The intervertebral disc is an avascular composite structure, comprised of the nucleus pulposus (NP) and the annulus fibrosus (AF). Previous tissue-level experiments either examined relative differences in swelling capacity of the two disc regions at a single time point or tested explant structures that did not replicate in situ boundary conditions. Previous joint-level studies that investigated time-dependent fluid flow into the disc provided limited information about swelling-induced intradiscal strains with respect to time and boundary constraints. Therefore, the objective of this study was to investigate time-dependent swelling behavior of the intervertebral disc ex situ. The first study investigated time-dependent free-swelling response of the whole disc and the disc's subcomponents separately (i.e., NP and AF). Findings from this study showed that the swelling rate and swelling capacity of NP explants under free-swelling conditions were greater than AF explants. The second study evaluated the effect of boundary conditions on in-plane strain distributions of intact discs and AF rings. Swelling-induced strain was highly heterogeneous in AF rings, where negative circumferential strains were observed in the inner AF and tensile circumferential strains were observed in the outer AF. Radial strains in AF rings were an order of magnitude greater than circumferential strains. Restricting fluid flow only to the outer AF periphery reduced the swelling of the inner AF. Swelling of intact discs affected both NP and AF swelling behaviors, where NP hydration decreased by 60%. Furthermore, the presence of the NP reduced peak radial strains in the AF and resulted in uniform strain distribution throughout the AF. In conclusion, these studies highlight that tissue hydration and swelling-induced strains largely depend on regional biochemical composition and geometric boundary constraints.

椎间盘是一种无血管的复合结构，由髓核（NP）和纤维环（AF）组成。先前的组织水平实验要么在单个时间点检查了两个椎间盘区域肿胀能力的相对差异，要么测试了不能复制就地边界条件的外植体结构。以前的关节水平研究调查了随时间变化的流体流入椎间盘的情况，因此就时间和边界约束而言，有关肿胀诱发的椎间盘内应变的信息有限。因此，本研究的目的是调查异位椎间盘的时间依赖性肿胀行为。第一项研究分别研究了整个椎间盘和椎间盘的各个子组件随时间变化的自由膨胀响应（即，NP和AF）。这项研究的结果表明，在自由溶胀条件下，NP外植体的溶胀率和溶胀能力大于AF外植体。第二项研究评估了边界条件对完整圆盘和AF环的面内应变分布的影响。膨胀引起的应变在AF环中是高度异质的，其中在内部AF中观察到负的周向应变，在外部AF中观察到拉伸的周向应变。AF环中的径向应变比周向应变大一个数量级。仅限制流体流向外部AF外围会减少内部AF的膨胀。完整椎间盘的肿胀会影响NP和AF肿胀行为，其中NP水合降低60％。此外，NP的存在降低了AF中的峰值径向应变，并导致整个AF中的应变均匀分布。总之，这些研究强调组织水合作用和肿胀诱导的菌株在很大程度上取决于区域生化成分和几何边界约束。