An automated approach for direct measurement of two-dimensional strain distributions within articular cartilage under unconfined compression
An automated approach for direct measurement of two-dimensional strain distributions within articular cartilage under unconfined compression
复制标题
DOI：
10.1115/1.1503795
复制
发表时间：
2002-10-01
影响因子：
1.7
通讯作者：
Hung, CT
中科院分区：
文献类型：
--
作者：
Wang, CCB;Deng, JM;Hung, CT
开发了一种用于测量原位二维应变场的自动化方法，并验证了其在软骨力学中的应用。这种方法结合了视频显微镜，优化的数字图像相关（DIC），薄板样条平滑（TPSS）和广义交叉验证（GCV）技术，以达到所需的效率和精度。结果表明，亚像素精度可以实现测量组织位移与这种方法的测量不确定度范围从0.25到0.30像素。变形梯度（从中确定应变）可以直接使用优化的DIC进行评估，测量不确定度为0.017类似于0.032。在软骨应变的实际测量中，TPSS和微分可用于从位移数据实现梯度的更准确测量。使用这种自动化的方法，二维应变场内未成熟的牛腕掌关节软骨标本无侧限压缩的特点（n =21）。深度依赖的表观弹性模量和泊松比也被确定，并发现在关节面最小，并随着深度增加。发现表观泊松比随着压缩应变的增加而降低，在25%压缩时，在关节面附近观察到的值低至0.01。表观泊松比随深度的变化被认为是一致的理论模型的软骨占其拉伸和压缩模量的差距。
An automated approach for measuring in situ two-dimensional strain fields was developed and validated for its application to cartilage mechanics. This approach combines video microscopy, optimized digital image correlation (DIC), thin-plate spline smoothing (TPSS) and generalized cross-validation (GCV) techniques to achieve the desired efficiency and accuracy. Results demonstrate that sub-pixel accuracies can be achieved for measuring tissue displacements with this methodology with a measurement uncertainty ranging from 0.25 to 0.30 pixels. The deformational gradients (from which the strains are determined) can be evaluated directly using the optimized DIC, with a measurement uncertainty of 0.017similar to0.032. In actual measurements of strain in cartilage, TPSS and differentiation can be used to achieve a more accurate measurement of the gradients from the displacement data. Using this automated approach, the two-dimensional strain fields inside immature bovine carpometacarpal joint cartilage specimens under unconfined compression were characterized (n =21). The depth-dependent apparent elastic modulus and Poissons ratio were also determined and found to be smallest at the articular surface and increasing with depth. The apparent Poisson's ratio is found to decrease with increasing compressive strain, with values as low as 0.01 observed near the articular surface at 25% compression. The variation of the apparent Poisson's ratio with depth is found to be consistent with a theoretical model of cartilage which accounts for the disparity in its tensile and compressive moduli.