Wilson W, van Donkelaar C C, van Rietbergen B, Huiskes R
Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, P.O. Box 513, 5600 MB, The Netherlands.
J Biomech. 2005 Jun;38(6):1195-204. doi: 10.1016/j.jbiomech.2004.07.003.
From a mechanical point of view, the most relevant components of articular cartilage are the tight and highly organized collagen network together with the charged proteoglycans. Due to the fixed charges of the proteoglycans, the cation concentration inside the tissue is higher than in the surrounding synovial fluid. This excess of ion particles leads to an osmotic pressure difference, which causes swelling of the tissue. The fibrillar collagen network resists straining and swelling pressures. This combination makes cartilage a unique, highly hydrated and pressurized tissue, enforced with a strained collagen network. Many theories to explain articular cartilage behavior under loading, expressed in computational models that either include the swelling behavior or the properties of the anisotropic collagen structure, can be found in the literature. The most common tests used to determine the mechanical quality of articular cartilage are those of confined compression, unconfined compression, indentation and swelling. All theories currently available in the literature can explain the cartilage response occurring in some of the above tests, but none of them can explain these for all of the tests. We hypothesized that a model including simultaneous mathematical descriptions of (1) the swelling properties due to the fixed-change densities of the proteoglycans and (2) the anisotropic viscoelastic collagen structure, can explain all these test simultaneously. To study this hypothesis we extended our fibril-reinforced poroviscoelastic finite element model with our biphasic swelling model. We have shown that the newly developed fibril-reinforced poroviscoelastic swelling (FPVES) model for articular cartilage can simultaneously account for the reaction force during swelling, confined compression, indentation and unconfined compression as well as the lateral deformation during unconfined compression. Using this theory it is possible to analyze the link between the collagen network and the swelling properties of articular cartilage.
从力学角度来看，关节软骨最相关的组成部分是紧密且高度有序的胶原蛋白网络以及带电荷的蛋白聚糖。由于蛋白聚糖的固定电荷，组织内部的阳离子浓度高于周围的滑液。这种离子颗粒的过量导致渗透压差异，进而引起组织肿胀。纤维状胶原蛋白网络抵抗应变和肿胀压力。这种组合使软骨成为一种独特的、高度水合且受压的组织，并由应变的胶原蛋白网络强化。在文献中可以找到许多用于解释关节软骨在加载下行为的理论，这些理论体现在计算模型中，这些模型要么包括肿胀行为，要么包括各向异性胶原蛋白结构的特性。用于确定关节软骨力学质量的最常见测试是受限压缩、非受限压缩、压痕和肿胀测试。目前文献中所有可用的理论都可以解释上述某些测试中出现的软骨反应，但没有一个能解释所有这些测试的反应。我们假设一个同时包含以下两方面数学描述的模型：（1）由于蛋白聚糖的固定电荷密度引起的肿胀特性，以及（2）各向异性粘弹性胶原蛋白结构，可以同时解释所有这些测试。为了研究这个假设，我们用双相肿胀模型扩展了我们的纤维增强多孔粘弹性有限元模型。我们已经表明，新开发的用于关节软骨的纤维增强多孔粘弹性肿胀（FPVES）模型可以同时解释肿胀、受限压缩、压痕和非受限压缩过程中的反作用力以及非受限压缩过程中的横向变形。利用这个理论，有可能分析胶原蛋白网络与关节软骨肿胀特性之间的联系。
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