Degradable polymers are being developed for medical applications and environmental sustainability. The molecular mechanism of degradation is known: a polymer dissociates in response to a trigger, such as light, water, or biomolecules. However, the spatial and temporal processes of degradation are poorly characterized. Here we show that degradation can be highly heterogeneous, and can readily lead to cracks that outrun erosion in speed by orders of magnitude. This paper studies crack growth in poly(glycerol sebacate) (PGS), a degradable elastomer developed for medical applications. The elastomer is a polyester in which ester bonds hydrolyze in the presence of water molecules. We prepare a sample of PGS with a precut crack, apply various loads, and record the crack growth using a camera. A small load opens a crack in PGS, and provides a path for water molecules to reach the crack tip, possibly by clearing the hydrophobic debris of reaction products, enabling hydrolysis at the crack tip to outrun elsewhere. We show that the speed of the hydrolytic crack depends on relative humidity, pH, and applied load. In a fixed environment, we identify two regimes of crack growth: one is sensitive to the magnitude of the applied load, and the other is not. The hydrolytic crack causes the polymer to lose its load-carrying capacity prematurely, and fragmented polymer particles can cause severe medical complications.

正在开发可降解聚合物以用于医疗应用和环境可持续性。降解的分子机理是已知的：聚合物响应于诸如光，水或生物分子的触发而解离。但是，退化的空间和时间过程的特征很差。在这里，我们表明降解可能是高度异质的，并且很容易导致裂纹，其速度超过腐蚀速度达几个数量级。本文研究了聚癸二酸甘油酯（PGS）中的裂纹扩展，该产品是为医疗应用开发的可降解弹性体。弹性体是在水分子存在下酯键水解的聚酯。我们准备了带有预切裂缝的PGS样品，施加各种载荷，并使用相机记录裂缝的增长。较小的载荷会在PGS中产生裂纹，并可能通过清除反应产物的疏水性碎片，使水分子到达裂纹尖端，从而使裂纹尖端的水解作用超出其他地方。我们表明，水解裂纹的速度取决于相对湿度，pH和施加的载荷。在固定的环境中，我们确定了两种裂纹扩展机制：一种对施加的载荷大小敏感，而另一种则不敏感。水解裂纹会导致聚合物过早地失去其承载能力，而破碎的聚合物颗粒会导致严重的医疗并发症。在固定的环境中，我们确定了两种裂纹扩展机制：一种对施加的载荷大小敏感，而另一种则不敏感。水解裂纹会导致聚合物过早地失去其承载能力，而破碎的聚合物颗粒会导致严重的医疗并发症。在固定的环境中，我们确定了两种裂纹扩展机制：一种对施加的载荷大小敏感，而另一种则不敏感。水解裂纹会导致聚合物过早失去其承载能力，而破碎的聚合物颗粒会导致严重的医疗并发症。