Gallium-alloyed metastable β Ti–Zr–Nb–Sn–Ta alloys with balanced mechanical, corrosion, and dual antibacterial–osteoblastic cytocompatibility for orthopedic implants

： Stress shielding and implant-associated infection are the primary causes of orthopedic implant failure. Low-modulus metastable β -Ti alloys are promising implant candidates, yet face the key challenge of balancing mechanical, corrosion-related, and biological properties. Herein, we developed a series of Gallium (Ga)-alloyed metastable β Ti-Zr-Nb-Sn-Ta (TZNST) alloys, and systematically investigated the effects of Ga content (0–2.5 at%, denoted as TZNST-Ga x ) on their microstructure, mechanical attributes, corrosion performance, and in vitro cytocompatibility and antibacterial efficacy. All as-cast TZNST-based alloys exhibited a single metastable β -phase structure, with Ga addition inducing fine dendritic structures. The TZNST-based alloys achieved a maximum 22% yield strength increment (638.3–780.7 MPa), approximately 50% compressive plasticity without catastrophic fracture, and a low elastic modulus (58.1–63.7 GPa). Among the series, TZNST-Ga 2.0 delivered the optimal comprehensive performance: it exhibited a 3.7-fold higher polarization resistance than the base alloy (TZNST-Ga 0.0 ) in Hanks’ Balanced Salt Solution (HBSS), a MC3T3-E1 cell viability of > 98%, and an inhibition rate of 88.80% against Escherichia coli ( E . coli ) and 85.12% against Staphylococcus aureus ( S. aureus ). The antibacterial efficacy of the Ga-containing TZNST alloys arises primarily from the sustained release of Ga 3 + ions from the passive film. This system possesses pH-responsive Ga 3+ ion release behavior. The release of Ga 3+ ions is remarkably promoted under acidic microenvironments, which endows the system with microenvironment-targeted antibacterial capability. It can be concluded that this class of Ga-alloyed β -Ti alloys can address two important clinical problems regarding orthopedic implants, representing a promising strategy for developing multifunctional biomedical titanium materials.