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首页> 美国卫生研究院文献>Springer Open Choice >Time-dependent failure in load-bearing polymers: a potential hazard in structural applications of polylactides
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Time-dependent failure in load-bearing polymers: a potential hazard in structural applications of polylactides

机译：承压聚合物中随时间变化的失效：聚丙交酯结构应用中的潜在危险

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With their excellent biocompatibility and relatively high mechanical strength, polylactides are attractive candidates for application in load-bearing, resorbable implants. Pre-clinical studies provided a proof of principle for polylactide cages as temporary constructs to facilitate spinal fusion, and several cages already made it to the market. However, also failures have been reported: clinical studies reported considerable amounts of subsidence with lumbar spinal fusion cages, and in an in vivo goat study, polylactide spinal cages failed after only three months of implantation, although mechanical testing had predicted sufficient strength for at least eight months. The failures appear to be related to the long-term performance of polylactides under static loading conditions, a phenomenon which is common to all glassy polymers and finds its origin in stress-activated molecular mobility leading to plastic flow. This paper reviews the mechanical properties and deformation kinetics of amorphous polylactides. Compression tests were performed with various strain rates, and static stress experiments were done to determine time-to failure. Pure PLLA appeared to have a higher yield strength than its co-polymers with d-lactide, but the kinetic behaviour of the polymers was the same: an excellent short-term strength at higher loading rates, but lifetime under static stress is rather poor. As spinal implants need to maintain mechanical integrity for a period of at least six months, this has serious implications for the clinical application of amorphous polylactides in load bearing situations. It is recommended that standards for mechanical testing of implants made of polymers be revised in order to consider this typical time-dependent behaviour.
机译：凭借其出色的生物相容性和相对较高的机械强度，聚丙交酯是用于承重，可吸收植入物的诱人候选物。临床前研究为聚乳酸笼作为促进脊柱融合的临时构建体提供了原理证明，并且已经有几种笼投放市场。然而，也有失败的报道：临床研究报告说，腰椎融合器沉陷程度相当大；在一项体内山羊研究中，尽管仅进行了机械测试，预示着足够的强度至少可以植入至少三个月，但是聚乳酸脊柱融合器在植入后仅三个月就失败了。八个月。这些失效似乎与聚丙交酯在静态载荷条件下的长期性能有关，这种现象是所有玻璃态聚合物所共有的现象，并且其起源是应力激活的分子迁移导致塑料流动。本文综述了无定形聚丙交酯的力学性能和变形动力学。进行了各种应变率的压缩测试，并进行了静态应力实验以确定失效时间。纯的PLLA似乎比其与d-丙交酯的共聚物具有更高的屈服强度，但是聚合物的动力学行为是相同的：在较高的加载速率下具有出色的短期强度，但在静态应力下的使用寿命却很差。由于脊柱植入物需要保持机械完整性至少六个月，这对于无定形聚丙交酯在承重情况下的临床应用具有严重的意义。建议修改由聚合物制成的植入物的机械测试标准，以考虑这种典型的时间依赖性行为。

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