Deptment of Mechanical Engineering, University of Birmingham, Birmingham, B15 2TT, UK.
Centre for Arthritis and Musculoskeletal Health, University of Aberdeen, AB25 2ZD, Foresterhill Aberdeen, UK.
BMC Musculoskelet Disord. 2022 Mar 8;23(1):228. doi: 10.1186/s12891-022-05169-0.
Articular cartilage is known to be a viscoelastic material, however little research has explored the impact of cartilage water content and bone density on its viscoelasticity. This study aimed to isolate subchondral bone density and hydration of articular cartilage and analyse their effects on the viscoelastic properties of articular cartilage.
Dynamic mechanical analysis was used to test samples at frequencies of 1, 8, 12, 29, 49, 71, and 88 Hz. Synthetic bone material with densities of 663.7 kg/m and 156.8 kg/m were used to mimic the bone mineral density (BMD). Dehydration occurred in a stepwise manner at relative humidity (RH) levels of 100%, 30%, and 1%. These relative humidity levels led to water contents of approximately 76%, 8.5%, and ≈ 0% by mass, respectively.
Samples from eight bovine femoral heads were tested under a sinusoidal load. Storage stiffness was lower on the lower substrate density. Storage stiffness, though, increased as cartilage samples were dehydrated from a water content of 76% to 8.5%; decreasing again as the water content was further reduced. Loss stiffness was lower on a lower density substrate and decreased as the water content decreased.
In conclusions, a decrease in hydration decreases the loss stiffness, but a non-linear relationship between hydration and storage stiffness may exist. Additionally, higher BMD values led to greater storage and loss stiffnesses.
关节软骨是一种粘弹性材料，然而，很少有研究探讨软骨水含量和骨密度对其粘弹性的影响。本研究旨在分离关节软骨的软骨下骨密度和水合作用，并分析它们对关节软骨粘弹性的影响。
采用动态力学分析方法，在 1、8、12、29、49、71 和 88 Hz 的频率下测试样本。使用密度分别为 663.7 kg/m 和 156.8 kg/m 的合成骨材料模拟骨矿物质密度（BMD）。在相对湿度（RH）为 100%、30%和 1%的条件下，逐步进行脱水。这些相对湿度水平分别导致水含量约为 76%、8.5%和约 0%（按质量计）。
对来自八个牛股骨的样本在正弦载荷下进行测试。在较低基质密度下，存储刚度较低。然而，随着软骨样本从水含量 76%脱水至 8.5%，存储刚度增加；当水含量进一步降低时，再次降低。在较低密度的基质上，损耗刚度较低，且随着水含量的降低而降低。
总之，水合作用的降低会降低损耗刚度，但水合作用与存储刚度之间可能存在非线性关系。此外，较高的 BMD 值导致更高的存储和损耗刚度。
