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Blank JL, Roth JD. An Apparatus for Measuring Combined Shear-Tensile Loading in Fibrous Tissues Ex Vivo. J Biomech Eng 2024; 146:074501. [PMID: 38183226 DOI: 10.1115/1.4064437] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2023] [Accepted: 12/27/2023] [Indexed: 01/07/2024]
Abstract
Soft tissues such as tendon and ligament undergo a combination of shear and tensile loading in vivo due to their boundary conditions at muscle and/or bone. Current experimental protocols are limited to pure tensile loading, biaxial loading, or simple shear, and thus may not fully characterize the mechanics of these tissues under physiological loading scenarios. Our objective was to create an experimental protocol to determine the shear modulus of fibrous tissues at different tensile loads. We assembled a four-actuator experimental system that facilitated shear deformation to be superimposed on a tissue subjected to an axial preload. We measured shear modulus in axially loaded electrospun nanofiber scaffolds with either randomly oriented or aligned fibers. We found that shear modulus in the nanofiber phantoms was shear-strain stiffening and dependent on both the axial load (p < 0.001) and fiber alignment (p < 0.001) of the scaffold. The proposed system can enhance our understanding of microstructure and functional mechanics in soft tissues, while also providing a platform to investigate the behavior of electrospun scaffolds for tissue regeneration. Our experimental protocol for determining loaded shear modulus would be further useful as a method to gauge tissue mechanics under loading conditions that are more representative of physiological loads applied to tendon and ligament.
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Affiliation(s)
- Jonathon L Blank
- Department of Mechanical Engineering, University of Wisconsin-Madison, 1513 University Avenue Room 3046, Madison, WI 53706
| | - Joshua D Roth
- Department of Mechanical Engineering, University of Wisconsin-Madison, Madison, WI 53705; Department of Orthopedics and Rehabilitation, University of Wisconsin-Madison, 1111 Highland Avenue Room 5037, Madison, WI 53705
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2
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Di Leonardo S, Monteleone A, Caruso P, Meecham-Garcia H, Pitarresi G, Burriesci G. Effect of the apron in the mechanical characterisation of hyperelastic materials by means of biaxial testing: A new method to improve accuracy. J Mech Behav Biomed Mater 2024; 150:106291. [PMID: 38103333 DOI: 10.1016/j.jmbbm.2023.106291] [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: 05/08/2023] [Revised: 11/28/2023] [Accepted: 11/30/2023] [Indexed: 12/19/2023]
Abstract
Biological soft tissues and polymers used in biomedical applications (e.g. in the cardiovascular area) are hyperelastic incompressible materials that commonly operate under multi-axial large deformation fields. Their characterisation requires biaxial tensile testing. Due to the typically small sample size, the gripping of the specimens commonly relies on rakes or sutures, where the specimen is punctured at the edges of the gauge area. This approach necessitates of an apron, excess of material around the gauge region. This work analyses the apron influence on the estimated mechanical response of biaxial tests performed by using a rakes gripping system, with the aim of verifying the test accuracy and propose improved solutions. In order to isolate the effect of the apron, avoiding the influence of anisotropy and inhomogeneity typical of most soft tissues, homogeneous and isotropic hyperplastic samples made from a uniform sheet of casted silicone were tested. The stress-strain response of specimens with different apron sizes/shapes was measured experimentally by means of biaxial testing and digital image correlation. Tests were replicated numerically, to interpret the experimental findings. The apron surrounding the gauge area acts as an additional annular constraint which stiffens the system, resulting in a significant overestimate in the stress values. This error can be avoided by introducing specific cuts in the apron. The study quantifies, for the first time, the correlation between the apron size/shape and the experimental stress overestimation, proposing a research protocol which, although identified on homogeneous hyperelastic materials, can be useful in providing more accurate characterisation of both, synthetic polymers and soft tissues.
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Affiliation(s)
| | | | - Patrizia Caruso
- Ri.MED Foundation, Palermo, Italy; Engineering Department, University of Palermo, Italy
| | | | | | - Gaetano Burriesci
- Ri.MED Foundation, Palermo, Italy; UCL Mechanical Engineering, University College London, UK.
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3
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Iannucci LE, Riak MB, Meitz E, Bersi MR, Gruev V, Lake SP. Effect of matrix properties on transmission and reflectance mode division-of-focal-plane Stokes polarimetry. JOURNAL OF BIOMEDICAL OPTICS 2023; 28:102902. [PMID: 37441242 PMCID: PMC10334992 DOI: 10.1117/1.jbo.28.10.102902] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/05/2023] [Revised: 05/18/2023] [Accepted: 05/23/2023] [Indexed: 07/15/2023]
Abstract
Significance Division-of-focal-plane Stokes polarimetry is emerging as a powerful tool for the microstructural characterization of soft tissues. How individual extracellular matrix (ECM) properties influence polarimetric signals in reflectance or transmission modes of quantitative polarized light imaging (QPLI) is not well understood. Aim We aimed to investigate how ECM properties affect outcomes obtained from division-of-focal-plane polarimetric imaging in reflectance or transmission modes. Approach Tunable collagen gel phantoms were used to modulate ECM properties of anisotropy, collagen density, crosslinking, and absorber density; the effects of degree of linear polarization (DoLP) and angle of polarization (AoP) on polarimetry outcomes were assessed. A model biological tissue (i.e., bovine tendon) was similarly imaged and evaluated using both reflectance and transmission modes. Results Reflectance QPLI resulted in decreased DoLP compared with transmission mode. A 90 deg shift in AoP was observed between modes but yielded similar spatial patterns. Collagen density had the largest effect on outcomes besides anisotropy in both imaging modes. Conclusions Both imaging modes were sufficiently sensitive to detect structural anisotropy differences in gels of varying fiber alignment. Conclusions drawn from phantom experiments should carry over when interpreting data from more complex tissues and can help provide context for interpretation of other Stokes polarimetry data.
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Affiliation(s)
- Leanne E. Iannucci
- Washington University in St. Louis, McKelvey School of Engineering, Department of Biomedical Engineering, St. Louis, Missouri, United States
| | - Matthew B. Riak
- Washington University in St. Louis, McKelvey School of Engineering, Department of Mechanical Engineering and Materials Science, St. Louis, Missouri, United States
| | - Ethan Meitz
- Washington University in St. Louis, McKelvey School of Engineering, Department of Mechanical Engineering and Materials Science, St. Louis, Missouri, United States
| | - Matthew R. Bersi
- Washington University in St. Louis, McKelvey School of Engineering, Department of Mechanical Engineering and Materials Science, St. Louis, Missouri, United States
| | - Viktor Gruev
- University of Illinois Urbana-Champaign, Department of Electrical and Computer Engineering, Champaign, Illinois, United States
| | - Spencer P. Lake
- Washington University in St. Louis, McKelvey School of Engineering, Department of Biomedical Engineering, St. Louis, Missouri, United States
- Washington University in St. Louis, McKelvey School of Engineering, Department of Mechanical Engineering and Materials Science, St. Louis, Missouri, United States
- Washington University in St. Louis, School of Medicine, Department of Orthopaedic Surgery, St. Louis, Missouri, United States
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4
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Luetkemeyer CM, Neu CP, Calve S. A method for defining tissue injury criteria reveals that ligament deformation thresholds are multimodal. Acta Biomater 2023; 168:252-263. [PMID: 37433358 PMCID: PMC10530537 DOI: 10.1016/j.actbio.2023.07.002] [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: 01/31/2023] [Revised: 07/05/2023] [Accepted: 07/06/2023] [Indexed: 07/13/2023]
Abstract
Soft tissue injuries (such as ligament, tendon, and meniscus tears) are the result of extracellular matrix damage from excessive tissue stretching. Deformation thresholds for soft tissues, however, remain largely unknown due to a lack of methods that can measure and compare the spatially heterogeneous damage and deformation that occurs in these materials. Here, we propose a full-field method for defining tissue injury criteria: multimodal strain limits for biological tissues analogous to yield criteria that exist for crystalline materials. Specifically, we developed a method for defining strain thresholds for mechanically-driven fibrillar collagen denaturation in soft tissues, using regional multimodal deformation and damage data. We established this new method using the murine medial collateral ligament (MCL) as our model tissue. Our findings revealed that multiple modes of deformation contribute to collagen denaturation in the murine MCL, contrary to the common assumption that collagen damage is driven only by strain in the direction of fibers. Remarkably, hydrostatic strain (computed here with an assumption of plane strain) was the best predictor of mechanically-driven collagen denaturation in ligament tissue, suggesting crosslink-mediated stress transfer plays a role in molecular damage accumulation. This work demonstrates that collagen denaturation can be driven by multiple modes of deformation and provides a method for defining deformation thresholds, or injury criteria, from spatially heterogeneous data. STATEMENT OF SIGNIFICANCE: Understanding the mechanics of soft tissue injuries is crucial for the development of new technology for injury detection, prevention, and treatment. Yet, tissue-level deformation thresholds for injury are unknown, due to a lack of methods that combine full-field measurements of multimodal deformation and damage in mechanically loaded soft tissues. Here, we propose a method for defining tissue injury criteria: multimodal strain thresholds for biological tissues. Our findings reveal that multiple modes of deformation contribute to collagen denaturation, contrary to the common assumption that collagen damage is driven by strain in the fiber direction alone. The method will inform the development of new mechanics-based diagnostic imaging, improve computational modeling of injury, and be employed to study the role of tissue composition in injury susceptibility.
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Affiliation(s)
- Callan M Luetkemeyer
- Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO, United States; Department of Mechanical Science and Engineering, University of Illinois Urbana-Champaign, Urbana, IL, United States.
| | - Corey P Neu
- Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO, United States; Biomedical Engineering Program, University of Colorado Boulder, Boulder, CO, United States; BioFrontiers Institute, University of Colorado Boulder, Boulder, CO, United States
| | - Sarah Calve
- Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO, United States; Biomedical Engineering Program, University of Colorado Boulder, Boulder, CO, United States; BioFrontiers Institute, University of Colorado Boulder, Boulder, CO, United States; Materials Science and Engineering Program, University of Colorado Boulder, Boulder, CO, United States
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5
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Middendorf JM, Budrow CJ, Ellingson AM, Barocas VH. The Lumbar Facet Capsular Ligament Becomes More Anisotropic and the Fibers Become Stiffer With Intervertebral Disc and Facet Joint Degeneration. J Biomech Eng 2023; 145:051004. [PMID: 36478033 PMCID: PMC9933886 DOI: 10.1115/1.4056432] [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: 07/21/2022] [Revised: 11/27/2022] [Accepted: 12/02/2022] [Indexed: 12/13/2022]
Abstract
Degeneration of the lumbar spine, and especially how that degeneration may lead to pain, remains poorly understood. In particular, the mechanics of the facet capsular ligament may contribute to low back pain, but the mechanical changes that occur in this ligament with spinal degeneration are unknown. Additionally, the highly nonlinear, heterogeneous, and anisotropic nature of the facet capsular ligament makes understanding mechanical changes more difficult. Clinically, magnetic resonance imaging (MRI)-based signs of degeneration in the facet joint and the intervertebral disc (IVD) correlate. Therefore, this study examined how the nonlinear, heterogeneous mechanics of the facet capsular ligament change with degeneration of the lumbar spine as characterized using MRI. Cadaveric human spines were imaged via MRI, and the L2-L5 facet joints and IVDs were scored using the Fujiwara and Pfirrmann grading systems. Then, the facet capsular ligament was isolated and biaxially loaded. The nonlinear mechanical properties of the ligament were obtained using a nonlinear generalized anisotropic inverse mechanics analysis (nGAIM). Then a Holzapfel-Gasser-Ogden (HGO) model was fit to the stress-strain data obtained from nGAIM. The facet capsular ligament is stiffer and more anisotropic at larger Pfirrmann grades and higher Fujiwara scores than at lower grades and scores. Analysis of ligament heterogeneity showed all tissues are highly heterogeneous, but no distinct spatial patterns of heterogeneity were found. These results show that degeneration of the lumbar spine including the facet capsular ligament appears to be occurring as a whole joint phenomenon and advance our understanding of lumbar spine degeneration.
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Affiliation(s)
- Jill M Middendorf
- Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218
| | | | - Arin M Ellingson
- Department of Rehabilitation Medicine, University of Minnesota, Minneapolis, MN 55455
| | - Victor H Barocas
- Biomedical Engineering, University of Minnesota, 7-105 Nils Hasselmo Hall, 312 Church Street SE, Minneapolis, MN 55455
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6
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Luetkemeyer CM, Neu CP, Calve S. A method for defining tissue injury criteria reveals ligament deformation thresholds are multimodal. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.31.526318. [PMID: 36778317 PMCID: PMC9915655 DOI: 10.1101/2023.01.31.526318] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Soft tissue injuries (such as ligament, tendon, and meniscus tears) are the result of extracellular matrix damage from excessive tissue stretching. Deformation thresholds for soft tissues, however, remain largely unknown due to a lack of methods that can measure and compare the spatially heterogeneous damage and deformation that occurs in these materials. Here, we propose a method for defining tissue injury criteria : multimodal strain limits for biological tissues analogous to yield criteria that exist for crystalline materials. Specifically, we developed a method for defining injury criteria for mechanically-driven fibrillar collagen denaturation in soft tissues, using regional multimodal deformation and damage data. We established this new method using the murine medial collateral ligament (MCL) as our model tissue. Our findings revealed that multiple modes of deformation contribute to collagen denaturation in the murine MCL, contrary to the common assumption that collagen damage is driven by strain in the fiber direction alone. Remarkably, our results indicated that hydrostatic strain, or volumetric expansion, may be the best predictor of mechanically-driven collagen denaturation in ligament tissue, suggesting crosslink-mediated stress transfer plays a role in molecular damage accumulation. This work demonstrates that collagen denaturation can be driven by multiple modes of deformation and provides a method for defining deformation thresholds, or injury criteria, from spatially heterogeneous data.
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7
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Blair MJ, Quinn KP. Single shot quantitative polarized light imaging system for rapid planar biaxial testing of soft tissues. Front Bioeng Biotechnol 2022; 10:1010307. [PMID: 36213065 PMCID: PMC9532628 DOI: 10.3389/fbioe.2022.1010307] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2022] [Accepted: 09/08/2022] [Indexed: 11/13/2022] Open
Abstract
Quantitative Polarized Light Imaging (QPLI) is an established technique used to compute the orientation of collagen fibers based on their birefringence. QPLI systems typically require rotating linear polarizers to obtain sufficient data to estimate orientation, which limits acquisition speeds and is not ideal for its application to mechanical testing. In this paper, we present a QPLI system designed with no moving parts; a single shot technique which is ideal to characterize collagen fiber orientation and kinematics during mechanical testing. Our single shot QPLI system (ssQPLI) sorts polarized light into four linear polarization states that are collected simultaneously by four cameras. The ssQPLI system was validated using samples with known orientation and retardation, and we demonstrate its use with planar biaxial testing of mouse skin. The ssQPLI system was accurate with a mean orientation error of 1.35° ± 1.58°. Skin samples were tested with multiple loading protocols and in each case the mean orientation of the collagen network reoriented to align in the direction of primary loading as expected. In summary, the ssQPLI system is effective at quantifying collagen fiber organization, and, when combined with mechanical testing, can rapidly provide pixel-wise measures of fiber orientation during biaxial loading.
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8
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Pearce D, Nemcek M, Witzenburg C. Combining Unique Planar Biaxial Testing with Full-Field Thickness and Displacement Measurement for Spatial Characterization of Soft Tissues. Curr Protoc 2022; 2:e493. [PMID: 35849021 DOI: 10.1002/cpz1.493] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Soft tissues rely on the incredible complexity of their microstructure for proper function. Local variations in material properties arise as tissues develop and adapt, often in response to changes in loading. A barrier to investigating the heterogeneous nature of soft tissues is the difficulty of developing experimental protocols and analysis tools that can accurately capture spatial variations in mechanical behavior. In this article, we detail protocols enabling mechanical characterizations of anisotropic, heterogeneous soft tissues or tissue analogs. We present a series of mechanical tests designed to maximize inhomogeneous strain fields and in-plane shear forces. A customized, 3D-printable gripping system reduces tissue handling and enhances shear. High-resolution imaging and laser micrometry capture full-field displacement and thickness, respectively. As the equipment necessary to conduct these protocols is commercially available, the experimental methods presented offer an accessible route toward addressing heterogeneity. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Unique biaxial testing of soft tissues and tissue analogs Basic Protocol 2: Full-field thickness measurement of soft tissues and tissue analogs Support Protocol 1: Creating and speckling cruciform-shaped samples for mechanical testing Support Protocol 2: Creating custom gripping system to minimize sample handling.
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Affiliation(s)
- Daniel Pearce
- Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin
| | - Mark Nemcek
- Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin
| | - Colleen Witzenburg
- Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin
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9
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van Vijven M, van Groningen B, Janssen RPA, van der Steen MC, van Doeselaar M, Stefanoska D, van Donkelaar CC, Ito K, Foolen J. Local variations in mechanical properties of human hamstring tendon autografts for anterior cruciate ligament reconstruction do not translate to a mechanically inferior strand. J Mech Behav Biomed Mater 2021; 126:105010. [PMID: 34896765 DOI: 10.1016/j.jmbbm.2021.105010] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Revised: 11/17/2021] [Accepted: 11/25/2021] [Indexed: 11/25/2022]
Abstract
A ruptured anterior cruciate ligament (ACL) is often reconstructed with a multiple-strand autograft of a semitendinosus tendon alone or combined with a gracilis tendon. Up to 10% of patients experience graft rupture. This potentially results from excessive local tissue strains under physiological loading which could either result in direct mechanical failure of the graft or induce mechanobiological weakening. Since the original location in the hamstring tendon cannot be traced back from an autograft rupture site, this study explored whether clinical outcome could be further improved by avoiding specific locations or regions of human semitendinosus and/or gracilis tendons in ACL grafts due to potential mechanical or biochemical inferiority. Additionally, it examined numerically which clinically relevant graft configurations experience the lowest strains - and therefore the lowest rupture risk - when loaded with equal force. Remnant full-length gracilis tendons from human ACL reconstructions and full-length semitendinosus- and ipsilateral gracilis tendons of human cadaveric specimens were subjected to a stress-relaxation test. Locations at high risk of mechanical failure were identified using particle tracking to calculate local axial strains. As biochemical properties, the water-, collagen-, glycosaminoglycan- and DNA content per tissue region (representing graft strands) were determined. A viscoelastic lumped parameter model per tendon region was calculated. These models were applied in clinically relevant virtual graft configurations, which were exposed to physiological loading. Configurations that provided lower stiffness - i.e., experiencing higher strains under equal force - were assumed to be at higher risk of failure. Suitability of the gracilis tendon proper to replace semitendinosus muscle-tendon junction strands was examined. Deviations in local axial strains from the globally applied strain were of similar magnitude as the applied strain. Locations of maximum strains were uniformly distributed over tendon lengths. Biochemical compositions varied between tissue regions, but no trends were detected. Viscoelastic parameters were not significantly different between regions within a tendon, although semitendinosus tendons were stiffer than gracilis tendons. Virtual grafts with a full-length semitendinosus tendon alone or combined with a gracilis tendon displayed the lowest strains, whereas strains increased when gracilis tendon strands were tested for their suitability to replace semitendinosus muscle-tendon junction strands. Locations experiencing high local axial strains - which could increase risk of rupture - were present, but no specific region within any of the investigated graft configurations was found to be mechanically or biochemically deviant. Consequently, no specific tendon region could be indicated to provide a higher risk of rupture for mechanical or biochemical reasons. The semitendinosus tendon provided superior stiffness to a graft compared to the gracilis tendon. Therefore, based on our results it would be recommended to use the semitendinosus tendon, and use the gracilis tendon in cases where further reinforcement of the graft is needed to attain the desired length and cross-sectional area. All these data support current clinical standards.
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Affiliation(s)
- M van Vijven
- Regenerative Engineering & Materials, Department of Biomedical Engineering, Eindhoven University of Technology, PO Box 513, 5600, MB, Eindhoven, the Netherlands; Institute for Complex Molecular Systems, Eindhoven University of Technology, PO Box 513, 5600, MB, Eindhoven, the Netherlands
| | - B van Groningen
- Department of Orthopaedic Surgery & Trauma, Máxima MC: Dominee Theodor Fliednerstraat 1, 5631, BM, Eindhoven, the Netherlands
| | - R P A Janssen
- Regenerative Engineering & Materials, Department of Biomedical Engineering, Eindhoven University of Technology, PO Box 513, 5600, MB, Eindhoven, the Netherlands; Department of Orthopaedic Surgery & Trauma, Máxima MC: Dominee Theodor Fliednerstraat 1, 5631, BM, Eindhoven, the Netherlands; Value-Based Health Care, Department of Paramedical Sciences, Fontys University of Applied Sciences, Postbus 347, 5600, AH, Eindhoven, the Netherlands
| | - M C van der Steen
- Department of Orthopaedic Surgery & Trauma, Máxima MC: Dominee Theodor Fliednerstraat 1, 5631, BM, Eindhoven, the Netherlands; Department of Orthopaedic Surgery & Trauma, Catharina Hospital Eindhoven, Michelangelolaan 2, 5623, EJ, Eindhoven, the Netherlands
| | - M van Doeselaar
- Regenerative Engineering & Materials, Department of Biomedical Engineering, Eindhoven University of Technology, PO Box 513, 5600, MB, Eindhoven, the Netherlands
| | - D Stefanoska
- Regenerative Engineering & Materials, Department of Biomedical Engineering, Eindhoven University of Technology, PO Box 513, 5600, MB, Eindhoven, the Netherlands
| | - C C van Donkelaar
- Regenerative Engineering & Materials, Department of Biomedical Engineering, Eindhoven University of Technology, PO Box 513, 5600, MB, Eindhoven, the Netherlands; Institute for Complex Molecular Systems, Eindhoven University of Technology, PO Box 513, 5600, MB, Eindhoven, the Netherlands
| | - K Ito
- Regenerative Engineering & Materials, Department of Biomedical Engineering, Eindhoven University of Technology, PO Box 513, 5600, MB, Eindhoven, the Netherlands; Institute for Complex Molecular Systems, Eindhoven University of Technology, PO Box 513, 5600, MB, Eindhoven, the Netherlands
| | - J Foolen
- Regenerative Engineering & Materials, Department of Biomedical Engineering, Eindhoven University of Technology, PO Box 513, 5600, MB, Eindhoven, the Netherlands; Institute for Complex Molecular Systems, Eindhoven University of Technology, PO Box 513, 5600, MB, Eindhoven, the Netherlands.
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10
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Shih ED, Provenzano PP, Witzenburg CM, Barocas VH, Grande AW, Alford PW. Characterizing Tissue Remodeling and Mechanical Heterogeneity in Cerebral Aneurysms. J Vasc Res 2021; 59:34-42. [PMID: 34758464 DOI: 10.1159/000519694] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2021] [Accepted: 09/14/2021] [Indexed: 11/19/2022] Open
Abstract
Accurately assessing the complex tissue mechanics of cerebral aneurysms (CAs) is critical for elucidating how CAs grow and whether that growth will lead to rupture. The factors that have been implicated in CA progression - blood flow dynamics, immune infiltration, and extracellular matrix remodeling - all occur heterogeneously throughout the CA. Thus, it stands to reason that the mechanical properties of CAs are also spatially heterogeneous. Here, we present a new method for characterizing the mechanical heterogeneity of human CAs using generalized anisotropic inverse mechanics, which uses biaxial stretching experiments and inverse analyses to determine the local Kelvin moduli and principal alignments within the tissue. Using this approach, we find that there is significant mechanical heterogeneity within a single acquired human CA. These results were confirmed using second harmonic generation imaging of the CA's fiber architecture and a correlation was observed. This approach provides a single-step method for determining the complex heterogeneous mechanics of CAs, which has important implications for future identification of metrics that can improve accuracy in prediction risk of rupture.
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Affiliation(s)
- Elizabeth D Shih
- Department of Biomedical Engineering, University of Minnesota Twin Cities, Minneapolis, Minnesota, USA
| | - Paolo P Provenzano
- Department of Biomedical Engineering, University of Minnesota Twin Cities, Minneapolis, Minnesota, USA
| | - Colleen M Witzenburg
- Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Victor H Barocas
- Department of Biomedical Engineering, University of Minnesota Twin Cities, Minneapolis, Minnesota, USA
| | - Andrew W Grande
- Department of Neurosurgery, University of Minnesota Twin Cities, Minneapolis, Minnesota, USA
| | - Patrick W Alford
- Department of Biomedical Engineering, University of Minnesota Twin Cities, Minneapolis, Minnesota, USA
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11
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Bermel EA, Thakral S, Claeson AA, Ellingson AM, Barocas VH. Asymmetric in-plane shear behavior of isolated cadaveric lumbar facet capsular ligaments: Implications for subject specific biomechanical models. J Biomech 2020; 105:109814. [PMID: 32423548 PMCID: PMC7336028 DOI: 10.1016/j.jbiomech.2020.109814] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Revised: 03/05/2020] [Accepted: 04/19/2020] [Indexed: 01/24/2023]
Abstract
The facet capsular ligaments (FCLs) flank the spinous process on the posterior aspect of the spine. The lumbar FCL is collagenous, with collagen fibers aligned primarily bone-to-bone (medial-lateral) and experiences significant shear, especially during spinal flexion and extension. We characterized the mechanical response of the lumbar FCL to in-plane shear, and we evaluated that response in the context of the fiber architecture. In-plane shear tests with both positive and negative shear (i.e., corresponding to flexion and to extension) were performed on eight cadaveric human L4-L5 FCLs. Our most striking observation was subject-dependent asymmetry in the response. All samples showed a toe region of low stiffness, transitioning to greater stiffness at higher strains, for both shear directions. Different samples showed profoundly different transition strains, with some samples stiffening more rapidly in positive shear and some in negative shear. This unpredictable asymmetry, which did not correlate with age, side, or degeneration state, suggesting that collagen fibers in the FCL are sometimes aligned at a slight positive angle from the bone-to-bone axis and sometimes at a negative angle. Fitting the experimental data to a fiber-composite-based finite element model supported this idea, yielding optimal fits with positive or negative off-axis fiber directions (-40° to +40°). Subsequent examination of selected FCLs by small-angle x-ray scattering (SAXS) showed a similar variability in fiber direction. We conclude that small individual differences in lumbar FCL architecture may have a significant effect on lumbar FCL mechanics, especially at moderate strains.
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Affiliation(s)
- Emily A Bermel
- University of Minnesota, Biomedical Engineering, 312 Church St. SE, 7-105 Nils Hasselmo Hall, Minneapolis, MN 55455, United States.
| | - Seema Thakral
- University of Minnesota, Characterization Facility, 100 Union St. SE, 14 Shepherd Labs, Minneapolis, MN 55455, United States.
| | - Amy A Claeson
- Zimmer Biomet Spine, 10225 Westmoor Dr., Westminster, CO 80021, United States.
| | - Arin M Ellingson
- University of Minnesota, Department of Rehabilitation Medicine, Divisions of Physical Therapy and Rehabilitation Science, 420 Delaware St SE, MMC 388, Minneapolis, MN 55455, United States.
| | - Victor H Barocas
- University of Minnesota, Biomedical Engineering, 312 Church St. SE, 7-105 Nils Hasselmo Hall, Minneapolis, MN 55455, United States.
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Korenczuk CE, Votava LE, Dhume RY, Kizilski SB, Brown GE, Narain R, Barocas VH. Isotropic Failure Criteria Are Not Appropriate for Anisotropic Fibrous Biological Tissues. J Biomech Eng 2019; 139:2613842. [PMID: 28334369 DOI: 10.1115/1.4036316] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The von Mises (VM) stress is a common stress measure for finite element models of tissue mechanics. The VM failure criterion, however, is inherently isotropic, and therefore may yield incorrect results for anisotropic tissues, and the relevance of the VM stress to anisotropic materials is not clear. We explored the application of a well-studied anisotropic failure criterion, the Tsai–Hill (TH) theory, to the mechanically anisotropic porcine aorta. Uniaxial dogbones were cut at different angles and stretched to failure. The tissue was anisotropic, with the circumferential failure stress nearly twice the axial (2.67 ± 0.67 MPa compared to 1.46 ± 0.59 MPa). The VM failure criterion did not capture the anisotropic tissue response, but the TH criterion fit the data well (R2 = 0.986). Shear lap samples were also tested to study the efficacy of each criterion in predicting tissue failure. Two-dimensional failure propagation simulations showed that the VM failure criterion did not capture the failure type, location, or propagation direction nearly as well as the TH criterion. Over the range of loading conditions and tissue geometries studied, we found that problematic results that arise when applying the VM failure criterion to an anisotropic tissue. In contrast, the TH failure criterion, though simplistic and clearly unable to capture all aspects of tissue failure, performed much better. Ultimately, isotropic failure criteria are not appropriate for anisotropic tissues, and the use of the VM stress as a metric of mechanical state should be reconsidered when dealing with anisotropic tissues.
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13
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Tusan CG, Man YH, Zarkoob H, Johnston DA, Andriotis OG, Thurner PJ, Yang S, Sander EA, Gentleman E, Sengers BG, Evans ND. Collective Cell Behavior in Mechanosensing of Substrate Thickness. Biophys J 2018; 114:2743-2755. [PMID: 29874622 PMCID: PMC6027966 DOI: 10.1016/j.bpj.2018.03.037] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2017] [Revised: 03/02/2018] [Accepted: 03/20/2018] [Indexed: 11/06/2022] Open
Abstract
Extracellular matrix stiffness has a profound effect on the behavior of many cell types. Adherent cells apply contractile forces to the material on which they adhere and sense the resistance of the material to deformation-its stiffness. This is dependent on both the elastic modulus and the thickness of the material, with the corollary that single cells are able to sense underlying stiff materials through soft hydrogel materials at low (<10 μm) thicknesses. Here, we hypothesized that cohesive colonies of cells exert more force and create more hydrogel deformation than single cells, therefore enabling them to mechanosense more deeply into underlying materials than single cells. To test this, we modulated the thickness of soft (1 kPa) elastic extracellular-matrix-functionalized polyacrylamide hydrogels adhered to glass substrates and allowed colonies of MG63 cells to form on their surfaces. Cell morphology and deformations of fluorescent fiducial-marker-labeled hydrogels were quantified by time-lapse fluorescence microscopy imaging. Single-cell spreading increased with respect to decreasing hydrogel thickness, with data fitting to an exponential model with half-maximal response at a thickness of 3.2 μm. By quantifying cell area within colonies of defined area, we similarly found that colony-cell spreading increased with decreasing hydrogel thickness but with a greater half-maximal response at 54 μm. Depth-sensing was dependent on Rho-associated protein kinase-mediated cellular contractility. Surface hydrogel deformations were significantly greater on thick hydrogels compared to thin hydrogels. In addition, deformations extended greater distances from the periphery of colonies on thick hydrogels compared to thin hydrogels. Our data suggest that by acting collectively, cells mechanosense rigid materials beneath elastic hydrogels at greater depths than individual cells. This raises the possibility that the collective action of cells in colonies or sheets may allow cells to sense structures of differing material properties at comparatively large distances.
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Affiliation(s)
- Camelia G Tusan
- Centre for Human Development, Stem Cells and Regeneration, Human Development and Health, Institute of Developmental Sciences, University of Southampton, Southampton, United Kingdom
| | - Yu-Hin Man
- Centre for Human Development, Stem Cells and Regeneration, Human Development and Health, Institute of Developmental Sciences, University of Southampton, Southampton, United Kingdom; Mechanical Engineering, University of Southampton, Southampton, United Kingdom
| | - Hoda Zarkoob
- Department of Biomedical Engineering, College of Engineering, University of Iowa, Iowa City, Iowa
| | - David A Johnston
- Biomedical Imaging Unit, Faculty of Medicine, University of Southampton, Southampton, United Kingdom
| | - Orestis G Andriotis
- Institute of Lightweight Design and Structural Biomechanics, Technische Universität Wien, Vienna, Austria
| | - Philipp J Thurner
- Institute of Lightweight Design and Structural Biomechanics, Technische Universität Wien, Vienna, Austria
| | - Shoufeng Yang
- Mechanical Engineering, University of Southampton, Southampton, United Kingdom; Department of Mechanical Engineering, Katholieke Universiteit Leuven, Leuven, Belgium
| | - Edward A Sander
- Department of Biomedical Engineering, College of Engineering, University of Iowa, Iowa City, Iowa
| | - Eileen Gentleman
- Centre for Craniofacial and Regenerative Biology, King's College London, London, United Kingdom
| | - Bram G Sengers
- Mechanical Engineering, University of Southampton, Southampton, United Kingdom
| | - Nicholas D Evans
- Centre for Human Development, Stem Cells and Regeneration, Human Development and Health, Institute of Developmental Sciences, University of Southampton, Southampton, United Kingdom; Mechanical Engineering, University of Southampton, Southampton, United Kingdom.
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14
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Zarkoob H, Chinnathambi S, Selby JC, Sander EA. Substrate deformations induce directed keratinocyte migration. J R Soc Interface 2018; 15:20180133. [PMID: 29899159 PMCID: PMC6030620 DOI: 10.1098/rsif.2018.0133] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2018] [Accepted: 05/18/2018] [Indexed: 12/18/2022] Open
Abstract
Cell migration is an essential part of many (patho)physiological processes, including keratinocyte re-epithelialization of healing wounds. Physical forces and mechanical cues from the wound bed (in addition to biochemical signals) may also play an important role in the healing process. Previously, we explored this possibility and found that polyacrylamide (PA) gel stiffness affected human keratinocyte behaviour and that mechanical deformations in soft (approx. 1.2 kPa) PA gels produced by neighbouring cells appeared to influence the process of de novo epithelial sheet formation. To clearly demonstrate that keratinocytes do respond to such deformations, we conducted a series of experiments where we observed the response of single keratinocytes to a prescribed local substrate deformation that mimicked a neighbouring cell or evolving multicellular aggregate via a servo-controlled microneedle. We also examined the effect of adding either Y27632 or blebbistatin on cell response. Our results indicate that keratinocytes do sense and respond to mechanical signals comparable to those that originate from substrate deformations imposed by neighbouring cells, a finding that could have important implications for the process of keratinocyte re-epithelialization that takes place during wound healing. Furthermore, the Rho/ROCK pathway and the engagement of NM II are both essential to substrate deformation-directed keratinocyte migration.
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Affiliation(s)
- Hoda Zarkoob
- Department of Biomedical Engineering, College of Engineering, University of Iowa, Iowa City, IA, USA
| | - Sathivel Chinnathambi
- Department of Biomedical Engineering, College of Engineering, University of Iowa, Iowa City, IA, USA
| | - John C Selby
- Department of Dermatology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA
| | - Edward A Sander
- Department of Biomedical Engineering, College of Engineering, University of Iowa, Iowa City, IA, USA
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15
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Zarkoob H, Chinnathambi S, Halberg SA, Selby JC, Magin TM, Sander EA. Mouse Keratinocytes Without Keratin Intermediate Filaments Demonstrate Substrate Stiffness Dependent Behaviors. Cell Mol Bioeng 2018; 11:163-174. [PMID: 31719883 PMCID: PMC6816603 DOI: 10.1007/s12195-018-0526-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Accepted: 04/26/2018] [Indexed: 10/17/2022] Open
Abstract
INTRODUCTION Traditionally thought to serve active vs. passive mechanical functions, respectively, a growing body of evidence suggests that actin microfilament and keratin intermediate filament (IF) networks, together with their associated cell-cell and cell-matrix anchoring junctions, may have a large degree of functional interdependence. Therefore, we hypothesized that the loss of keratin IFs in a knockout mouse keratinocyte model would affect the kinematics of colony formation, i.e., the spatiotemporal process by which individual cells join to form colonies and eventually a nascent epithelial sheet. METHODS Time-lapse imaging and deformation tracking microscopy was used to observe colony formation for both wild type (WT) and keratin-deficient knockout (KO) mouse keratinocytes over 24 h. Cells were cultured under high calcium conditions on collagen-coated substrates with nominal stiffnesses of ~ 1.2 kPa (soft) and 24 kPa (stiff). Immunofluorescent staining of actin and selected adhesion proteins was also performed. RESULTS The absence of keratin IFs markedly affected cell morphology, spread area, and cytoskeleton and adhesion protein organization on both soft and stiff substrates. Strikingly, an absence of keratin IFs also significantly reduced the ability of mouse keratinocytes to mechanically deform the soft substrate. Furthermore, KO cells formed colonies more efficiently on stiff vs. soft substrates, a behavior opposite to that observed for WT keratinocytes. CONCLUSIONS Collectively, these data are strongly supportive of the idea that an interdependence between actin microfilaments and keratin IFs does exist, while further suggesting that keratin IFs may represent an important and under-recognized component of keratinocyte mechanosensation and the force generation apparatus.
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Affiliation(s)
- Hoda Zarkoob
- Department of Biomedical Engineering, College of Engineering, University of Iowa, 5629 Seamans Center, Iowa City, IA USA
| | - Sathivel Chinnathambi
- Department of Biomedical Engineering, College of Engineering, University of Iowa, 5629 Seamans Center, Iowa City, IA USA
| | - Spencer A. Halberg
- Department of Biomedical Engineering, College of Engineering, University of Iowa, 5629 Seamans Center, Iowa City, IA USA
| | - John C. Selby
- Department of Dermatology, Carver College of Medicine, University of Iowa, Iowa City, IA USA
| | - Thomas M. Magin
- Division of Cell and Developmental Biology and SIKT, Institute of Biology, University of Leipzig, 04103 Leipzig, Germany
| | - E. A. Sander
- Department of Biomedical Engineering, College of Engineering, University of Iowa, 5629 Seamans Center, Iowa City, IA USA
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16
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Zhang S, Zarei V, Winkelstein BA, Barocas VH. Multiscale mechanics of the cervical facet capsular ligament, with particular emphasis on anomalous fiber realignment prior to tissue failure. Biomech Model Mechanobiol 2018; 17:133-145. [PMID: 28821971 PMCID: PMC5809183 DOI: 10.1007/s10237-017-0949-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2017] [Accepted: 08/04/2017] [Indexed: 12/11/2022]
Abstract
The facet capsular ligaments encapsulate the bilateral spinal facet joints and are common sources of painful injury due to afferent innervation. These ligaments exhibit architectural complexity, which is suspected to contribute to the experimentally observed lack of co-localization between macroscopic strain and microstructural tissue damage. The heterogeneous and multiscale nature of this ligament, combined with challenges in experimentally measuring its microscale mechanics, hinders the ability to understand sensory mechanisms under normal or injurious loading. Therefore, image-based, subject-specific, multiscale finite-element models were constructed to predict the mechanical responses of the human cervical facet capsular ligament under uniaxial tensile stretch. The models precisely simulated the force-displacement responses for all samples ([Formula: see text]) and showed promise in predicting the magnitude and location of peak regional strains at two different displacements. Yet, there was a loss of agreement between the model and experiment in terms of fiber organization at large tissue stretch, possibly due to a lack of accounting for tissue failure. The mean fiber stretch ratio predicted by the models was found to be significantly higher in regions that exhibited anomalous fiber realignment experimentally than in regions with normal realignment ([Formula: see text]). The development of microstructural abnormalities was associated with the predicted fiber-level stretch ([Formula: see text]), but not with the elemental maximum principal stress or maximum principal strain by logistic regression. The multiscale models elucidate a potential mechanical basis for predicting injury-prone tissue domains and for defining the relationships between macroscopic ligament stretch and microscale pathophysiology in the subfailure regime.
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Affiliation(s)
- Sijia Zhang
- Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Vahhab Zarei
- Department of Mechanical Engineering, University of Minnesota - Twin Cities, Minneapolis, MN, 55455, USA
| | - Beth A Winkelstein
- Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, 19104, USA
- Department of Neurosurgery, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Victor H Barocas
- Department of Biomedical Engineering, University of Minnesota - Twin Cities, Minneapolis, MN, 55455, USA.
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17
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Berg‐Johansen B, Fields AJ, Liebenberg EC, Li A, Lotz JC. Structure-function relationships at the human spinal disc-vertebra interface. J Orthop Res 2018; 36:192-201. [PMID: 28590060 PMCID: PMC5720932 DOI: 10.1002/jor.23627] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/16/2016] [Accepted: 05/28/2017] [Indexed: 02/04/2023]
Abstract
Damage at the intervertebral disc-vertebra interface associates with back pain and disc herniation. However, the structural and biomechanical properties of the disc-vertebra interface remain underexplored. We sought to measure mechanical properties and failure mechanisms, quantify architectural features, and assess structure-function relationships at this vulnerable location. Vertebra-disc-vertebra specimens from human cadaver thoracic spines were scanned with micro-computed tomography (μCT), surface speckle-coated, and loaded to failure in uniaxial tension. Digital image correlation (DIC) was used to calculate local surface strains. Failure surfaces were scanned using scanning electron microscopy (SEM), and adjacent sagittal slices were analyzed with histology and SEM. Seventy-one percent of specimens failed initially at the cartilage endplate-bone interface of the inner annulus region. Histology and SEM both indicated a lack of structural integration between the cartilage endplate (CEP) and bone. The interface failure strength was increased in samples with higher trabecular bone volume fraction in the vertebral endplates. Furthermore, failure strength decreased with degeneration, and in discs with thicker CEPs. Our findings indicate that poor structural connectivity between the CEP and vertebra may explain the structural weakness at this region, and provide insight into structural features that may contribute to risk for disc-vertebra interface injury. The disc-vertebra interface is the site of failure in the majority of herniation injuries. Here we show new structure-function relationships at this interface that may motivate the development of diagnostics, prevention strategies, and treatments to improve the prognosis for many low back pain patients with disc-vertebra interface injuries. © 2017 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 36:192-201, 2018.
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Affiliation(s)
- Britta Berg‐Johansen
- University of California513 Parnassus Avenue, S‐1157San FranciscoCalifornia94143‐0514
| | - Aaron J. Fields
- University of California513 Parnassus Avenue, S‐1157San FranciscoCalifornia94143‐0514
| | - Ellen C. Liebenberg
- University of California513 Parnassus Avenue, S‐1157San FranciscoCalifornia94143‐0514
| | - Alfred Li
- University of California513 Parnassus Avenue, S‐1157San FranciscoCalifornia94143‐0514
| | - Jeffrey C. Lotz
- University of California513 Parnassus Avenue, S‐1157San FranciscoCalifornia94143‐0514
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18
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Witzenburg CM, Dhume RY, Shah SB, Korenczuk CE, Wagner HP, Alford PW, Barocas VH. Failure of the Porcine Ascending Aorta: Multidirectional Experiments and a Unifying Microstructural Model. J Biomech Eng 2017; 139:2588206. [PMID: 27893044 DOI: 10.1115/1.4035264] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2016] [Indexed: 01/15/2023]
Abstract
The ascending thoracic aorta is poorly understood mechanically, especially its risk of dissection. To make better predictions of dissection risk, more information about the multidimensional failure behavior of the tissue is needed, and this information must be incorporated into an appropriate theoretical/computational model. Toward the creation of such a model, uniaxial, equibiaxial, peel, and shear lap tests were performed on healthy porcine ascending aorta samples. Uniaxial and equibiaxial tests showed anisotropy with greater stiffness and strength in the circumferential direction. Shear lap tests showed catastrophic failure at shear stresses (150-200 kPa) much lower than uniaxial tests (750-2500 kPa), consistent with the low peel tension (∼60 mN/mm). A novel multiscale computational model, including both prefailure and failure mechanics of the aorta, was developed. The microstructural part of the model included contributions from a collagen-reinforced elastin sheet and interlamellar connections representing fibrillin and smooth muscle. Components were represented as nonlinear fibers that failed at a critical stretch. Multiscale simulations of the different experiments were performed, and the model, appropriately specified, agreed well with all experimental data, representing a uniquely complete structure-based description of aorta mechanics. In addition, our experiments and model demonstrate the very low strength of the aorta in radial shear, suggesting an important possible mechanism for aortic dissection.
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Affiliation(s)
- Colleen M Witzenburg
- Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455
| | - Rohit Y Dhume
- Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455
| | - Sachin B Shah
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455
| | | | - Hallie P Wagner
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455
| | - Patrick W Alford
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455
| | - Victor H Barocas
- Department of Biomedical Engineering, University of Minnesota, 7-105 Nils Hasselmo Hall, 312 Church Street SE, Minneapolis, MN 55455 e-mail:
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19
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Zarei V, Liu CJ, Claeson AA, Akkin T, Barocas VH. Image-based multiscale mechanical modeling shows the importance of structural heterogeneity in the human lumbar facet capsular ligament. Biomech Model Mechanobiol 2017; 16:1425-1438. [PMID: 28361294 PMCID: PMC5704991 DOI: 10.1007/s10237-017-0896-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2016] [Accepted: 03/13/2017] [Indexed: 12/12/2022]
Abstract
The lumbar facet capsular ligament (FCL) primarily consists of aligned type I collagen fibers that are mainly oriented across the joint. The aim of this study was to characterize and incorporate in-plane local fiber structure into a multiscale finite element model to predict the mechanical response of the FCL during in vitro mechanical tests, accounting for the heterogeneity in different scales. Characterization was accomplished by using entire-domain polarization-sensitive optical coherence tomography to measure the fiber structure of cadaveric lumbar FCLs ([Formula: see text]). Our imaging results showed that fibers in the lumbar FCL have a highly heterogeneous distribution and are neither isotropic nor completely aligned. The averaged fiber orientation was [Formula: see text] ([Formula: see text] in the inferior region and [Formula: see text] in the middle and superior regions), with respect to lateral-medial direction (superior-medial to inferior-lateral). These imaging data were used to construct heterogeneous structural models, which were then used to predict experimental gross force-strain behavior and the strain distribution during equibiaxial and strip biaxial tests. For equibiaxial loading, the structural model fit the experimental data well but underestimated the lateral-medial forces by [Formula: see text]16% on average. We also observed pronounced heterogeneity in the strain field, with stretch ratios for different elements along the lateral-medial axis of sample typically ranging from about 0.95 to 1.25 during a 12% strip biaxial stretch in the lateral-medial direction. This work highlights the multiscale structural and mechanical heterogeneity of the lumbar FCL, which is significant both in terms of injury prediction and microstructural constituents' (e.g., neurons) behavior.
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Affiliation(s)
- Vahhab Zarei
- Departments of Mechanical Engineering, University of Minnesota-Twin Cities, Minneapolis, MN, USA
| | - Chao J Liu
- Departments of Biomedical Engineering, Universityof Minnesota-Twin Cities, Minneapolis, MN, USA
| | - Amy A Claeson
- Departments of Biomedical Engineering, Universityof Minnesota-Twin Cities, Minneapolis, MN, USA
| | - Taner Akkin
- Departments of Biomedical Engineering, Universityof Minnesota-Twin Cities, Minneapolis, MN, USA
| | - Victor H Barocas
- Departments of Biomedical Engineering, Universityof Minnesota-Twin Cities, Minneapolis, MN, USA.
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20
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Romito E, Shazly T, Spinale FG. In vivo assessment of regional mechanics post-myocardial infarction: A focus on the road ahead. J Appl Physiol (1985) 2017; 123:728-745. [PMID: 28235858 DOI: 10.1152/japplphysiol.00589.2015] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2015] [Revised: 01/13/2017] [Accepted: 02/18/2017] [Indexed: 12/21/2022] Open
Abstract
Cardiovascular disease, particularly the occurrence of myocardial infarction (MI), remains a leading cause of morbidity and mortality (Go et al., Circulation 127: e6-e245, 2013; Go et al. Circulation 129: e28-e292, 2014). There is growing recognition that a key factor for post-MI outcomes is adverse remodeling and changes in the regional structure, composition, and mechanical properties of the MI region itself. However, in vivo assessment of regional mechanics post-MI can be confounded by the species, temporal aspects of MI healing, as well as size, location, and extent of infarction across myocardial wall. Moreover, MI regional mechanics have been assessed over varying phases of the cardiac cycle, and thus, uniform conclusions regarding the material properties of the MI region can be difficult. This review assesses past studies that have performed in vivo measures of MI mechanics and attempts to provide coalescence on key points from these studies, as well as offer potential recommendations for unifying approaches in terms of regional post-MI mechanics. A uniform approach to biophysical measures of import will allow comparisons across studies, as well as provide a basis for potential therapeutic markers.
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Affiliation(s)
- Eva Romito
- University of South Carolina School of Engineering and Computing, Columbia, South Carolina; .,Cardiovascular Translational Research Center, University of South Carolina School of Medicine, Columbia, South Carolina
| | - Tarek Shazly
- University of South Carolina School of Engineering and Computing, Columbia, South Carolina
| | - Francis G Spinale
- University of South Carolina School of Engineering and Computing, Columbia, South Carolina.,Cardiovascular Translational Research Center, University of South Carolina School of Medicine, Columbia, South Carolina.,Department of Cell Biology and Anatomy, University of South Carolina School of Medicine, Columbia, South Carolina; and.,William Jennings Bryan Dorn Veteran Affairs Medical Center, Columbia, South Carolina
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21
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Claeson AA, Barocas VH. Planar biaxial extension of the lumbar facet capsular ligament reveals significant in-plane shear forces. J Mech Behav Biomed Mater 2016; 65:127-136. [PMID: 27569760 DOI: 10.1016/j.jmbbm.2016.08.019] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Revised: 08/02/2016] [Accepted: 08/09/2016] [Indexed: 10/21/2022]
Abstract
The lumbar facet capsular ligament (FCL) articulates with six degrees of freedom during spinal motions of flexion/extension, lateral bending, and axial rotation. The lumbar FCL is composed of highly aligned collagen fiber bundles on the posterior surface (oriented primarily laterally between the rigid articular facets) and irregularly oriented elastin on the anterior surface. Because the FCL is a capsule, it has multiple insertion sites across the lumbar facet joint, which, along with its material structure, give rise to complicated deformations in vivo. We performed planar equibiaxial mechanical tests on excised healthy cadaveric lumbar FCLs (n=6) to extract normal and shear reaction forces, and fit sample-specific two-fiber-family finite element models to the experimental force data. An eight-parameter anisotropic, hyperelastic model was used. Shear forces at maximum extension (mean values of 1.68N and 3.01N in the two directions) were of comparable magnitude to the normal forces perpendicular to the aligned collagen fiber bundles (4.67N) but smaller than normal forces in the fiber direction (16.11N). Inclusion of the experimental shear forces in the model optimization yielded fits with highly aligned fibers oriented at a specific angle across all samples, typically with one fiber population aligned nearly horizontally and the other at an oblique angle. Conversely, models fit to only the normal force data resulted in a broad range of fiber angles with low specificity. We found that shear forces generated through planar equibiaxial extension aided the model fit in describing the anisotropic nature of the FCL surface.
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Affiliation(s)
- Amy A Claeson
- Department of Biomedical Engineering, University of Minnesota - Twin Cities, Minneapolis, MN, USA
| | - Victor H Barocas
- Department of Biomedical Engineering, University of Minnesota - Twin Cities, Minneapolis, MN, USA.
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22
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Atluri K, De Jesus AM, Chinnathambi S, Brouillette MJ, Martin JA, Salem AK, Sander EA. Blebbistatin-Loaded Poly(d,l-lactide- co-glycolide) Particles For Treating Arthrofibrosis. ACS Biomater Sci Eng 2016; 2:1097-1107. [PMID: 33445238 DOI: 10.1021/acsbiomaterials.6b00082] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Joint immobility is a debilitating complication of articular trauma that is characterized by thickening and stiffening of the joint capsule and the formation of fibrotic lesions inside joints. Capsule release surgery can temporarily restore mobility, but contraction often recurs due to the contractile activities of fibroblasts, which exert tension on the capsule ECM via nonmuscle myosin II. Based on these findings we hypothesized that blebbistatin, a drug that reversibly inhibits the activity of this protein, would relax ECM tension imposed by fibroblasts and reduce fibrosis. In this study, we characterized the effectiveness of blebbistatin as an anticontractile treatment. Given that sustained suppression of contractile activity may be required to achieve capsule release and reduce fibrosis, we compared the effects on fibroblast-mediated collagen ECM displacement of blebbistatin-loaded poly(lactide-co-gylcolide) (PLGA) particles versus bolus blebbistatin dosing. Time-lapse imaging of fluorescent microspheres embedded in collagen gels confirmed that PLGA/blebbistatin inhibited force generation and reduced both gel displacement and rate of displacement. In addition, collagen production at 10 days was significantly reduced. Taken together, these data indicate that blebbistatin-loaded PLGA particles can be used to inhibit fibroblast force-generation and reduce collagen production and lay the foundation for optimization of drug delivery technology for treating arthrofibrosis.
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Affiliation(s)
- K Atluri
- Division of Pharmaceutics and Translational Therapeutics, University of Iowa College of Pharmacy, 115 South Grand Avenue, Iowa City, Iowa 52242, United States
| | - A M De Jesus
- Department of Biomedical Engineering, University of Iowa College of Engineering, 1402 Seamans Center, Iowa City, Iowa 52242, United States
| | - S Chinnathambi
- Department of Biomedical Engineering, University of Iowa College of Engineering, 1402 Seamans Center, Iowa City, Iowa 52242, United States
| | - M J Brouillette
- Department of Orthopaedics and Rehabilitation, University of Iowa Roy J and Lucille A Carver College of Medicine, 25 South Grand Avenue, Iowa City, Iowa 52242, United States
| | - J A Martin
- Department of Orthopaedics and Rehabilitation, University of Iowa Roy J and Lucille A Carver College of Medicine, 25 South Grand Avenue, Iowa City, Iowa 52242, United States
| | - A K Salem
- Division of Pharmaceutics and Translational Therapeutics, University of Iowa College of Pharmacy, 115 South Grand Avenue, Iowa City, Iowa 52242, United States.,Department of Biomedical Engineering, University of Iowa College of Engineering, 1402 Seamans Center, Iowa City, Iowa 52242, United States
| | - E A Sander
- Department of Biomedical Engineering, University of Iowa College of Engineering, 1402 Seamans Center, Iowa City, Iowa 52242, United States
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23
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Witzenburg CM, Barocas VH. A nonlinear anisotropic inverse method for computational dissection of inhomogeneous planar tissues. Comput Methods Biomech Biomed Engin 2016; 19:1630-46. [PMID: 27140845 DOI: 10.1080/10255842.2016.1176154] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Quantification of the mechanical behavior of soft tissues is challenging due to their anisotropic, heterogeneous, and nonlinear nature. We present a method for the 'computational dissection' of a tissue, by which we mean the use of computational tools both to identify and to analyze regions within a tissue sample that have different mechanical properties. The approach employs an inverse technique applied to a series of planar biaxial experimental protocols. The aggregated data from multiple protocols provide the basis for (1) segmentation of the tissue into regions of similar properties, (2) linear analysis for the small-strain behavior, assuming uniform, linear, anisotropic behavior within each region, (3) subsequent nonlinear analysis following each individual experimental protocol path and using local linear properties, and (4) construction of a strain energy data set W(E) at every point in the material by integrating the differential stress-strain functions along each strain path. The approach has been applied to simulated data and captures not only the general nonlinear behavior but also the regional differences introduced into the simulated tissue sample.
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Affiliation(s)
- Colleen M Witzenburg
- a Department of Mechanical Engineering , University of Minnesota , Minneapolis , MN , USA
| | - Victor H Barocas
- b Department of Biomedical Engineering , University of Minnesota , Minneapolis , MN , USA
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De Jesus AM, Aghvami M, Sander EA. A Combined In Vitro Imaging and Multi-Scale Modeling System for Studying the Role of Cell Matrix Interactions in Cutaneous Wound Healing. PLoS One 2016; 11:e0148254. [PMID: 26840835 PMCID: PMC4739727 DOI: 10.1371/journal.pone.0148254] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2015] [Accepted: 01/15/2016] [Indexed: 12/22/2022] Open
Abstract
Many cell types remodel the extracellular matrix of the tissues they inhabit in response to a wide range of environmental stimuli, including mechanical cues. Such is the case in dermal wound healing, where fibroblast migrate into and remodel the provisional fibrin matrix in a complex manner that depends in part on the local mechanical environment and the evolving multi-scale mechanical interactions of the system. In this study, we report on the development of an image-based multi-scale mechanical model that predicts the short-term (24 hours), structural reorganization of a fibrin gel by fibroblasts. These predictive models are based on an in vitro experimental system where clusters of fibroblasts (i.e., explants) were spatially arranged into a triangular geometry onto the surface of fibrin gels that were subjected to either Fixed or Free in-plane mechanical constraints. Experimentally, regional differences in short-term structural remodeling and cell migration were observed for the two gel boundary conditions. A pilot experiment indicated that these small differences in the short-term remodeling of the fibrin gel translate into substantial differences in long-term (4 weeks) remodeling, particularly in terms of collagen production. The multi-scale models were able to predict some regional differences in remodeling and qualitatively similar reorganization patterns for the two boundary conditions. However, other aspects of the model, such as the magnitudes and rates of deformation of gel, did not match the experiments. These discrepancies between model and experiment provide fertile ground for challenging model assumptions and devising new experiments to enhance our understanding of how this multi-scale system functions. These efforts will ultimately improve the predictions of the remodeling process, particularly as it relates to dermal wound healing and the reduction of patient scarring. Such models could be used to recommend patient-specific mechanical-based treatment dependent on parameters such as wound geometry, location, age, and health.
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Affiliation(s)
- Aribet M. De Jesus
- Department of Biomedical Engineering, University of Iowa, Iowa City, IA, United States of America
| | - Maziar Aghvami
- Department of Biomedical Engineering, University of Iowa, Iowa City, IA, United States of America
| | - Edward A. Sander
- Department of Biomedical Engineering, University of Iowa, Iowa City, IA, United States of America
- * E-mail:
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25
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Witzenburg CM, Dhume RY, Lake SP, Barocas VH. Automatic Segmentation of Mechanically Inhomogeneous Tissues Based on Deformation Gradient Jump. IEEE TRANSACTIONS ON MEDICAL IMAGING 2016; 35:29-41. [PMID: 26168433 PMCID: PMC4739827 DOI: 10.1109/tmi.2015.2453316] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Variations in properties, active behavior, injury, scarring, and/or disease can all cause a tissue's mechanical behavior to be heterogeneous. Advances in imaging technology allow for accurate full-field displacement tracking of both in vitro and in vivo deformation from an applied load. While detailed strain fields provide some insight into tissue behavior, material properties are usually determined by fitting stress-strain behavior with a constitutive equation. However, the determination of the mechanical behavior of heterogeneous soft tissue requires a spatially varying constitutive equation (i.e., one in which the material parameters vary with position). We present an approach that computationally dissects the sample domain into many homogeneous subdomains, wherein subdomain boundaries are formed by applying a betweenness based graphical analysis to the deformation gradient field to identify locations with large discontinuities. This novel partitioning technique successfully determined the shape, size and location of regions with locally similar material properties for: (1) a series of simulated soft tissue samples prescribed with both abrupt and gradual changes in anisotropy strength, prescribed fiber alignment, stiffness, and nonlinearity, (2) tissue analogs (PDMS and collagen gels) which were tested biaxially and speckle tracked (3) and soft tissues which exhibited a natural variation in properties (cadaveric supraspinatus tendon), a pathologic variation in properties (thoracic aorta containing transmural plaque), and active behavior (contracting cardiac sheet). The routine enables the dissection of samples computationally rather than physically, allowing for the study of small tissues specimens with unknown and irregular inhomogeneity.
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Affiliation(s)
- Colleen M. Witzenburg
- University of Minnesota, Minneapolis, MN 55455 USA and is now with the University of Virginia, Charlottesville, VA 22908 USA
| | | | - Spencer P. Lake
- University of Minnesota, Minneapolis, MN 55455 USA as is now with Washington University, St. Louis, MO 63130 USA
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26
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Schmidt JB, Chen K, Tranquillo RT. Effects of Intermittent and Incremental Cyclic Stretch on ERK Signaling and Collagen Production in Engineered Tissue. Cell Mol Bioeng 2015; 9:55-64. [PMID: 27114743 DOI: 10.1007/s12195-015-0415-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Intermittent cyclic stretching and incrementally increasing strain amplitude cyclic stretching were explored to overcome the reported adaptation of fibroblasts in response to constant amplitude cyclic stretching, with the goals of accelerating collagen production and understanding the underlying cell signaling. The effects of constant amplitude, intermittent, and incremental cyclic stretching regimens were investigated for dermal fibroblasts entrapped in a fibrin gel by monitoring the extracellular signal-regulated kinase (ERK1/2) and p38 pathways, collagen transcription, and finally the deposited collagen protein. Activation of ERK1/2, which has been shown to be necessary for stretch-induced collagen transcription, was maximal at 15 min and decayed by 1 h. ERK1/2 was reactivated by an additional onset of stretching or by an increment in the strain amplitude 6 h after the initial stimulus, which was approximately the lifetime of activated p38, a known ERK1/2 inhibitor. While both intermittent and incremental regimens reactivated ERK1/2, only incremental stretching increased collagen production compared to samples stretched with constant amplitude, resulting in a 37% increase in collagen per cell after 2 weeks. This suggests that a regimen with small, frequent increments in strain amplitude is optimal for this system and should be used in bioreactors for engineered tissues requiring high collagen content.
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Affiliation(s)
- Jillian B Schmidt
- Department of Chemical Engineering & Materials Science, University of Minnesota, 7-114 Nils Hasselmo Hall, 312 Church St. SE, Minneapolis, MN 55455, USA
| | - Kelley Chen
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455, USA
| | - Robert T Tranquillo
- Department of Chemical Engineering & Materials Science, University of Minnesota, 7-114 Nils Hasselmo Hall, 312 Church St. SE, Minneapolis, MN 55455, USA; Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455, USA
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27
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Claeson AA, Yeh YJ, Black AJ, Akkin T, Barocas VH. Marker-Free Tracking of Facet Capsule Motion Using Polarization-Sensitive Optical Coherence Tomography. Ann Biomed Eng 2015; 43:2953-66. [PMID: 26055969 DOI: 10.1007/s10439-015-1349-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2014] [Accepted: 05/27/2015] [Indexed: 12/28/2022]
Abstract
We proposed and tested a method by which surface strains of biological tissues can be captured without the use of fiducial markers by instead, utilizing the inherent structure of the tissue. We used polarization-sensitive optical coherence tomography (PS OCT) to obtain volumetric data through the thickness and across a partial surface of the lumbar facet capsular ligament during three cases of static bending. Reflectivity and phase retardance were calculated from two polarization channels, and a power spectrum analysis was performed on each a-line to extract the dominant banding frequency (a measure of degree of fiber alignment) through the maximum value of the power spectrum (maximum power). Maximum powers of all a-lines for each case were used to create 2D visualizations, which were subsequently tracked via digital image correlation. In-plane strains were calculated from measured 2D deformations and converted to 3D surface strains by including out-of-plane motion obtained from the PS OCT image. In-plane strains correlated with 3D strains (R(2) ≥ 0.95). Using PS OCT for marker-free motion tracking of biological tissues is a promising new technique because it relies on the structural characteristics of the tissue to monitor displacement instead of external fiducial markers.
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Affiliation(s)
- Amy A Claeson
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, 55455, USA.
| | - Yi-Jou Yeh
- Department of Electrical Engineering, University of Minnesota, Minneapolis, MN, 55455, USA
| | - Adam J Black
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, 55455, USA
| | - Taner Akkin
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, 55455, USA
| | - Victor H Barocas
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, 55455, USA.
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Abstract
Restoration of epidermal organization and function in response to a variety of pathophysiological insults is critically dependent on coordinated keratinocyte migration, proliferation, and stratification during the process of wound healing. These processes are mediated by the reconfiguration of both cell-cell (desmosomes, adherens junctions) and cell-matrix (focal adhesions, hemidesmosomes) junctions and the cytoskeletal filament networks that they serve to interconnect. In this study, we investigated the role of substrate elasticity (stiffness) on keratinocyte colony formation in vitro during the process of nascent epithelial sheet formation as triggered by the calcium switch model of keratinocyte culture. Keratinocytes cultured on pepsin digested type I collagen coated soft (nominal E = 1.2 kPa) polyacrylamide gels embedded with fluorescent microspheres exhibited (i) smaller spread contact areas, (ii) increased migration velocities, and (iii) increased rates of colony formation with more cells per colony than did keratinocytes cultured on stiff (nominal E = 24 kPa) polyacrylamide gels. As assessed by tracking of embedded microsphere displacements, keratinocytes cultured on soft substrates generated large local substrate deformations that appeared to recruit adjacent keratinocytes into joining an evolving colony. Together with the observed differences in keratinocyte kinematics and substrate deformations, we developed two ad hoc analyses, termed distance rank (DR) and radius of cooperativity (RC), that help to objectively ascribe what we perceive as increasingly cooperative behavior of keratinocytes cultured on soft versus stiff gels during the process of colony formation. We hypothesize that the differences in keratinocyte colony formation observed in our experiments could be due to cell-cell mechanical signaling generated via local substrate deformations that appear to be correlated with the increased expression of β4 integrin within keratinocytes positioned along the periphery of an evolving cell colony.
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Pyne JD, Genovese K, Casaletto L, Vande Geest JP. Sequential-digital image correlation for mapping human posterior sclera and optic nerve head deformation. J Biomech Eng 2014; 136:021002. [PMID: 24337344 DOI: 10.1115/1.4026224] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2013] [Accepted: 12/12/2013] [Indexed: 01/26/2023]
Abstract
Optic nerve head (ONH) deformations may be involved in the onset or further development of glaucoma, including in patients with relatively normal intraocular pressures (IOPs). Characterizing posterior scleral deformations over physiological pressures may provide a better understanding of how changes in IOP lead to changes in the mechanical environment of the ONH and possibly retinal ganglion cell death. Pressure inflation measurement test protocols are commonly used to measure deformation of the peripapillary sclera with full-field noncontact optical methods. The purpose of this work was to develop and validate a new sequential 3D digital image correlation (S-DIC) approach for quantification of posterior scleral pressure induced deformation that improves z (in-depth) resolution of the DIC measurement without losing in-plane sensitivity, while also being able to contour and map deformations of the complex-shaped ONH. Our approach combines two orthogonal axes of parallax with standard 3D DIC methods using a single high-resolution camera. The enhanced capabilities of S-DIC with respect to standard 3D DIC has been demonstrated by carrying out a complete benchmark for shape, deformation, and strain measurement on an object of known complex geometry. Our S-DIC method provided a reconstruction accuracy of 0.17% and an uncertainty in z-position measurement of 8 μm. The developed methodology has also been applied to a human posterior scleral shell, including the full peripapillary sclera and optic nerve. The relatively inexpensive S-DIC approach may provide new information on the biomechanical deformations of the optic nerve head and, thus, the death of retinal ganglion cells in primary open angle glaucoma.
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30
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Sancho A, Vázquez L, De-Juan-Pardo EM. Effect of cold storage on collagen-based hydrogels for the three-dimensional culture of adipose-derived stem cells. Biofabrication 2014; 6:035017. [DOI: 10.1088/1758-5082/6/3/035017] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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31
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De Jesús AM, Sander EA. Observing and quantifying fibroblast-mediated fibrin gel compaction. J Vis Exp 2014:e50918. [PMID: 24458198 DOI: 10.3791/50918] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
Cells embedded in collagen and fibrin gels attach and exert traction forces on the fibers of the gel. These forces can lead to local and global reorganization and realignment of the gel microstructure. This process proceeds in a complex manner that is dependent in part on the interplay between the location of the cells, the geometry of the gel, and the mechanical constraints on the gel. To better understand how these variables produce global fiber alignment patterns, we use time-lapse differential interference contrast (DIC) microscopy coupled with an environmentally controlled bioreactor to observe the compaction process between geometrically spaced explants (clusters of fibroblasts). The images are then analyzed with a custom image processing algorithm to obtain maps of the strain. The information obtained from this technique can be used to probe the mechanobiology of various cell-matrix interactions, which has important implications for understanding processes in wound healing, disease development, and tissue engineering applications.
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32
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Hadi MF, Sander EA, Barocas VH. Multiscale model predicts tissue-level failure from collagen fiber-level damage. J Biomech Eng 2013; 134:091005. [PMID: 22938372 DOI: 10.1115/1.4007097] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Excessive tissue-level forces communicated to the microstructure and extracellular matrix of soft tissues can lead to damage and failure through poorly understood physical processes that are multiscale in nature. In this work, we propose a multiscale mechanical model for the failure of collagenous soft tissues that incorporates spatial heterogeneity in the microstructure and links the failure of discrete collagen fibers to the material response of the tissue. The model, which is based on experimental failure data derived from different collagen gel geometries, was able to predict the mechanical response and failure of type I collagen gels, and it demonstrated that a fiber-based rule (at the micrometer scale) for discrete failure can strongly shape the macroscale failure response of the gel (at the millimeter scale). The model may be a useful tool in predicting the macroscale failure conditions for soft tissues and engineered tissue analogs. In addition, the multiscale model provides a framework for the study of failure in complex fiber-based mechanical systems in general.
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Affiliation(s)
- Mohammad F Hadi
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455, USA.
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Robertson C, Ikemura K, Krasieva TB, George SC. Multiscale analysis of collagen microstructure with generalized image correlation spectroscopy and the detection of tissue prestress. Biomaterials 2013; 34:6127-32. [PMID: 23642533 DOI: 10.1016/j.biomaterials.2013.04.019] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2013] [Accepted: 04/10/2013] [Indexed: 12/13/2022]
Abstract
Prestress in tissue is currently detected through destructive methods which obviate both in vivo and longitudinal assessment. We hypothesized that prestress could be detected and quantified by analyzing the microstructure of the extracellular matrix at different spatial scales using non-invasive and non-destructive optical imaging. A simple model of tissue prestress was created using fibroblast-mediated contraction of collagen gels around a central mandrel. Using a quantitative, multiscale, image processing technique, termed generalized image correlation spectroscopy (GICS) of second harmonic images, collagen fiber number and alignment at three different length scales characteristic of the collagen fibril, collagen fiber, and cell were analyzed. GICS fiber alignment (σ(maj/min)) was significantly different across load state, level of prestress, and length scale. The largest fiber ratio, and thus highest alignment, was seen in prestressed, externally loaded gels at a length scale equivalent to the size of the fibroblast cells. Alignment at both fiber and cell scale correlated with prestress in this model. We conclude that GICS of second harmonic images of collagen can predict prestress, and that microstructural organization at the collagen fiber and cell scale are the primary determinants of prestress in cellularized collagen gels.
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Affiliation(s)
- Claire Robertson
- Department of Biomedical Engineering, University of California, Irvine, CA, USA
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Fee TJ, Dean DR, Eberhardt AW, Berry JL. A novel device to quantify the mechanical properties of electrospun nanofibers. J Biomech Eng 2013; 134:104503. [PMID: 23083203 DOI: 10.1115/1.4007635] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Mechanical deformation of cell-seeded electrospun matrices plays an important role in cell signaling. However, electrospun biomaterials have inherently complex geometries due to the random deposition of fibers during the electrospinning process. This confounds attempts at quantifying strains exerted on adherent cells during electrospun matrix deformation. We have developed a novel mechanical test platform that allows deposition and tensile testing of electrospun fibers in a highly parallel arrangement to simplify mechanical analysis of the fibers alone and with adherent cells. The device is capable of optically recording fiber strain in a cell culture environment. Here we report on the mechanical and viscoelastic properties of highly parallel electrospun poly(ε-caprolactone) fibers. Force-strain data derived from this device will drive the development of cellular mechanotransduction studies as well as the customization of electrospun matrices for specific engineered tissue applications.
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Affiliation(s)
- Timothy J Fee
- Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
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Mechanics and kinematics of soft tissue under indentation are determined by the degree of initial collagen fiber alignment. J Mech Behav Biomed Mater 2012; 13:25-35. [PMID: 22842273 DOI: 10.1016/j.jmbbm.2012.03.017] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2011] [Revised: 03/15/2012] [Accepted: 03/28/2012] [Indexed: 11/20/2022]
Abstract
While several studies have evaluated how the degree of collagen alignment affects the response of soft tissues to tensile loading, the role of fibrillar organization in indentation is less understood. Collagen-based tissue-equivalents (TEs) provide a convenient model system to explore structure-function relationships since their microstructural properties can be easily controlled during fabrication. The purpose of this study was to evaluate the role of initial collagen alignment on the mechanical and structural behavior of soft tissues subjected to indentation using TEs as a model system. Cell-compacted TEs with either isotropic or highly anisotropic fiber alignment were subjected to four-step incremental stress-relaxation indentation tests. The mechanical properties, collagen reorganization and 2D strain patterns were quantified at each indentation step and compared between groups. While no differences were seen in the peak force response, significant differences were seen in relaxation behavior, fiber kinematics and tissue strain. Specifically, highly aligned samples exhibited a slower relaxation rate, smaller changes in collagen fiber orientation, larger changes in strength of alignment, and larger strain magnitudes compared to isotropic samples. Results demonstrate the significant role that microstructural organization plays in mediating the response of soft tissues to a non-tensile (i.e., indentation) mechanical stimulus.
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36
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Witzenburg C, Raghupathy R, Kren SM, Taylor DA, Barocas VH. Mechanical changes in the rat right ventricle with decellularization. J Biomech 2012; 45:842-9. [PMID: 22209312 PMCID: PMC3294143 DOI: 10.1016/j.jbiomech.2011.11.025] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/30/2011] [Indexed: 11/30/2022]
Abstract
The stiffness, anisotropy, and heterogeneity of freshly dissected (control) and perfusion-decellularized rat right ventricles were compared using an anisotropic inverse mechanics method. Cruciform tissue samples were speckled and then tested under a series of different biaxial loading configurations with simultaneous force measurement on all four arms and displacement mapping via image correlation. Based on the displacement and force data, the sample was segmented into piecewise homogeneous partitions. Tissue stiffness and anisotropy were characterized for each partition using a large-deformation extension of the general linear elastic model. The perfusion-decellularized tissue had significantly higher stiffness than the control, suggesting that the cellular contribution to stiffness, at least under the conditions used, was relatively small. Neither anisotropy nor heterogeneity (measured by the partition standard deviation of the modulus and anisotropy) varied significantly between control and decellularized samples. We thus conclude that although decellularization produces quantitative differences in modulus, decellularized tissue can provide a useful model of the native tissue extracellular matrix. Further, the large-deformation inverse method presented herein can be used to characterize complex soft tissue behaviors.
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Affiliation(s)
- Colleen Witzenburg
- Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455
| | - Ramesh Raghupathy
- Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455
| | - Stefan M. Kren
- Center for Cardiovascular Repair, Department of Integrative Biology and Physiology, University of Minnesota, Minneapolis, MN 55455
| | - Doris A. Taylor
- Center for Cardiovascular Repair, Department of Integrative Biology and Physiology, University of Minnesota, Minneapolis, MN 55455
| | - Victor H. Barocas
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455
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