Plasma Pretreatment Enhances the Stability and Antibacterial Activity of Polydopamine Coatings on Zirconia Abutments

OBJECTIVE: The objective of this study was to enhance the stability and antibacterial activity of polydopamine (PDA) coatings on zirconia via plasma pretreatment, with the aim of constructing a durable antibacterial and cytocompatible surface for zirconia implant abutments. METHODS: Zirconia disks were divided into four groups: untreated (ZrO₂), plasma‑pretreated zirconia (PP‑ZrO₂), PDA-coated zirconia (PDA‑ZrO₂), and plasma-pretreated PDA-coating zirconia (PP + PDA‑ZrO₂). Physicochemical stability before and after simulated oral ageing (4 weeks in simulated body fluid plus 600 thermocycles) was evaluated by energy‑dispersive X‑ray spectroscopy, X‑ray photoelectron spectroscopy, and Raman spectroscopy; additionally, zeta potential measurements were performed to characterize surface charge. Antibacterial activity against Streptococcus mutans and Escherichia coli was assessed by colony‑forming unit counting and scanning electron microscopy. Human gingival fibroblast proliferation was evaluated using the CCK‑8 assay, and cell adhesion/spreading morphology was observed by scanning electron microscopy after 4, 12, and 24 hours of co‑culture; spreading area was quantitatively analysed at 4 hours. RESULTS: Plasma pretreatment significantly enhanced the deposition uniformity and density of the PDA coating. After ageing, the PP + PDA‑ZrO₂ group retained higher nitrogen content (5.41% vs 3.48% in PDA‑ZrO₂-AT; P < .001) and exhibited more stable chemical states, indicating improved coating stability. Raman spectroscopy showed that plasma pretreatment preserved the catechol peaks of PDA after ageing, whereas they decreased on the PDA‑ZrO₂ surface. Zeta potential measurements showed that the surface charge shifted from -29.3 mV (ZrO₂) to -23.1 mV after plasma treatment (P < .001), while PDA coating rendered the surface more negative (-39.2 mV; P < .001 vs ZrO₂); the combined modification resulted in an intermediate value (-36.4 mV; P < .001 vs ZrO₂). In antibacterial assays, the PP + PDA-ZrO₂ surface exhibited exceptional inhibitory rates of 99.71% against S. mutans and 82.44% against E. coli. These values markedly surpassed those of PP-ZrO₂ (72.65% and 36.89%; P < .001), demonstrating enhanced efficacy in preventing bacterial adhesion and disrupting cell membranes. In addition, the PP + PDA‑ZrO₂ surface promoted human gingival fibroblast proliferation and enhanced cell adhesion and spreading at 4, 12, and 24 hours, with the largest spreading area observed at 4 hours (P < .001 vs ZrO₂ and PP‑ZrO₂). CONCLUSION: By improving coating stability and antibacterial performance, plasma pretreatment optimizes the biofunctionality of PDA-zirconia composites. The resultant surface not only exhibits definite antimicrobial properties but also facilitates fibroblast attachment and growth, which are critical for soft tissue integration. These findings provide a promising basis for advancing modified zirconia abutments towards clinical application. CLINICAL RELEVANCE: By addressing the critical issue of PDA coating durability on inert zirconia, plasma pretreatment enables a stable, antibacterial surface with enhanced cell adhesion ability, which may help reduce peri‑implant diseases and support soft tissue sealing around abutments.