Tungsten Oxide-contained PEO Coatings on Ti–6Al-4 V Alloys: Enhanced Surface Characteristics and Bioactivity for Bio-implant

Abstract This study presents a novel approach to enhance the multifunctionality of Ti–6Al-4 V alloys for bio-implant surfaces by integrating tungsten oxide (WO3) nanoparticles with hydroxyapatite (HA) through dual-stage processing: direct incorporation during plasma electrolytic oxidation (PEO) at 280 V for 180 s, followed by hydrothermal treatment (HT) at 120 °C for 18 h. Unlike previous works that primarily focus on either single-step coating or basic surface modifications, this work uniquely combines PEO and HT to achieve a synergistic effect on microstructural evolution, phase integration, and coating densification. Advanced characterization revealed that the coating step significantly modifies the crystallinity and morphology of WO3 and HA phases, promoting a compact, interlocking porous layer with improved mechanical and chemical stability. The formation of an interlock bridging zone between the inner TiO2 oxide and outer composite layer further enhances adhesion strength and structural integrity, ensuring long-term coating durability under physiological conditions. SBF immersion for 48 h confirmed enhanced apatite-forming ability in the WO3-doped and hydrothermally treated coatings compared with the undoped surface, indicating superior in vitro bioactivity. The coatings exhibit enhanced corrosion resistance via lowered chloride ion degradation and generate reactive oxygen species (ROS) contributing to potent antibacterial activity against Staphylococcus aureus and Escherichia coli. This novel dual-function strategy with biocompatible aspects of WO3 with the osteoconductive properties of HA offers a promising pathway for durable, antimicrobial implant surfaces that support tissue integration and longevity beyond conventional PEO coatings. This approach extends beyond existing studies by emphasizing the mechanistic role of HA/WO3 in orchestrating phase interactions and surface chemistry to realize improved biological and electrochemical performance tailored for dental and orthopedic implants.