School of Engineering, University of Liverpool, Liverpool L69 3GH, UK.
Key Laboratory for Biomechanics and Mechanobiology of the Ministry of Education, School of Biological Science and Medical Engineering, Beihang University, People's Republic of China.
J R Soc Interface. 2021 Feb;18(175):20200849. doi: 10.1098/rsif.2020.0849. Epub 2021 Feb 3.
This study aims to estimate the material properties of the porcine vitreous while testing it in close to its natural physiological conditions. Eighteen porcine eyes were tested within 48 h post-mortem. A custom-built computer-controlled test rig was designed to support, load and monitor the behaviour of eye globes while being subjected to dynamic rotation cycles mimicking saccade eye movement. Specimens were glued to the base of a container, surrounded by gelatin, frozen and cut in half to expose the vitreous. After thawing, the container was subjected to concentric dynamic rotations of up to 5°, 10° or 15°, while taking 50 MP photos of the specimen every 2 ms. The images were analysed by a digital image correlation algorithm to trace the movement of marked points on the vitreous surface with different radii from the centre of the posterior chamber. The initial camera image was used in building a finite-element model of the test set-up, which was used in an inverse analysis exercise to estimate the material properties of the vitreous. Angular displacements of the monitored points were up to 3.3°, 4.1° and 3.9° in response to eye rotations of 5°, 10° and 15°, respectively. With the experimental relationships between eye rotation and angular displacements used as target behaviour, the inverse analysis exercise estimated the initial shear modulus, the long-term shear modulus and the viscoelastic decay constant of the porcine vitreous as 2.10 ± 0.15 Pa, 0.50 ± 0.04 Pa and 1.20 ± 0.09 s, respectively. Consideration of the viscoelasticity of the vitreous was essential to represent its experimental behaviour. Testing the vitreous in close to its normal physiological conditions produced estimations of the initial shear modulus and long-term shear modulus that were, respectively, smaller and larger than reported values (Zimberlin . 2010 6, 3632-3635. (doi:10.1039/b925407b), Liu . 2013 46, 1321-7. (doi:10.1016/j.jbiomech.2013.02.006), Rossi . 2011 52, 3994-4002. (doi:10.1167/iovs.10-6477)).
本研究旨在测试猪玻璃体的材料特性，同时尽可能接近其生理条件。18 只猪眼在死后 48 小时内进行测试。设计了一个定制的计算机控制测试装置，用于在模拟眼球运动的动态旋转周期中支撑、加载和监测眼球的行为。将标本粘在容器底部，周围是明胶，冷冻后切成两半，暴露玻璃体。解冻后，容器以高达 5°、10°或 15°的同心动态旋转，同时每 2 毫秒对标本拍摄 50 张 MP 照片。通过数字图像相关算法分析图像，以跟踪玻璃体表面不同半径处标记点的运动。初始相机图像用于构建测试装置的有限元模型，该模型用于反分析练习，以估计玻璃体的材料特性。监测点的角位移分别达到 3.3°、4.1°和 3.9°，对应于眼球的 5°、10°和 15°旋转。使用实验关系作为目标行为，将眼球旋转与角位移的关系用于反分析练习，估计猪玻璃体的初始剪切模量、长期剪切模量和粘弹性衰减常数分别为 2.10±0.15 Pa、0.50±0.04 Pa 和 1.20±0.09 s。考虑玻璃体的粘弹性对于代表其实验行为至关重要。在接近正常生理条件下测试玻璃体，产生的初始剪切模量和长期剪切模量估计值分别小于和大于报告值（Zimberlin. 2010 6, 3632-3635. (doi:10.1039/b925407b)，Liu. 2013 46, 1321-7. (doi:10.1016/j.jbiomech.2013.02.006)，Rossi. 2011 52, 3994-4002. (doi:10.1167/iovs.10-6477)）。
