Chemo-Mechanics of Biodegradable Polymers

可生物降解的聚合物是设计成逐渐分解成无害成分的材料，并在完成其结构功能后最终消失。作为传统惰性塑料的潜在替代品，它们吸引了巨大的兴趣，试图解决塑料污染问题。应用包括可持续包装、农用薄膜和渔网等。生物可降解聚合物也是设计临时生物医学植入器械（例如支架、缝线或骨科固定装置）的首选材料，这要归功于其生物相容性和可调机械性能。从工程设计的角度来看，生物可降解聚合物由于看似矛盾的要求而带来了新的挑战：它们需要在完成其预期功能后相对快速地降解，但它们还必须在使用过程中保持合适的机械性能（刚度，强度，韧性）。解决这些挑战需要对决定这些材料性能的化学-机械耦合效应有基本的了解。一方面，在水中的化学降解逐渐降低材料的机械性能并导致溶胀。另一方面，由外部施加的载荷或几何缺陷引起的机械应力显著影响降解速率。该研究旨在阐明力学在水环境中聚合物化学降解中的作用。这将通过整合模型聚合物（PLA）在负载下降解的系统实验和新的基于物理的本构模型耦合力学和化学（水解反应和水和反应产物的扩散）来实现。所提出的模型将在强大的计算工具中实现，从而能够在复杂的负载条件下对可生物降解的组件进行计算机测试直至失效。最终，该研究旨在回答以下问题：“我们能否利用机械效应来控制特定应用的降解速率和失效模式？".该项目提供的新知识、模型和计算工具将直接与包装、工程和医疗保健领域的广泛应用相关。其优势包括具有目标机械和降解性能的聚合物系统配方指南，以及组件级的设计指南和预测模拟工具。这将减少对昂贵和耗时的试错实验方法的需求，并提高可生物降解设备的性能和安全性。

Biodegradable polymers are materials designed to gradually break down into harmless constituents, and eventually disappear after having fulfilled their structural function. They are attracting enormous interest as potential replacements to traditional inert plastics in an attempt to address the plastic pollution problem. Applications include sustainable packaging, agricultural films and fishing nets, among others. Biodegradable polymers are also materials of choice for the design of temporary biomedical implantable devices (e.g. stents, sutures, or orthopaedic fixtures), thanks to their biocompatibility and tunable mechanical properties. From an engineering design perspective, biodegradable polymers introduce new challenges due to seemingly contradictory requirements: they need to degrade relatively fast after having completed their intended function, but they must also maintain suitable mechanical properties (stiffness, strength, toughness) during service. Addressing these challenges requires a fundamental understanding of the coupled chemo-mechanical effects that dictate the performance of these materials. On the one hand, chemical degradation in water progressively decreases the mechanical properties of the material and causes swelling. On the other hand, mechanical stresses arising from externally-applied loads or geometrical imperfections significantly impact the degradation rate. The proposed research aims to elucidate the role of mechanics in the chemical degradation of polymers in aqueous environment. This will be achieved by integrating systematic experiments on model polymers (PLA) degrading under loads and new physics-based constitutive models coupling mechanics and chemistry (hydrolysis reaction and diffusion of water and reaction products). The proposed models will be implemented within robust computational tools enabling the in-silico testing of biodegradable components under complex loading conditions up to failure. Ultimately, the research aims to answer the following question: "can we harness mechanical effects to control the degradation rate and failure mode for specific applications?". The new knowledge, models and computational tools delivered by this project will be directly relevant for a broad range of applications in packaging, engineering and healthcare. Benefits include guidelines for the formulation of polymer systems with targeted mechanical and degradation properties, as well as design guidelines and predictive simulation tools at component level. These will reduce the need for costly and time-consuming trial-and-error experimental approaches, and improve performance and safety of biodegradable devices.