Department of Mechanical Engineering, University of California, Berkeley, United States.
Department of Mechanical Engineering, University of California, Berkeley, United States; Department of Orthopaedic Surgery, University of California, San Francisco, United States.
J Biomech. 2019 May 24;89:34-39. doi: 10.1016/j.jbiomech.2019.04.008. Epub 2019 Apr 10.
The high water content of the intervertebral disc is essential to its load bearing function and viscoelastic mechanical behavior. One of the primary biochemical changes associated with disc degeneration is the loss of proteoglycans, which leads to tissue dehydration. While previous studies have reported the effects of in vivo degeneration on annulus fibrosus (AF) failure mechanics, the independent role of water remains unclear, as does the tissue's rate-dependent failure response. Our first objective was to determine the effect of loading rate on AF failure properties in tension; our second objective was to quantify the effect of water content on failure properties. Water content was altered through enzymatic digestion of glycosaminoglycans (GAGs) and through osmotic loading. Bovine AF specimens were tested monotonically to failure along the circumferential direction at 0.00697%/s or 6.97%/s. Increased loading rate resulted in a ∼50% increase in linear-region modulus, failure stress, and strain energy density across all treatment groups (p < 0.001). Decreased GAG and water contents resulted in decreased modulus, failure stress, and strain energy density; however, these differences were only observed at the low loading rate (p < 0.05; no changes at high rate). Osmotic loading was used to evaluate the effect of hydration independently from GAG composition, resulting in similar decreases in water content, modulus, and strain energy density. This suggests that hydration is essential for maintaining tissue stiffness and energy absorption capacity, rather than strength, and that GAGs contribute to tissue strength independently from mediating water content.
椎间盘的高含水量对于其承载功能和粘弹性机械性能至关重要。与椎间盘退变相关的主要生化变化之一是蛋白聚糖的丢失，这导致组织脱水。虽然先前的研究已经报道了体内退变对纤维环（AF）失效力学的影响，但水的独立作用以及组织的速率依赖性失效响应仍不清楚。我们的首要目标是确定加载速率对拉伸中 AF 失效特性的影响；我们的第二个目标是量化含水量对失效特性的影响。通过糖胺聚糖（GAG）的酶消化和渗透加载来改变水含量。牛 AF 标本沿周向在 0.00697%/s 或 6.97%/s 的速度下单调加载至失效。增加加载速率会导致所有处理组的线性区域模量、失效应力和应变能密度增加约 50%（p<0.001）。GAG 和水含量的减少导致模量、失效应力和应变能密度降低；然而，这些差异仅在低加载速率下观察到（p<0.05；在高加载速率下没有变化）。渗透加载用于评估水合作用对 GAG 组成的独立影响，导致水含量、模量和应变能密度相似的降低。这表明水合作用对于维持组织刚度和能量吸收能力至关重要，而不是强度，并且 GAG 独立于介导水含量而有助于组织强度。
