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Boix-Lemonche G, Hildebrand T, Haugen HJ, Petrovski G, Nogueira LP. Contrast-enhanced Micro-CT 3D visualization of cell distribution in hydrated human cornea. Heliyon 2024; 10:e25828. [PMID: 38356495 PMCID: PMC10865036 DOI: 10.1016/j.heliyon.2024.e25828] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2023] [Revised: 01/27/2024] [Accepted: 02/02/2024] [Indexed: 02/16/2024] Open
Abstract
Background The cornea, a vital component of the human eye, plays a crucial role in maintaining visual clarity. Understanding its ultrastructural organization and cell distribution is fundamental for elucidating corneal physiology and pathology. This study comprehensively examines the microarchitecture of the hydrated human cornea using contrast-enhanced micro-computed tomography (micro-CT). Method Fresh human corneal specimens were carefully prepared and hydrated to mimic their in vivo state. Contrast enhancement with Lugol's iodine-enabled high-resolution Micro-CT imaging. The cells' three-dimensional (3D) distribution within the cornea was reconstructed and analyzed. Results The micro-CT imaging revealed exquisite details of the corneal ultrastructure, including the spatial arrangement of cells throughout its depth. This novel approach allowed for the visualization of cells' density and distribution in different corneal layers. Notably, our findings highlighted variations in cell distribution between non-hydrated and hydrated corneas. Conclusions This study demonstrates the potential of contrast-enhanced micro-CT as a valuable tool for non-destructive, 3D visualization and quantitative analysis of cell distribution in hydrated human corneas. These insights contribute to a better understanding of corneal physiology and may have implications for research in corneal diseases and tissue engineering.
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Affiliation(s)
- Gerard Boix-Lemonche
- Center for Eye Research and Innovative Diagnostics, Department of Ophthalmology, Institute for Clinical Medicine, Faculty of Medicine, University of Oslo, Norway
| | | | | | - Goran Petrovski
- Center for Eye Research and Innovative Diagnostics, Department of Ophthalmology, Institute for Clinical Medicine, Faculty of Medicine, University of Oslo, Norway
- Department of Ophthalmology, and Norwegian Center for Stem Cell Research, Oslo University Hospital, Oslo, Norway
- Department of Ophthalmology, University of Split School of Medicine and University Hospital Centre, Split, Croatia
- UKLO Network, University St. Kliment Ohridski – Bitola, Bitola, Macedonia
| | - Liebert Parreiras Nogueira
- Oral Research Laboratory, Institute of Clinical Dentistry, Faculty of Dentistry, University of Oslo, Oslo, Norway
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Hatami-Marbini H, Mehr JA. Regional differences in electroactive response of the sclera. Proc Inst Mech Eng H 2024; 238:149-159. [PMID: 38294347 DOI: 10.1177/09544119231217240] [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] [Indexed: 02/01/2024]
Abstract
The sclera exhibits mechanical response when subjected to an external electric stimulation. The scleral electroactive response is a function of its charge density, mechanical properties, thickness, and strength of the applied electric voltage. The primary objective of the present work was to investigate the regional differences in the electroactive response of porcine sclera. To this end, we cut scleral strips in meridional directions from superior-temporal, superior-nasal, inferior-temporal, and inferior-nasal quadrants. In addition, we excised samples circumferentially from the posterior, equatorial, and anterior regions. The electroactive bending response of these samples was measured under 10 and 15 V in 0.15 M NaCl solution. The meridional samples were tested under two different configurations by clamping them either from their anterior or posterior end. It was observed that the scleral electroactive deformation increased with increasing the the electric voltage. Furthermore, regardless of the region from which meridional strips were excised, their electroactive response was considerably larger when they were clamped from their anterior end. Unlike meridional strips, the electroactive response of circumferential samples was significantly dependent on the location, that is, the average maximum bending angle of posterior samples was significantly larger than that of equatorial and anterior strips. The regionally different electroactive bending response of the sclera was discussed in terms of the variation in its biochemical and biomechanical properties throughout the eyeball.
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Affiliation(s)
- Hamed Hatami-Marbini
- Computational Biomechanics Research Laboratory, Mechanical and Industrial Engineering Department, University of Illinois at Chicago, Chicago, IL, USA
| | - Jafar Arash Mehr
- Computational Biomechanics Research Laboratory, Mechanical and Industrial Engineering Department, University of Illinois at Chicago, Chicago, IL, USA
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Mehr JA, Hatami-Marbini H. Finite Deformation of Scleral Tissue under Electrical Stimulation: An Arbitrary Lagrangian-Eulerian Finite Element Method. Bioengineering (Basel) 2023; 10:920. [PMID: 37627805 PMCID: PMC10451613 DOI: 10.3390/bioengineering10080920] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2023] [Revised: 06/28/2023] [Accepted: 07/13/2023] [Indexed: 08/27/2023] Open
Abstract
The sclera is considered as the principal load-bearing tissue within the eye. The sclera is negatively charged; thus, it exhibits mechanical response to electrical stimulation. We recently demonstrated the electroactive behavior of sclera by performing experimental measurements that captured the deformation of the tip of scleral strips subjected to electric voltage. We also numerically analyzed the electromechanical response of the tissue using a chemo-electro-mechanical model. In the pre-sent study, we extended our previous work by experimentally characterizing the deformation profile of scleral strips along their length under electrical stimulation. In addition, we improved our previous mathematical model such that it could numerically capture the large deformation of samples. For this purpose, we considered the transient variability of the fixed charge density and the coupling between mechanical and chemo-electrical phenomena. These improvements in-creased the accuracy of the computational model, resulting in a better numerical representation of experimentally measured bending angles.
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Affiliation(s)
| | - Hamed Hatami-Marbini
- Mechanical and Industrial Engineering Department, University of Illinois Chicago, Chicago, IL 60607, USA
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Quinlan RA, Clark JI. Insights into the biochemical and biophysical mechanisms mediating the longevity of the transparent optics of the eye lens. J Biol Chem 2022; 298:102537. [PMID: 36174677 PMCID: PMC9638808 DOI: 10.1016/j.jbc.2022.102537] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 09/20/2022] [Accepted: 09/22/2022] [Indexed: 11/18/2022] Open
Abstract
In the human eye, a transparent cornea and lens combine to form the "refracton" to focus images on the retina. This requires the refracton to have a high refractive index "n," mediated largely by extracellular collagen fibrils in the corneal stroma and the highly concentrated crystallin proteins in the cytoplasm of the lens fiber cells. Transparency is a result of short-range order in the spatial arrangement of corneal collagen fibrils and lens crystallins, generated in part by post-translational modifications (PTMs). However, while corneal collagen is remodeled continuously and replaced, lens crystallins are very long-lived and are not replaced and so accumulate PTMs over a lifetime. Eventually, a tipping point is reached when protein aggregation results in increased light scatter, inevitably leading to the iconic protein condensation-based disease, age-related cataract (ARC). Cataracts account for 50% of vision impairment worldwide, affecting far more people than other well-known protein aggregation-based diseases. However, because accumulation of crystallin PTMs begins before birth and long before ARC presents, we postulate that the lens protein PTMs contribute to a "cataractogenic load" that not only increases with age but also has protective effects on optical function by stabilizing lens crystallins until a tipping point is reached. In this review, we highlight decades of experimental findings that support the potential for PTMs to be protective during normal development. We hypothesize that ARC is preventable by protecting the biochemical and biophysical properties of lens proteins needed to maintain transparency, refraction, and optical function.
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Affiliation(s)
- Roy A Quinlan
- Department of Biosciences, Durham University, South Road Science Site, Durham, United Kingdom; Department of Biological Structure, University of Washington, Seattle, Washington, USA.
| | - John I Clark
- Department of Biological Structure, University of Washington, Seattle, Washington, USA.
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Hatami-Marbini H, Mehr JA. Modeling and experimental investigation of electromechanical properties of scleral tissue; a CEM model using an anisotropic hyperelastic constitutive relation. Biomech Model Mechanobiol 2022; 21:1325-1337. [PMID: 35962249 DOI: 10.1007/s10237-022-01590-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2021] [Accepted: 05/01/2022] [Indexed: 12/15/2022]
Abstract
The sclera is a soft tissue primarily consisting of collagen fibers, elastin, and proteoglycans. The proteoglycans are composed of a core protein and negatively charged glycosaminoglycan side chains. The fixed electric charges inside the scleral extracellular matrix play a key role in its swelling and are expected to cause the tissue to deform in response to an electric field. However, the electroactive response of the sclera has not yet been investigated. The present work experimentally demonstrates that sclera behaves similar to an anionic electrosensitive hydrogel and develops a chemo-electro-mechanical (CEM) mathematical framework for its electromechanical response. In the numerical model, a hyperelastic constitutive law with distributed collagen fibers is used to capture the nonlinear mechanical properties of the sclera, and the coupled Poisson-Nernst-Planck equations represent the distribution of mobile ions throughout the domain. After calibrating the proposed numerical CEM model against the experimental measurements, we employ it to investigate the effects of different parameters on the scleral electromechanical response including the voltage and fixed charge density. The experimental and numerical findings of the present study confirm that sclera behaves as an electroactive hydrogel and provide new insight into the mechanical response of this ocular tissue.
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Affiliation(s)
- Hamed Hatami-Marbini
- Mechanical and Industrial Engineering Department, University of Illinois at Chicago, 2039 Engineering Research Facility, 842 West Taylor St, Chicago, IL, 60607, USA.
| | - Jafar Arash Mehr
- Mechanical and Industrial Engineering Department, University of Illinois at Chicago, 2039 Engineering Research Facility, 842 West Taylor St, Chicago, IL, 60607, USA
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Wang Y, Ma J, Wei S, Liu Y, Li X. Investigation of the effect of solution pH value on rabbit corneal stroma biomechanics. Int Ophthalmol 2022; 42:2255-2265. [PMID: 35075572 DOI: 10.1007/s10792-022-02226-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2021] [Accepted: 01/09/2022] [Indexed: 11/28/2022]
Abstract
PURPOSE To facilitate the protection of corneal stability during corneal epithelium defects by determining the effect of solution pH on corneal stroma biomechanics. METHODS Thirty rabbit corneas were extracted, and the epithelium was scraped off. The samples were immediately subjected to inflation tests with pressures ranging from 0.3 to 6 kPa at baseline and in three subsequent test cycles. During a 10-min interval between cycles, specimens were randomly divided into four groups; in three of these groups, phosphate-buffered saline (PBS) drops with pH values of 6.9, 7.4, or 7.9 were applied to the surface once per minute, whereas the fourth group did not receive drops. RESULTS The corneal thickness significantly increased following the administration of PBS, while the corneal tangent modulus significantly decreased. At 2.5 and 4.5 kPa, the modulus reduction was significantly smaller in the specimens treated with pH 6.9 PBS than in those treated with pH 7.4 or 7.9 PBS, adjusted for changes in corneal thickness. Linear fitting of the pressure-modulus plot revealed that the regression coefficient significantly decreased over time. The reduction in the coefficient was most prominent in the PBS-treated groups, and the administration of pH 6.9 PBS elicited the smallest reduction among those three groups, adjusted for corneal thickness changes. CONCLUSION The study demonstrated that the administration of PBS drops with various pH values affected corneal biomechanics independent of corneal stromal swelling, and the impact of slightly acidic PBS was minimal. The effect became more prominent as posterior pressure increased. The research provides the basis for mediating the pH value of tear film and drops to maintain biomechanical stability of epithelium defects corneal stroma.
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Affiliation(s)
- Yuexin Wang
- Department of Ophthalmology, Beijing Key Laboratory of Restoration of Damaged Ocular Nerve, Peking University Third Hospital, 49 North Garden Road, Haidian District, Beijing, 100191, China
- Beijing Key Laboratory of Restoration of Damaged Ocular Nerve, Peking University Third Hospital, Beijing, China
| | - Jiahui Ma
- Department of Ophthalmology, Peking University People's Hospital, Beijing, China
- Eye Diseases and Optometry Institute, Peking University Health Science Center, Beijing, China
| | - Shanshan Wei
- Department of Ophthalmology, Beijing Key Laboratory of Restoration of Damaged Ocular Nerve, Peking University Third Hospital, 49 North Garden Road, Haidian District, Beijing, 100191, China
- Beijing Key Laboratory of Restoration of Damaged Ocular Nerve, Peking University Third Hospital, Beijing, China
| | - Yushi Liu
- Department of Ophthalmology, Beijing Key Laboratory of Restoration of Damaged Ocular Nerve, Peking University Third Hospital, 49 North Garden Road, Haidian District, Beijing, 100191, China
- Beijing Key Laboratory of Restoration of Damaged Ocular Nerve, Peking University Third Hospital, Beijing, China
| | - Xuemin Li
- Department of Ophthalmology, Beijing Key Laboratory of Restoration of Damaged Ocular Nerve, Peking University Third Hospital, 49 North Garden Road, Haidian District, Beijing, 100191, China.
- Beijing Key Laboratory of Restoration of Damaged Ocular Nerve, Peking University Third Hospital, Beijing, China.
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Mehr JA, Hatami-Marbini H. Experimental and numerical analysis of electroactive characteristics of scleral tissue. Acta Biomater 2022; 143:127-137. [PMID: 35038585 DOI: 10.1016/j.actbio.2022.01.017] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2021] [Revised: 01/04/2022] [Accepted: 01/10/2022] [Indexed: 11/15/2022]
Abstract
The sclera provides mechanical support to retina and protects internal contents of the eye against external injuries. The scleral extracellular matrix is mainly composed of collagen fibers and proteoglycans (PGs). At physiological pH, collagen molecules are neutral but PGs contain negatively charged glycosaminoglycan chains. Thus, the sclera can be considered as a polyelectrolyte hydrogel and is expected to exhibit mechanical response when subjected to electrical stimulations. In this study, we mounted scleral strips, dissected from the posterior part of porcine eyes, at the center of a custom-designed container between two electrodes. The container was filled with NaCl solution and the bending deformation of scleral strips as a function of the applied electric voltage was measured experimentally. It was found that scleral strips reached to an average bending angle of 3°, 10° and 23° when subjected to 5V, 10V, and 15V, respectively. We also created a chemo-electro-mechanical finite element model for simulating the experimental measurements by solving coupled Poisson-Nernst-Plank and equilibrium mechanical field equations. The scleral fixed charge density and modulus of elasticity were found by fitting the experimental data. The ion concentration distribution inside the domain was found numerically and was used to explain the underlying mechanisms for the scleral electroactive response. The numerical simulations were also used to investigate the effects of various parameters such as the electric voltage and fixed charge density on the scleral deformation under an electric field. STATEMENT OF SIGNIFICANCE: This manuscript investigates the electroactive response of scleral tissue. It demonstrates that the sclera deforms mechanically when subjected to electrical stimulations. A chemo-electro-mechanical model is also presented in order to numerically capture the electromechanical response of the sclera. This numerical model is used to explain the experimental observations by finding the ion distribution inside the tissue under an electric field. This work is significant because it shows that the sclera is an electroactive polyanionic hydrogel and it provides new information about the underlying mechanisms governing its mechanical and electrical properties.
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Affiliation(s)
- Jafar Arash Mehr
- Mechanical and Industrial Engineering Department, University of Illinois at Chicago, Chicago, IL USA
| | - Hamed Hatami-Marbini
- Mechanical and Industrial Engineering Department, University of Illinois at Chicago, Chicago, IL USA.
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Atta G, Tempfer H, Kaser-Eichberger A, Traweger A, Heindl LM, Schroedl F. Is the human sclera a tendon-like tissue? A structural and functional comparison. Ann Anat 2021; 240:151858. [PMID: 34798297 DOI: 10.1016/j.aanat.2021.151858] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Revised: 09/22/2021] [Accepted: 11/09/2021] [Indexed: 12/17/2022]
Abstract
Collagen rich connective tissues fulfill a variety of important functions throughout the human body, most of which having to resist mechanical challenges. This review aims to compare structural and functional aspects of tendons and sclera, two tissues with distinct location and function, but with striking similarities regarding their cellular content, their extracellular matrix and their low degree of vascularization. The description of these similarities meant to provide potential novel insight for both the fields of orthopedic research and ophthalmology.
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Affiliation(s)
- Ghada Atta
- Department of Ophthalmology, University of Cologne, Faculty of Medicine and University Hospital Cologne, Cologne, Germany; Institute for Tendon and Bone Regeneration, Spinal Cord Injury and Tissue Regeneration Center Salzburg, Paracelsus Medical University, Salzburg, Austria
| | - Herbert Tempfer
- Institute for Tendon and Bone Regeneration, Spinal Cord Injury and Tissue Regeneration Center Salzburg, Paracelsus Medical University, Salzburg, Austria; Austrian Cluster for Tissue Regeneration, Vienna, Austria
| | - Alexandra Kaser-Eichberger
- Center for Anatomy and Cell Biology, Institute of Anatomy and Cell Biology - Salzburg, Paracelsus Medical University, Strubergasse 21, 5020 Salzburg, Austria
| | - Andreas Traweger
- Institute for Tendon and Bone Regeneration, Spinal Cord Injury and Tissue Regeneration Center Salzburg, Paracelsus Medical University, Salzburg, Austria; Austrian Cluster for Tissue Regeneration, Vienna, Austria
| | - Ludwig M Heindl
- Department of Ophthalmology, University of Cologne, Faculty of Medicine and University Hospital Cologne, Cologne, Germany; Center for Integrated Oncology (CIO) Aachen - Bonn - Cologne - Düsseldorf, Cologne, Germany
| | - Falk Schroedl
- Center for Anatomy and Cell Biology, Institute of Anatomy and Cell Biology - Salzburg, Paracelsus Medical University, Strubergasse 21, 5020 Salzburg, Austria.
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Dynamics of keratoconus progression after prior successful accelerated cross-linking treatment during and after pregnancy. J Cataract Refract Surg 2021; 48:599-603. [PMID: 34433777 DOI: 10.1097/j.jcrs.0000000000000801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2021] [Accepted: 08/19/2021] [Indexed: 11/27/2022]
Abstract
PURPOSE To evaluate the effectiveness of previously applied successful accelerated cross-linking (CXL) treatment in keratoconus stabilization during and after pregnancy. SETTING Ankara Yildirim Beyazit University, Ataturk Training and Research Hospital, Turkey. DESIGN Prospective, clinical study. METHODS Patients who became pregnant with stable keratoconus (after having an accelerated CXL procedure) were included. Uncorrected (UDVA) and corrected distance visual acuity (CDVA), manifest astigmatism (MA), keratometry (K)1, K2, K-max, central corneal thickness (CCT), thinnest corneal thickness (TCT), anterior (AE) and posterior elevation (PE) were recorded at baseline (before CXL), before pregnancy (the last visit after CXL), during pregnancy (3rd trimester) and after pregnancy (the last visit after pregnancy). RESULTS Study included 24 eyes of 19 patients. The mean time between CXL and conception was 12.4±5.1 months. The mean post-partum follow-up period was 27.6±13.3 months. The mean UDVA, CDVA, MA, and PE values did not show any significant differences during and after pregnancy compared to the post CXL values (p>0.05). The mean K-max flattened significantly after the CXL procedure (p=0.011), however it increased during pregnancy (p=0.037:after CXL-pregnancy) and then decreased back to the pre-pregnancy level after pregnancy (p=0.035:pregnancy-after pregnancy). The mean K1, K2, AE, CCT, and TCT remained stable during pregnancy and significantly decreased after pregnancy (p<0.05). CONCLUSION Keratoconus appears to progress during pregnancy in corneas that have previously received successful accelerated CXL treatment. However, this progress is mostly temporary, and generally regression occurs after delivery.
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Pachenari M, Hatami-Marbini H. Regional Differences in the Glycosaminoglycan Role in Porcine Scleral Hydration and Mechanical Behavior. Invest Ophthalmol Vis Sci 2021; 62:28. [PMID: 33749719 PMCID: PMC7991977 DOI: 10.1167/iovs.62.3.28] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose This study characterized the role of glycosaminoglycans (GAGs) in the hydration, thickness, and biomechanical properties of posterior and anterior porcine sclera. Methods The scleral discs and strips were obtained from the anterior and posterior parts of porcine eyes, and their initial hydration and thickness were measured. The anterior and posterior scleral discs were used to show the efficacy of the GAG removal protocol by quantifying their GAG content. The strips were divided into three groups of PBS treatment, buffer treatment, and enzyme treatment in order to assess the effects of different treatment procedures on the thickness, hydration, and viscoelastic properties of the samples. The mechanical properties of the strips were determined by performing uniaxial tensile stress relaxation experiments. Results It was found that the control and buffer groups had insignificant differences in all measured quantities. The samples from the posterior region had a significantly larger GAG content and thickness in comparison with those from anterior region; however, there was an insignificant difference in their hydration. The GAG depletion process decreased the hydration of both anterior and posterior samples significantly (P < 0.05). Furthermore, the mechanical tests showed that the removal of GAGs resulted in stiffer mechanical behavior in both anterior and posterior samples (P < 0.05). In particular, the peak stress and equilibrium stress were significantly larger for the strips in the enzyme treatment group. Conclusions GAGs and their interaction with the collagen network are important in defining the hydration and mechanical properties of both posterior and anterior sclera.
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Affiliation(s)
- Mohammad Pachenari
- Computational Biomechanics Research Laboratory, Mechanical and Industrial Engineering Department, University of Illinois at Chicago, Chicago, Illinois, United States
| | - Hamed Hatami-Marbini
- Computational Biomechanics Research Laboratory, Mechanical and Industrial Engineering Department, University of Illinois at Chicago, Chicago, Illinois, United States
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Eckes S, Braun J, Wack JS, Ritz U, Nickel D, Schmitz K. Rose Bengal Crosslinking to Stabilize Collagen Sheets and Generate Modulated Collagen Laminates. Int J Mol Sci 2020; 21:E7408. [PMID: 33049938 PMCID: PMC7582313 DOI: 10.3390/ijms21197408] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2020] [Revised: 10/05/2020] [Accepted: 10/07/2020] [Indexed: 01/07/2023] Open
Abstract
For medical application, easily accessible biomaterials with tailored properties are desirable. Collagen type I represents a biomaterial of choice for regenerative medicine and tissue engineering. Here, we present a simple method to modify the properties of collagen and to generate collagen laminates. We selected three commercially available collagen sheets with different thicknesses and densities and examined the effect of rose bengal and green light collagen crosslinking (RGX) on properties such as microstructure, swelling degree, mechanical stability, cell compatibility and drug release. The highest impact of RGX was measured for Atelocollagen, for which the swelling degree was reduced from 630% (w/w) to 520% (w/w) and thickness measured under force application increased from 0.014 mm to 0.455 mm, indicating a significant increase in mechanical stability. Microstructural analysis revealed that the sponge-like structure was replaced by a fibrous structure. While the initial burst effect during vancomycin release was not influenced by crosslinking, RGX increased cell proliferation on sheets of Atelocollagen and on Collagen Solutions. We furthermore demonstrate that RGX can be used to covalently attach different sheets to create materials with combined properties, making the modification and combination of readily available sheets with RGX an attractive approach for clinical application.
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Affiliation(s)
- Stefanie Eckes
- Clemens-Schöpf-Institute of Organic Chemistry and Biochemistry, Technical University of Darmstadt, Alarich-Weiss-Straße 8, 64287 Darmstadt, Germany
| | - Joy Braun
- Department of Orthopaedics and Traumatology, BiomaTiCS, University Medical Center, Johannes Gutenberg University, Langenbeckstraße 1, 55131 Mainz, Germany
| | - Julia S Wack
- Clemens-Schöpf-Institute of Organic Chemistry and Biochemistry, Technical University of Darmstadt, Alarich-Weiss-Straße 8, 64287 Darmstadt, Germany
| | - Ulrike Ritz
- Department of Orthopaedics and Traumatology, BiomaTiCS, University Medical Center, Johannes Gutenberg University, Langenbeckstraße 1, 55131 Mainz, Germany
| | - Daniela Nickel
- Berufsakademie Sachsen-Staatliche Studienakademie Glauchau, University of Cooperative Education, Kopernikusstraße 51, 08371 Glauchau, Germany
| | - Katja Schmitz
- Clemens-Schöpf-Institute of Organic Chemistry and Biochemistry, Technical University of Darmstadt, Alarich-Weiss-Straße 8, 64287 Darmstadt, Germany
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Espana EM, Birk DE. Composition, structure and function of the corneal stroma. Exp Eye Res 2020; 198:108137. [PMID: 32663498 PMCID: PMC7508887 DOI: 10.1016/j.exer.2020.108137] [Citation(s) in RCA: 92] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Revised: 06/29/2020] [Accepted: 06/30/2020] [Indexed: 12/13/2022]
Abstract
No other tissue in the body depends more on the composition and organization of the extracellular matrix (ECM) for normal structure and function than the corneal stroma. The precise arrangement and orientation of collagen fibrils, lamellae and keratocytes that occurs during development and is needed in adults to maintain stromal function is dependent on the regulated interaction of multiple ECM components that contribute to attain the unique properties of the cornea: transparency, shape, mechanical strength, and avascularity. This review summarizes the contribution of different ECM components, their structure, regulation and function in modulating the properties of the corneal stroma. Fibril forming collagens (I, III, V), fibril associated collagens with interrupted triple helices (XII and XIV), network forming collagens (IV, VI and VIII) as well as small leucine-rich proteoglycans (SLRP) expressed in the stroma: decorin, biglycan, lumican, keratocan, and fibromodulin are some of the ECM components reviewed in this manuscript. There are spatial and temporal differences in the expression of these ECM components, as well as interactions among them that contribute to stromal function. Unique regions within the stroma like Bowman's layer and Descemet's layer are discussed. To define the complexity of corneal stroma composition and structure as well as the relationship to function is a daunting task. Our knowledge is expanding, and we expect that this review provides a comprehensive overview of current knowledge, definition of gaps and suggests future research directions.
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Affiliation(s)
- Edgar M Espana
- Department of Molecular Pharmacology and Physiology, USA; Cornea, External Disease and Refractive Surgery, Department of Ophthalmology, University of South Florida, Morsani College of Medicine, Tampa, FL, USA
| | - David E Birk
- Department of Molecular Pharmacology and Physiology, USA.
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13
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Sun X, Chen D, Liu X, Yan X, Wu Y. Effect of enzyme-induced collagen crosslinking on porcine sclera. Biochem Biophys Res Commun 2020; 528:134-139. [PMID: 32451081 DOI: 10.1016/j.bbrc.2020.05.078] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Accepted: 05/11/2020] [Indexed: 01/25/2023]
Abstract
This study aims to evaluate the effect of a new type of collagen crosslinking (CXL) mediated by microbial transglutaminases (Tgases) on sclera. Porcine eyes were divided into two groups according to the different crosslinking procedures used: the double-sided CXL group (D-CXL group) and the single-sided CXL group (S-CXL group). In the D-CXL group, 4.0 × 14.0 mm scleral strips harvested from 40 porcine eyeballs were incubated with 1 U/ml Tgases for 30 min at 37 °C. Parallel scleral strips from the same eyeball were incubated with PBS under the same conditions as the controls. In the S-CXL group, 80 whole globes were directly incubated with 1 U/ml Tgases and PBS as the controls for 30 min at 37 °C. After incubation, 4.0 × 14.0 mm scleral strips were cut from each eyeball. Biomechanical testing and light microscopy were used. In the D-CXL group, the general elastic modulus of the Tgases-treated scleral strips was 14.89 ± 6.05 MPa, and the controls was 6.72 ± 2.58 MPa, indicating an increase of 121% with Tgases treatment. In the S-CXL group, the general elastic modulus of the Tgases-treated scleral strips was 12.88 ± 4.29 MPa, and the controls was 7.00 ± 2.45 MPa, indicating an increase of 84% with Tgases treatment. In both the D-CXL and S-CXL groups, significant increases in scleral rigidity were observed compared to that of the respective controls (P < 0.05). The histology indicated increased collagen bundle density, decreased interfibrillar spaces and increased interlamellar spaces after CXL. In conclusion, scleral collagen crosslinking mediated by Tgases produced a significant increase in biomechanical strength.
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Affiliation(s)
- Xiaona Sun
- Department of Ophthalmology, Peking University First Hospital, Peking University, Beijing, 100034, China
| | - Duo Chen
- School of Biological Science and Medical Engineering, Key Laboratory for Biomechanics and Mechanobiology of Ministry of Education, Beihang University, Beijing, 100191, China; Beijing Advanced Innovation Centre for Biomedical Engineering, Beihang University, Beijing 100083, China
| | - Xiaoyu Liu
- School of Biological Science and Medical Engineering, Key Laboratory for Biomechanics and Mechanobiology of Ministry of Education, Beihang University, Beijing, 100191, China; Beijing Advanced Innovation Centre for Biomedical Engineering, Beihang University, Beijing 100083, China
| | - Xiaoming Yan
- Department of Ophthalmology, Peking University First Hospital, Peking University, Beijing, 100034, China.
| | - Yuan Wu
- Department of Ophthalmology, Peking University First Hospital, Peking University, Beijing, 100034, China.
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14
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Hydration related changes in tensile response of posterior porcine sclera. J Mech Behav Biomed Mater 2020; 104:103562. [DOI: 10.1016/j.jmbbm.2019.103562] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2019] [Revised: 11/05/2019] [Accepted: 11/26/2019] [Indexed: 11/18/2022]
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15
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Clayson K, Sandwisch T, Ma Y, Pavlatos E, Pan X, Liu J. Corneal Hydration Control during Ex Vivo Experimentation Using Poloxamers. Curr Eye Res 2019; 45:111-117. [PMID: 31474157 DOI: 10.1080/02713683.2019.1663387] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Purpose: The purpose of this study was to develop an effective treatment method using poloxamers to restore and maintain physiological hydration in postmortem porcine and human corneas during ex vivo experimentation, and to compare corneal inflation response with or without treatment.Materials and Methods: Corneal buttons obtained from whole globes (n = 30 porcine, n = 8 human) were treated with various concentrations of poloxamer 188 (P188, a synthetic macromolecule surfactant) for 24 hrs to identify the concentration that would return the cornea to near-physiological hydration (i.e. H = 3.2). Whole globes (n = 12 porcine, n = 16 human) were also used to monitor central corneal thickness (CCT) during deswelling treatment. Inflation testing from 5 to 30 mmHg was performed in the porcine globes and a subset of human globes to characterize the mechanical response of the cornea after treatment.Results: Physiological hydration was obtained after 24 hrs immersion in 3.25% P188 for porcine corneas and 4.25% P188 treatment for human corneas. CCT was stabilized and returned to physiological levels after 24 hrs of treatment in 3.25% P188 in porcine (891 ± 66 µm) and 4.25% P188 in human (574 ± 34 µm) whole globes. Corneal axial strains at 30 mmHg were significantly larger at physiological hydration than in swollen cornea in both porcine (-6.42%±1.50% vs. -3.64%±1.05%, p = .004) and human (-2.85%±0.09% in vs. -1.53%±0.27%, p = .031) eyes.Conclusions: Our results suggest that P188 treatment was effective in restoring and maintaining near physiological corneal hydration during ex vivo testing, and hydration appeared to significantly impact corneal inflation response in both porcine and human eyes.
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Affiliation(s)
- Keyton Clayson
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, USA.,Biophysics Graduate Program, The Ohio State University, Columbus, Ohio, USA
| | - Thomas Sandwisch
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, USA
| | - Yanhui Ma
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, USA
| | - Elias Pavlatos
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, USA
| | - Xueliang Pan
- Department of Biomedical Informatics, The Ohio State University, Columbus, Ohio, USA
| | - Jun Liu
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, USA.,Biophysics Graduate Program, The Ohio State University, Columbus, Ohio, USA.,Department of Ophthalmology and Visual Science, The Ohio State University, Columbus, Ohio, USA
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16
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He F, Liu J, Ye P, Wu J, Liang G, Xu W. Biophysical and microstructural changes of swelling cornea caused by endothelial cells damage. Physiol Res 2019; 68:827-833. [PMID: 31424248 DOI: 10.33549/physiolres.934011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Biophysical properties and microstructural changes of swelling cornea which caused by endothelial cells damage will be evaluated. Swelling cornea models were established by endothelial cells damage in 114 Sprague Dawley rats. Relative gray value, swelling rate and light transmittance were measured to evaluated the biophysical properties and microstructure changes were observed by transmission electron microscopy. Relative gray value decreased while swelling rate rose along with time and both of them reached relative stability after 7 days. Light transmittance showed a decline trend with time even after corneal thickness had reached stable stage. Observed by transmission electron microscopy, interfibrillar distance increased, fewer proteoglycans coating appeared and remnants proteoglycan branches became thinner and longer in 7 days. Diameter of fibrils didn't change obviously with time. In cornea edema models caused by endothelial cells damage, the changes of biophysical property and microstructure can help us evaluate corneal edema accurately and objectively.
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Affiliation(s)
- F He
- Eye Center, Second Affiliated Hospital of Zhejiang University, College of Medicine, Hangzhou, China.
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17
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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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18
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Midgett DE, Jefferys JL, Quigley HA, Nguyen TD. The Contribution of Sulfated Glycosaminoglycans to the Inflation Response of the Human Optic Nerve Head. Invest Ophthalmol Vis Sci 2019; 59:3144-3154. [PMID: 30025126 PMCID: PMC6018372 DOI: 10.1167/iovs.18-23845] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Purpose In this study, we measured the effect of the removal of sulfated glycosaminoglycans (sGAGs) on the pressure-induced strains of the human lamina cribrosa (LC). Methods We applied an ex vivo inflation method to measure the three-dimensional (3D) deformation response of six human LCs to pressure, before and after the degradation of chondroitin and dermatan sulfates. The experiment used a laser-scanning microscope (LSM) to acquire the second harmonic generation (SHG) signal of the collagen structure in the LC. Digital volume correlation (DVC) was used to calculate the deformation in the LC after a change in pressure from 5 to 45 mm Hg. Results The average strains between 5 and 45 mm Hg in the LC decreased significantly after sGAG degradation (P ≤ 0.03), with the greatest change occurring in regions of previously high strain (P ≤ 0.003) and the peripheral regions of the LC (P ≤ 0.02). The stiffening effect was greater in the LC of middle-aged (42–49 years) donors compared with those of older (64–88 years) donors (P < 0.0001). Conclusions The LC experienced less strain at the same pressures after most sGAGs were removed. These results suggest that the natural decrease in sGAGs within the LC with age may contribute to the stiffer inflation response of older LC to IOP. Likewise, the increase in the amount of sGAGs observed in the LC of glaucomatous eyes, may contribute to a more compliant LC, which may affect the susceptibility and progression of axon damage.
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Affiliation(s)
- Dan E Midgett
- Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, Maryland, United States
| | - Joan L Jefferys
- Wilmer Ophthalmological Institute, School of Medicine, The Johns Hopkins University, Baltimore, Maryland, United States
| | - Harry A Quigley
- Wilmer Ophthalmological Institute, School of Medicine, The Johns Hopkins University, Baltimore, Maryland, United States
| | - Thao D Nguyen
- Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, Maryland, United States
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19
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Tuchina DK, Bashkatov AN, Genina EA, Tuchin VV. The Effect of Immersion Agents on the Weight and Geometric Parameters of Myocardial Tissue in Vitro. Biophysics (Nagoya-shi) 2019. [DOI: 10.1134/s0006350918050238] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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20
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Sdobnov AY, Darvin ME, Genina EA, Bashkatov AN, Lademann J, Tuchin VV. Recent progress in tissue optical clearing for spectroscopic application. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2018; 197:216-229. [PMID: 29433855 DOI: 10.1016/j.saa.2018.01.085] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2017] [Revised: 01/25/2018] [Accepted: 01/31/2018] [Indexed: 05/03/2023]
Abstract
This paper aims to review recent progress in optical clearing of the skin and over naturally turbid biological tissues and blood using this technique in vivo and in vitro with multiphoton microscopy, confocal Raman microscopy, confocal microscopy, NIR spectroscopy, optical coherence tomography, and laser speckle contrast imaging. Basic principles of the technique, its safety, advantages and limitations are discussed. The application of optical clearing agent on a tissue allows for controlling the optical properties of tissue. Optical clearing-induced reduction of tissue scattering significantly facilitates the observation of deep-located tissue regions, at the same time improving the resolution and image contrast for a variety of optical imaging methods suitable for clinical applications, such as diagnostics and laser treatment of skin diseases, mucosal tumor imaging, laser disruption of pathological abnormalities, etc.
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Affiliation(s)
- A Yu Sdobnov
- Faculty of Information Technology and Electrical Engineering, University of Oulu, Oulu 90570, Finland; Research-Educational Institute of Optics and Biophotonics, Saratov State University (National Research University of Russia), Astrakhanskaya 83, 410012 Saratov, Russian Federation.
| | - M E Darvin
- Center of Experimental and Applied Cutaneous Physiology, Department of Dermatology, Venerology and Allergology, Charité - Universitätsmedizin Berlin, Corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, Berlin Institute of Health, Charitéplatz 1, 10117 Berlin, Germany
| | - E A Genina
- Research-Educational Institute of Optics and Biophotonics, Saratov State University (National Research University of Russia), Astrakhanskaya 83, 410012 Saratov, Russian Federation; Interdisciplinary Laboratory of Biophotonics, Tomsk State University (National Research University of Russia), Lenin's av. 36, 634050 Tomsk, Russian Federation
| | - A N Bashkatov
- Research-Educational Institute of Optics and Biophotonics, Saratov State University (National Research University of Russia), Astrakhanskaya 83, 410012 Saratov, Russian Federation; Interdisciplinary Laboratory of Biophotonics, Tomsk State University (National Research University of Russia), Lenin's av. 36, 634050 Tomsk, Russian Federation
| | - J Lademann
- Center of Experimental and Applied Cutaneous Physiology, Department of Dermatology, Venerology and Allergology, Charité - Universitätsmedizin Berlin, Corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, Berlin Institute of Health, Charitéplatz 1, 10117 Berlin, Germany
| | - V V Tuchin
- Research-Educational Institute of Optics and Biophotonics, Saratov State University (National Research University of Russia), Astrakhanskaya 83, 410012 Saratov, Russian Federation; Interdisciplinary Laboratory of Biophotonics, Tomsk State University (National Research University of Russia), Lenin's av. 36, 634050 Tomsk, Russian Federation; Laboratory of Laser Diagnostics of Technical and Living Systems, Institute of Precision Mechanics and Control RAS, Rabochaya 24, 410028 Saratov, Russian Federation
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21
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Hayes S, White T, Boote C, Kamma-Lorger CS, Bell J, Sorenson T, Terrill N, Shebanova O, Meek KM. The structural response of the cornea to changes in stromal hydration. J R Soc Interface 2018; 14:rsif.2017.0062. [PMID: 28592658 PMCID: PMC5493790 DOI: 10.1098/rsif.2017.0062] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2017] [Accepted: 05/12/2017] [Indexed: 11/12/2022] Open
Abstract
The primary aim of this study was to quantify the relationship between corneal structure and hydration in humans and pigs. X-ray scattering data were collected from human and porcine corneas equilibrated with polyethylene glycol (PEG) to varying levels of hydration, to obtain measurements of collagen fibril diameter, interfibrillar spacing (IFS) and intermolecular spacing. Both species showed a strong positive linear correlation between hydration and IFS2 and a nonlinear, bi-phasic relationship between hydration and fibril diameter, whereby fibril diameter increased up to approximately physiological hydration, H = 3.0, with little change thereafter. Above H = 3.0, porcine corneas exhibited a larger fibril diameter than human corneas (p < 0.001). Intermolecular spacing also varied with hydration in a bi-phasic manner but reached a maximum value at a lower hydration (H = 1.5) than fibril diameter. Human corneas displayed a higher intermolecular spacing than porcine corneas at all hydrations (p < 0.0001). Human and porcine corneas required a similar PEG concentration to reach physiological hydration, suggesting that the total fixed charge that gives rise to the swelling pressure is the same. The difference in their structural responses to hydration can be explained by variations in molecular cross-linking and intra/interfibrillar water partitioning.
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Affiliation(s)
- Sally Hayes
- Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, UK
| | - Tomas White
- Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, UK
| | - Craig Boote
- Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, UK
| | - Christina S Kamma-Lorger
- Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, UK.,ALBA Synchrotron Light Source, Cerdanyola del Vallès, Barcelona, Spain
| | - James Bell
- Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, UK
| | | | | | | | - Keith M Meek
- Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, UK
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22
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Pavlatos E, Chen H, Clayson K, Pan X, Liu J. Imaging Corneal Biomechanical Responses to Ocular Pulse Using High-Frequency Ultrasound. IEEE TRANSACTIONS ON MEDICAL IMAGING 2018; 37:663-670. [PMID: 29408793 PMCID: PMC5826553 DOI: 10.1109/tmi.2017.2775146] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Imaging corneal biomechanical changes or abnormalities is important for better clinical diagnosis and treatment of corneal diseases. We propose a novel ultrasound-based method, called ocular pulse elastography (OPE), to image corneal deformation during the naturally occurring ocular pulse. Experiments on animal and human donor eyes, as well as synthetic radiofrequency (RF) data, were used to evaluate the efficacy of the OPE method. Using very high-frequency ultrasound (center frequency = 55 MHz), correlation-based speckle tracking yielded an accuracy of less than 10% error for axial tissue displacements of or above. Satisfactory speckle tracking was achieved for out-of-plane displacements up to . Using synthetic RF data with or without a pre-defined uniform strain, the OPE method detected strains down to 0.0001 axially and 0.00025 laterally with an error less than 10%. Experiments in human donor eyes showed excellent repeatability with an intraclass correlation of 0.98. The measurement outcome from OPE was also shown to be highly correlated with that of standard inflation. These results suggest the feasibility of OPE as a potential clinical tool for evaluating corneal biomechanics in vivo.
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23
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Wells HC, Sizeland KH, Kelly SJ, Kirby N, Hawley A, Mudie S, Haverkamp RG. Collagen Fibril Intermolecular Spacing Changes with 2-Propanol: A Mechanism for Tissue Stiffness. ACS Biomater Sci Eng 2017; 3:2524-2532. [DOI: 10.1021/acsbiomaterials.7b00418] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Hannah C. Wells
- School
of Engineering and Advanced Technology, Massey University, Private Bag
11222, Palmerston North 4442, New Zealand
| | - Katie H. Sizeland
- School
of Engineering and Advanced Technology, Massey University, Private Bag
11222, Palmerston North 4442, New Zealand
- Australian Synchrotron, 800 Blackburn
Road, Clayton, Melbourne, Victoria 3168, Australia
| | - Susyn J.R. Kelly
- School
of Engineering and Advanced Technology, Massey University, Private Bag
11222, Palmerston North 4442, New Zealand
| | - Nigel Kirby
- Australian Synchrotron, 800 Blackburn
Road, Clayton, Melbourne, Victoria 3168, Australia
| | - Adrian Hawley
- Australian Synchrotron, 800 Blackburn
Road, Clayton, Melbourne, Victoria 3168, Australia
| | - Stephen Mudie
- Australian Synchrotron, 800 Blackburn
Road, Clayton, Melbourne, Victoria 3168, Australia
| | - Richard G. Haverkamp
- School
of Engineering and Advanced Technology, Massey University, Private Bag
11222, Palmerston North 4442, New Zealand
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24
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Sizeland KH, Wells HC, Kelly SJR, Edmonds R, Kirby NM, Hawley A, Mudie ST, Ryan TM, Haverkamp RG. The influence of water, lanolin, urea, proline, paraffin and fatliquor on collagen D-spacing in leather. RSC Adv 2017. [DOI: 10.1039/c7ra05560a] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Water, lanolin and Lipsol interact with collagen to alter the structure at the fibrillar scale.
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Affiliation(s)
- K. H. Sizeland
- Australian Synchrotron
- Melbourne
- Australia
- School of Engineering and Advanced Technology
- Massey University
| | - H. C. Wells
- School of Engineering and Advanced Technology
- Massey University
- Palmerston North
- New Zealand
| | - S. J. R. Kelly
- School of Engineering and Advanced Technology
- Massey University
- Palmerston North
- New Zealand
| | - R. L. Edmonds
- Leather and Shoe Research Association
- Palmerston North
- New Zealand
| | | | - A. Hawley
- Australian Synchrotron
- Melbourne
- Australia
| | | | - T. M. Ryan
- Australian Synchrotron
- Melbourne
- Australia
| | - R. G. Haverkamp
- School of Engineering and Advanced Technology
- Massey University
- Palmerston North
- New Zealand
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25
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Aldahlawi NH, Hayes S, O'Brart DPS, Akhbanbetova A, Littlechild SL, Meek KM. Enzymatic Resistance of Corneas Crosslinked Using Riboflavin in Conjunction With Low Energy, High Energy, and Pulsed UVA Irradiation Modes. Invest Ophthalmol Vis Sci 2016; 57:1547-52. [PMID: 27046119 PMCID: PMC5321166 DOI: 10.1167/iovs.15-18769] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE To investigate the effect of various riboflavin/ultraviolet light (UVA) crosslinking (CXL) protocols on corneal enzymatic resistance. METHODS A total of 66 enucleated porcine eyes, with the corneal epithelium removed, were divided into 6 groups. Group 1 remained untreated. Groups 2 to 6 received riboflavin/dextran for 30 minutes. Group 3 underwent standard CXL (SCXL) with 3 mW/cm(2) UVA for 30 minutes (total energy dose 5.4 J/cm(2)). Groups 4 and 5 underwent high intensity CXL (HCXL) using 30 mW/cm(2) UVA for 3 minutes (5.4 J/cm(2)) and 30 mW/cm(2) for 4 minutes (7.2 J/cm(2)), respectively. Group 6 was exposed to 8 minutes of 30 mW/cm(2) UVA in a 10-second on/10-second off pulsed-radiation mode (p-HCXL; 7.2 J/cm(2)). A central 8-mm disk from each cornea was submerged in pepsin digest solution at 23°C and measured daily. After 13 days, the dry weight was recorded from 5 samples in each group. RESULTS The CXL-treated corneas took longer to digest than nonirradiated corneas (P < 0.0001). Differences in digestion time also were observed between CXL groups, such that, HCXL (5.4 J/cm(2)) < SCXL (5.4 J/cm(2)) < HCXL (7.2 J/cm(2)) < p-HCXL (7.2 J/cm(2); P < 0.0001). The dry weight of the SCXL (5.4 J/cm(2)) group was higher than the HCXL (5.4 and 7.2 J/cm(2); P < 0.001) and p-HCXL 7.2 J/cm(2) (P <0.05) groups. No difference was detected between the HCXL and p-HCXL 7.2 J/cm(2) groups. CONCLUSIONS The intensity and distribution of the crosslinks formed within the cornea vary with different UVA protocols. The precise location and amount of crosslinking needed to prevent disease progression is unknown.
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Affiliation(s)
- Nada H Aldahlawi
- Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom 2Cardiff Institute for Tissue Engineering and Repair (CITER), Cardiff University, Cardiff, United Kingdom
| | - Sally Hayes
- Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom 2Cardiff Institute for Tissue Engineering and Repair (CITER), Cardiff University, Cardiff, United Kingdom
| | - David P S O'Brart
- Keratoconus Research Institute, Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom
| | - Alina Akhbanbetova
- Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom 2Cardiff Institute for Tissue Engineering and Repair (CITER), Cardiff University, Cardiff, United Kingdom
| | - Stacy L Littlechild
- Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom 2Cardiff Institute for Tissue Engineering and Repair (CITER), Cardiff University, Cardiff, United Kingdom
| | - Keith M Meek
- Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom 2Cardiff Institute for Tissue Engineering and Repair (CITER), Cardiff University, Cardiff, United Kingdom
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26
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Gardner SJ, White N, Albon J, Knupp C, Kamma-Lorger CS, Meek KM. Measuring the Refractive Index of Bovine Corneal Stromal Cells Using Quantitative Phase Imaging. Biophys J 2016; 109:1592-9. [PMID: 26488650 PMCID: PMC4624349 DOI: 10.1016/j.bpj.2015.08.046] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2015] [Revised: 08/24/2015] [Accepted: 08/27/2015] [Indexed: 11/30/2022] Open
Abstract
The cornea is the primary refractive lens in the eye and transmits >90% of incident visible light. It has been suggested that the development of postoperative corneal haze could be due to an increase in light scattering from activated corneal stromal cells. Quiescent keratocytes are thought to produce crystallins that match the refractive index of their cytoplasm to the surrounding extracellular material, reducing the amount of light scattering. To test this, we measured the refractive index (RI) of bovine corneal stromal cells, using quantitative phase imaging of live cells in vitro, together with confocal microscopy. The RI of quiescent keratocytes (RI = 1.381 ± 0.004) matched the surrounding matrix, thus supporting the hypothesis that keratocyte cytoplasm does not scatter light in the normal cornea. We also observed that the RI drops after keratocyte activation (RI = 1.365 ± 0.003), leading to a mismatch with the surrounding intercellular matrix. Theoretical scattering models showed that this mismatch would reduce light transmission in the cornea. We conclude that corneal transparency depends on the matching of refractive indices between quiescent keratocytes and the surrounding tissue, and that after surgery or wounding, the resulting RI mismatch between the activated cells and their surrounds significantly contributes to light scattering.
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Affiliation(s)
| | - Nick White
- Optometry and Vision Sciences, Cardiff University, Cardiff, UK
| | - Julie Albon
- Optometry and Vision Sciences, Cardiff University, Cardiff, UK
| | - Carlo Knupp
- Optometry and Vision Sciences, Cardiff University, Cardiff, UK
| | | | - Keith M Meek
- Optometry and Vision Sciences, Cardiff University, Cardiff, UK.
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Tuchin VV. Polarized light interaction with tissues. JOURNAL OF BIOMEDICAL OPTICS 2016; 21:71114. [PMID: 27121763 DOI: 10.1117/1.jbo.21.7.071114] [Citation(s) in RCA: 132] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Accepted: 03/22/2016] [Indexed: 05/02/2023]
Abstract
This tutorial-review introduces the fundamentals of polarized light interaction with biological tissues and presents some of the recent key polarization optical methods that have made possible the quantitative studies essential for biomedical diagnostics. Tissue structures and the corresponding models showing linear and circular birefringence, dichroism, and chirality are analyzed. As the basis for a quantitative description of the interaction of polarized light with tissues, the theory of polarization transfer in a random medium is used. This theory employs the modified transfer equation for Stokes parameters to predict the polarization properties of single- and multiple-scattered optical fields. The near-order of scatterers in tissues is accounted for to provide an adequate description of tissue polarization properties. Biomedical diagnostic techniques based on polarized light detection, including polarization imaging and spectroscopy, amplitude and intensity light scattering matrix measurements, and polarization-sensitive optical coherence tomography are described. Examples of biomedical applications of these techniques for early diagnostics of cataracts, detection of precancer, and prediction of skin disease are presented. The substantial reduction of light scattering multiplicity at tissue optical clearing that leads to a lesser influence of scattering on the measured intrinsic polarization properties of the tissue and allows for more precise quantification of these properties is demonstrated.
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Affiliation(s)
- Valery V Tuchin
- Saratov National Research State University, Research-Educational Institute of Optics and Biophotonics, 83 Astrakhanskaya street, Saratov 410012, RussiabInstitute of Precision Mechanics and Control of Russian Academy of Sciences, 24 Rabochaya street, Sarat
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Aldahlawi NH, Hayes S, O'Brart DPS, Meek KM. Standard versus accelerated riboflavin-ultraviolet corneal collagen crosslinking: Resistance against enzymatic digestion. J Cataract Refract Surg 2016; 41:1989-96. [PMID: 26603408 PMCID: PMC4670830 DOI: 10.1016/j.jcrs.2015.10.004] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2015] [Revised: 04/10/2015] [Accepted: 04/27/2015] [Indexed: 11/26/2022]
Abstract
PURPOSE To examine the effect of standard and accelerated corneal collagen crosslinking (CXL) on corneal enzymatic resistance. SETTING School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom. DESIGN Experimental study. METHODS Sixty-six enucleated porcine eyes (with corneal epithelium removed) were assigned to 6 groups. Group 1 remained untreated, group 2 received dextran eyedrops, and groups 3 to 6 received riboflavin/dextran eyedrops. Group 4 had standard CXL (3 mW/cm(2) ultraviolet-A for 30 minutes), whereas groups 5 and 6 received accelerated CXL (9 mW/cm(2) for 10 minutes and 18 mW/cm(2) for 5 minutes, respectively). Trephined central 8.0 mm buttons from each cornea underwent pepsin digestion. Corneal diameter was measured daily, and the dry weight of 5 samples from each group was recorded after 12 days of digestion. RESULTS All CXL groups (4 to 6) took longer to digest and had a greater dry weight at 12 days (P < .0001) than the nonirradiated groups (1 to 3) (P < .0001). The time taken for complete digestion to occur did not differ between the standard and accelerated CXL groups, but the dry weights at 12 days showed significant differences between treatments: standard CXL 3 mW > accelerated CXL 9 mW > accelerated CXL 18 mW (P < .0001). CONCLUSIONS Standard and accelerated CXL both increased corneal enzymatic resistance; however, the amount of CXL might be less when accelerated CXL is used. The precise amount of CXL needed to prevent disease progression is not yet known. FINANCIAL DISCLOSURE No author has a financial or proprietary interest in any material or method mentioned.
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Affiliation(s)
- Nada H Aldahlawi
- From the Structural Biophysics Research Group (Aldahlawi, Hayes, Meek), School of Optometry and Vision Sciences, Cardiff University, Cardiff, and the Keratoconus Research Institute (O'Brart), Department of Ophthalmology, St Thomas Hospital, London, United Kingdom
| | - Sally Hayes
- From the Structural Biophysics Research Group (Aldahlawi, Hayes, Meek), School of Optometry and Vision Sciences, Cardiff University, Cardiff, and the Keratoconus Research Institute (O'Brart), Department of Ophthalmology, St Thomas Hospital, London, United Kingdom
| | - David P S O'Brart
- From the Structural Biophysics Research Group (Aldahlawi, Hayes, Meek), School of Optometry and Vision Sciences, Cardiff University, Cardiff, and the Keratoconus Research Institute (O'Brart), Department of Ophthalmology, St Thomas Hospital, London, United Kingdom
| | - Keith M Meek
- From the Structural Biophysics Research Group (Aldahlawi, Hayes, Meek), School of Optometry and Vision Sciences, Cardiff University, Cardiff, and the Keratoconus Research Institute (O'Brart), Department of Ophthalmology, St Thomas Hospital, London, United Kingdom.
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Murienne BJ, Chen ML, Quigley HA, Nguyen TD. The contribution of glycosaminoglycans to the mechanical behaviour of the posterior human sclera. J R Soc Interface 2016; 13:20160367. [PMID: 27358279 PMCID: PMC4938097 DOI: 10.1098/rsif.2016.0367] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Accepted: 06/06/2016] [Indexed: 01/26/2023] Open
Abstract
We characterized the structural and mechanical changes after experimental digestion of sulfated glycosaminoglycans (s-GAGs) in the human posterior sclera, using ultrasound thickness measurements and an inflation test with three-dimensional digital image correlation (3D-DIC). Each scleral specimen was first incubated in a buffer solution to return to full hydration, inflation tested, treated in a buffer solution with chondroitinase ABC (ChABC), then inflation tested again. After each test series, the thickness of eight locations was measured. After enzymatic treatment, the average scleral thickness decreased by 13.3% (p < 0.001) and there was a stiffer overall stress-strain response (p < 0.05). The stress-strain response showed a statistically significant increase in the low-pressure stiffness, high-pressure stiffness and hysteresis. Thus, s-GAGs play a measurable role in the mechanical behaviour of the posterior human sclera.
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Affiliation(s)
- Barbara J Murienne
- Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD, USA
| | - Michelle L Chen
- Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD, USA
| | - Harry A Quigley
- Glaucoma Center of Excellence, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Thao D Nguyen
- Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD, USA
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Dextran Preserves Native Corneal Structure During Decellularization. Tissue Eng Part C Methods 2016; 22:561-72. [DOI: 10.1089/ten.tec.2016.0017] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
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31
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Cheng X, Petsche SJ, Pinsky PM. A structural model for the in vivo human cornea including collagen-swelling interaction. J R Soc Interface 2016; 12:20150241. [PMID: 26156299 DOI: 10.1098/rsif.2015.0241] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
A structural model of the in vivo cornea, which accounts for tissue swelling behaviour, for the three-dimensional organization of stromal fibres and for collagen-swelling interaction, is proposed. Modelled as a binary electrolyte gel in thermodynamic equilibrium, the stromal electrostatic free energy is based on the mean-field approximation. To account for active endothelial ionic transport in the in vivo cornea, which modulates osmotic pressure and hydration, stromal mobile ions are shown to satisfy a modified Boltzmann distribution. The elasticity of the stromal collagen network is modelled based on three-dimensional collagen orientation probability distributions for every point in the stroma obtained by synthesizing X-ray diffraction data for azimuthal angle distributions and second harmonic-generated image processing for inclination angle distributions. The model is implemented in a finite-element framework and employed to predict free and confined swelling of stroma in an ionic bath. For the in vivo cornea, the model is used to predict corneal swelling due to increasing intraocular pressure (IOP) and is adapted to model swelling in Fuchs' corneal dystrophy. The biomechanical response of the in vivo cornea to a typical LASIK surgery for myopia is analysed, including tissue fluid pressure and swelling responses. The model provides a new interpretation of the corneal active hydration control (pump-leak) mechanism based on osmotic pressure modulation. The results also illustrate the structural necessity of fibre inclination in stabilizing the corneal refractive surface with respect to changes in tissue hydration and IOP.
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Affiliation(s)
- Xi Cheng
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
| | - Steven J Petsche
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
| | - Peter M Pinsky
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
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Jastrzebska M, Tarnawska D, Wrzalik R, Chrobak A, Grelowski M, Wylegala E, Zygadlo D, Ratuszna A. New insight into the shortening of the collagen fibril D-period in human cornea. J Biomol Struct Dyn 2016; 35:551-563. [PMID: 26872619 DOI: 10.1080/07391102.2016.1153520] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Collagen fibrils type I display a typical banding pattern, so-called D-periodicity, of about 67 nm, when visualized by atomic force or electron microscopy imaging. Herein we report on a significant shortening of the D-period for human corneal collagen fibrils type I (21 ± 4 nm) upon air-drying, whereas no changes in the D-period were observed for human scleral collagen fibrils type I (64 ± 4 nm) measured under the same experimental conditions as the cornea. It was also found that for the corneal stroma fixed with glutaraldehyde and air-dried, the collagen fibrils show the commonly accepted D-period of 61 ± 8 nm. We used the atomic force microscopy method to image collagen fibrils type I present in the middle layers of human cornea and sclera. The water content in the cornea and sclera samples was varying in the range of .066-.085. Calculations of the D-period using the theoretical model of the fibril and the FFT approach allowed to reveal the possible molecular mechanism of the D-period shortening in the corneal collagen fibrils upon drying. It was found that both the decrease in the shift and the simultaneous reduction in the distance between tropocollagen molecules can be responsible for the experimentally observed effect. We also hypothesize that collagen type V, which co-assembles with collagen type I into heterotypic fibrils in cornea, could be involved in the observed shortening of the corneal D-period.
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Affiliation(s)
- Maria Jastrzebska
- a Department of Solid State Physics, A. Chelkowski Institute of Physics , University of Silesia , Uniwersytecka 4, 40-007 Katowice , Poland.,d Silesian Center for Education and Interdisciplinary Research , University of Silesia , 75 Pułku Piechoty 1, 41-500 Chorzów , Poland
| | - Dorota Tarnawska
- b Faculty of Medicine and Division of Dentistry in Zabrze, Clinical Department of Ophthalmology , Medical University of Silesia , Panewnicka 65, 40-760 Katowice , Poland.,c Department of Biophysics and Molecular Physics, A. Chelkowski Institute of Physics , University of Silesia , Uniwersytecka 4, 40-007 Katowice , Poland.,d Silesian Center for Education and Interdisciplinary Research , University of Silesia , 75 Pułku Piechoty 1, 41-500 Chorzów , Poland
| | - Roman Wrzalik
- c Department of Biophysics and Molecular Physics, A. Chelkowski Institute of Physics , University of Silesia , Uniwersytecka 4, 40-007 Katowice , Poland.,d Silesian Center for Education and Interdisciplinary Research , University of Silesia , 75 Pułku Piechoty 1, 41-500 Chorzów , Poland
| | - Artur Chrobak
- a Department of Solid State Physics, A. Chelkowski Institute of Physics , University of Silesia , Uniwersytecka 4, 40-007 Katowice , Poland.,d Silesian Center for Education and Interdisciplinary Research , University of Silesia , 75 Pułku Piechoty 1, 41-500 Chorzów , Poland
| | - Michal Grelowski
- d Silesian Center for Education and Interdisciplinary Research , University of Silesia , 75 Pułku Piechoty 1, 41-500 Chorzów , Poland
| | - Edward Wylegala
- b Faculty of Medicine and Division of Dentistry in Zabrze, Clinical Department of Ophthalmology , Medical University of Silesia , Panewnicka 65, 40-760 Katowice , Poland
| | - Dorota Zygadlo
- d Silesian Center for Education and Interdisciplinary Research , University of Silesia , 75 Pułku Piechoty 1, 41-500 Chorzów , Poland
| | - Alicja Ratuszna
- a Department of Solid State Physics, A. Chelkowski Institute of Physics , University of Silesia , Uniwersytecka 4, 40-007 Katowice , Poland.,d Silesian Center for Education and Interdisciplinary Research , University of Silesia , 75 Pułku Piechoty 1, 41-500 Chorzów , Poland
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Khan MFJ, Nag TC, Igathinathane C, Osuagwu UL, Rubini M. A new method of detecting changes in corneal health in response to toxic insults. Micron 2015; 78:45-53. [PMID: 26312735 DOI: 10.1016/j.micron.2015.07.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2015] [Accepted: 07/19/2015] [Indexed: 11/25/2022]
Abstract
The size and arrangement of stromal collagen fibrils (CFs) influence the optical properties of the cornea and hence its function. The spatial arrangement of the collagen is still questionable in relation to the diameter of collagen fibril. In the present study, we introduce a new parameter, edge-fibrillar distance (EFD) to measure how two collagen fibrils are spaced with respect to their closest edges and their spatial distribution through normalized standard deviation of EFD (NSDEFD) accessed through the application of two commercially available multipurpose solutions (MPS): ReNu and Hippia. The corneal buttons were soaked separately in ReNu and Hippia MPS for five hours, fixed overnight in 2.5% glutaraldehyde containing cuprolinic blue and processed for transmission electron microscopy. The electron micrographs were processed using ImageJ user-coded plugin. Statistical analysis was performed to compare the image processed equivalent diameter (ED), inter-fibrillar distance (IFD), and EFD of the CFs of treated versus normal corneas. The ReNu-soaked cornea resulted in partly degenerated epithelium with loose hemidesmosomes and Bowman's collagen. In contrast, the epithelium of the cornea soaked in Hippia was degenerated or lost but showed closely packed Bowman's collagen. Soaking the corneas in both MPS caused a statistically significant decrease in the anterior collagen fibril, ED and a significant change in IFD, and EFD than those of the untreated corneas (p<0.05, for all comparisons). The introduction of EFD measurement in the study directly provided a sense of gap between periphery of the collagen bundles, their spatial distribution; and in combination with ED, they showed how the corneal collagen bundles are spaced in relation to their diameters. The spatial distribution parameter NSDEFD indicated that ReNu treated cornea fibrils were uniformly distributed spatially, followed by normal and Hippia. The EFD measurement with relatively lower standard deviation and NSDEFD, a characteristic of uniform CFs distribution, can be an additional parameter used in evaluating collagen organization and accessing the effects of various treatments on corneal health and transparency.
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Affiliation(s)
- Mohammad Faisal Jamal Khan
- Medical Genetics Unit, Department of Biomedical and Specialty Surgical Sciences, University of Ferrara, Via Fossato di Mortara 74, I-44121 Ferrara, Italy.
| | - Tapas C Nag
- Department of Anatomy, All India Institute of Medical Sciences, New Delhi 110029, India
| | - C Igathinathane
- Department of Agricultural and Biosystems Engineering, North Dakota State University, 1221 Albrecht Boulevard, Fargo, ND 58102, USA
| | - Uchechukwu L Osuagwu
- Faculty of Health, Visual and Ophthalmic Optics Group (Chronic Disease and Ageing Domain), Institute of Health and Biomedical Innovation, School of Optometry and Vision Sciences, Q Block, Kelvin Grove, Brisbane, Queensland 4059, Australia
| | - Michele Rubini
- Medical Genetics Unit, Department of Biomedical and Specialty Surgical Sciences, University of Ferrara, Via Fossato di Mortara 74, I-44121 Ferrara, Italy
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Meek KM, Knupp C. Corneal structure and transparency. Prog Retin Eye Res 2015; 49:1-16. [PMID: 26145225 PMCID: PMC4655862 DOI: 10.1016/j.preteyeres.2015.07.001] [Citation(s) in RCA: 466] [Impact Index Per Article: 51.8] [Reference Citation Analysis] [Abstract] [Key Words] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2015] [Revised: 06/28/2015] [Accepted: 07/01/2015] [Indexed: 12/13/2022]
Abstract
The corneal stroma plays several pivotal roles within the eye. Optically, it is the main refracting lens and thus has to combine almost perfect transmission of visible light with precise shape, in order to focus incoming light. Furthermore, mechanically it has to be extremely tough to protect the inner contents of the eye. These functions are governed by its structure at all hierarchical levels. The basic principles of corneal structure and transparency have been known for some time, but in recent years X-ray scattering and other methods have revealed that the details of this structure are far more complex than previously thought and that the intricacy of the arrangement of the collagenous lamellae provides the shape and the mechanical properties of the tissue. At the molecular level, modern technologies and theoretical modelling have started to explain exactly how the collagen fibrils are arranged within the stromal lamellae and how proteoglycans maintain this ultrastructure. In this review we describe the current state of knowledge about the three-dimensional stromal architecture at the microscopic level, and about the control mechanisms at the nanoscopic level that lead to optical transparency.
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Affiliation(s)
- Keith M Meek
- Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Maindy Road, Cardiff CF24 4HQ, UK.
| | - Carlo Knupp
- Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Maindy Road, Cardiff CF24 4HQ, UK
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35
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Tuchina DK, Shi R, Bashkatov AN, Genina EA, Zhu D, Luo Q, Tuchin VV. Ex vivo optical measurements of glucose diffusion kinetics in native and diabetic mouse skin. JOURNAL OF BIOPHOTONICS 2015; 8:332-46. [PMID: 25760425 DOI: 10.1002/jbio.201400138] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2014] [Revised: 01/21/2015] [Accepted: 02/16/2015] [Indexed: 05/22/2023]
Abstract
The aim of this study was to estimate the glucose diffusion coefficients ex vivo in skin of mice with diabetes induced in vivo by alloxan in comparison to non-diabetic mice. The temporal dependences of collimated transmittance of tissue samples immersed in glucose solutions were measured in the VIS-NIR spectral range to quantify the glucose diffusion/permeability coefficients and optical clearing efficiency of mouse skin. The average thickness of intact healthy and diabetic skin was 0.023 ± 0.006 cm and 0.019 ± 0.005 cm, respectively. Considerable differences in optical and kinetic properties of diabetic and non-diabetic skin were found: clearing efficiency was 1.5-fold better and glucose diffusivity was 2-fold slower for diabetic skin. Experimental Setup for measuring collimated transmittance spectra of mouse skin samples.
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Affiliation(s)
- Daria K Tuchina
- Britton Chance Center for Biomedical Photonics, Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, 430074, China; Research-Educational Institute of Optics and Biophotonics, Saratov State University, Saratov, 410012, Russia.
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Quantock AJ, Winkler M, Parfitt GJ, Young RD, Brown DJ, Boote C, Jester JV. From nano to macro: studying the hierarchical structure of the corneal extracellular matrix. Exp Eye Res 2015; 133:81-99. [PMID: 25819457 PMCID: PMC4379421 DOI: 10.1016/j.exer.2014.07.018] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2014] [Revised: 07/17/2014] [Accepted: 07/21/2014] [Indexed: 01/22/2023]
Abstract
In this review, we discuss current methods for studying ocular extracellular matrix (ECM) assembly from the 'nano' to the 'macro' levels of hierarchical organization. Since collagen is the major structural protein in the eye, providing mechanical strength and controlling ocular shape, the methods presented focus on understanding the molecular assembly of collagen at the nanometre level using X-ray scattering through to the millimetre to centimetre level using non-linear optical (NLO) imaging of second harmonic generated (SHG) signals. Three-dimensional analysis of ECM structure is also discussed, including electron tomography, serial block face scanning electron microscopy (SBF-SEM) and digital image reconstruction. Techniques to detect non-collagenous structural components of the ECM are also presented, and these include immunoelectron microscopy and staining with cationic dyes. Together, these various approaches are providing new insights into the structural blueprint of the ocular ECM, and in particular that of the cornea, which impacts upon our current understanding of the control of corneal shape, pathogenic mechanisms underlying ectatic disorders of the cornea and the potential for corneal tissue engineering.
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Affiliation(s)
- Andrew J Quantock
- Structural Biophysics Group, Cardiff Centre for Vision Science, School of Optometry and Vision Sciences, Cardiff University, Cardiff, Wales, UK
| | - Moritz Winkler
- Department of Ophthalmology and Biomedical Engineering, University of California, Irvine, Irvine, CA, USA
| | - Geraint J Parfitt
- Department of Ophthalmology and Biomedical Engineering, University of California, Irvine, Irvine, CA, USA
| | - Robert D Young
- Structural Biophysics Group, Cardiff Centre for Vision Science, School of Optometry and Vision Sciences, Cardiff University, Cardiff, Wales, UK
| | - Donald J Brown
- Department of Ophthalmology and Biomedical Engineering, University of California, Irvine, Irvine, CA, USA
| | - Craig Boote
- Structural Biophysics Group, Cardiff Centre for Vision Science, School of Optometry and Vision Sciences, Cardiff University, Cardiff, Wales, UK
| | - James V Jester
- Department of Ophthalmology and Biomedical Engineering, University of California, Irvine, Irvine, CA, USA.
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Cheng X, Pinsky PM. Mechanisms of self-organization for the collagen fibril lattice in the human cornea. J R Soc Interface 2013; 10:20130512. [PMID: 23904589 DOI: 10.1098/rsif.2013.0512] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The transparency of the human cornea depends on the regular lattice arrangement of the collagen fibrils and on the maintenance of an optimal hydration--the achievement of both depends on the presence of stromal proteoglycans (PGs) and their linear sidechains of negatively charged glycosaminoglycans (GAGs). Although the GAGs produce osmotic pressure by the Donnan effect, the means by which they exert positional control of the lattice is less clear. In this study, a theoretical model based on equilibrium thermodynamics is used to describe restoring force mechanisms that may control and maintain the fibril lattice and underlie corneal transparency. Electrostatic-based restoring forces that result from local charge density changes induced by fibril motion, and entropic elastic restoring forces that arise from duplexed GAG structures that bridge neighbouring fibrils, are described. The model allows for the possibility that fibrils have a GAG-dense coating that adds an additional fibril force mechanism preventing fibril aggregation. Swelling pressure predictions are used to validate the model with results showing excellent agreement with experimental data over a range of hydration from 30 to 200% of normal. The model suggests that the electrostatic restoring force is dominant, with the entropic forces from GAG duplexes being an order or more smaller. The effect of a random GAG organization, as observed in recent imaging, is considered in a dynamic model of the lattice that incorporates randomness in both the spatial distribution of GAG charge and the topology of the GAG duplexes. A striking result is that the electrostatic restoring forces alone are able to reproduce the image-based lattice distribution function for the human cornea, and thus dynamically maintain the short-range order of the lattice.
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Affiliation(s)
- Xi Cheng
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
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Murtomäki L, Vainikka T, Pescina S, Nicoli S. Drug Adsorption on Bovine and Porcine Sclera Studied with Streaming Potential. J Pharm Sci 2013; 102:2264-72. [DOI: 10.1002/jps.23585] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2013] [Revised: 04/02/2013] [Accepted: 04/12/2013] [Indexed: 01/20/2023]
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Tang J, Liu J. Ultrasonic measurement of scleral cross-sectional strains during elevations of intraocular pressure: method validation and initial results in posterior porcine sclera. J Biomech Eng 2012; 134:091007. [PMID: 22938374 PMCID: PMC5413139 DOI: 10.1115/1.4007365] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2012] [Revised: 08/09/2012] [Indexed: 10/28/2022]
Abstract
BACKGROUND Scleral biomechanical properties may be important in the pathogenesis and progression of glaucoma. The goal of this study is to develop and validate an ultrasound method for measuring cross-sectional distributive strains in the sclera during elevations of intraocular pressure (IOP). METHOD OF APPROACH Porcine globes (n = 5) were tested within 24 hs postmortem. The posterior scleral shells were dissected and mounted onto a custom-built pressurization chamber. A high-frequency (55-MHz) ultrasound system (Vevo660, VisualSonics Inc., Toronto) was employed to acquire the radio frequency data during scans of the posterior pole along both circumferential and meridian directions. The IOP was gradually increased from 5 to 45 mmHg. The displacement fields were obtained from correlation-based ultrasound speckle tracking. A least-square strain estimator was used to calculate the strains in both axial and lateral directions. Experimental validation was performed by comparing tissue displacements calculated from ultrasound speckle tracking with those induced by an actuator. Theoretical analysis and simulation experiments were performed to optimize the ultrasound speckle tracking method and evaluate the accuracy and signal-to-noise ratio (SNR) in strain estimation. RESULTS Porcine sclera exhibited significantly larger axial strains (e.g., -5.1 ± 1.5% at 45 mmHg, meridian direction) than lateral strains (e.g., 2.2 ± 0.7% at 45 mmHg, meridian direction) during IOP elevations (P's < 0.01). The strain magnitudes increased nonlinearly with pressure increase. The strain maps displayed heterogeneity through the thickness. The lateral strains were significantly smaller in the circumferential direction than the meridian direction at 45 mmHg (P < 0.05). Experimental validation showed that the ultrasound speckle tracking method was capable of tracking displacements at the accuracy of sub-micron to micron. Theoretical analysis predicted the dependence of the strain estimation SNR on the strain level, as well as signal processing parameters such as kernel size. Simulation results showed that ultrasound speckle tracking had a high accuracy for estimating strains of 1-5% and a high SNR for strains of 0.5-5%. CONCLUSIONS A new experimental method based on ultrasound speckle tracking has been developed for obtaining cross-sectional strain maps of the posterior sclera. This method provides a useful tool to examine distributive strains through the thickness of the sclera during elevations of IOP.
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Affiliation(s)
- Junhua Tang
- Department of Biomedical Engineering, Ohio State University, Columbus, OH 43210, USA
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Highly sensitive single-fibril erosion assay demonstrates mechanochemical switch in native collagen fibrils. Biomech Model Mechanobiol 2012; 12:291-300. [PMID: 22584606 DOI: 10.1007/s10237-012-0399-2] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2011] [Accepted: 04/23/2012] [Indexed: 12/25/2022]
Abstract
It has been established that the enzyme susceptibility of collagen, the predominant load-bearing protein in vertebrates, is altered by applied tension. However, whether tensile force increases or decreases the susceptibility to enzyme is a matter of contention. It is critical to establish a definitive understanding of the direction and magnitude of the force versus catalysis rate (k C ) relationship if we are to properly interpret connective tissue development, growth, remodeling, repair, and degeneration. In this investigation, we examine collagen/enzyme mechanochemistry at the smallest scale structurally relevant to connective tissue: the native collagen fibril. A single-fibril mechanochemical erosion assay with nN force resolution was developed which permits detection of the loss of a few layers of monomer from the fibril surface. Native type I fibrils (bovine) held at three levels of tension were exposed to Clostridium histolyticum collagenase A. Fibrils held at zero-load failed rapidly and consistently (20 min) while fibrils at 1.8 pN/monomer failed more slowly (35-55 min). Strikingly, fibrils at 23.9 pN/monomer did not exhibit detectable degradation. The extracted force versus k C data were combined with previous single-molecule results to produce a "master curve" which suggests that collagen degradation is governed by an extremely sensitive mechanochemical switch.
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Tang J, Liu J. Variance of speed of sound and correlation with acoustic impedance in canine corneas. ULTRASOUND IN MEDICINE & BIOLOGY 2011; 37:1714-1721. [PMID: 21821348 DOI: 10.1016/j.ultrasmedbio.2011.06.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2011] [Revised: 06/16/2011] [Accepted: 06/20/2011] [Indexed: 05/31/2023]
Abstract
The clinical standard for measuring corneal thickness is ultrasound pachymetry that assumes a constant speed of sound. The purpose of this study was to examine the variance of speed of sound and its relationship with acoustic impedance in healthy eyes of canines with a large age span. Corneal speed of sound and acoustic impedance were measured in 34 canine eyes at room temperature (21 ± 1°C). The mean speed of sound was 1577 ± 10 m/s ranging from 1553 to 1594 m/s. There was a strong correlation between speed of sound and acoustic impedance (R = 0.84, p < 0.001). Corneal speed of sound had a small variance in healthy canines over 1-year-old, but was significantly lower in younger canines suggesting an age effect. The strong correlation between corneal speed of sound and acoustic impedance may offer a potential means to noninvasively detect abnormal speed of sound for more accurate corneal thickness estimation.
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Affiliation(s)
- Junhua Tang
- Department of Biomedical Engineering, The Ohio State University, Columbus, OH 43210, USA
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Hayes S, Boote C, Kamma-Lorger CS, Rajan MS, Harris J, Dooley E, Hawksworth N, Hiller J, Terill NJ, Hafezi F, Brahma AK, Quantock AJ, Meek KM. Riboflavin/UVA collagen cross-linking-induced changes in normal and keratoconus corneal stroma. PLoS One 2011; 6:e22405. [PMID: 21850225 PMCID: PMC3151245 DOI: 10.1371/journal.pone.0022405] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2011] [Accepted: 06/21/2011] [Indexed: 11/18/2022] Open
Abstract
Purpose To determine the effect of Ultraviolet-A collagen cross-linking with hypo-osmolar and iso-osmolar riboflavin solutions on stromal collagen ultrastructure in normal and keratoconus ex vivo human corneas. Methods Using small-angle X-ray scattering, measurements of collagen D-periodicity, fibril diameter and interfibrillar spacing were made at 1 mm intervals across six normal post-mortem corneas (two above physiological hydration (swollen) and four below (unswollen)) and two post-transplant keratoconus corneal buttons (one swollen; one unswollen), before and after hypo-osmolar cross-linking. The same parameters were measured in three other unswollen normal corneas before and after iso-osmolar cross-linking and in three pairs of swollen normal corneas, in which only the left was cross-linked (with iso-osmolar riboflavin). Results Hypo-osmolar cross-linking resulted in an increase in corneal hydration in all corneas. In the keratoconus corneas and unswollen normal corneas, this was accompanied by an increase in collagen interfibrillar spacing (p<0.001); an increase in fibril diameter was also seen in two out of four unswollen normal corneas and one unswollen keratoconus cornea (p<0.001). Iso-osmolar cross-linking resulted in a decrease in tissue hydration in the swollen normal corneas only. Although there was no consistent treatment-induced change in hydration in the unswollen normal samples, iso-osmolar cross-linking of these corneas did result in a compaction of collagen fibrils and a reduced fibril diameter (p<0.001); these changes were not seen in the swollen normal corneas. Collagen D-periodicity was not affected by either treatment. Conclusion The observed structural changes following Ultraviolet-A cross-linking with hypo-osmolar or iso-osmolar riboflavin solutions are more likely a consequence of treatment-induced changes in tissue hydration rather than cross-linking.
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Affiliation(s)
- Sally Hayes
- Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom
| | - Craig Boote
- Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom
| | - Christina S. Kamma-Lorger
- Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom
| | - Madhavan S. Rajan
- Vision and Eye Research Unit, Anglia Ruskin University, Cambridge, United Kingdom
| | - Jonathan Harris
- Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom
| | - Erin Dooley
- Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom
| | | | | | - Nick J. Terill
- Diamond Light Source, Didcot, Oxfordshire, United Kingdom
| | - Farhad Hafezi
- Division of Ophthalmology, Geneva University Hospitals, Geneva, Switzerland
| | - Arun K. Brahma
- Manchester Royal Eye Hospital, Manchester, United Kingdom
| | - Andrew J. Quantock
- Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom
| | - Keith M. Meek
- Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom
- * E-mail:
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Svensson RB, Hassenkam T, Grant CA, Magnusson SP. Tensile properties of human collagen fibrils and fascicles are insensitive to environmental salts. Biophys J 2011; 99:4020-7. [PMID: 21156145 DOI: 10.1016/j.bpj.2010.11.018] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2010] [Revised: 11/05/2010] [Accepted: 11/09/2010] [Indexed: 10/18/2022] Open
Abstract
To carry out realistic in vitro mechanical testing on anatomical tissue, a choice has to be made regarding the buffering environment. Therefore, it is important to understand how the environment may influence the measurement to ensure the highest level of accuracy. The most physiologically relevant loading direction of tendon is along its longitudinal axis. Thus, in this study, we focus on the tensile mechanical properties of two hierarchical levels from human patellar tendon, namely: individual collagen fibrils and fascicles. Investigations on collagen fibrils and fascicles were made at pH 7.4 in solutions of phosphate-buffered saline at three different concentrations as well as two HEPES buffered solutions containing NaCl or NaCl + CaCl2. An atomic force microscope technique was used for tensile testing of individual collagen fibrils. Only a slight increase in relative energy dissipation was observed at the highest phosphate-buffered saline concentration for both the fibrils and fascicles, indicating a stabilizing effect of ionic screening, but changes were much less than reported for radial compression. Due to the small magnitude of the effects, the tensile mechanical properties of collagen fibrils and fascicles from the patellar tendon of mature humans are essentially insensitive to environmental salt concentration and composition at physiological pH.
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Affiliation(s)
- René B Svensson
- Nano-Science Center, Institute of Sports Medicine Copenhagen, Bispebjerg Hospital and Center for Healthy Aging, Faculty of Health Science, University of Copenhagen, Copenhagen, Denmark
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Abstract
In this article, we discuss the optical immersion method based on refractive index matching of scatterers (e.g., collagen, elastin fibers, cells and cell compartments) and the ground material (interstitial fluid and/or cytoplasm) of tissue and blood under the action of exogenous optical clearing agents. We analyze the optical clearing of fibrous and cell-structured tissues and blood from the point of view of receiving more valuable, normally hidden, information from spectroscopic and polarization measurements, confocal microscopy, optical coherence and optical projection tomography, as well as from nonlinear spectroscopies, such as two-photon fluorescence and second-harmonic generation techniques. Some important applications of the immersion technique to glucose sensing, drug delivery monitoring, improvements of image contrast and imaging depth, nondistortive delivery of laser radiation and precision tissue laser photodisruption, among others, are also described.
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Affiliation(s)
- Elina A Genina
- Research-Educational Institute of Optics and Biophotonics, Saratov State University, 410012 Saratov, Russia
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Hsueh CM, Lo W, Chen WL, Hovhannisyan VA, Liu GY, Wang SS, Tan HY, Dong CY. Structural characterization of edematous corneas by forward and backward second harmonic generation imaging. Biophys J 2009; 97:1198-205. [PMID: 19686668 DOI: 10.1016/j.bpj.2009.05.040] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2008] [Revised: 04/09/2009] [Accepted: 05/04/2009] [Indexed: 10/20/2022] Open
Abstract
The purpose of this study was to image and quantify the structural changes of corneal edema by second harmonic generation (SHG) microscopy. Bovine cornea was used as an experimental model to characterize structural alterations in edematous corneas. Forward SHG and backward SHG signals were simultaneously collected from normal and edematous bovine corneas to reveal the morphological differences between them. In edematous cornea, both an uneven expansion in the lamellar interspacing and an increased lamellar thickness in the posterior stroma (depth > 200 microm) were identified, whereas the anterior stroma, composed of interwoven collagen architecture, remained unaffected. Our findings of heterogeneous structural alteration at the microscopic scale in edematous corneas suggest that the strength of collagen cross-linking is heterogeneous in the corneal stroma. In addition, we found that qualitative backward SHG collagen fiber imaging and depth-dependent signal decay can be used to detect and diagnose corneal edema. Our work demonstrates that SHG imaging can provide morphological information for the investigation of corneal edema biophysics, and may be applied in the evaluation of advancing corneal edema in vivo.
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Affiliation(s)
- Chiu-Mei Hsueh
- Department of Physics, National Taiwan University, Taipei, Taiwan
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Simonenko GV, Kirillova ES, Tuchin VV. Mathematical model for describing of kinetics of tissue optical clearing. ACTA ACUST UNITED AC 2009. [DOI: 10.3103/s1060992x09020106] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Elsheikh A, Wang D, Rama P, Campanelli M, Garway-Heath D. Experimental Assessment of Human Corneal Hysteresis. Curr Eye Res 2009; 33:205-13. [DOI: 10.1080/02713680701882519] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Doughty MJ, Bergmanson JPG. Use of a Corneal Stroma Perfusion Technique and Transmission Electron Microscopy to Assess Ultrastructural Changes Associated with Exposure to Slightly Acidic pH 5.75 Solutions. Curr Eye Res 2009; 33:45-57. [DOI: 10.1080/02713680701805742] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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