Department of Mechanics, Mathematics and Management, Politecnico di Bari, Via Orabona 4, 70100, Bari, Italy; Department of Mechanical Engineering, Imperial College London, South Kensington Campus, Exhibition Road, London SW7 2AZ, United Kingdom.
Department of Mechanical Engineering, University of Delaware, Newark, DE, United States of America.
Acta Biomater. 2021 Apr 15;125:90-99. doi: 10.1016/j.actbio.2021.02.040. Epub 2021 Mar 3.
Loading-induced cartilage exudation causes loss of fluid from the tissue, joint space thinning and, in a long term prospective, the insurgence of osteoarthritis. Fortunately, experiments show that joints recover interstitial fluid and thicken during articulation after static loading, thus reversing the exudation process. Here, we provide the first original theoretical explanation to this crucial phenomenon, by implementing a numerical model capable of accounting for the multiscale porous lubrication occurring in joints. We prove that sliding-induced rehydration occurs because of hydrodynamic reasons and is specifically related to a wedge effect at the contact inlet. Furthermore, numerically predicted rehydration rates are consistent with experimentally measured rates and corroborate the robustness of the model here proposed. The paper provides key information, in terms of fundamental lubrication multiscale mechanisms, to understand the rehydration of cartilage and, more generally, of any biological tissue exhibiting a significant porosity: such a theoretical framework is, thus, crucial to inform the design of new effective cartilage-mimicking biomaterials. STATEMENT OF SIGNIFICANCE: Motion and, precisely, joints articulation ensures that cartilage tissues preserve adequate level of hydration and, thus, maintain excellent mechanical properties in terms of high resilience, considerable load-carrying capacity and remarkably low friction. Conversely, when statically loaded, cartilage starts to exudate, causing joint space thinning and, in the long term, possible osteoarthritis; joints motion is, thus, the key to prevent the degradation of the tissues. By developing a numerical multiscale lubrication theory, and by corroborating this approach with experiments, we provide the first original theoretical explanation to this motion-induced cartilage rehydration mechanism. Assessing the rehydration hydrodynamic origin is, in fact, fundamental not only to understand the joints physiology, but also to highlight a key requirement for cartilage-mimicking biomaterials.
加载引起的软骨渗出会导致组织失水、关节间隙变窄，从长远来看，还会导致骨关节炎的发生。幸运的是，实验表明，在静态加载后关节进行活动时，关节会重新吸收间质液并增厚，从而逆转渗出过程。在这里，我们通过实施一个能够解释关节中多尺度多孔润滑的数值模型，为这一关键现象提供了第一个原创理论解释。我们证明，由于流体动力原因，滑动诱导的再水化会发生，并且与接触入口处的楔形效应特别相关。此外，数值预测的再水化速率与实验测量的速率一致，证实了所提出模型的稳健性。本文提供了有关基本润滑多尺度机制的关键信息，以了解软骨的再水化，更一般地说，了解任何表现出显著多孔性的生物组织的再水化：因此，这种理论框架对于告知新的有效的模仿软骨的生物材料的设计至关重要。
运动，确切地说是关节活动，确保软骨组织保持足够的水合水平，从而在高弹性、高承载能力和极低摩擦等方面保持出色的机械性能。相反，当受到静态加载时，软骨开始渗出，导致关节间隙变窄，从长远来看，可能会导致骨关节炎；因此，关节运动是防止组织退化的关键。通过开发数值多尺度润滑理论，并通过实验验证该方法，我们为这种运动诱导的软骨再水化机制提供了第一个原创理论解释。评估再水化的流体动力起源不仅对于理解关节生理学至关重要，而且对于突出模仿软骨的生物材料的一个关键要求也很重要。
