Chlorine-Functionalized Nano-Hydroxyapatite Coatings Enhance Osseointegration in Immediate Implantation by Modulating Host–Bacteria Competition

Abstract

Immediate implantation integrates three surgical procedures into one and shortens the treatment cycle, showing great clinical value. However, in patients with periodontitis, the high risk of infection remains a major challenge. A critical failure factor lies in the first 24 h after implantation, when host cells and pathogenic bacteria compete for occupancy on the implant surface, yet effective strategies to regulate this process are still lacking. To address this issue, we developed a nano-hydroxyapatite/chloride ion composite coating (MAO(Ti)-nHA-Cl) using combined micro-arc oxidation and anodization. The Ti–Cl structure within the coating sustainably generates low-dose hypochlorous acid (HClO), which disrupts bacterial cell walls and effectively inhibits adhesion and proliferation of pathogenic bacteria. This design allows timely intervention in the cell–bacteria competitive adhesion process during the early postoperative window. Our results showed that MAO(Ti)-nHA-Cl significantly suppressed common oral pathogens, while enhancing MC3T3-E1 cell adhesion, upregulation of osteogenic genes, and mineralized differentiation. In a rat femoral infection model, the coating reduced inflammatory responses and promoted new bone formation. Collectively, this study provides a strategy to regulate host–bacteria competition at the implant interface, offering theoretical support for early osseointegration in immediate implantation for periodontitis patients and suggesting a new direction for functionalized implant surface design.