High entropy and biodegradable alloy strategies for biomedical implants with controlled degradation

High-entropy alloys (HEAs) and biodegradable metallic systems represent emerging frontiers in biomaterials for orthopedic, cardiovascular, and tissue-regenerative applications. Conventional Ti-6Al-4 V and Co–Cr alloys offer high strength but suffer from stress shielding, adverse ion release, and the need for removal surgery. Bio-high-entropy alloys (Bio-HEAs) based on multi-principal, non-toxic elements (Ti, Zr, Nb, Ta, Hf) provide bone-like modulus, high strength, and superior corrosion resistance, whereas Mg-, Zn- and Fe-based biodegradable alloys are designed to resorb after fulfilling their structural role. This review examines how these trajectories converge in biodegradable high-entropy alloys (BHEAs), which seek to couple entropy-stabilized microstructures with controlled, bio-benign degradation and ion-mediated biofunctionality. Beyond summarizing recent developments, it introduces a mechanistic design matrix linking phase-potential gaps, phase topology, porosity and corrosion-product characteristics to corrosion morphology and ion-dose profiles in candidate BHEAs. A degradation-rate–elastic-modulus “safe operating window” for temporary load-bearing implants is constructed by aggregating representative in-vitro corrosion and mechanical data from Mg-, Zn-, Fe-based alloys and Ti-centered Bio-HEAs. The review explicitly distinguishes experimentally supported observations from forward-looking design hypotheses, including Ti/Zr/Nb/Ta-rich matrices coupled to finely dispersed Mg/Zn-rich sacrificial phases and architected implants enabled by additive manufacturing, providing a convergence-focused framework beyond existing Bio-HEA and biodegradable alloy reviews.