Cao Li, Youn Inchan, Guilak Farshid, Setton Lori A
Department of Biomedical Engineering, Duke University, Durham, NC 27708, USA.
J Biomech Eng. 2006 Oct;128(5):766-71. doi: 10.1115/1.2246237.
The mechanical properties of articular cartilage serve as important measures of tissue function or degeneration, and are known to change significantly with osteoarthritis. Interest in small animal and mouse models of osteoarthritis has increased as studies reveal the importance of genetic background in determining predisposition to osteoarthritis. While indentation testing provides a method of determining cartilage mechanical properties in situ, it has been of limited value in studying mouse joints due to the relatively small size of the joint and thickness of the cartilage layer. In this study, we developed a micro-indentation testing system to determine the compressive and biphasic mechanical properties of cartilage in the small joints of the mouse. A nonlinear optimization program employing a genetic algorithm for parameter estimation, combined with a biphasic finite element model of the micro-indentation test, was developed to obtain the biphasic, compressive material properties of articular cartilage. The creep response and material properties of lateral tibial plateau cartilage were obtained for wild-type mouse knee joints, by the micro-indentation testing and optimization algorithm. The newly developed genetic algorithm was found to be efficient and accurate when used with the finite element simulations for nonlinear optimization to the experimental creep data. The biphasic mechanical properties of mouse cartilage in compression (average values: Young's modulus, 2.0 MPa; Poisson's ratio, 0.20; and hydraulic permeability, 1.1 x 10(-16) m4/N-s) were found to be of similar orders of magnitude as previous findings for other animal cartilages, including human, bovine, rat, and rabbit and demonstrate the utility of the new test methods. This study provides the first available data for biphasic compressive properties in mouse cartilage and suggests a promising method for detecting altered cartilage mechanics in small animal models of osteoarthritis.
关节软骨的力学性能是衡量组织功能或退变的重要指标，并且已知其会随着骨关节炎而发生显著变化。随着研究揭示遗传背景在决定骨关节炎易感性方面的重要性，对骨关节炎的小动物和小鼠模型的兴趣有所增加。虽然压痕测试提供了一种在原位测定软骨力学性能的方法，但由于关节相对较小以及软骨层较薄，它在研究小鼠关节方面的价值有限。在本研究中，我们开发了一种微压痕测试系统，以确定小鼠小关节中软骨的压缩和双相力学性能。开发了一种采用遗传算法进行参数估计的非线性优化程序，并结合微压痕测试的双相有限元模型，以获得关节软骨的双相压缩材料性能。通过微压痕测试和优化算法，获得了野生型小鼠膝关节外侧胫骨平台软骨的蠕变响应和材料性能。结果发现，新开发的遗传算法与有限元模拟一起用于对实验蠕变数据进行非线性优化时，高效且准确。小鼠软骨在压缩状态下的双相力学性能（平均值：杨氏模量为2.0兆帕；泊松比为0.20；水力渗透率为1.1×10⁻¹⁶立方米⁴/牛顿·秒）与先前对包括人类、牛、大鼠和兔子在内的其他动物软骨的研究结果处于相似的数量级，证明了新测试方法的实用性。本研究提供了小鼠软骨双相压缩性能的首个可用数据，并提出了一种在骨关节炎小动物模型中检测软骨力学改变的有前景的方法。
