Department of Mechanical and Automotive Engineering, Gachon University, Seongnam-Si, Gyeonggi-do 461-701, Republic of Korea.
Biomed Res Int. 2013;2013:197479. doi: 10.1155/2013/197479. Epub 2012 Dec 30.
The Poisson ratio (PR) is a fundamental mechanical parameter that approximates the ratio of relative change in cross sectional area to tensile elongation. However, the PR of extraocular muscle (EOM) is almost never measured because of experimental constraints. The problem was overcome by determining changes in EOM dimensions using computed X-ray tomography (CT) at microscopic resolution during tensile elongation to determine transverse strain indicated by the change in cross-section. Fresh bovine EOM specimens were prepared. Specimens were clamped in a tensile fixture within a CT scanner (SkyScan, Belgium) with temperature and humidity control and stretched up to 35% of initial length. Sets of 500-800 contiguous CT images were obtained at 10-micron resolution before and after tensile loading. Digital 3D models were then built and discretized into 6-8-micron-thick elements. Changes in longitudinal thickness of each microscopic element were determined to calculate strain. Green's theorem was used to calculate areal strain in transverse directions orthogonal to the stretching direction. The mean PR from discretized 3D models for every microscopic element in 14 EOM specimens averaged 0.457 ± 0.004 (SD). The measured PR of bovine EOM is thus near the limit of incompressibility.
泊松比（PR）是一个基本的机械参数，它近似于横截面积相对变化与拉伸伸长的比值。然而，由于实验限制，眼外肌（EOM）的 PR 几乎从未被测量过。通过在拉伸伸长过程中使用计算 X 射线断层摄影术（CT）以微观分辨率确定 EOM 尺寸的变化，克服了这个问题，该方法可通过横截面的变化来确定横向应变。准备了新鲜的牛眼外肌标本。将标本在 CT 扫描仪（比利时 SkyScan）内的拉伸夹具中夹紧，同时进行温度和湿度控制，并将其拉伸至初始长度的 35%。在拉伸前和拉伸后，以 10 微米的分辨率获得了 500-800 组连续的 CT 图像。然后构建数字 3D 模型，并将其离散化到 6-8 微米厚的元素中。确定每个微观元素的纵向厚度变化，以计算应变。使用格林定理计算与拉伸方向正交的横向方向的面积应变。在 14 个 EOM 标本的每个微观元素的离散化 3D 模型中，平均泊松比为 0.457±0.004（标准差）。因此，牛眼外肌的测量泊松比接近不可压缩性的极限。
