Batool Syeda, Roth Bradley J, Xia Yang
Department of Physics, Oakland University, Rochester, MI 48309, USA.
Materials (Basel). 2024 Jan 1;17(1):238. doi: 10.3390/ma17010238.
The mechanical response of articular cartilage (AC) under compression is anisotropic and depth-dependent. AC is osmotically active, and its intrinsic osmotic swelling pressure is balanced by its collagen fibril network. This mechanism requires the collagen fibers to be under a state of tensile pre-strain. A simple mathematical model is used to explain the depth-dependent strain calculations observed in articular cartilage under 1D axial compression (perpendicular to the articular surface). The collagen fibers are under pre-strain, influenced by proteoglycan concentration (fixed charged density, FCD) and collagen stiffness against swelling stress. The stiffness is introduced in our model as an anisotropic modulus that varies with fibril orientation through tissue depth. The collagen fibers are stiffer to stretching parallel to their length than perpendicular to it; when combined with depth-varying FCD, the model successfully predicts how tissue strains decrease with depth during compression. In summary, this model highlights that the mechanical properties of cartilage depend not only on proteoglycan concentration but also on the intrinsic properties of the pre-strained collagen network. These properties are essential for the proper functioning of articular cartilage.
关节软骨（AC）在压缩下的力学响应具有各向异性且与深度有关。AC具有渗透活性，其内在的渗透肿胀压力由其胶原纤维网络平衡。该机制要求胶原纤维处于拉伸预应变状态。一个简单的数学模型用于解释在一维轴向压缩（垂直于关节表面）下关节软骨中观察到的与深度相关的应变计算。胶原纤维处于预应变状态，受蛋白聚糖浓度（固定电荷密度，FCD）和胶原抗肿胀应力刚度的影响。在我们的模型中，刚度被引入为一个各向异性模量，它随纤维方向通过组织深度而变化。胶原纤维平行于其长度方向的拉伸比垂直于其长度方向的拉伸更硬；当与随深度变化的FCD相结合时，该模型成功预测了压缩过程中组织应变如何随深度减小。总之，该模型强调软骨的力学性能不仅取决于蛋白聚糖浓度，还取决于预应变胶原网络的内在特性。这些特性对于关节软骨的正常功能至关重要。
