Department of Mechanical Engineering, University of Delaware Newark, DE 19716, United States.
J Biomech. 2012 Apr 5;45(6):1036-41. doi: 10.1016/j.jbiomech.2011.12.019. Epub 2012 Jan 28.
Interstitial fluid pressurization, a consequence of a biphasic tissue structure, is essential to the load bearing and lubrication properties of articular cartilage. Focal tissue degradation may interfere with this protective mechanism, eventually leading to gross degeneration and osteoarthritis. Our long-term goal is to determine whether local contacts can be used as a means to probe local tissue integrity and functionality. In the present work, Hertzian rate-controlled microindentation was used as a model of the more complicated sliding system to directly determine the effects of contact radius and deformation rate on interstitial load support. During localized contact between a steel spherical probe and bovine articular cartilage, the equilibrium and non-equilibrium responses were well-fit by the Hertz model (R(2)>0.998) with a mean equilibrium contact modulus of 0.93 MPa. The effective contact modulus and fluid load fraction were independent of indentation depth, contact radius, and normal force; both increased monotonically with indentation rate. At 21 μm/s indentation rate, the cartilage was effectively stiffened by 6-fold with the fluid pressure supporting 85% of the contact force. The results motivated a simple analytical model that directly links the tribomechanical response (including fluid load support) and the Peclet number to measurable material properties and controllable experimental variables. This paper demonstrates that tribological contacts can be used to probe local functional properties. Such measurements can add important insights into the roles of focal tissue damage and impaired local functionality in the pathogenesis of osteoarthritis.
间质液压力是双相组织结构的结果，对于关节软骨的承载和润滑性能至关重要。局灶性组织降解可能会干扰这种保护机制，最终导致严重的退行性变和骨关节炎。我们的长期目标是确定局部接触是否可以用作探测局部组织完整性和功能的手段。在本工作中，赫兹率控制微压痕被用作更复杂的滑动系统的模型，直接确定接触半径和变形率对间质液承载的影响。在钢球探针和牛关节软骨之间的局部接触中，赫兹模型（R(2)>0.998）很好地拟合了平衡和非平衡响应，平均平衡接触模量为 0.93 MPa。有效接触模量和流体载荷分数与压痕深度、接触半径和法向力无关；均随压痕速率单调增加。在 21 μm/s 的压痕速率下，软骨的刚度增加了 6 倍，而流体压力支撑了 85%的接触力。结果激发了一个简单的分析模型，该模型直接将摩擦力学响应（包括流体载荷支撑）与佩克莱数联系起来，与可测量的材料特性和可控的实验变量联系起来。本文证明了摩擦接触可以用来探测局部功能特性。这种测量可以为局灶性组织损伤和局部功能障碍在骨关节炎发病机制中的作用提供重要的见解。
