Defect‐Induced Local Piezoresponse of Anodic Nanotube Arrays on Ti‐Rich Medium‐Entropy Alloy for Stimulus‐Responsive Bioactive and Antibacterial Surfaces

ABSTRACT Developing implant surfaces with electromechanically active properties offers the potential to mimic the natural electromechanical cues of bone, thereby enhancing cell‐material interactions and improving implant biofunctionality. This study reports that anodically grown TiO 2 (B)‐containing nanotube arrays on a Ti‐rich medium‐entropy alloy (Ti 65 –Zr 18 –Nb 16 –Mo 1 ) exhibit a measurable electromechanical response arising from defect‐ and structure‐related local symmetry disruption. Nanotubes were fabricated via anodic oxidation at systematically varied voltages and durations, followed by microwave‐assisted thermal treatment. Structural analyses confirmed the formation of TiO 2 (B)‐rich nanotubes, with a maximum fraction of 70.6% (30 V, 30 min). EPR spectroscopy verified abundant oxygen‐vacancy‐related defect states, supporting the proposed defect‐induced local symmetry‐breaking mechanism. The optimized nanotube architecture exhibited lower interfacial charge‐transfer resistance and the highest longitudinal piezoelectric coefficient ( d 33 = 1.40 pC/N). Ultrasonic stimulation enhanced apatite deposition, MG‐63 cell adhesion and proliferation, and antibacterial activity, increasing bactericidal rates from 76.1% to 91.3% for S. aureus and from 69.3% to 90.2% for E. coli . These results establish a structure‐defect‐electromechanical response‐bioactivity relationship, highlighting TiO 2 (B)‐rich nanotube arrays on Ti‐rich medium‐entropy alloys as promising multifunctional implant coatings.