Chemo-Mechanics of Biodegradable Polymers

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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.