential, because the fact that collagen does not distend much prevents the passive dilation of a focal weakness to a sizable IA. Chronic macrophage infiltration of the IA wall promotes this SMC-mediated growth and is a potential target for drug therapy. Once the IA wall grows, it is subjected to changes in wall tension and flow conditions as a result of the change in geometry and has to remodel accordingly to avoid rupture. Flow affects this remodeling process. CONCLUSIONS Flow triggers an inflammatory reaction that predisposes the arterial wall to IA initiation and growth and affects the associated remodeling of the UIA wall. This chronic inflammation is a putative target for drug therapy that would stabilize UIAs or prevent UIA formation. Moreover, once this coupling between IA wall remodeling and flow is understood, data from patient-specific flow models can be gathered as part of the diagnostic workup and utilized to improve risk assessment for UIA initiation, progression, and eventual rupture.
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Affiliation(s)
- Juhana Frösen
- 1Department of Neurosurgery, and.,2Hemorrhagic Brain Pathology Research Group, Kuopio University Hospital, Kuopio, Finland
| | - Juan Cebral
- 3Bioengineering Department, Volgenau School of Engineering, George Mason University, Fairfax, Virginia
| | - Anne M Robertson
- 4Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania; and
| | - Tomohiro Aoki
- 5Department of Molecular Pharmacology, Research Institute, and.,6Core Research for Evolutional Science and Technology (CREST) from Japan Agency for Medical Research and Development (AMED), National Cerebral and Cardiovascular Center, Suita, Osaka, Japan
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32
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Nguyen N, Nath N, Deseri L, Tzeng E, Velankar SS, Pocivavsek L. Wrinkling instabilities for biologically relevant fiber-reinforced composite materials with a case study of Neo-Hookean/Ogden-Gasser-Holzapfel bilayer. Biomech Model Mechanobiol 2020; 19:2375-2395. [PMID: 32535739 DOI: 10.1007/s10237-020-01345-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Accepted: 05/12/2020] [Indexed: 02/03/2023]
Abstract
Wrinkling is a ubiquitous surface phenomenon in many biological tissues and is believed to play an important role in arterial health. As arteries are highly nonlinear, anisotropic, multilayered composite systems, it is necessary to investigate wrinkling incorporating these material characteristics. Several studies have examined surface wrinkling mechanisms with nonlinear isotropic material relationships. Nevertheless, wrinkling associated with anisotropic constitutive models such as Ogden-Gasser-Holzapfel (OGH), which is suitable for soft biological tissues, and in particular arteries, still requires investigation. Here, the effects of OGH parameters such as fibers' orientation, stiffness, and dispersion on the onset of wrinkling, wrinkle wavelength and amplitude are elucidated through analysis of a bilayer system composed of a thin, stiff neo-Hookean membrane and a soft OGH substrate subjected to compression. Critical contractile strain at which wrinkles occur is predicted using both finite element analysis and analytical linear perturbation approach. Results suggest that besides stiffness mismatch, anisotropic features associated with fiber stiffness and distribution might be used in natural layered systems to adjust wrinkling and subsequent folding behaviors. Further analysis of a bilayer system with fibers in the (x-y) plane subjected to compression in the x direction shows a complex dependence of wrinkling strain and wavelength on fiber angle, stiffness, and dispersion. This behavior is captured by an approximation utilizing the linearized anisotropic properties derived from OGH model. Such understanding of wrinkling in this artery wall-like system will help identify the role of wrinkling mechanisms in biological artery in addition to the design of its synthetic counterparts.
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Affiliation(s)
- Nhung Nguyen
- Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, USA
| | - Nandan Nath
- Department of Surgery, University of Pittsburgh, Pittsburgh, USA
| | - Luca Deseri
- Department of Civil, Enviromental and Mechanical Engineering, University of Trento - Italy, Trento, Italy.,Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, USA.,Department of Civil and Enviromental Engineering, Carnegie Mellon University, Pittsburgh, USA.,Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, USA.,Department of Nanomedicine, The Houston Methodist Research Institute, Houston, USA
| | - Edith Tzeng
- Department of Surgery, University of Pittsburgh, Pittsburgh, USA
| | - Sachin S Velankar
- Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, USA.,Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, USA
| | - Luka Pocivavsek
- Department of Surgery, The University of Chicago, Chicago, USA.
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Tondnevis F, Keshvari H, Mohandesi JA. Fabrication, characterization, and in vitro evaluation of electrospun polyurethane‐gelatin‐carbon nanotube scaffolds for cardiovascular tissue engineering applications. J Biomed Mater Res B Appl Biomater 2020; 108:2276-2293. [DOI: 10.1002/jbm.b.34564] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2019] [Revised: 11/26/2019] [Accepted: 01/08/2020] [Indexed: 12/11/2022]
Affiliation(s)
- Farbod Tondnevis
- Biomaterials Group, Faculty of Biomedical EngineeringAmirkabir University of Technology P.O. Box 15875‐4413, Tehran Iran
| | - Hamid Keshvari
- Biomaterials Group, Faculty of Biomedical EngineeringAmirkabir University of Technology P.O. Box 15875‐4413, Tehran Iran
| | - Jamshid Aghazadeh Mohandesi
- Department of Mining and Metallurgical EngineeringAmirkabir University of Technology P.O. Box 15875‐4413, Tehran Iran
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34
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Cavinato C, Badel P, Krasny W, Avril S, Morin C. Experimental Characterization of Adventitial Collagen Fiber Kinematics Using Second-Harmonic Generation Imaging Microscopy: Similarities and Differences Across Arteries, Species and Testing Conditions. MULTI-SCALE EXTRACELLULAR MATRIX MECHANICS AND MECHANOBIOLOGY 2020. [DOI: 10.1007/978-3-030-20182-1_5] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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35
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Ayyalasomayajula V, Pierrat B, Badel P. A computational model for understanding the micro-mechanics of collagen fiber network in the tunica adventitia. Biomech Model Mechanobiol 2019; 18:1507-1528. [PMID: 31065952 PMCID: PMC6748894 DOI: 10.1007/s10237-019-01161-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2018] [Accepted: 04/26/2019] [Indexed: 12/11/2022]
Abstract
Abdominal aortic aneurysm is a prevalent cardiovascular disease with high mortality rates. The mechanical response of the arterial wall relies on the organizational and structural behavior of its microstructural components, and thus, a detailed understanding of the microscopic mechanical response of the arterial wall layers at loads ranging up to rupture is necessary to improve diagnostic techniques and possibly treatments. Following the common notion that adventitia is the ultimate barrier at loads close to rupture, in the present study, a finite element model of adventitial collagen network was developed to study the mechanical state at the fiber level under uniaxial loading. Image stacks of the rabbit carotid adventitial tissue at rest and under uniaxial tension obtained using multi-photon microscopy were used in this study, as well as the force-displacement curves obtained from previously published experiments. Morphological parameters like fiber orientation distribution, waviness, and volume fraction were extracted for one sample from the confocal image stacks. An inverse random sampling approach combined with a random walk algorithm was employed to reconstruct the collagen network for numerical simulation. The model was then verified using experimental stress-stretch curves. The model shows the remarkable capacity of collagen fibers to uncrimp and reorient in the loading direction. These results further show that at high stretches, collagen network behaves in a highly non-affine manner, which was quantified for each sample. A comprehensive parameter study to understand the relationship between structural parameters and their influence on mechanical behavior is presented. Through this study, the model was used to conclude important structure-function relationships that control the mechanical response. Our results also show that at loads close to rupture, the probability of failure occurring at the fiber level is up to 2%. Uncertainties in usually employed rupture risk indicators and the stochastic nature of the event of rupture combined with limited knowledge on the microscopic determinants motivate the development of such an analysis. Moreover, this study will advance the study of coupling microscopic mechanisms to rupture of the artery as a whole.
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Affiliation(s)
- Venkat Ayyalasomayajula
- Mines Saint-Étienne, Univ Lyon, Univ Jean Monnet, INSERM, U1059 SAINBIOSE, Centre CIS, 42023, Saint-Étienne, France.
| | - Baptiste Pierrat
- Mines Saint-Étienne, Univ Lyon, Univ Jean Monnet, INSERM, U1059 SAINBIOSE, Centre CIS, 42023, Saint-Étienne, France
| | - Pierre Badel
- Mines Saint-Étienne, Univ Lyon, Univ Jean Monnet, INSERM, U1059 SAINBIOSE, Centre CIS, 42023, Saint-Étienne, France
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36
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Trachet B, Ferraro M, Lovric G, Aslanidou L, Logghe G, Segers P, Stergiopulos N. Synchrotron-based visualization and segmentation of elastic lamellae in the mouse carotid artery during quasi-static pressure inflation. J R Soc Interface 2019; 16:20190179. [PMID: 31238834 DOI: 10.1098/rsif.2019.0179] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
In computational aortic biomechanics, aortic and arterial tissue are typically modelled as a homogeneous layer, making abstraction not only of the layered structure of intima, media and adventitia but also of the microstructure that exists within these layers. Here, we present a novel method to visualize the microstructure of the tunica media along the entire circumference of the vessel. To that end, we developed a pressure-inflation device that is compatible with synchrotron-based phase-contrast imaging. Using freshly excised left common carotid arteries from n = 12 mice, we visualized how the lamellae and interlamellar layers inflate as the luminal pressure is increased from 0 to 120 mm Hg in quasi-static steps. A graph-based segmentation algorithm subsequently allowed us to automatically segment each of the three lamellae, resulting in a three-dimensional geometry that represents lamellae, interlamellar layers and adventitia at nine different pressure levels. Our results demonstrate that the three elastic lamellae unfold and stretch simultaneously as luminal pressure is increased. In the long term, we believe that the results presented in this work can be a first step towards a better understanding of the mechanics of the arterial microstructure.
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Affiliation(s)
- Bram Trachet
- 1 Institute of Bioengineering, Ecole Polytechnique Fédérale de Lausanne , Lausanne , Switzerland.,2 IBiTech-bioMMeda , Ghent University, Ghent , Belgium
| | - Mauro Ferraro
- 1 Institute of Bioengineering, Ecole Polytechnique Fédérale de Lausanne , Lausanne , Switzerland
| | - Goran Lovric
- 3 Centre d'Imagerie BioMédicale, Ecole Polytechnique Fédérale de Lausanne , Lausanne , Switzerland.,4 Swiss Light Source, Paul Scherrer Institute , Villigen , Switzerland
| | - Lydia Aslanidou
- 1 Institute of Bioengineering, Ecole Polytechnique Fédérale de Lausanne , Lausanne , Switzerland
| | | | | | - Nikolaos Stergiopulos
- 1 Institute of Bioengineering, Ecole Polytechnique Fédérale de Lausanne , Lausanne , Switzerland
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Brazile BL, Hua Y, Jan NJ, Wallace J, Gogola A, Sigal IA. Thin Lamina Cribrosa Beams Have Different Collagen Microstructure Than Thick Beams. Invest Ophthalmol Vis Sci 2019; 59:4653-4661. [PMID: 30372734 PMCID: PMC6149225 DOI: 10.1167/iovs.18-24763] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Purpose To compare the collagen microstructural crimp characteristics between thin and thick lamina cribrosa (LC) beams. Methods Seven eyes from four sheep were fixed at 5 mm Hg IOP in 10% formalin. For each eye, one to three coronal cryosections through the LC were imaged with polarized light microscopy and analyzed to visualize the LC and determine collagen fiber microstructure. For every beam, we measured its width and three characteristics of the crimp of its collagen fibers: waviness, tortuosity, and amplitude. Linear mixed effects models were used to test whether crimp characteristics were associated with the LC beam width. Results For each eye and over all the eyes, LC beam width was positively associated with crimp waviness and tortuosity, and negatively associated with crimp amplitude (P's < 0.0001). Thin beams, average width 13.11 μm, had average (SD) waviness, tortuosity, and amplitude of 0.27 (0.17) radians, 1.017 (0.028) and 1.88 (1.41) μm, respectively. For thick beams, average width 26.10 μm, these characteristics were 0.33 (0.18) radians, 1.025 (0.037) and 1.58 (1.36) μm, respectively. Conclusions Our results suggest heterogeneity in LC beam mechanical properties. Thin beams were less wavy than their thicker counterparts, suggesting that thin beams may stiffen at lower IOP than thick beams. This difference may allow thin beams to support similar amounts of IOP-induced force as thicker beams, thus providing a similar level of structural support to the axons at physiologic IOP, despite the differences in width. Measurements of beam-level mechanical properties are needed to confirm these predictions.
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Affiliation(s)
- Bryn L Brazile
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States
| | - Yi Hua
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States
| | - Ning-Jiun Jan
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States.,Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Jacob Wallace
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States
| | - Alexandra Gogola
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States
| | - Ian A Sigal
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States.,Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States.,McGowan Institute for Regenerative Medicine, University of Pittsburgh School of Medicine and University of Pittsburgh, Pittsburgh, Pennsylvania, United States.,The Louis J. Fox Center for Vision Restoration of UPMC and the University of Pittsburgh, Pittsburgh, Pennsylvania, United States
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Bhogal P, Pederzani G, Grytsan A, Loh Y, Brouwer PA, Andersson T, Gundiah N, Robertson AM, Watton PN, Söderman M. The unexplained success of stentplasty vasospasm treatment : Insights using Mechanistic Mathematical Modeling. Clin Neuroradiol 2019; 29:763-774. [PMID: 30915482 DOI: 10.1007/s00062-019-00776-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2018] [Accepted: 03/08/2019] [Indexed: 11/29/2022]
Abstract
BACKGROUND Cerebral vasospasm (CVS) following subarachnoid hemorrhage occurs in up to 70% of patients. Recently, stents have been used to successfully treat CVS. This implies that the force required to expand spastic vessels and resolve vasospasm is lower than previously thought. OBJECTIVE We develop a mechanistic model of the spastic arterial wall to provide insight into CVS and predict the forces required to treat it. MATERIAL AND METHODS The arterial wall is modelled as a cylindrical membrane using a constrained mixture theory that accounts for the mechanical roles of elastin, collagen and vascular smooth muscle cells (VSMC). We model the pressure diameter curve prior to CVS and predict how it changes following CVS. We propose a stretch-based damage criterion for VSMC and evaluate if several commercially available stents are able to resolve vasospasm. RESULTS The model predicts that dilatation of VSMCs beyond a threshold of mechanical failure is sufficient to resolve CVS without damage to the underlying extracellular matrix. Consistent with recent clinical observations, our model predicts that existing stents have the potential to provide sufficient outward force to successfully treat CVS and that success will be dependent on an appropriate match between stent and vessel. CONCLUSION Mathematical models of CVS can provide insights into biological mechanisms and explore treatment approaches. Improved understanding of the underlying mechanistic processes governing CVS and its mechanical treatment may assist in the development of dedicated stents.
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Affiliation(s)
- P Bhogal
- Department of Interventional Neuroradiology, The Royal London Hospital, Whitechapel Road, E1 1BB, London, UK.
| | - G Pederzani
- Department of Computer Science, University of Sheffield, Sheffield, UK.,Insigneo Institute for in silico Medicine, University of Sheffield, Sheffield, UK
| | - A Grytsan
- Insigneo Institute for in silico Medicine, University of Sheffield, Sheffield, UK
| | - Y Loh
- Uniformed Services University, University of California, Los Angeles, USA.,Swedish Neuroscience Institute, 550 17th Avenue Seattle, 98122, Washington, USA
| | - P A Brouwer
- The Karolinska University Hospital, 171 76, Stockholm, Sweden
| | - T Andersson
- The Karolinska University Hospital, 171 76, Stockholm, Sweden.,AZ Groeninge, Kortrijk, Belgium
| | - Namrata Gundiah
- Department of Mechanical Engineering, Indian Institute of Science, Bangalore, India
| | - Anne M Robertson
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA, USA
| | - Paul N Watton
- Department of Computer Science, University of Sheffield, Sheffield, UK.,Insigneo Institute for in silico Medicine, University of Sheffield, Sheffield, UK.,Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA, USA
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Gogola A, Jan NJ, Brazile B, Lam P, Lathrop KL, Chan KC, Sigal IA. Spatial Patterns and Age-Related Changes of the Collagen Crimp in the Human Cornea and Sclera. Invest Ophthalmol Vis Sci 2019; 59:2987-2998. [PMID: 30025116 PMCID: PMC5995484 DOI: 10.1167/iovs.17-23474] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Purpose Collagen is the main load-bearing component of the eye, and collagen crimp is a critical determinant of tissue mechanical behavior. We test the hypothesis that collagen crimp morphology varies over the human cornea and sclera and with age. Methods We analyzed 42 axial whole-globe sections from 20 normal eyes of 20 human donors, ranging in age from 0.08 (1 month) to 97 years. The sections were imaged using polarized light microscopy to obtain μm-scale fiber bundle/lamellae orientation from two corneal and six scleral regions. Crimp morphology was quantified through waviness, tortuosity, and amplitude. Results Whole-globe median waviness, tortuosity, and amplitude were 0.127 radians, 1.002, and 0.273 μm, respectively. These parameters, however, were not uniform over the globe, instead exhibiting distinct, consistent patterns. All crimp parameters decreased significantly with age, with significantly different age-related decreases between regions. The crimp morphology of the limbus changed the most drastically with age, such that it had the largest crimp in neonates, and among the smallest in the elderly. Conclusions Age-related decreases in crimp parameters are likely one of the mechanisms underlying age-related stiffening of the sclera and cornea, potentially influencing sensitivity to IOP. Further work is needed to determine the biomechanical implications of the crimp patterns observed. The comparatively large changes in the crimp morphology of the limbus, especially in the early years of life, suggest that crimp in this region may play a role in eye development, although the exact nature of this is unclear.
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Affiliation(s)
- Alexandra Gogola
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Ning-Jiun Jan
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States.,Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Bryn Brazile
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Po Lam
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Kira L Lathrop
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States.,Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Kevin C Chan
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States.,Department of Ophthalmology, New York University, New York, New York, United States.,Department of Radiology, New York University, New York, New York, United States
| | - Ian A Sigal
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States.,Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
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Rachev A, Shazly T. A structure-based constitutive model of arterial tissue considering individual natural configurations of elastin and collagen. J Mech Behav Biomed Mater 2019; 90:61-72. [DOI: 10.1016/j.jmbbm.2018.09.047] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2018] [Revised: 09/13/2018] [Accepted: 09/29/2018] [Indexed: 12/20/2022]
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Wang S, Tokgoz A, Huang Y, Zhang Y, Feng J, Sastry P, Sun C, Figg N, Lu Q, Sutcliffe MPF, Teng Z, Gillard JH. Bayesian Inference-Based Estimation of Normal Aortic, Aneurysmal and Atherosclerotic Tissue Mechanical Properties: From Material Testing, Modeling and Histology. IEEE Trans Biomed Eng 2019; 66:2269-2278. [PMID: 30703001 DOI: 10.1109/tbme.2018.2886681] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
OBJECTIVE Mechanical properties of healthy, aneurysmal, and atherosclerotic arterial tissues are essential for assessing the risk of lesion development and rupture. Strain energy density function (SEDF) has been widely used to describe these properties, where material constants of the SEDF are traditionally determined using the ordinary least square (OLS) method. However, the material constants derived using OLS are usually dependent on initial guesses. METHODS To avoid such dependencies, Bayesian inference-based estimation was used to fit experimental stress-stretch curves of 312 tissue strips from 8 normal aortas, 19 aortic aneurysms, and 21 carotid atherosclerotic plaques to determine the constants, C1, D1, and D2 of the modified Mooney-Rivlin SEDF. RESULTS Compared with OLS, material constants varied much less with prior in the Bayesian inference-based estimation. Moreover, fitted material constants differed amongst distinct tissue types. Atherosclerotic tissues associated with the biggest D2, an indicator of the rate of increase in stress during stretching, followed by aneurysmal tissues and those from normal aortas. Histological analyses showed that C1 and D2 were associated with elastin content and details of the collagen configuration, specifically, waviness and dispersion, in the structure. CONCLUSION Bayesian inference-based estimation robustly determines material constants in the modified Mooney-Rivlin SEDF and these constants can reflect the inherent physiological and pathological features of the tissue structure. SIGNIFICANCE This study suggested a robust procedure to determine the material constants in SEDF and demonstrated that the obtained constants can be used to characterize tissues from different types of lesions, while associating with their inherent microstructures.
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Gade PS, Robertson AM, Chuang CY. Multiphoton Imaging of Collagen, Elastin, and Calcification in Intact Soft-Tissue Samples. CURRENT PROTOCOLS IN CYTOMETRY 2019; 87:e51. [PMID: 30379412 PMCID: PMC6314890 DOI: 10.1002/cpcy.51] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Multiphoton-induced second-harmonic generation and two-photon excitation enable imaging of collagen and elastin fibers at micron-level resolution to depths of hundreds of microns, without the use of exogenous stains. These attributes can be leveraged for quantitative analysis of the 3D architecture of collagen and elastin fibers within intact, soft tissue specimens such as the artery and bladder wall. This architecture influences the function of intramural cells and also plays a primary role in determining tissue passive mechanical properties. Calcification deposition in soft tissues is a highly prevalent pathology in both older and diseased populations that can alter tissue properties. In this unit, we provide a protocol for simultaneous multiphoton microscopy (MPM) imaging and analysis of 3D collagen and elastin structures with calcification, which is effective for fixed and fresh intact samples. We also provide an associated micro-CT protocol to identify regions of interest in the samples as a means to target the MPM imaging. © 2018 by John Wiley & Sons, Inc.
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Affiliation(s)
- Piyusha S. Gade
- Department of Bioengineerin, University of Pittsburgh Pittsburgh, PA
| | - Anne M. Robertson
- Department of Bioengineerin, University of Pittsburgh Pittsburgh, PA
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh Pittsburgh, PA
| | - Chih-Yuan Chuang
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh Pittsburgh, PA
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Cebral JR, Mut F, Gade P, Cheng F, Tobe Y, Frosen J, Robertson AM. Combining data from multiple sources to study mechanisms of aneurysm disease: Tools and techniques. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2018; 34:e3133. [PMID: 30055087 PMCID: PMC6231954 DOI: 10.1002/cnm.3133] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2018] [Revised: 06/14/2018] [Accepted: 07/15/2018] [Indexed: 05/31/2023]
Abstract
INTRODUCTION Connecting local hemodynamics, biomechanics, and tissue properties in cerebral aneurysms is important for understanding the processes of wall degeneration and subsequent aneurysm progression and rupture. This challenging problem requires integration of data from multiple sources. METHODS This paper describes the tools and techniques developed to integrate data from multiple sources, including clinical information, 3D imaging, intraoperative videos, ex vivo micro-computed tomography (CT), and multiphoton microscopy. Central to this approach is a 3D tissue model constructed from micro-CT images of aneurysm samples resected during neurosurgery. This model is aligned to vascular models constructed from 3D clinical images and is used to map and compare flow, biomechanics, and tissue data. RESULTS The approach is illustrated with data of three human intracranial aneurysms. These case studies demonstrated the ability of this approach to study relationships between different factors affecting the aneurysm wall and produced provocative observations that will be further studied with larger series. For instance, "atherosclerotic" and "hyperplastic" looking parts of the aneurysm corresponded to thicker walls and occurred in regions of recirculating flow and low wall shear stress (WSS); thin regions were associated with inflow jets, flow impingement, and high WSS; blebs had walls of varying structures, including calcified, thin, or hyperplastic walls. CONCLUSIONS The current approach enables the study of interactions of multiple factors thought to be responsible for the progressive degradation and weakening of the aneurysm wall during its evolution.
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Affiliation(s)
- Juan R Cebral
- Bioengineering Department, Volgenau School of Engineering, George Mason University, Fairfax, Virginia, USA
| | - Fernando Mut
- Bioengineering Department, Volgenau School of Engineering, George Mason University, Fairfax, Virginia, USA
| | - Piyusha Gade
- Mechanical Engineering and Materials Science and Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Fangzhou Cheng
- Mechanical Engineering and Materials Science and Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Yasutaka Tobe
- Mechanical Engineering and Materials Science and Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Juhana Frosen
- Hemorrhagic Brain Pathology Research Group, Neurocenter, Kuopio University Hospital, Kuopio, Finland
| | - Anne M Robertson
- Mechanical Engineering and Materials Science and Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
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Lee KW, Gade PS, Dong L, Zhang Z, Aral AM, Gao J, Ding X, Stowell CE, Nisar MU, Kim K, Reinhardt DP, Solari MG, Gorantla VS, Robertson AM, Wang Y. A biodegradable synthetic graft for small arteries matches the performance of autologous vein in rat carotid arteries. Biomaterials 2018; 181:67-80. [DOI: 10.1016/j.biomaterials.2018.07.037] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2018] [Revised: 07/23/2018] [Accepted: 07/24/2018] [Indexed: 12/17/2022]
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Holzapfel GA, Ogden RW. Biomechanical relevance of the microstructure in artery walls with a focus on passive and active components. Am J Physiol Heart Circ Physiol 2018; 315:H540-H549. [DOI: 10.1152/ajpheart.00117.2018] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The microstructure of arteries, consisting, in particular, of collagen, elastin, and vascular smooth muscle cells, plays a very significant role in their biomechanical response during a cardiac cycle. In this article, we highlight the microstructure and the contributions of each of its components to the overall mechanical behavior. We also describe the changes of the microstructure that occur as a result of abdominal aortic aneurysms and disease, such as atherosclerosis. We also focus on how the passive and active constituents are incorporated into a mathematical model without going into detail of the mathematical formulation. We conclude by mentioning open problems toward a better characterization of the biomechanical aspects of arteries that will be beneficial for a better understanding of cardiovascular pathophysiology.
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Affiliation(s)
- Gerhard A. Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
- Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, Trondheim, Norway
| | - Ray W. Ogden
- School of Mathematics and Statistics, University of Glasgow, Scotland, United Kingdom
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Hill MR, Philp CJ, Billington CK, Tatler AL, Johnson SR, O'Dea RD, Brook BS. A theoretical model of inflammation- and mechanotransduction-driven asthmatic airway remodelling. Biomech Model Mechanobiol 2018; 17:1451-1470. [PMID: 29968161 PMCID: PMC6154265 DOI: 10.1007/s10237-018-1037-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2017] [Accepted: 05/22/2018] [Indexed: 12/28/2022]
Abstract
Inflammation, airway hyper-responsiveness and airway remodelling are well-established hallmarks of asthma, but their inter-relationships remain elusive. In order to obtain a better understanding of their inter-dependence, we develop a mechanochemical morphoelastic model of the airway wall accounting for local volume changes in airway smooth muscle (ASM) and extracellular matrix in response to transient inflammatory or contractile agonist challenges. We use constrained mixture theory, together with a multiplicative decomposition of growth from the elastic deformation, to model the airway wall as a nonlinear fibre-reinforced elastic cylinder. Local contractile agonist drives ASM cell contraction, generating mechanical stresses in the tissue that drive further release of mitogenic mediators and contractile agonists via underlying mechanotransductive signalling pathways. Our model predictions are consistent with previously described inflammation-induced remodelling within an axisymmetric airway geometry. Additionally, our simulations reveal novel mechanotransductive feedback by which hyper-responsive airways exhibit increased remodelling, for example, via stress-induced release of pro-mitogenic and pro-contractile cytokines. Simulation results also reveal emergence of a persistent contractile tone observed in asthmatics, via either a pathological mechanotransductive feedback loop, a failure to clear agonists from the tissue, or a combination of both. Furthermore, we identify various parameter combinations that may contribute to the existence of different asthma phenotypes, and we illustrate a combination of factors which may predispose severe asthmatics to fatal bronchospasms.
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Affiliation(s)
- Michael R Hill
- Centre for Mathematical Medicine and Biology, School of Mathematical Sciences, University of Nottingham, Room C25, Mathematical Sciences Building, University Park, Nottingham, NG7 2RD, UK.
| | - Christopher J Philp
- Division of Respiratory Medicine, Nottingham Biomedical Research Centre, University of Nottingham, D Floor, South Block, Queen's Medical Centre Campus, Nottingham, NG7 2UH, UK
| | - Charlotte K Billington
- Division of Respiratory Medicine, Nottingham Biomedical Research Centre, University of Nottingham, D Floor, South Block, Queen's Medical Centre Campus, Nottingham, NG7 2UH, UK
| | - Amanda L Tatler
- Division of Respiratory Medicine, Nottingham Biomedical Research Centre, Nottingham City Hospital, University of Nottingham, Hucknall Road, Nottingham, NG5 1PB, UK
| | - Simon R Johnson
- Division of Respiratory Medicine, Nottingham Biomedical Research Centre, University of Nottingham, D Floor, South Block, Queen's Medical Centre Campus, Nottingham, NG7 2UH, UK
| | - Reuben D O'Dea
- Centre for Mathematical Medicine and Biology, School of Mathematical Sciences, University of Nottingham, Room C28, Mathematical Sciences Building, University Park, Nottingham, NG7 2RD, UK
| | - Bindi S Brook
- Centre for Mathematical Medicine and Biology, School of Mathematical Sciences, University of Nottingham, Room C26, Mathematical Sciences Building, University Park, Nottingham, NG7 2RD, UK
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Sang C, Maiti S, Fortunato RN, Kofler J, Robertson AM. A Uniaxial Testing Approach for Consistent Failure in Vascular Tissues. J Biomech Eng 2018; 140:2675125. [PMID: 29560496 PMCID: PMC5938069 DOI: 10.1115/1.4039577] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Although uniaxial tensile testing is commonly used to evaluate failure properties of vascular tissue, there is no established protocol for specimen shape or gripping method. Large percentages of specimens are reported to fail near the clamp and can potentially confound the studies, or, if discarded will result in sample waste. The objective of this study is to identify sample geometry and clamping conditions that can achieve consistent failure in the midregion of small arterial specimens, even for vessels from older individuals. Failure location was assessed in 17 dogbone specimens from human cerebral and sheep carotid arteries using soft inserts. For comparison with commonly used protocols, an additional 22 rectangular samples were tested using either sandpaper or foam tape inserts. Midsample failure was achieved in 94% of the dogbone specimens, while only 14% of the rectangular samples failed in the midregion, the other 86% failing close to the clamps. Additionally, we found midregion failure was more likely to be abrupt, caused by cracking or necking. In contrast, clamp failure was more likely to be gradual and included a delamination mode not seen in midregion failure. Hence, this work provides an approach that can be used to obtain consistent midspecimen failure, avoiding confounding clamp-related artifacts. Furthermore, with consistent midregion failure, studies can be designed to image the failure process in small vascular samples providing valuable quantitative information about changes to collagen and elastin structure during the failure process.
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Affiliation(s)
- Chao Sang
- Department of Mechanical Engineering and
Materials Science,
University of Pittsburgh,
636 Benedum Hall 3700 O'Hara Street,
Pittsburgh, PA 15261
e-mail:
| | - Spandan Maiti
- Department of Bioengineering,
University of Pittsburgh,
302 Benedum Hall 3700 O'Hara Street,
Pittsburgh, PA 15261
e-mail:
| | - Ronald N. Fortunato
- Department of Mechanical Engineering and
Materials Science,
University of Pittsburgh,
636 Benedum Hall 3700 O'Hara Street,
Pittsburgh, PA 15261
e-mail:
| | - Julia Kofler
- Department of Pathology,
University of Pittsburgh,
S701.3 Scaife Hall,
Pittsburgh, PA 15261
e-mail:
| | - Anne M. Robertson
- Department of Mechanical Engineering and
Materials Science,
University of Pittsburgh,
440 Benedum Hall 3700 O'Hara Street,
Pittsburgh, PA 15261
e-mail:
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Cai H, Hao Z, Xiao L, Wan C, Tong L. The collagen microstructural changes of rat menisci and tibiofemoral cartilages under the influence of mechanical loading: An in vitro wear test of whole joints. Technol Health Care 2018; 25:207-217. [PMID: 28582908 DOI: 10.3233/thc-171323] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
BACKGROUND Knee osteoarthritis (OA) is suggested to be induced by multi-factors, and mechanical environment is regarded as a risky factor. OBJECTIVE To investigate the effect of isolated mechanical factor on cartilage. METHODS An active wear test system was designed to perform parameters-controlled in vitro wear tests on rat knee joints with specific load magnitude, flexion-extension angle, and movement frequency. Six hind limbs of 9-month-old male Sprague-Dawley rats, with an additional spring on the medial side, were worn by using the custom-designed apparatus. Researchers observed both the menisci and tibial cartilages of these hind limbs using multiphoton laser scanning microscopy to analyze the change of the collagen microstructure caused by wear. RESULTS Collagen microstructure of both the medial and lateral meniscus became disordered under cyclic load. Some tissues on the surface of the medial tibial cartilage were removed and the middle layer of the medial compartment displayed cracks. On the contrary, the lateral tibial cartilage was intact. CONCLUSIONS The results implied that cyclic load caused menisci microstructure disarrangement prior to tibial cartilage damage and the collagen structure of mid-layer tibial cartilage failed before that of the superficial layer under the kinematics adopted in the study.
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Affiliation(s)
- Haoliuyang Cai
- Department of Mechanical Engineering, Tsinghua University, Beijing, China
| | - Zhixiu Hao
- Department of Mechanical Engineering, Tsinghua University, Beijing, China.,State Key Laboratory of Tribology, Tsinghua University, Beijing, China
| | - Liying Xiao
- Department of Mechanical Engineering, Tsinghua University, Beijing, China
| | - Chao Wan
- Department of Engineering Mechanics, Tsinghua University, Beijing, China
| | - Lingying Tong
- Department of Mechanical Engineering, Tsinghua University, Beijing, China.,State Key Laboratory of Tribology, Tsinghua University, Beijing, China
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Jan NJ, Sigal IA. Collagen fiber recruitment: A microstructural basis for the nonlinear response of the posterior pole of the eye to increases in intraocular pressure. Acta Biomater 2018; 72:295-305. [PMID: 29574185 DOI: 10.1016/j.actbio.2018.03.026] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Revised: 03/09/2018] [Accepted: 03/14/2018] [Indexed: 01/27/2023]
Abstract
Our goal was to quantify and characterize how the collagen fiber crimp waviness of the lamina cribrosa (LC) and peripapillary sclera (PPS) changes with intraocular pressure (IOP). Thirteen sheep (ovine) eyes were immersion and perfusion fixed while maintaining IOP at 0, 10, 15, 20, or 50 mmHg. Coronal optic nerve head (ONH) sections (30 µm) were imaged with polarized light microscopy (PLM) and analyzed for collagen fiber orientation and waviness (SD of fiber orientation). In the LC, the waviness of every LC beam was measured. In the PPS, at least 900 collagen bundles were measured per eye. Using the waviness at 50 mmHg IOP, we defined tissue-specific thresholds to determine the fraction of loaded or recruited fibers. We found that fiber waviness decreased with IOP (P < 0.001). At every IOP, the waviness of the collagen fibers, and the fraction of fibers recruited in the LC were smaller or equal than those of the PPS (P < 0.001). At 15 mmHg IOP, both LC and PPS had ¾ recruited fibers and ¼ left in reserve. The decreased waviness with IOP and associated fiber recruitment is experimental evidence of fiber-based nonlinear biomechanical behavior of the ONH. At all IOPs the PPS had an equal or larger fraction of fibers recruited than the LC. That both LC and PPS had the same fraction of recruited and reserve fibers at normal IOP suggests that this may be an optimal fraction of recruitment for healthy eyes. Whether this extends to human eyes remains unknown. STATEMENT OF SIGNIFICANCE Collagen fibers exhibit a natural waviness or crimp that largely determine the nonlinear biomechanics of soft tissue. Experimental measurements of crimp morphology in the sheep eye, and how it changes with intraocular pressure (IOP), however, are exceedingly sparse. We quantified how posterior eye crimp changes with increasing IOP. We found that the lamina cribrosa and peripapillary sclera have fundamentally different crimp, and with increasing IOP, have different proportions of fibers that straighten, or get recruited, versus remaining wavy, or in reserve. Interestingly, at physiologic IOP of 15 mmHg, both tissues had about ¾ fibers recruited and ¼ fibers in reserve, indicating there may be an optimal fraction of fibers.
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Jan NJ, Brazile BL, Hu D, Grube G, Wallace J, Gogola A, Sigal IA. Crimp around the globe; patterns of collagen crimp across the corneoscleral shell. Exp Eye Res 2018; 172:159-170. [PMID: 29660327 DOI: 10.1016/j.exer.2018.04.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Revised: 04/05/2018] [Accepted: 04/09/2018] [Indexed: 12/20/2022]
Abstract
Our goal was to systematically quantify the collagen crimp morphology around the corneoscleral shell, and test the hypothesis that collagen crimp is not uniform over the globe. Axial longitudinal cryosections (30 μm) of three sheep eyes, fixed at 0 mmHg IOP, were imaged using polarized light microscopy to quantify the local collagen in 8 regions: two corneal (central and peripheral) and six scleral (limbus, anterior-equatorial, equatorial, posterior-equatorial, posterior and peripapillary). Collagen crimp period (length of one wave), tortuosity (path length divided by end-to-end length), waviness (SD of orientation), amplitude (half the peak to trough distance), and conformity (width of contiguous similarly oriented bundles) were measured in each region. Measurements were obtained on 8216 collagen fiber bundles. When pooling measurements across the whole eye globe, the median crimp values were: 23.9 μm period, 13.2 μm conformity, 0.63 μm amplitude, 1.006 tortuosity, and 12.7° waviness. However, all parameters varied significantly across the globe. Median bundle periods in the central cornea, limbus, and peripapillary sclera (PPS) were 14.1 μm, 29.5 μm, and 22.9 μm, respectively. Median conformities were 20.8 μm, 14.5 μm, and 15.1 μm, respectively. Median tortuosities were 1.005, 1.007, and 1.007, respectively. Median waviness' were 11.4°, 13.2°, and 13.2°, respectively. Median amplitudes were 0.35 μm, 0.87 μm, and 0.65 μm, respectively. All parameters varied significantly across the globe. All regions differed significantly from one another on at least one parameter. Regions with small periods had large conformities, and bundles with high tortuosity had high waviness and amplitude. Waviness, tortuosity, and amplitude, associated with nonlinear biomechanical behavior, exhibited "double hump" distributions, whereas period and conformity, representing tissue organization, were substantially different between sclera and cornea. Though the biomechanical implications and origin of the patterns observed remain unclear, our findings of well-defined patterns of collagen crimp across the corneoscleral shell, consistent between eyes, support the existence of mechanisms that regulate collagen characteristics at the regional or smaller levels. These results are experimental data necessary for more realistic models of ocular biomechanics and remodeling.
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Affiliation(s)
- Ning-Jiun Jan
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, USA; Department of Ophthalmology, University of Pittsburgh School of Medicine, USA
| | - Bryn L Brazile
- Department of Ophthalmology, University of Pittsburgh School of Medicine, USA
| | - Danielle Hu
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, USA; Department of Ophthalmology, University of Pittsburgh School of Medicine, USA
| | - Garrett Grube
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, USA
| | - Jacob Wallace
- Department of Ophthalmology, University of Pittsburgh School of Medicine, USA
| | - Alexandra Gogola
- Department of Ophthalmology, University of Pittsburgh School of Medicine, USA
| | - Ian A Sigal
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, USA; Department of Ophthalmology, University of Pittsburgh School of Medicine, USA; McGowan Institute for Regenerative Medicine, University of Pittsburgh School of Medicine and University of Pittsburgh, USA; The Louis J. Fox Center for Vision Restoration of UPMC and the University of Pittsburgh, Pittsburgh, PA, USA.
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