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Tits A, Ruffoni D. Joining soft tissues to bone: Insights from modeling and simulations. Bone Rep 2021; 14:100742. [PMID: 34150954 PMCID: PMC8190669 DOI: 10.1016/j.bonr.2020.100742] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Revised: 12/14/2020] [Accepted: 12/18/2020] [Indexed: 01/16/2023] Open
Abstract
Entheses are complex multi-tissue regions of the musculoskeletal system serving the challenging task of connecting highly dissimilar materials such as the compliant tendon to the much stiffer bone, over a very small region. The first aim of this review is to highlight mathematical and computational models that have been developed to investigate the many attachment strategies present at entheses at different length scales. Entheses are also relevant in the medical context due to the high prevalence of orthopedic injuries requiring the reattachment of tendons or ligaments to bone, which are associated with a rather poor long-term clinical outcome. The second aim of the review is to report on the computational works analyzing the whole tendon to bone complex as well as targeting orthopedic relevant issues. Modeling approaches have provided important insights on anchoring mechanisms and surgical repair strategies, that would not have been revealed with experiments alone. We intend to demonstrate the necessity of including, in future models, an enriched description of enthesis biomechanical behavior in order to unravel additional mechanical cues underlying the development, the functioning and the maintaining of such a complex biological interface as well as to enhance the development of novel biomimetic adhesive, attachment procedures or tissue engineered implants.
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Affiliation(s)
- Alexandra Tits
- Mechanics of Biological and Bioinspired Materials Laboratory, Department of Aerospace and Mechanical Engineering, University of Liège, Liège, Belgium
| | - Davide Ruffoni
- Mechanics of Biological and Bioinspired Materials Laboratory, Department of Aerospace and Mechanical Engineering, University of Liège, Liège, Belgium
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2
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Wang S, Hatami-Marbini H. Constitutive Modeling of Corneal Tissue: Influence of Three-Dimensional Collagen Fiber Microstructure. J Biomech Eng 2021; 143:031002. [PMID: 32909596 DOI: 10.1115/1.4048401] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2019] [Indexed: 07/25/2024]
Abstract
The cornea, the transparent tissue in the front of the eye, along with the sclera, plays a vital role in protecting the inner structures of the eyeball. The precise shape and mechanical strength of this tissue are mostly determined by the unique microstructure of its extracellular matrix. A clear picture of the 3D arrangement of collagen fibrils within the corneal extracellular matrix has recently been obtained from the secondary harmonic generation images. However, this important information about the through-thickness distribution of collagen fibrils was seldom taken into account in the constitutive modeling of the corneal behavior. This work creates a generalized structure tensor (GST) model to investigate the mechanical influence of collagen fibril through-thickness distribution. It then uses numerical simulations of the corneal mechanical response in inflation experiments to assess the efficacy of the proposed model. A parametric study is also done to investigate the influence of model parameters on numerical predictions. Finally, a brief comparison between the performance of this new constitutive model and a recent angular integration (AI) model from the literature is given.
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Affiliation(s)
- Shuolun Wang
- Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, IL 60607
| | - Hamed Hatami-Marbini
- Mechanical and Industrial Engineering, University of Illinois at Chicago, 2033 Engineering Research Facility, 842 W. Taylor Street, Chicago, IL 60607
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Xu M, Ramirez-Garcia MA, Narang H, Buckley MR, Lerner AL, Yoon G. Individualized Characterization of the Distribution of Collagen Fibril Dispersion Using Optical Aberrations of the Cornea for Biomechanical Models. Invest Ophthalmol Vis Sci 2021; 61:54. [PMID: 32866268 PMCID: PMC7463181 DOI: 10.1167/iovs.61.10.54] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose The spatial distribution of collagen fibril dispersion has a significant impact on both corneal biomechanical and optical behaviors. The goal of this study was to demonstrate a novel method to characterize collagen fibril dispersion using intraocular pressure (IOP)-induced changes in corneal optical aberrations for individualized finite-element (FE) modeling. Methods The method was tested through both numerical simulations and ex vivo experiments. Inflation tests were simulated in FE models with three assumed patterns of collagen fibril dispersion and experimentally on three rhesus monkey corneas. Geometry, matrix stiffness, and the IOP-induced changes in wavefront aberrations were measured, and the collagen fibril dispersion was characterized. An individualized corneal model with customized collagen fibril dispersion was developed, and the estimated optical aberrations were compared with the measured data. Results For the theoretical investigations, three assumed distributions of fibril dispersion were all successfully characterized. The estimated optical aberrations closely matched the measured data, with average root-mean-square (RMS) differences of 0.29, 0.24, and 0.10 µm for the three patterns, respectively. The overall features of the IOP-induced changes in optical aberrations were estimated for two ex vivo monkey corneas, with average RMS differences of 0.57 and 0.43 µm. Characterization of the fibril dispersion in the third cornea might have been affected by corneal hydration, resulting in an increased RMS difference, 0.8 µm. Conclusions A more advanced corneal model with individualized distribution of collagen fibril dispersion can be developed and used to improve our ability to understand both biomechanical and optical behaviors of the cornea.
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Affiliation(s)
- Mengchen Xu
- Department of Mechanical Engineering, University of Rochester, Rochester, New York, United States
| | - Manuel A Ramirez-Garcia
- Department of Biomedical Engineering, University of Rochester, Rochester, New York, United States
| | - Harshita Narang
- Department of Biomedical Engineering, University of Rochester, Rochester, New York, United States
| | - Mark R Buckley
- Department of Biomedical Engineering, University of Rochester, Rochester, New York, United States
| | - Amy L Lerner
- Department of Mechanical Engineering, University of Rochester, Rochester, New York, United States.,Department of Biomedical Engineering, University of Rochester, Rochester, New York, United States
| | - Geunyoung Yoon
- Flaum Eye Institute, The Institute of Optics, Center for Visual Science, Department of Biomedical Engineering, University of Rochester, Rochester, New York, United States
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Site of clear corneal incision in cataract surgery and its effects on surgically induced astigmatism. Sci Rep 2020; 10:3955. [PMID: 32127591 PMCID: PMC7054299 DOI: 10.1038/s41598-020-60985-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2019] [Accepted: 02/17/2020] [Indexed: 11/22/2022] Open
Abstract
Clear corneal incision (CCI) is a commonly used surgical approach in cataract surgery. In this prospective study, we evaluated the effect of CCI site on surgically induced astigmatism (SIA) and other postoperative astigmatic changes. CCIs were constructed based on the steep meridian of the total corneal refractive power in the 4.0-mm-zone (TCRP4.0), and patients were divided into four groups: temporal, superotemporal, superonasal, and superior according to the site of the incision. TCRP4.0 analysis demonstrated a statistically significant reduction of astigmatism with superior incisions (P < 0.001), and the combined mean polar values for SIA changed significantly in the temporal (Hotelling T2 = 1.977), superotemporal (Hotelling T2 = 0.544), superonsal (Hotelling T2 = 1.066), and superior incision groups (Hotelling T2 = 1.134) (all P < 0.001). The posterior axis alignment should be considered in cataract surgery with CCI, and the SIA is affected by axis rotation, and incision orientation.
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Wang BH, Xu YS, Xie WJ, Yao YF. Effects of corneal thickness distribution and apex position on postoperative refractive status after full-bed deep anterior lamellar keratoplasty. J Zhejiang Univ Sci B 2019; 19:863-870. [PMID: 30387336 DOI: 10.1631/jzus.b1800230] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
OBJECTIVE To investigate the effects of corneal thickness distribution and apex position on postoperative refractive status after full-bed deep anterior lamellar keratoplasty (FBDALK). METHODS This is a retrospective analysis of patients who were diagnosed with advanced keratoconus between 2011 and 2014 in our hospital. The base of the cone in all patients did not exceed the central cornea at a 6-mm range. The FBDALK was performed by a same surgeon. All patients had a complete corneal suture removal and the follow-up records were intact. Patients who had graft-bed misalignment or who were complicated with a cataract or glaucoma were excluded. Uncorrected visual acuity (UCVA), best spectacle corrected visual acuity (BSCVA), and Pentacam examination data were recorded at two years postoperatively. The recorded data included the superior-inferior (S-I) and nasal-temporal (N-T) corneal thickness differences in 2, 4, 6, and 8 mm diameter concentric circles with the corneal apex as the center (S-I2 mm, S-I4 mm, S-I6 mm, S-I8 mm, N-T2 mm, N-T4 mm, N-T6 mm, and N-T8 mm), the linear, X-axis, and Y-axis distance between the corneal pupillary center and the cornea apex, total corneal astigmatism at a zone of 3 mm diameter from the corneal apex (TA3 mm), the astigmatic vector values J0 and J45, and the corneal total higher-order aberration for 3 and 6 mm pupil diameters (HOA3 mm and HOA6 mm). Statistical analysis was performed by SPSS 15.0. RESULTS A total of 47 eyes of 46 patients met the criteria and were included in this study. The mean follow-up time was (28±7) months. The mean UCVA was 0.45±0.23 (logMAR) (MAR: minimum angle of resolution) and the mean BSCVA was 0.19±0.15 (logMAR), which were all significantly positively correlated with postoperative TA3 mm and HOA3 mm. The mean S-I corneal thickness differences were (44.62±37.74) μm, and the mean N-T was (38.57±32.29) μm. S-I2 mm was significantly positively correlated with J0 (r=0.31), J45 (r=0.42), HOA3 mm (r=0.37), and HOA6 mm (r=0.48). S-I4 mm and S-I8 mm were significantly positively correlated with HOA3 mm (r=0.30, r=0.40) and HOA6 mm (r=0.46, r=0.35). The X-axis distance between corneal pupillary center and corneal apex was significantly positively correlated with J45 (r=0.29). CONCLUSIONS In patients with advanced keratoconus after FBDALK, the unevenly distributed thickness at corneal pupillary area and the misalignment of corneal apex and pupillary center might cause significant regular and irregular astigmatism, which affected the postoperative visual quality.
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Affiliation(s)
- Bing-Hong Wang
- Department of Ophthalmology, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou 310016, China
| | - Ye-Sheng Xu
- Department of Ophthalmology, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou 310016, China
| | - Wen-Jia Xie
- Department of Ophthalmology, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou 310016, China
| | - Yu-Feng Yao
- Department of Ophthalmology, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou 310016, China
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Zhou HY, Cao Y, Wu J, Zhang WS. Role of corneal collagen fibrils in corneal disorders and related pathological conditions. Int J Ophthalmol 2017; 10:803-811. [PMID: 28546941 DOI: 10.18240/ijo.2017.05.24] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2016] [Accepted: 03/23/2017] [Indexed: 01/24/2023] Open
Abstract
The cornea is a soft tissue located at the front of the eye with the principal function of transmitting and refracting light rays to precisely sense visual information. Corneal shape, refraction, and stromal stiffness are to a large part determined by corneal fibrils, the arrangements of which define the corneal cells and their functional behaviour. However, the modality and alignment of native corneal collagen lamellae are altered in various corneal pathological states such as infection, injury, keratoconus, corneal scar formation, and keratoprosthesis. Furthermore, corneal recuperation after corneal pathological change is dependent on the balance of corneal collagen degradation and contraction. A thorough understanding of the characteristics of corneal collagen is thus necessary to develop viable therapies using the outcome of strategies using engineered corneas. In this review, we discuss the composition and distribution of corneal collagens as well as their degradation and contraction, and address the current status of corneal tissue engineering and the progress of corneal cross-linking.
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Affiliation(s)
- Hong-Yan Zhou
- Department of Ophthalmology, China-Japan Union Hospital of Jilin University, Changchun 130033, Jilin Province, China
| | - Yan Cao
- Department of Ophthalmology, China-Japan Union Hospital of Jilin University, Changchun 130033, Jilin Province, China
| | - Jie Wu
- Department of Ophthalmology, China-Japan Union Hospital of Jilin University, Changchun 130033, Jilin Province, China
| | - Wen-Song Zhang
- Department of Ophthalmology, the Second Hospital of Jilin University, Changchun 130000, Jilin Province, China
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Valdetaro GP, Aldrovani M, Padua IRM, Cristovam PC, Gomes JAP, Laus JL. Supra-organization and optical anisotropies of the extracellular matrix in the amniotic membrane and limbal stroma before and after explant culture. BIOMEDICAL OPTICS EXPRESS 2016; 7:4982-4994. [PMID: 28018719 PMCID: PMC5175546 DOI: 10.1364/boe.7.004982] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Revised: 08/08/2016] [Accepted: 08/10/2016] [Indexed: 05/13/2023]
Abstract
In this research we evaluated the supramolecular organizations and the optical anisotropical properties of the de-epithelialized human amniotic membrane and rabbit limbal stroma, before and after explant culture. Birefringence, monochromatic light spectral absorption and linear dichroism of the main extracellular matrix biopolymers, that is, the fibrillar collagens and proteoglycans, were investigated by polarized light microscopy combined with image analysis. Our results demonstrated that the culture procedure-induced stimuli altered the supra-organizational characteristics (in terms of collagens/proteoglycans spatial orientation and ordered-aggregational state) of the amniotic and limbal extracellular matrix, which led to changes in optical anisotropical properties.
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Affiliation(s)
- Gisele P. Valdetaro
- Ophthalmology Unit, Department of Small Animal Medicine and Surgery, Faculty of Agrarian and Veterinary Sciences, UNESP Jaboticabal, 14884-900, SP, Brazil
| | - Marcela Aldrovani
- Ophthalmology Unit, Department of Small Animal Medicine and Surgery, Faculty of Agrarian and Veterinary Sciences, UNESP Jaboticabal, 14884-900, SP, Brazil
| | - Ivan R. M. Padua
- Ophthalmology Unit, Department of Small Animal Medicine and Surgery, Faculty of Agrarian and Veterinary Sciences, UNESP Jaboticabal, 14884-900, SP, Brazil
| | - Priscila C. Cristovam
- Ocular Surface Advanced Center, Federal University of São Paulo, UNIFESP São Paulo, 04039-002, SP, Brazil
| | - José A. P. Gomes
- Ocular Surface Advanced Center, Federal University of São Paulo, UNIFESP São Paulo, 04039-002, SP, Brazil
| | - José L. Laus
- Ophthalmology Unit, Department of Small Animal Medicine and Surgery, Faculty of Agrarian and Veterinary Sciences, UNESP Jaboticabal, 14884-900, SP, Brazil
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Skjønsfjell ET, Kringeland T, Granlund H, Høydalsvik K, Diaz A, Breiby DW. Retrieving the spatially resolved preferred orientation of embedded anisotropic particles by small-angle X-ray scattering tomography. J Appl Crystallogr 2016. [DOI: 10.1107/s1600576716005574] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Experimental nondestructive methods for probing the spatially varying arrangement and orientation of ultrastructures in hierarchical materials are in high demand. While conventional computed tomography (CT) is the method of choice for nondestructively imaging the interior of objects in three dimensions, it retrieves only scalar density fields. In addition to the traditional absorption contrast, other contrast mechanisms for image formation based on scattering and refraction are increasingly used in combination with CT methods, improving both the spatial resolution and the ability to distinguish materials of similar density. Being able to obtain vectorial information, like local growth directions and crystallite orientations, in addition to scalar density fields, is a longstanding scientific desire. In this work, it is demonstrated that, under certain conditions, the spatially varying preferred orientation of anisotropic particles embedded in a homogeneous matrix can be retrieved using CT with small-angle X-ray scattering as the contrast mechanism. Specifically, orientation maps of filler talc particles in injection-moulded isotactic polypropylene are obtained nondestructively under the key assumptions that the preferred orientation varies slowly in space and that the orientation of the flake-shaped talc particles is confined to a plane. It is expected that the method will find application inin situstudies of the mechanical deformation of composites and other materials with hierarchical structures over a range of length scales.
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Chung CW, Girard MJA, Jan NJ, Sigal IA. Use and Misuse of Laplace's Law in Ophthalmology. Invest Ophthalmol Vis Sci 2016; 57:236-45. [PMID: 26803799 PMCID: PMC4727525 DOI: 10.1167/iovs.15-18053] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
PURPOSE Laplace's Law, with its compactness and simplicity, has long been employed in ophthalmology for describing the mechanics of the corneoscleral shell. We questioned the appropriateness of Laplace's Law for computing wall stress in the eye considering the advances in knowledge of ocular biomechanics. METHODS In this manuscript we recapitulate the formulation of Laplace's Law, as well as common interpretations and uses in ophthalmology. Using numerical modeling, we study how Laplace's Law cannot account for important characteristics of the eye, such as variations in globe shape and size or tissue thickness, anisotropy, viscoelasticity, or that the eye is a living, dynamic organ. RESULTS We show that accounting for various geometrical and material factors, excluded from Laplace's Law, can alter estimates of corneoscleral wall stress as much as 456% and, therefore, that Laplace's Law is unreliable. CONCLUSIONS We conclude by illustrating how computational techniques, such as finite element modeling, can account for the factors mentioned above, and are thus more suitable tools to provide quantitative characterization of corneoscleral biomechanics.
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Affiliation(s)
- Cheuk Wang Chung
- Department of Biomedical Engineering, National University of Singapore, Singapore
| | - Michaël J A Girard
- Department of Biomedical Engineering, National University of Singapore, Singapore 2Singapore Eye Research Institute, Singapore National Eye Centre, Singapore
| | - Ning-Jiun Jan
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States 4Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Ian A Sigal
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States 4Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
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10
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Holzapfel GA, Niestrawska JA, Ogden RW, Reinisch AJ, Schriefl AJ. Modelling non-symmetric collagen fibre dispersion in arterial walls. J R Soc Interface 2016; 12:rsif.2015.0188. [PMID: 25878125 DOI: 10.1098/rsif.2015.0188] [Citation(s) in RCA: 123] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
New experimental results on collagen fibre dispersion in human arterial layers have shown that the dispersion in the tangential plane is more significant than that out of plane. A rotationally symmetric dispersion model is not able to capture this distinction. For this reason, we introduce a new non-symmetric dispersion model, based on the bivariate von Mises distribution, which is used to construct a new structure tensor. The latter is incorporated in a strain-energy function that accommodates both the mechanical and structural features of the material, extending our rotationally symmetric dispersion model (Gasser et al. 2006 J. R. Soc. Interface 3, 15-35. (doi:10.1098/rsif.2005.0073)). We provide specific ranges for the dispersion parameters and show how previous models can be deduced as special cases. We also provide explicit expressions for the stress and elasticity tensors in the Lagrangian description that are needed for a finite-element implementation. Material and structural parameters were obtained by fitting predictions of the model to experimental data obtained from human abdominal aortic adventitia. In a finite-element example, we analyse the influence of the fibre dispersion on the homogeneous biaxial mechanical response of aortic strips, and in a final example the non-homogeneous stress distribution is obtained for circumferential and axial strips under fixed extension. It has recently become apparent that this more general model is needed for describing the mechanical behaviour of a variety of fibrous tissues.
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Affiliation(s)
- Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Kronesgasse 5-I, 8010 Graz, Austria
| | - Justyna A Niestrawska
- Institute of Biomechanics, Graz University of Technology, Kronesgasse 5-I, 8010 Graz, Austria
| | - Ray W Ogden
- School of Mathematics and Statistics, University of Glasgow, University Gardens, Glasgow G12 8QW, UK
| | - Andreas J Reinisch
- Institute of Biomechanics, Graz University of Technology, Kronesgasse 5-I, 8010 Graz, Austria
| | - Andreas J Schriefl
- Institute of Biomechanics, Graz University of Technology, Kronesgasse 5-I, 8010 Graz, Austria
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11
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Schaff F, Bech M, Zaslansky P, Jud C, Liebi M, Guizar-Sicairos M, Pfeiffer F. Six-dimensional real and reciprocal space small-angle X-ray scattering tomography. Nature 2015; 527:353-6. [PMID: 26581292 DOI: 10.1038/nature16060] [Citation(s) in RCA: 87] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2015] [Accepted: 09/22/2015] [Indexed: 11/09/2022]
Abstract
When used in combination with raster scanning, small-angle X-ray scattering (SAXS) has proven to be a valuable imaging technique of the nanoscale, for example of bone, teeth and brain matter. Although two-dimensional projection imaging has been used to characterize various materials successfully, its three-dimensional extension, SAXS computed tomography, poses substantial challenges, which have yet to be overcome. Previous work using SAXS computed tomography was unable to preserve oriented SAXS signals during reconstruction. Here we present a solution to this problem and obtain a complete SAXS computed tomography, which preserves oriented scattering information. By introducing virtual tomography axes, we take advantage of the two-dimensional SAXS information recorded on an area detector and use it to reconstruct the full three-dimensional scattering distribution in reciprocal space for each voxel of the three-dimensional object in real space. The presented method could be of interest for a combined six-dimensional real and reciprocal space characterization of mesoscopic materials with hierarchically structured features with length scales ranging from a few nanometres to a few millimetres--for example, biomaterials such as bone or teeth, or functional materials such as fuel-cell or battery components.
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Affiliation(s)
- Florian Schaff
- Lehrstuhl für Biomedizinische Physik, Physik-Department &Institut für Medizintechnik, Technische Universität München, 85748 Garching, Germany
| | - Martin Bech
- Department of Medical Radiation Physics, Clinical Sciences, Lund, Lund University, 22185 Lund, Sweden
| | - Paul Zaslansky
- Julius Wolff Institute, Charité - Universitätsmedizin Berlin, 13353 Berlin, Germany
| | - Christoph Jud
- Lehrstuhl für Biomedizinische Physik, Physik-Department &Institut für Medizintechnik, Technische Universität München, 85748 Garching, Germany
| | | | | | - Franz Pfeiffer
- Lehrstuhl für Biomedizinische Physik, Physik-Department &Institut für Medizintechnik, Technische Universität München, 85748 Garching, Germany.,Institut für diagnostische und interventionelle Radiologie, Klinikum rechts der Isar, Technische Universität München, 81675 München, Germany
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Sánchez P, Moutsouris K, Pandolfi A. Biomechanical and optical behavior of human corneas before and after photorefractive keratectomy. J Cataract Refract Surg 2014; 40:905-17. [PMID: 24857438 DOI: 10.1016/j.jcrs.2014.03.020] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2013] [Revised: 03/13/2014] [Accepted: 03/15/2014] [Indexed: 11/26/2022]
Abstract
PURPOSE To evaluate numerically the biomechanical and optical behavior of human corneas and quantitatively estimate the changes in refractive power and stress caused by photorefractive keratectomy (PRK). SETTING Athineum Refractive Center, Athens, Greece, and Politecnico di Milano, Milan, Italy. DESIGN Retrospective comparative interventional cohort study. METHODS Corneal topographies of 10 human eyes were taken with a scanning-slit corneal topographer (Orbscan II) before and after PRK. Ten patient-specific finite element models were created to estimate the strain and stress fields in the cornea in preoperative and postoperative configurations. The biomechanical response in postoperative eyes was computed by directly modeling the postoperative geometry from the topographer and by reproducing the corneal ablation planned for the PRK with a numerical reprofiling procedure. RESULTS Postoperative corneas were more compliant than preoperative corneas. In the optical zone, corneal thinning decreased the mechanical stiffness, causing local resteepening and making the central refractive power more sensitive to variations in intraocular pressure (IOP). At physiologic IOP, the postoperative corneas had a mean 7% forward increase in apical displacement and a mean 20% increase in the stress components at the center of the anterior surface over the preoperative condition. CONCLUSION Patient-specific numerical models of the cornea can provide quantitative information on the changes in refractive power and in the stress field caused by refractive surgery. FINANCIAL DISCLOSURES No author has a financial or proprietary interest in any material or method mentioned.
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Affiliation(s)
- Paolo Sánchez
- From the Department of Biomechanical Engineering (Sánchez), Technical University, Delft, the Netherlands; the Athineum Refractive Center (Moutsouris), Athens, Greece; the Dipartimento di Ingegneria Civile e Ambientale, Politecnico di Milano (Pandolfi), Milan, Italy
| | - Kyros Moutsouris
- From the Department of Biomechanical Engineering (Sánchez), Technical University, Delft, the Netherlands; the Athineum Refractive Center (Moutsouris), Athens, Greece; the Dipartimento di Ingegneria Civile e Ambientale, Politecnico di Milano (Pandolfi), Milan, Italy
| | - Anna Pandolfi
- From the Department of Biomechanical Engineering (Sánchez), Technical University, Delft, the Netherlands; the Athineum Refractive Center (Moutsouris), Athens, Greece; the Dipartimento di Ingegneria Civile e Ambientale, Politecnico di Milano (Pandolfi), Milan, Italy.
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13
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Asher R, Gefen A, Moisseiev E, Varssano D. Etiology of Keratoconus: proposed biomechanical pathogenesis. ACTA ACUST UNITED AC 2014. [DOI: 10.1186/2196-050x-1-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Abstract
Background
The etiology of keratoconus most likely involves substantial biomechanical interactions. The goal of this study was to characterize corneal biomechanics using computer modeling techniques in order to elucidate the pathogenesis of keratoconus in biomechanical terms.
Methods
Finite element models of the cornea that are based on anatomical dimensions were developed. Cases comprising of thinned regions as well as regions with degraded isotropic mechanical properties and a case of gradual stiffening towards the limbus were subjected to normal intraocular pressures. The resulting deformations and dioptric power maps were analyzed and compared. Three additional cases that are based on a model of a thin plate were used to demonstrate the effect a transition from orthotropic to isotropic mechanical properties would have in terms of deformations and diopteric power maps.
Results
Results show that under 10mmHg intraocular pressure, decreasing the modulus of elasticity and thinning have opposite effects on the dioptric power maps of a homogenous isotropic cornea. When the thickness was maintained at 500 microns and the stiffness was decreased from 0.4 MPa to 0.04 MPa there was an increase of more than 40 diopters. For a cornea with a constant modulus of elasticity value of 0.4 MPa, 350 microns decrease in thickness resulted in a decrease of approximately 25 diopters. The anisotropic non-homogenous characteristics of the cornea have shown to be critical for maintaining the morphology of a healthy corneal.
Conclusions
Degradation of the circumferential fibers may very well be an initiating factor of a biomechanical process in which a bulge is gradually created from a presumably healthy cornea under normal underlying pressures and therefore, the identification of the early stages of keratoconus might be achievable by monitoring the in-vivo corneal fiber distribution.
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14
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Campbell IC, Coudrillier B, Ross Ethier C. Biomechanics of the Posterior Eye: A Critical Role in Health and Disease. J Biomech Eng 2014; 136:021005. [DOI: 10.1115/1.4026286] [Citation(s) in RCA: 76] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Accepted: 12/19/2013] [Indexed: 01/16/2023]
Abstract
The posterior eye is a complex biomechanical structure. Delicate neural and vascular tissues of the retina, choroid, and optic nerve head that are critical for visual function are subjected to mechanical loading from intraocular pressure, intraocular and extraorbital muscles, and external forces on the eye. The surrounding sclera serves to counteract excessive deformation from these forces and thus to create a stable biomechanical environment for the ocular tissues. Additionally, the eye is a dynamic structure with connective tissue remodeling occurring as a result of aging and pathologies such as glaucoma and myopia. The material properties of these tissues and the distribution of stresses and strains in the posterior eye is an area of active research, relying on a combination of computational modeling, imaging, and biomechanical measurement approaches. Investigators are recognizing the increasing importance of the role of the collagen microstructure in these material properties and are undertaking microstructural measurements to drive microstructurally-informed models of ocular biomechanics. Here, we review notable findings and the consensus understanding on the biomechanics and microstructure of the posterior eye. Results from computational and numerical modeling studies and mechanical testing of ocular tissue are discussed. We conclude with some speculation as to future trends in this field.
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Affiliation(s)
- Ian C. Campbell
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA 30332
- Rehabilitation Research and Development Center of Excellence, Atlanta VA Medical Center, 1670 Clairmont Road, Decatur, GA 30032
| | - Baptiste Coudrillier
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA 30332
| | - C. Ross Ethier
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA 30332
- Rehabilitation Research and Development Center of Excellence, Atlanta VA Medical Center, 1670 Clairmont Road, Decatur, GA 30032
- Department of Ophthalmology, School of Medicine, Emory University, Atlanta, GA 30322
- Department of Bioengineering, Imperial College London, London SW7 2AZ, UK e-mail:
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Abstract
An efficient method for X-ray diffraction data collection mapping on a given curved surface has been developed. The method uses a laser–video autozalignment system to collect a map of heights on a fine mesh grid. It also reconstructs the surface geometry and determines surface normals on a three-dimensional surface fit. An algorithm was used to calculate the required rotation and tilt angles to coincide the sample normal with the diffraction center before each exposure. A set of diffraction frames collected using this technique was analyzed in order to superimpose a phase transformation map onto a typical zirconia ceramic sample. With this method, mapping of phase and stresses on a complex surface has been demonstrated. This approach is broadly applicable to many important areas of study.
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16
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Whang WJ, Byun YS, Joo CK. Steep Axis Incision Versus Temporal Incision in Microcoaxial Cataract Surgery. JOURNAL OF THE KOREAN OPHTHALMOLOGICAL SOCIETY 2011. [DOI: 10.3341/jkos.2011.52.1.29] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
- Woong-Joo Whang
- Department of Ophthalmology, Seoul St. Mary's Hospital, The Catholic University of Korea School of Medicine, Seoul, Korea
| | - Yong-Soo Byun
- Department of Ophthalmology, Seoul St. Mary's Hospital, The Catholic University of Korea School of Medicine, Seoul, Korea
| | - Choun-Ki Joo
- Department of Ophthalmology, Seoul St. Mary's Hospital, The Catholic University of Korea School of Medicine, Seoul, Korea
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17
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Nguyen TD, Boyce BL. An inverse finite element method for determining the anisotropic properties of the cornea. Biomech Model Mechanobiol 2010; 10:323-37. [PMID: 20602142 DOI: 10.1007/s10237-010-0237-3] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2009] [Accepted: 06/18/2010] [Indexed: 11/24/2022]
Abstract
An inverse finite element method was developed to determine the anisotropic properties of bovine cornea from an in vitro inflation experiment. The experiment used digital image correlation (DIC) to measure the three-dimensional surface geometry and displacement field of the cornea at multiple pressures. A finite element model of a bovine cornea was developed using the DIC measured surface geometry of the undeformed specimen. The model was applied to determine five parameters of an anisotropic hyperelastic model that minimized the error between the measured and computed surface displacement field and to investigate the sensitivity of the measured bovine inflation response to variations in the anisotropic properties of the cornea. The results of the parameter optimization revealed that the collagen structure of bovine cornea exhibited a high degree of anisotropy in the limbus region, which agreed with recent histological findings, and a transversely isotropic central region. The parameter study showed that the bovine corneal response to the inflation experiment was sensitive to the shear modulus of the matrix at pressures below the intraocular pressure, the properties of the collagen lamella at higher pressures, and the degree of anisotropy in the limbus region. It was not sensitive to a weak collagen anisotropy in the central region.
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Affiliation(s)
- T D Nguyen
- Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, MD 21218, USA.
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18
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van Turnhout MC, Kranenbarg S, van Leeuwen JL. Modeling optical behavior of birefringent biological tissues for evaluation of quantitative polarized light microscopy. JOURNAL OF BIOMEDICAL OPTICS 2009; 14:054018. [PMID: 19895120 DOI: 10.1117/1.3241986] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Quantitative polarized light microscopy (qPLM) is a popular tool for the investigation of birefringent architectures in biological tissues. Collagen, the most abundant protein in mammals, is such a birefringent material. Interpretation of results of qPLM in terms of collagen network architecture and anisotropy is challenging, because different collagen networks may yield equal qPLM results. We created a model and used the linear optical behavior of collagen to construct a Jones or Mueller matrix for a histological cartilage section in an optical qPLM train. Histological sections of tendon were used to validate the basic assumption of the model. Results show that information on collagen densities is needed for the interpretation of qPLM results in terms of collagen anisotropy. A parameter that is independent of the optical system and that measures collagen fiber anisotropy is introduced, and its physical interpretation is discussed. With our results, we can quantify which part of different qPLM results is due to differences in collagen densities and which part is due to changes in the collagen network. Because collagen fiber orientation and anisotropy are important for tissue function, these results can improve the biological and medical relevance of qPLM results.
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Affiliation(s)
- Mark C van Turnhout
- Wageningen University, Department of Animal Sciences, Experimental Zoology Group, P.O. Box 338, Wageningen, 6700 AH, The Netherlands.
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19
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Meek KM, Boote C. The use of X-ray scattering techniques to quantify the orientation and distribution of collagen in the corneal stroma. Prog Retin Eye Res 2009; 28:369-92. [PMID: 19577657 DOI: 10.1016/j.preteyeres.2009.06.005] [Citation(s) in RCA: 149] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The bulk of the corneal stroma is comprised of a layered network of fibrillar collagen. Determining the architecture of this unique structure may help us to better understand the cornea's biomechanical and optical function. The analysis of diffraction patterns obtained when X-rays are passed through the regularly arranged collagen molecules and fibrils of the stromal matrix yields quantitative data on fibrillar organisation, including the orientation and distribution of collagen lamellae within the corneal plane. In recent years, by exploiting the radiation from powerful synchrotron sources, techniques have been developed to enable the mapping of collagen fibril, and therefore lamellar, directions across whole corneas. This article aims to summarise the use of X-ray diffraction to map the orientation and distribution of collagen in the corneal stroma. The implications of the knowledge gained so far are discussed in relation to the optical and biomechanical properties of the cornea, and their alteration due to disease and surgical intervention.
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Affiliation(s)
- Keith M Meek
- Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, UK.
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20
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Meek KM. Corneal collagen-its role in maintaining corneal shape and transparency. Biophys Rev 2009; 1:83-93. [PMID: 28509987 PMCID: PMC5425665 DOI: 10.1007/s12551-009-0011-x] [Citation(s) in RCA: 109] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2009] [Accepted: 05/14/2009] [Indexed: 10/20/2022] Open
Abstract
Corneal collagen has a number of properties that allow it to fulfil its role as the main structural component within the tissue. Fibrils are narrow, uniform in diameter and precisely organised. These properties are vital to maintain transparency and to provide the biomechanical prerequisites necessary to sustain shape and provide strength. This review describes the structure and arrangement of corneal collagen from the nanoscopic to the macroscopic level, and how this relates to the maintenance of the form and transparency of the cornea.
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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 4LU, UK.
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21
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Corneal transparency: genesis, maintenance and dysfunction. Brain Res Bull 2009; 81:198-210. [PMID: 19481138 DOI: 10.1016/j.brainresbull.2009.05.019] [Citation(s) in RCA: 122] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2009] [Revised: 04/14/2009] [Accepted: 05/20/2009] [Indexed: 02/01/2023]
Abstract
Optimal vision is contingent upon transparency of the cornea. Corneal neovascularization, trauma and, surgical procedures such as photorefractive keratectomy and graft rejection after penetrating keratoplasty can lead to corneal opacification. In this article we identify the underlying basis of corneal transparency and factors that compromise the integrity of the cornea. With evidence from work on animal models and clinical studies, we explore the molecular mechanisms of both corneal avascularity and its dysfunction. We also seek to review therapeutic regimens that can safely salvage and restore corneal transparency.
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22
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Boote C, Hayes S, Young RD, Kamma-Lorger CS, Hocking PM, Elsheikh A, Inglehearn CF, Ali M, Meek KM. Ultrastructural changes in the retinopathy, globe enlarged (rge) chick cornea. J Struct Biol 2009; 166:195-204. [PMID: 19258040 PMCID: PMC2680986 DOI: 10.1016/j.jsb.2009.01.009] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2008] [Revised: 01/15/2009] [Accepted: 01/27/2009] [Indexed: 11/15/2022]
Abstract
In the cornea, the precise organisation of fibrillar collagen and associated proteoglycans comprising the stromal extracellular matrix plays a major role in governing tissue form and function. Recently, abnormal collagen alignment was noted in the misshapen corneas of mature chickens affected by the retinopathy, globe enlarged (rge) mutation. Here we further characterize corneal ultrastructural changes as the rge eye develops post-hatch. Wide-angle X-ray scattering disclosed alteration to dominant collagen lamellae directions in the rge chick cornea, compared to age-matched controls. These changes accompanied eye globe enlargement and corneal flattening in affected birds, manifesting as a progressive loss of circumferential collagen alignment in the peripheral cornea and limbus in birds older than 1 month. Collagen intermolecular separation was unchanged in rge. However, small-angle X-ray scattering results suggest collagen fibril separation and diameter increase more rapidly towards the corneal periphery in rge at 3 months post-hatch compared to controls, although central collagen fibril diameter was unchanged. By transmission electron microscopy utilising cuprolinic blue stain, the morphology and distribution of stromal proteoglycans were unaltered in rge corneas otherwise demonstrating abnormal collagen fibril organisation. From a numerical simulation of tissue mechanics, progressive remodelling of stromal collagen in rge during globe enlargement post-hatch appears to be related to the corneal morphometric changes presented by the disease.
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Affiliation(s)
- Craig Boote
- Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, Maindy Road, Cardiff CF24 4LU, UK.
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23
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Pandolfi A, Holzapfel GA. Three-dimensional modeling and computational analysis of the human cornea considering distributed collagen fibril orientations. J Biomech Eng 2009; 130:061006. [PMID: 19045535 DOI: 10.1115/1.2982251] [Citation(s) in RCA: 127] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Experimental tests on human corneas reveal distinguished reinforcing collagen lamellar structures that may be well described by a structural constitutive model considering distributed collagen fibril orientations along the superior-inferior and the nasal-temporal meridians. A proper interplay between the material structure and the geometry guarantees the refractive function and defines the refractive properties of the cornea. We propose a three-dimensional computational model for the human cornea that is able to provide the refractive power by analyzing the structural mechanical response with the nonlinear regime and the effect the intraocular pressure has. For an assigned unloaded geometry we show how the distribution of the von Mises stress at the top surface of the cornea and through the corneal thickness and the refractive power depend on the material properties and the fibril dispersion. We conclude that a model for the human cornea must not disregard the peculiar collagen fibrillar structure, which equips the cornea with the unique biophysical, mechanical, and optical properties.
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Affiliation(s)
- Anna Pandolfi
- Dipartimento di Ingegneria Strutturale, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy.
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24
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Nguyen TD, Jones RE, Boyce BL. A nonlinear anisotropic viscoelastic model for the tensile behavior of the corneal stroma. J Biomech Eng 2008; 130:041020. [PMID: 18601462 DOI: 10.1115/1.2947399] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Tensile strip experiments of bovine corneas have shown that the tissue exhibits a nonlinear rate-dependent stress-strain response and a highly nonlinear creep response that depends on the applied hold stress. In this paper, we present a constitutive model for the finite deformation, anisotropic, nonlinear viscoelastic behavior of the corneal stroma. The model formulates the elastic and viscous response of the stroma as the average of the elastic and viscous response of the individual lamellae weighted by a probability density function of the preferred in-plane lamellar orientations. The result is a microstructure-based model that incorporates the viscoelastic properties of the matrix and lamellae and the lamellar architecture in the response of the stroma. In addition, the model includes a fully nonlinear description of the viscoelastic response of the lamellar(fiber) level. This is in contrast to previous microstructure-based models of fibrous soft tissues, which relied on quasilinear viscoelastic formulations of the fiber viscoelasticity. Simulations of recent tensile strip experiments show that the model is able to predict, well within the bounds of experimental error and natural variations, the cyclic stress-strain behavior and nonlinear creep behavior observed in uniaxial tensile experiments of excised strips of bovine cornea.
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Affiliation(s)
- T D Nguyen
- Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, MD 21218, USA.
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25
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Nagy LJ, MacRae S, Yoon G, Wyble M, Wang J, Cox I, Huxlin KR. Photorefractive keratectomy in the cat eye: biological and optical outcomes. J Cataract Refract Surg 2007; 33:1051-64. [PMID: 17531702 PMCID: PMC1993426 DOI: 10.1016/j.jcrs.2007.02.021] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2006] [Accepted: 02/12/2007] [Indexed: 10/23/2022]
Abstract
PURPOSE To quantify optical and biomechanical properties of the feline cornea before and after photorefractive keratectomy (PRK) and assess the relative contribution of different biological factors to refractive outcome. SETTING Department of Ophthalmology, University of Rochester, Rochester, New York, USA. METHODS Adult cats had 6.0 diopter (D) myopic or 4.0 D hyperopic PRK over 6.0 or 8.0 mm optical zones (OZ). Preoperative and postoperative wavefront aberrations were measured, as were intraocular pressure (IOP), corneal hysteresis, the corneal resistance factor, axial length, corneal thickness, and radii of curvature. Finally, postmortem immunohistochemistry for vimentin and alpha-smooth muscle actin was performed. RESULTS Photorefractive keratectomy changed ocular defocus, increased higher-order aberrations, and induced myofibroblast differentiation in cats. However, the intended defocus corrections were only achieved with 8.0 mm OZs. Long-term flattening of the epithelial and stromal surfaces was noted after myopic, but not after hyperopic, PRK. The IOP was unaltered by PRK; however, corneal hysteresis and the corneal resistance factor decreased. Over the ensuing 6 months, ocular aberrations and the IOP remained stable, while central corneal thickness, corneal hysteresis, and the corneal resistance factor increased toward normal levels. CONCLUSIONS Cat corneas exhibited optical, histological, and biomechanical reactions to PRK that resembled those previously described in humans, especially when the OZ size was normalized to the total corneal area. However, cats exhibited significant stromal regeneration, causing a return to preoperative corneal thickness, corneal hysteresis and the corneal resistance factor without significant regression of optical changes induced by the surgery. Thus, the principal effects of laser refractive surgery on ocular wavefront aberrations can be achieved despite clear interspecies differences in corneal biology.
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Affiliation(s)
- Lana J Nagy
- Department of Ophthalmology, University of Rochester, 601 Elmwood Avenue, Rochester, NY 14642, USA
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26
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Hayes S, Boote C, Lewis J, Sheppard J, Abahussin M, Quantock AJ, Purslow C, Votruba M, Meek KM. Comparative Study of Fibrillar Collagen Arrangement in the Corneas of Primates and Other Mammals. Anat Rec (Hoboken) 2007; 290:1542-50. [DOI: 10.1002/ar.20613] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Borasio E, Mehta JS, Maurino V. Torque and flattening effects of clear corneal temporal and on-axis incisions for phacoemulsification. J Cataract Refract Surg 2006; 32:2030-8. [PMID: 17137979 DOI: 10.1016/j.jcrs.2006.09.010] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2005] [Accepted: 08/29/2006] [Indexed: 10/23/2022]
Abstract
PURPOSE To compare the torque and flattening effect induced by temporal or on-axis clear corneal incisions (CCIs) for phacoemulsification. SETTING Moorfields Eye Hospital, London, United Kingdom. METHODS Randomized controlled clinical trial on 62 eyes with cataract and mild to moderate corneal astigmatism (<2.60 diopters [D]) having phacoemulsification with a temporal CCI (temporal group) or on-axis CCI (on-axis group). Corneal astigmatism was assessed by corneal topography preoperatively and 3 weeks after surgery. The meridian of the incisions was marked on the cornea before local anesthesia was given to avoid anesthesia-related cyclotorsion. The surgically induced astigmatism (SIA) vector, torque, flattening effect, and accuracy of incision placement were analyzed in the 2 groups and compared with a paired t test. RESULTS Three weeks after surgery, the on-axis CCI induced slightly more flattening of the meridian of the incision (mean -0.63 +/- 0.57 D [SD]) than the temporal CCI (mean -0.50 +/- 0.44 D); however, the differences were not statistically significant (P = .31). Simple algebraic difference showed a mean increase in astigmatism magnitude of 0.12 +/- 0.52 D in the temporal group and a mean reduction of 0.21 +/- 0.53 D in the on-axis group (P = .02). The mean absolute torque was 0.28 +/- 0.27 D and 0.53 +/- 0.37 D, respectively (P<.005). The absolute angle of error of incision placement (alpha) was greater after on-axis CCIs (mean 25.9 +/- 20.1 degrees) than after temporal CCIs (mean 14.5 +/- 14.3 degrees) (P = .01). CONCLUSIONS In eyes with preoperative astigmatism less than 2.60 D, on-axis CCI phacoemulsification induced slightly more flattening along the incision meridian than temporal CCI phacoemulsification, although the differences were not significant. The on-axis CCI was associated with significantly greater absolute torque and angle of error than the temporal CCI. These factors could limit the benefit of placing the incision on axis when the aim is to reduce preoperative astigmatism in phacoemulsification.
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Gruverman A, Wu D, Rodriguez BJ, Kalinin SV, Habelitz S. High-resolution imaging of proteins in human teeth by scanning probe microscopy. Biochem Biophys Res Commun 2006; 352:142-6. [PMID: 17112467 DOI: 10.1016/j.bbrc.2006.10.182] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2006] [Accepted: 10/30/2006] [Indexed: 10/23/2022]
Abstract
High-resolution studies of dental tissues are of considerable interest for biomedical engineering and clinical applications. In this paper, we demonstrate the application of piezoresponse force microscopy (PFM) to nanoscale imaging of internal structure of human teeth by monitoring the local mechanical response to an electrical bias applied via a conductive tip. It is shown that PFM is capable of detecting dissimilar components of dental tissues, namely, proteins and calcified matrix, which have resembling morphology but different piezoelectric properties. It is demonstrated that collagen fibrils revealed in chemically treated intertubular dentin exhibit high piezoelectric activity and can be visualized in PFM with spatial resolution of 10 nm. Evidence of the presence of protein inclusions of 100-200 nm wide and several micrometers long in tooth enamel has been obtained. Furthermore, it is found that the peritubular dentin and intertubular dentin exhibit different piezoelectric behavior suggesting different concentration of collagen fibrils. The obtained results demonstrate a high potential of PFM in providing an additional insight into the structure of dental tissues. It is suggested that the PFM approach can be used to study the structure of a wide range of biological materials by monitoring their electromechanical behavior at the nanoscale.
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Affiliation(s)
- A Gruverman
- Department of Materials Science, North Carolina State University, Raleigh, NC 27695, USA.
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Rodriguez BJ, Kalinin SV, Shin J, Jesse S, Grichko V, Thundat T, Baddorf AP, Gruverman A. Electromechanical imaging of biomaterials by scanning probe microscopy. J Struct Biol 2006; 153:151-9. [PMID: 16403652 DOI: 10.1016/j.jsb.2005.10.008] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2005] [Revised: 09/23/2005] [Accepted: 10/04/2005] [Indexed: 10/25/2022]
Abstract
The majority of calcified and connective tissues possess complex hierarchical structure spanning the length scales from nanometers to millimeters. Understanding the biological functionality of these materials requires reliable methods for structural imaging on the nanoscale. Here, we demonstrate an approach for electromechanical imaging of the structure of biological samples on the length scales from tens of microns to nanometers using piezoresponse force microscopy (PFM), which utilizes the intrinsic piezoelectricity of biopolymers such as proteins and polysaccharides as the basis for high-resolution imaging. Nanostructural imaging of a variety of protein-based materials, including tooth, antler, and cartilage, is demonstrated. Visualization of protein fibrils with sub-10nm spatial resolution in a human tooth is achieved. Given the near-ubiquitous presence of piezoelectricity in biological systems, PFM is suggested as a versatile tool for micro- and nanostructural imaging in both connective and calcified tissues.
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Affiliation(s)
- B J Rodriguez
- Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
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30
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Kee CS, Hung LF, Qiao-Grider Y, Ramamirtham R, Smith EL. Astigmatism in monkeys with experimentally induced myopia or hyperopia. Optom Vis Sci 2005; 82:248-60. [PMID: 15829845 PMCID: PMC1810233 DOI: 10.1097/01.opx.0000159357.61498.6b] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
PURPOSE Astigmatism is the most common ametropia found in humans and is often associated with large spherical ametropias. However, little is known about the etiology of astigmatism or the reason(s) for the association between spherical and astigmatic refractive errors. This study examines the frequency and characteristics of astigmatism in infant monkeys that developed axial ametropias as a result of altered early visual experience. METHODS Data were obtained from 112 rhesus monkeys that experienced a variety of lens-rearing regimens that were intended to alter the normal course of emmetropization. These visual manipulations included form deprivation (n = 13); optically imposed defocus (n = 48); and continuous ambient lighting with (n = 6) or without optically imposed defocus (n = 6). In addition, data from 19 control monkeys and 39 infants reared with an optically imposed astigmatism were used for comparison purposes. The lens-rearing period started at approximately 3 weeks of age and ended by 4 to 5 months of age. Refractive development for all monkeys was assessed periodically throughout the treatment and subsequent recovery periods by retinoscopy, keratometry, and A-scan ultrasonography. RESULTS In contrast to control monkeys, the monkeys that had experimentally induced axial ametropias frequently developed significant amounts of astigmatism (mean refractive astigmatism = 0.37 +/- 0.33 D [control] vs. 1.24 +/- 0.81 D [treated]; two-sample t-test, p < 0.0001), especially when their eyes exhibited relative hyperopic shifts in refractive error. The astigmatism was corneal in origin (Pearson's r; p < 0.001 for total astigmatism and the JO and J45 components), and the axes of the astigmatism were typically oblique and bilaterally mirror symmetric. Interestingly, the astigmatism was not permanent; the majority of the monkeys exhibited substantial reductions in the amount of astigmatism at or near the end of the lens-rearing procedures. CONCLUSIONS In infant monkeys, visual conditions that alter axial growth can also alter corneal shape. Similarities between the astigmatic errors in our monkeys and some astigmatic errors in humans suggest that vision-dependent changes in eye growth may contribute to astigmatism in humans.
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Affiliation(s)
- Chea-Su Kee
- College of Optometry, University of Houston, Houston, Texas 77204-2020, USA.
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