Polydopamine-Assisted Zn2TiO4–ZnO Heterostructure Formation on Titanium with Decent Osteogenic and Antibacterial Activity

Implant-associated infections and inadequate osseointegration are major contributors to orthopedic implant failures. Although hydrothermally grown zinc oxide (ZnO) nanorods on titanium (Ti) implants enhance antibacterial activity, their aggressive degradation and uncontrolled Zn²⁺ leaching do not meet the requirements for bone implants and can damage the surrounding tissues. This study introduces a crystal-damage-free nanoengineering mechanism to enhance the stability of ZnO nanorods by utilizing a carbon nanolayer as a sacrificial template between the ZnO core and TiO₂. This mechanism induced the formation of a hybrid Zn₂TiO₄ heterostructure within the carbon layer at a low temperature of 500 °C by reducing the required activation energy. This carbon layer acts as a diffusion barrier, allowing the unilateral diffusion of ZnO into TiO₂ while preventing Ti diffusion into the ZnO core. The resulting ZnO@TiO₂-6 heterostructure controlled Zn²⁺ leaching and exhibited significant osteogenic activity of MC3T3-E1 cells and potent antibacterial efficacy against S. aureus and E. coli due to the differential landscape of osteoblasts and bacteria. In vivo studies further confirm that ZnO@TiO₂-6 heterostructure eradicated 90% of bacteria, alleviated inflammation, and enhanced biocompatibility. Unlike Ti implants, which lack antibacterial properties, and ZnO alone, which induces inflammation, ZnO@TiO₂-6 nanorods provide enhanced stability, sustained Zn²⁺ release, optimized ROS levels, and dual antibacterial and osteogenic functions, making them a promising advancement for orthopedic and dental implants.