1
|
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.
Collapse
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
| |
Collapse
|
2
|
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.
Collapse
Affiliation(s)
| | - Hamed Hatami-Marbini
- Mechanical and Industrial Engineering Department, University of Illinois Chicago, Chicago, IL 60607, USA
| |
Collapse
|
3
|
Jan NJ, Lee PY, Wallace J, Iasella M, Gogola A, Wang B, Sigal IA. Stretch-Induced Uncrimping of Equatorial Sclera Collagen Bundles. J Biomech Eng 2023; 145:054503. [PMID: 36459150 PMCID: PMC9791674 DOI: 10.1115/1.4056354] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Revised: 11/20/2022] [Accepted: 11/21/2022] [Indexed: 12/03/2022]
Abstract
Stretch-induced collagen uncrimping underlies the nonlinear mechanical behavior of the sclera according to what is often called the process of recruitment. We recently reported experimental measurements of sclera collagen crimp and pressure-induced uncrimping. Our studies, however, were cross-sectional, providing statistical descriptions of crimp with no information on the effects of stretch on specific collagen bundles. Data on bundle-specific uncrimping is necessary to better understand the effects of macroscale input on the collagen microscale and tissue failure. Our goal in this project was to measure bundle-specific stretch-induced collagen uncrimping of sclera. Three goat eyes were cryosectioned sagittally (30 μm). Samples of equatorial sclera were isolated, mounted to a custom uni-axial stretcher and imaged with polarized light microscopy at various levels of clamp-to-clamp stretch until failure. At each stretch level, local strain was measured using image tracking techniques. The level of collagen crimping was determined from the bundle waviness, defined as the circular standard deviation of fiber orientation along a bundle. Eye-specific recruitment curves were then computed using eye-specific waviness at maximum stretch before sample failure to define fibers as recruited. Nonlinear mixed effect models were used to determine the associations of waviness to local strain and recruitment to clamp-to-clamp stretch. Waviness decreased exponentially with local strain (p < 0.001), whereas bundle recruitment followed a sigmoidal curve with clamp-to-clamp stretch (p < 0.001). Individual bundle responses to stretch varied substantially, but recruitment curves were similar across sections and eyes. In conclusion, uni-axial stretch caused measurable bundle-specific uncrimping, with the sigmoidal recruitment pattern characteristic of fiber-reinforced soft tissues.
Collapse
Affiliation(s)
- Ning-Jiun Jan
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15213
| | - Po-Yi Lee
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15213
| | - Jacob Wallace
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15213
| | - Michael Iasella
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15213
| | - Alexandra Gogola
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213
| | - Bingrui Wang
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213
| | - Ian A. Sigal
- Department of Ophthalmology, Laboratory of Ocular Biomechanics, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15213
| |
Collapse
|