Surface characterization and enhanced antibacterial activity of micro-arc oxidized Ti-2.5Ag alloy against Porphyromonas gingivalis: role of surface physicochemistry and controlled Ag⁺ release.

Titanium implants remain susceptible to bacterial colonization by Porphyromonas gingivalis, a keystone pathogen in peri-implantitis, and although silver (Ag) incorporation and micro-arc oxidation (MAO) have each been explored individually, their combined effect on low-silver titanium alloys against anaerobic oral pathogens remains poorly characterized. This study fabricated CP-Ti, Ti-2.5Ag (Ti+Ag), and MAO-treated Ti-2.5Ag (Ti+Ag+MAO) surfaces and evaluated their physicochemical properties and antibacterial performance against P. gingivalis over seven days. MAO generated a micro-porous TiO₂ oxide layer (32.6% porosity) incorporating phosphorus and silicon, significantly increasing roughness Ra = 0.0846 µm; p < 0.01) and hydrophilicity (contact angle: 36.33°-41.34°; p < 0.05) versus CP-Ti. Cumulative Ag⁺ release from Ti + Ag + MAO reached 0.844 ppb by day 7, approximately twice that of Ti + Ag (0.399 ppb; p < 0.05), following a multiphasic release profile. Against P. gingivalis, Ti + Ag + MAO achieved adherent bacterial inhibition exceeding 91% by day 7 (versus 73% for Ti+Ag), with dead-cell percentages rising from 57.56% to 76.25% (p < 0.001 vs. both comparators). Crystal violet and protein leakage assays confirmed sustained anti-biofilm activity and progressive membrane disruption (p < 0.01-0.001), consistent with the observed Ag⁺ release kinetics. These findings demonstrate that MAO synergistically amplifies the antibacterial efficacy of Ti-2.5Ag through combined anti-adhesive and sustained ion-release-mediated mechanisms, establishing Ti + Ag + MAO as a promising multifunctional strategy for reducing peri-implant infections.