June R K, Neu C P, Barone J R, Fyhrie D P
Department of Cellular and Molecular Medicine, University of California, San Diego, San Diego, CA, 92093.
Mater Sci Eng C Mater Biol Appl. 2011 May 10;31(4):781-788. doi: 10.1016/j.msec.2010.11.029.
Articular cartilage is the load bearing soft tissue that covers the contacting surfaces of long bones in articulating joints. Healthy cartilage allows for smooth joint motion, while damaged cartilage prohibits normal function in debilitating joint diseases such as osteoarthritis. Knowledge of cartilage mechanical function through the progression of osteoarthritis, and in response to innovative regeneration treatments, requires a comprehensive understanding of the molecular nature of interacting extracellular matrix constituents and interstitial fluid. The objectives of this study were therefore to (1) examine the timescale of cartilage stress-relaxation using different mechanistic models and (2) develop and apply a novel (termed "sticky") polymer mechanics model to cartilage stress-relaxation based on temporary binding of constituent macromolecules. Using data from calf cartilage samples, we found that different models captured distinct timescales of cartilage stress-relaxation: monodisperse polymer reptation best described the first second of relaxation, sticky polymer mechanics best described data from ∼1-100 seconds of relaxation, and a model of inviscid fluid flow through a porous elastic matrix best described data from 100 seconds to equilibrium. Further support for the sticky polymer model was observed using experimental data where cartilage stress-relaxation was measured in either low or high salt concentration. These data suggest that a complete understanding of cartilage mechanics, especially in the short time scales immediately following loading, requires appreciation of both fluid flow and the polymeric behavior of the extracellular matrix.
关节软骨是覆盖在关节中长骨接触表面的承重软组织。健康的软骨能使关节运动顺畅，而受损的软骨会导致诸如骨关节炎等使人衰弱的关节疾病出现功能异常。要了解骨关节炎发展过程中以及对创新再生治疗作出反应时软骨的力学功能，就需要全面了解细胞外基质成分与组织液相互作用的分子本质。因此，本研究的目的是：（1）使用不同的力学模型研究软骨应力松弛的时间尺度；（2）基于组成大分子的临时结合，开发并应用一种新颖的（称为“粘性”）聚合物力学模型来描述软骨应力松弛。利用来自小牛软骨样本的数据，我们发现不同的模型捕捉到了软骨应力松弛的不同时间尺度：单分散聚合物链爬行最能描述松弛的前一秒，粘性聚合物力学最能描述约1至100秒松弛过程中的数据，而无粘性流体通过多孔弹性基质的模型最能描述100秒至平衡阶段的数据。在低盐或高盐浓度下测量软骨应力松弛的实验数据也进一步支持了粘性聚合物模型。这些数据表明，要全面理解软骨力学，尤其是在加载后的短时间尺度内，需要同时考虑流体流动和细胞外基质的聚合物行为。
