Insights into nano-ZrO₂ reinforced self-antibacterial Ti–3Cu composites <i>via</i> laser metal deposition: content-optimized bioactive nano-ZrO₂ integrated for wear resistance, <i>in vitro</i> antibacterial and biological proper

Ti alloys are sensitive to fretting wear, which leads to early failure of their implants. Wear is a major factor in determining the long-term clinical performance. This work explored the increase of wear resistance in antibacterial Ti-Cu alloys, by incorporating biocompatible nano-ZrO₂ using laser metal deposition (LMD). The content of the reinforcing nano-ZrO₂ played a crucial role in performance. There was good densification quality for ≤3 wt%. The densification quality declined and there were macrocracks for ≥5 wt%. Both the prior β grains and the α grains initially decreased in size followed by coarsening as the ZrO₂ content increased, with the minimum at 3 wt%. The yield strength increased with increasing ZrO₂ content, and the elastic modulus increased from 5 wt%. The wear rate decreased initially and then increased with increasing ZrO₂ contents, reaching the lowest wear rate at 3 wt%. The corrosion resistance in body fluid was a minimum between 3 and 5 wt%, with less or more leading to a decrease in corrosion resistance. <i>In vitro</i> antibacterial tests and <i>MC3T3-E1</i> cell culture assays indicated that ZrO₂ contents of up to 10 wt% achieved good antibacterial effects while maintaining good biocompatibility. The comprehensive test results allowed screening and optimization of the processability and wear-related performance. 3 wt% ZrO₂ contents provided the best overall performance. The mechanisms for various content bioactive nano-ZrO₂ integrated for wear resistance, <i>in vitro</i> antibacterial and biological properties were explored. This work aimed to understand how ZrO₂ concentrations influenced the overall performance and to identify the optimal content for wear resistance and related biofunctionality.