A phase-field model of mechanically-assisted corrosion of bioabsorbable metals

Magnesium alloys exhibit great potential for use as implants that gradually and entirely dissolve in the human body after healing. Rapid corrosion in body fluids and the susceptibility to pitting corrosion and stress corrosion cracking are the main reasons limiting the widespread use of Mg alloys as a biodegradable material. The concurrence of mechanical loading and a corrosive environment dramatically accelerates the corrosion rate and promotes crack propagation, leading to the sudden failure of implants. A phase-field model is developed to simulate the corrosion of bioabsorbable metals in biological fluids. The model incorporates both Mg dissolution and the transport of Mg ions in solution. The framework captures pitting corrosion and incorporates the role of mechanical fields in enhancing the corrosion of biodegradable metals. The model is validated against in vitro corrosion data on Mg alloys immersed in simulated body fluid. The potential of the model to capture mechano-chemical effects is demonstrated by considering bioabsorbable coronary stents subjected to mechanical loading. The results show that pitting severely compromises the structural integrity of the stent and the application of mechanical loading initiates a pit-to-crack transition and crack propagations, leading to premature fracture after a short time in solution. This work extends phase-field modeling to biomaterial degradation and provides a novel mechanistic tool for assessing the service life of bioabsorbable medical devices