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Jan NJ, Lee PY, Wallace J, Iasella M, Gogola A, Wang B, Sigal IA. Stretch-Induced Uncrimping of Equatorial Sclera Collagen Bundles. J Biomech Eng 2023; 145:054503. [PMID: 36459150 PMCID: PMC9791674 DOI: 10.1115/1.4056354] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Revised: 11/20/2022] [Accepted: 11/21/2022] [Indexed: 12/03/2022]
Abstract
Stretch-induced collagen uncrimping underlies the nonlinear mechanical behavior of the sclera according to what is often called the process of recruitment. We recently reported experimental measurements of sclera collagen crimp and pressure-induced uncrimping. Our studies, however, were cross-sectional, providing statistical descriptions of crimp with no information on the effects of stretch on specific collagen bundles. Data on bundle-specific uncrimping is necessary to better understand the effects of macroscale input on the collagen microscale and tissue failure. Our goal in this project was to measure bundle-specific stretch-induced collagen uncrimping of sclera. Three goat eyes were cryosectioned sagittally (30 μm). Samples of equatorial sclera were isolated, mounted to a custom uni-axial stretcher and imaged with polarized light microscopy at various levels of clamp-to-clamp stretch until failure. At each stretch level, local strain was measured using image tracking techniques. The level of collagen crimping was determined from the bundle waviness, defined as the circular standard deviation of fiber orientation along a bundle. Eye-specific recruitment curves were then computed using eye-specific waviness at maximum stretch before sample failure to define fibers as recruited. Nonlinear mixed effect models were used to determine the associations of waviness to local strain and recruitment to clamp-to-clamp stretch. Waviness decreased exponentially with local strain (p < 0.001), whereas bundle recruitment followed a sigmoidal curve with clamp-to-clamp stretch (p < 0.001). Individual bundle responses to stretch varied substantially, but recruitment curves were similar across sections and eyes. In conclusion, uni-axial stretch caused measurable bundle-specific uncrimping, with the sigmoidal recruitment pattern characteristic of fiber-reinforced soft tissues.
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Affiliation(s)
- Ning-Jiun Jan
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15213
| | - Po-Yi Lee
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15213
| | - Jacob Wallace
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15213
| | - Michael Iasella
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15213
| | - Alexandra Gogola
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213
| | - Bingrui Wang
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213
| | - Ian A. Sigal
- Department of Ophthalmology, Laboratory of Ocular Biomechanics, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15213
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Ni L, Riesterer J, Wang H, Berry L, Blackburn K, Chuang J, Kim W, Xu G, Moroi SE, Argento A. Method for the biomechanical analysis of aqueous veins and perilimbal sclera by three-dimensional photoacoustic imaging and strain field calculation. Sci Rep 2021; 11:22108. [PMID: 34764362 PMCID: PMC8585983 DOI: 10.1038/s41598-021-01458-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Accepted: 10/12/2021] [Indexed: 11/09/2022] Open
Abstract
A method motivated by the eye's aqueous veins is described for the imaging and strain calculation within soft biological tissues. A challenge to the investigation of the biomechanics of the aqueous vein-perilimbal sclera tissue complex is resolution of tissue deformations as a function of intraocular pressure and the subsequent calculation of strain (a normalized measure of deformation). The method involves perfusion of the eye with a contrast agent during conduction of non-invasive, optical resolution photoacoustic microscopy. This imaging technique permits three-dimensional displacement measurements of tracked points on the inner walls of the veins which are used in a finite element model to determine the corresponding strains. The methods are validated against two standard strain measurement methods. Representative porcine globe perfusion experiments are presented that demonstrate the power of the method to determine complex strain fields in the veins dependent on intraocular pressure as well as vein anatomy. In these cases, veins are observed to move radially outward during increases in intraocular pressure and to possess significant spatial strain variation, possibly influenced by their branching patterns. To the authors' knowledge, these are the only such quantitative, data driven, calculations of the aqueous vein strains available in the open literature.
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Affiliation(s)
- Linyu Ni
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA
| | - John Riesterer
- Department of Mechanical Engineering, University of Michigan-Dearborn, 4901 Evergreen Road, Dearborn, MI, 48128, USA
| | - Huaizhou Wang
- Department of Ophthalmology and Visual Sciences, Kellogg Eye Center, University of Michigan, Ann Arbor, MI, 48105, USA.,Currently at Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing, China
| | - Layla Berry
- Department of Mechanical Engineering, University of Michigan-Dearborn, 4901 Evergreen Road, Dearborn, MI, 48128, USA
| | - Kara Blackburn
- Department of Ophthalmology and Visual Sciences, Kellogg Eye Center, University of Michigan, Ann Arbor, MI, 48105, USA
| | - Jonathan Chuang
- Department of Ophthalmology and Visual Sciences, Kellogg Eye Center, University of Michigan, Ann Arbor, MI, 48105, USA
| | - Wonsuk Kim
- Department of Mechanical Engineering, University of Michigan-Dearborn, 4901 Evergreen Road, Dearborn, MI, 48128, USA
| | - Guan Xu
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA.,Department of Ophthalmology and Visual Sciences, Kellogg Eye Center, University of Michigan, Ann Arbor, MI, 48105, USA
| | - Sayoko E Moroi
- Department of Ophthalmology and Visual Sciences, Kellogg Eye Center, University of Michigan, Ann Arbor, MI, 48105, USA.,Department of Ophthalmology and Visual Sciences, Havener Eye Institute, The Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA
| | - Alan Argento
- Department of Mechanical Engineering, University of Michigan-Dearborn, 4901 Evergreen Road, Dearborn, MI, 48128, USA.
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Zhou H, Simmons CS, Sarntinoranont M, Subhash G. Raman Spectroscopy Methods to Characterize the Mechanical Response of Soft Biomaterials. Biomacromolecules 2020; 21:3485-3497. [PMID: 32833438 DOI: 10.1021/acs.biomac.0c00818] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Raman spectroscopy has been used extensively to characterize the influence of mechanical deformation on microstructure changes in biomaterials. While traditional piezo-spectroscopy has been successful in assessing internal stresses of hard biomaterials by tracking prominent peak shifts, peak shifts due to applied loads are near or below the resolution limit of the spectrometer for soft biomaterials with moduli in the kilo- to mega-Pascal range. In this Review, in addition to peak shifts, other spectral features (e.g., polarized intensity and intensity ratio) that provide quantitative assessments of microstructural orientation and secondary structure in soft biomaterials and their strain dependence are discussed. We provide specific examples for each method and classify sensitive Raman characteristic bands common across natural (e.g., soft tissue) and synthetic (e.g., polymeric scaffolds) soft biomaterials upon mechanical deformation. This Review can provide guidance for researchers aiming to analyze micromechanics of soft tissues and engineered tissue constructs by Raman spectroscopy.
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Affiliation(s)
- Hui Zhou
- Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida 32611, United States
| | - Chelsey S Simmons
- Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida 32611, United States
| | - Malisa Sarntinoranont
- Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida 32611, United States
| | - Ghatu Subhash
- Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida 32611, United States
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Boote C, Sigal IA, Grytz R, Hua Y, Nguyen TD, Girard MJA. Scleral structure and biomechanics. Prog Retin Eye Res 2019; 74:100773. [PMID: 31412277 DOI: 10.1016/j.preteyeres.2019.100773] [Citation(s) in RCA: 144] [Impact Index Per Article: 28.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2019] [Revised: 08/07/2019] [Accepted: 08/08/2019] [Indexed: 12/18/2022]
Abstract
As the eye's main load-bearing connective tissue, the sclera is centrally important to vision. In addition to cooperatively maintaining refractive status with the cornea, the sclera must also provide stable mechanical support to vulnerable internal ocular structures such as the retina and optic nerve head. Moreover, it must achieve this under complex, dynamic loading conditions imposed by eye movements and fluid pressures. Recent years have seen significant advances in our knowledge of scleral biomechanics, its modulation with ageing and disease, and their relationship to the hierarchical structure of the collagen-rich scleral extracellular matrix (ECM) and its resident cells. This review focuses on notable recent structural and biomechanical studies, setting their findings in the context of the wider scleral literature. It reviews recent progress in the development of scattering and bioimaging methods to resolve scleral ECM structure at multiple scales. In vivo and ex vivo experimental methods to characterise scleral biomechanics are explored, along with computational techniques that combine structural and biomechanical data to simulate ocular behaviour and extract tissue material properties. Studies into alterations of scleral structure and biomechanics in myopia and glaucoma are presented, and their results reconciled with associated findings on changes in the ageing eye. Finally, new developments in scleral surgery and emerging minimally invasive therapies are highlighted that could offer new hope in the fight against escalating scleral-related vision disorder worldwide.
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Affiliation(s)
- Craig Boote
- Structural Biophysics Research Group, School of Optometry & Vision Sciences, Cardiff University, UK; Ophthalmic Engineering & Innovation Laboratory (OEIL), Department of Biomedical Engineering, National University of Singapore, Singapore; Newcastle Research & Innovation Institute Singapore (NewRIIS), Singapore.
| | - Ian A Sigal
- Laboratory of Ocular Biomechanics, Department of Ophthalmology, University of Pittsburgh, USA
| | - Rafael Grytz
- Department of Ophthalmology & Visual Sciences, University of Alabama at Birmingham, USA
| | - Yi Hua
- Laboratory of Ocular Biomechanics, Department of Ophthalmology, University of Pittsburgh, USA
| | - Thao D Nguyen
- Department of Mechanical Engineering, Johns Hopkins University, USA
| | - Michael J A Girard
- Ophthalmic Engineering & Innovation Laboratory (OEIL), Department of Biomedical Engineering, National University of Singapore, Singapore; Singapore Eye Research Institute (SERI), Singapore National Eye Centre, Singapore
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Ouyang X, Han Y, Xie Y, Wu Y, Guo S, Cheng M, Wang G. The collagen metabolism affects the scleral mechanical properties in the different processes of scleral remodeling. Biomed Pharmacother 2019; 118:109294. [PMID: 31404770 DOI: 10.1016/j.biopha.2019.109294] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Revised: 07/12/2019] [Accepted: 07/31/2019] [Indexed: 01/15/2023] Open
Abstract
PURPOSE To increase the understanding of collagen metabolism as related to scleral remodeling in the process of emmetropization and myopization. METHODS An eyelid suture that lasted 60 days was performed on one-month-old rabbits to establish an experimental monocular visual deprivation myopia model and the axial length was recorded. HE staining and transmission electron microscope were used to observe the scleral structure. The Instron 5544 was used to measure scleral elastic modulus after measuring the scleral thickness. The content of scleral tissue collagen was determined by detecting the hydroxyproline quantity and the collagen I α1, MMP-2, and TIMP-2 mRNA expression were detected by RT-PCR Kit. RESULTS During regular emmetropization, the scleral collagen synthesis was higher than decomposition and the diameter of collagen fibrils increased, and then the sclera thickened and mechanical properties improved. During myopization, the scleral collagen decomposition was higher than synthesis and the diameter of collagen fibrils was smaller, and then the sclera thinner and mechanical properties lower, which resulted in a difference in scleral tissue strain. CONCLUSION The results suggested that there were different scleral remodeling process between the emmetropization and myopization, and the collagen metabolism affected the scleral mechanical properties and scleral remodeling and then affected the scleral growth, axial elongation, and even myopization.
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Affiliation(s)
- Xinli Ouyang
- Key Laboratory of Biological Medicines in Universities of Shandong Province, Weifang Medical University, Weifang, 261053, China
| | - Yangyang Han
- Key Laboratory of Biological Medicines in Universities of Shandong Province, Weifang Medical University, Weifang, 261053, China
| | - Yongfang Xie
- Key Laboratory of Biological Medicines in Universities of Shandong Province, Weifang Medical University, Weifang, 261053, China
| | - Yide Wu
- Key Laboratory of Biological Medicines in Universities of Shandong Province, Weifang Medical University, Weifang, 261053, China
| | - Shaojia Guo
- Key Laboratory of Biological Medicines in Universities of Shandong Province, Weifang Medical University, Weifang, 261053, China
| | - Min Cheng
- Key Laboratory of Biological Medicines in Universities of Shandong Province, Weifang Medical University, Weifang, 261053, China
| | - Guohui Wang
- Key Laboratory of Biological Medicines in Universities of Shandong Province, Weifang Medical University, Weifang, 261053, China.
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Lamy R, Chan E, Lee OT, Phone A, Salgaonkar VA, Diederich CJ, Stewart JM. 880 kHz ultrasound treatment for drug delivery to the vitreous humor. Am J Transl Res 2018; 10:3162-3170. [PMID: 30416658 PMCID: PMC6220232] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2018] [Accepted: 09/17/2018] [Indexed: 06/09/2023]
Abstract
Clinical management of many chronic ophthalmological disorders requires direct delivery of drugs into the vitreous. There is an important need to investigate novel needle-less alternatives to deliver drugs to the vitreous. The purpose of this study is to assess the effects of a needle-less system using ultrasound to enhance vitreal delivery of small molecules through the sclera in an ex vivo model and to evaluate whether changes in permeability are mainly due to the heat generated by sonication. An eye cup containing 1 mL of sodium fluorescein 0.1% was placed on top of the sclera of cadaveric rabbit eyes. Treated eyes were sonicated for 10 minutes, and left in contact with the fluorescein solution for an additional 50 minutes. Control eyes received the same exposure to fluorescein solution (60 minutes) in the eye cup without ultrasound treatment. Vitreous humor was collected and analyzed using a fluorescence spectrophotometer to calculate the concentration of fluorescein that diffused into the vitreous humor. An additional set of eyes was treated using a heating probe to evaluate whether changes in permeability were mainly due to heat. Vitreous samples from ultrasound-treated eyes showed a 44.6% higher concentration of fluorescein compared to control eyes. The concentration of fluorescein in the vitreous of heat-treated eyes did not show a significant difference when compared to control eyes. Thus, phonophoresis is a promising needle-less method for vitreal drug delivery, and local heating conducted to the surface of the sclera should be mitigated because it does not enhance the efficacy of the method.
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Affiliation(s)
- Ricardo Lamy
- Department of Ophthalmology, University of CaliforniaSan Francisco, CA, USA
| | - Elliot Chan
- Department of Ophthalmology, University of CaliforniaSan Francisco, CA, USA
| | - On-Tat Lee
- Department of Ophthalmology, University of CaliforniaSan Francisco, CA, USA
| | - Audrey Phone
- Department of Ophthalmology, University of CaliforniaSan Francisco, CA, USA
| | - Vasant A Salgaonkar
- Department of Radiation Oncology, University of CaliforniaSan Francisco, CA, USA
| | - Chris J Diederich
- Department of Radiation Oncology, University of CaliforniaSan Francisco, CA, USA
| | - Jay M Stewart
- Department of Ophthalmology, University of CaliforniaSan Francisco, CA, USA
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Man X, Arroyo E, Dunbar M, Reed DM, Shah N, Kagemann L, Kim W, Moroi SE, Argento A. Perilimbal sclera mechanical properties: Impact on intraocular pressure in porcine eyes. PLoS One 2018; 13:e0195882. [PMID: 29718942 PMCID: PMC5931674 DOI: 10.1371/journal.pone.0195882] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Accepted: 03/31/2018] [Indexed: 11/24/2022] Open
Abstract
There is extensive knowledge on the relationship of posterior scleral biomechanics and intraocular pressure (IOP) load on glaucomatous optic neuropathy; however, the role for biomechanical influence of the perilimbal scleral tissue on the aqueous humor drainage pathway, including the distal venous outflow system, and IOP regulation is not fully understood. The purpose of this work is to study the outflow characteristics of perfused porcine eyes relative to the biomechanical properties of the perilimbal sclera, the posterior sclera and the cornea. Enucleated porcine eyes from eleven different animals were perfused with surrogate aqueous at two fixed flow rates while monitoring their IOP. After perfusion, mechanical stress-strain and relaxation tests were conducted on specimens of perilimbal sclera, posterior sclera, and cornea from the same perfused eyes. Statistical analysis of the data demonstrated a strong correlation between increased tangent modulus of the perilimbal sclera tissues and increased perfusion IOP (R2 = 0.74, p = 0.0006 at lower flow rate and R2 = 0.71, p = 0.0011 at higher flow rate). In contrast, there were no significant correlations between IOP and the tangent modulus of the other tissues (Posterior sclera: R2 = 0.17 at lower flow rate and R2 = 0.30 at higher flow rate; cornea: R2 = 0.02 at lower flow rate and R2<0.01 at higher flow rate) nor the viscoelastic properties of any tissue (R2 ≤ 0.08 in all cases). Additionally, the correlation occurred for IOP and not net outflow facility (R2 ≤ 0.12 in all cases). These results provide new evidence that IOP in perfused porcine eyes is strongly influenced by the tangent modulus, sometimes called the tissue stiffness, of the most anterior portion of the sclera, i.e. the limbus.
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Affiliation(s)
- Xiaofei Man
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, United States of America
- Department of Ophthalmology, Xin Hua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, People’s Republic of China
| | - Elizabeth Arroyo
- Department of Mechanical Engineering, University of Michigan-Dearborn, Dearborn, Michigan, United States of America
| | - Martha Dunbar
- Department of Mechanical Engineering, University of Michigan-Dearborn, Dearborn, Michigan, United States of America
- Department of Mechanical Engineering, Northwestern University, Evanston, Illinois, United States of America
| | - David M. Reed
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Neil Shah
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, United States of America
- Department of Ophthalmology, Loyola University Medical Center, Maywood, Illinois, United States of America
| | - Larry Kagemann
- Department of Ophthalmology, NYU Langone Medical Center, NYU School of Medicine, New York, New York, United States of America
- Division of Ophthalmic and Ear, Nose and Throat Devices, Office of Device Evaluation, Center for Devices and Radiological Health, Food and Drug Administration, Silver Spring, Maryland, United States of America
| | - Wonsuk Kim
- Department of Mechanical Engineering, University of Michigan-Dearborn, Dearborn, Michigan, United States of America
| | - Sayoko E. Moroi
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Alan Argento
- Department of Mechanical Engineering, University of Michigan-Dearborn, Dearborn, Michigan, United States of America
- * E-mail:
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The elastic modulus and collagen of sclera increase during the early growth process. J Mech Behav Biomed Mater 2018; 77:566-571. [PMID: 29096121 DOI: 10.1016/j.jmbbm.2017.10.024] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Revised: 10/12/2017] [Accepted: 10/16/2017] [Indexed: 11/20/2022]
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