New MAO coatings on multiprincipal equimassic β TiNbTaZr and TiNbTaZrMo alloys

β titanium alloys are essential in biomedical applications due to their combination of high strength, low elastic modulus, and biocompatibility. Although high-entropy alloys (BioHEAs) containing Nb, Zr, Ta, and Mo offer high mechanical strength, their elevated elastic modulus can lead to stress shielding in orthopedic applications. To address these limitations, β-stable alloys with enhanced mechanical and surface properties are being developed to support osseointegration and cellular adhesion. The work focuses on innovative medium (MEA) and high entropy (HEA) equimassic β Ti alloys (quaternary Ti-25Ta-25Nb-25Zr and quinary Ti-20Zr-20Ta-20Nb-20Mo in wt.%) treated with micro-arc oxidation (MAO) to optimize their performance as biomaterials. The MAO process generated bioactive coatings enriched with Ca, P, and Mg, promoting bone cell proliferation. X-ray diffraction (XRD) identified β phase structures and revealed amorphous or partially crystalline coatings, with a ZrO₂ cubic phase noted in the MEA quaternary Ti-25Ta-25Nb-25Zr alloy. Surface morphology assessments showed porous and lamellar topographies that varied with alloy composition, resulting in increased hydrophilicity and optimal roughness. Confocal microscopy confirmed that the MAO coating thickness on MEA quaternary Ti-25Ta-25Nb-25Zr (10.4 μm) surpassed that on HEA (high entropy alloy) quinary Ti-20Zr-20Ta-20Nb-20Mo (4.2 μm). Cell viability and adhesion assays indicated significant biocompatibility, particularly for MEA (medium entropy alloy) quaternary Ti-25Ta-25Nb-25Zr, which benefits from a Mo-free composition. These results underscore the potential of these multiprincipal equimassic bcc (body centered cubic) β alloys for biomedical applications, possibly enhancing osteoblast attachment and sustain cell viability effectively.