Time-dependent coupled degradation–mechanics modeling of load transfer in biodegradable Mg–2Zn orthopedic implants
Abstract
Biodegradable magnesium alloys have emerged as promising candidates for orthopedic fixation due to their favorable mechanical compatibility and inherent ability to degrade in physiological environments. However, corrosion-induced degradation leads to time-dependent changes in implant geometry and stiffness, significantly influencing load transfer and biomechanical performance. In this study, a time-dependent multiphysics computational framework is developed to investigate the coupled effects of degradation and mechanical behavior in a biodegradable Mg–2Zn implant embedded in cortical bone. The model integrates corrosion-driven geometry reduction with stiffness degradation and finite element analysis to simulate the evolving bone–implant interaction under dominant axial compressive loading conditions over a 12-month healing period. The results demonstrate that progressive degradation reduces the implant elastic modulus from 43 GPa to 20.9 GPa, leading to improved stiffness compatibility and enhanced load sharing with surrounding bone. Consequently, the average cortical bone stress increases from 12.4 MPa to 16.4 MPa, corresponding to approximately 32% stress recovery, while the stress shielding index decreases by nearly 60%. Despite material loss, implant stresses remain well below the yield strength, indicating adequate structural integrity throughout the healing process. Parametric analyses further reveal that implant diameter and degradation rate critically govern the balance between mechanical stability and stress shielding mitigation. These findings highlight the importance of degradation-controlled design and demonstrate the potential of multiphysics modeling as a predictive tool for optimizing next-generation biodegradable magnesium-based orthopedic implants.