Modeling the response of exogenously crosslinked tissue to cyclic loading: The effects of permanent set.
Modeling the response of exogenously crosslinked tissue to cyclic loading: The effects of permanent set.
复制标题
模拟外源交联组织对循环载荷的响应：永久变形的影响。
DOI：
10.1016/j.jmbbm.2017.07.013
复制
发表时间：
2017
影响因子：
3.9
通讯作者：
Sacks,MichaelS
中科院分区：
文献类型：
--
作者：
Zhang,Will;Sacks,MichaelS
由外源性交联胶原组织制成的生物假体心脏瓣膜（bhv）仍然是最流行的心脏瓣膜替代设计。然而，BHV的使用寿命仍然限制在10-15年，部分原因是BHV失效的机制尚不清楚。实验证据表明，bhv在活体操作中会发生显著的几何变化，从而导致应力集中，从而对结构损伤产生重大影响。这些变化似乎不是由于塑性变形，因为小叶只在弹性状态下变形。此外，6500万周期时间点未检测到结构损伤。相反，我们发现这种不可恢复的变形类似于在弹性体中观察到的永久固定效应，这允许材料的参考结构随着时间的推移而演变。我们假设戊二醛的断裂愈合反应是导致外源性交联软组织永久固定的潜在机制。戊二醛的连续断裂愈合过程允许部分外源性交联基质（被认为是细胞外基质的非纤维部分）在负载状态下重新交联。因此，这种永久固立机制可以用来解释bhv早期随时间变化的力学响应和几何形状。为了模拟永久集效应，我们假设外生交联矩阵的参考构型随着时间的推移而变化。胶原纤维结构因尺寸变化而发生的变化使我们能够预测随后机械反应的变化。结果表明，单独的永久集可以解释，更重要的是，预测生物材料的力学反应如何随时间变化。此外，我们发现在应变控制和应力控制的循环加载研究中，永久设定速率常数没有差异。我们的一个重要发现是，胶原纤维结构对永久凝固效应所能引起的最大几何变化有限制作用。这是由于胶原纤维的募集随着几何形状的变化而永久定形增加。这意味着，在永久坐封基本结束后，我们可以根据预测的最终BHV几何形状来优化BHV的几何形状。因此，我们开发了第一个外源性交联软组织中永久固定效应的结构本构模型，该模型可以帮助模拟BHV设计，减少循环加载期间BHV几何形状的变化，从而有可能提高BHV的耐久性。
Bioprosthetic heart valves (BHVs), fabricated from exogenously crosslinked collagenous tissues, remain the most popular heart valve replacement design. However, the life span of BHVs remains limited to 10–15 years, in part because the mechanisms that underlie BHV failure remain poorly understood. Experimental evidence indicates that BHVs undergo significant changes in geometry within vivooperation, which lead to stress concentrations that can have significant impact on structural damage. These changes do not appear to be due to plastic deformation, as the leaflets only deform in the elastic regime. Moreover, structural damage was not detected by the 65 million cycle time point. Instead, we found that this nonrecoverable deformation is similar to the permanent set effect observed in elastomers, which allows the reference configuration of the material to evolve over time. We hypothesize that the scission-healing reaction of glutaraldehyde is the underlying mechanism responsible for permanent set in exogenously crosslinked soft tissues. The continuous scission-healing process of glutaraldehyde allows a portion of the exogenously crosslinked matrix, which is considered to be the non-fibrous part of the extra-cellular matrix, to be re-crosslinked in the loaded state. Thus, this mechanism for permanent set can be used to explain the time evolving mechanical response and geometry of BHVs in the early stage. To model the permanent set effect, we assume that the exogenously crosslinked matrix undergoes changes in reference configurations over time. The changes in the collagen fiber architecture due to dimensional changes allow us to predict subsequent changes in mechanical response. Results show that permanent set alone can explain and, more importantly, predict how the mechanical response of the biomaterial change with time. Furthermore, we found is no difference in permanent set rate constants between the strain controlled and the stress controlled cyclic loading studies. An important finding we have is that the collagen fiber architecture has a limiting effect on the maximum changes in geometry that the permanent set effect can induce. This is due to the recruitment of collagen fibers as the changes in geometry due to permanent set increase. This means we can potentially optimize the BHV geometry based on the predicted the final BHV geometry after permanent set has largely ceased. Thus, we have developed the first structural constitutive model for the permanent set effect in exogenously crosslinked soft tissue, which can help to simulate BHV designs and reduce changes in BHV geometry during cyclic loading and thus potentially increasing BHV durability.