Long-lasting renewable antibacterial porous polymeric coatings enable titanium biomaterials to prevent and treat peri-implant infection

Dental implants, predominantly made of titanium for their mechanical properties and biocompatibility, are widely used but remain susceptible to bacterial colonization and peri-implant infection. Early after implantation (especially within the first 4 weeks before complete osseointegration), the interface is vulnerable, leading to a high risk of infection and early implant loss. Existing antibacterial surface strategies (physisorbed coatings, antibiotic/peptide-based layers) often suffer from weak adhesion or rapid decline in efficacy, failing to provide long-lasting protection over the 3-month osseointegration period. Peri-implantitis in later stages is difficult to reverse with current mechanical debridement and antibiotics due to complex surfaces and resistance risks. The study aims to develop a titanium surface modification that provides both long-lasting antibacterial protection to cover osseointegration and renewable antibacterial capability to treat peri-implantitis by simple in situ rechlorination.

Prior approaches to antibacterial titanium surfaces include non-covalent adsorption of agents (which desorb quickly), and chemically immobilized antibiotics/antimicrobial peptides (with rapid efficacy decline). Other modalities (e.g., silver incorporation, photocatalysis, quaternary ammonium polymers) have shown antibacterial effects but often lack durability or renewability. N-halamines are noted for broad-spectrum activity, stability in wet/dry conditions, and rechargeability through rechlorination, and have been used in water disinfection, wound dressings, food packaging, and medical tubing. However, their application to dental implants with persistent and renewable antibacterial function has been rarely reported. This work leverages amide and amine N-halamine structures to balance rapid action and durability in a porous, grafted polymer coating.

Coating preparation: Titanium disks (9.5 mm × 0.3 mm) were polished and alkali-heat treated in 5 M NaOH at 60 °C for 24 h to form a porous Ti–OH surface. A silane coupling agent (KH570) introduced C–C bonds, followed by surface-initiated grafting of poly(acrylic acid) (PAA) using acrylic acid and azobisisobutyronitrile at 60 °C under nitrogen to yield Ti–PAA. Amination was performed by immersing Ti–PAA in excess ethanediamine (with 2-chloro-4,6-dimethoxy-1,3,5-triazine activation) at 80 °C, yielding Ti–PAA–NH. N-halamine functionalization was achieved by chlorination in excess NaOCl (10% active chlorine) in an ice bath for 2 h, producing Ti–PAA–NCl (Ti–PAA–NCI in the text). Structure characterization: FTIR identified conversion of carboxyl groups to amide/amine and N–Cl inductive shift; GPC of cleaved chains gave Mw ≈ 17,140. SEM/EDS mapped uniform Cl distribution; pore size reduced to ~100–300 nm while preserving porous morphology. Surface roughness (CLSM Psa), water contact angle, and AFM-derived Young’s modulus were measured. Chlorine loading was quantified by iodometric/thiosulfate titration. Thermal stability was assessed by TGA under a sterilization-relevant profile (to 121 °C, 20 min hold). Storage stability and renewability: Samples stored up to 8 weeks (dark) were titrated for available Cl+. Dechlorination with Na2S2O3 followed by rechlorination either by immersion in 10% NaOCl (2 h, ice bath) or by clinically relevant irrigation with 5% NaOCl at pH 7 for 15 min. Antibacterial activity (in vitro): Against Staphylococcus aureus (aerobe) and Porphyromonas gingivalis (anaerobe). Release killing: CFU counting from culture media after 12 h exposure. Contact killing: CFU from bacteria detached by ultrasonication from sample surfaces. SEM and LIVE/DEAD CLSM visualized morphology and viability. Long-lasting and cyclic antibacterial tests: Ti–PAA–NCl stored in PBS for 0–12 weeks then challenged with P. gingivalis for 24 h; cyclic tests repeated 27 times with 24 h bacterial exposure per cycle, ultrasonic detachment, ethanol disinfection between cycles; rechlorination performed after 12 weeks storage or after 27 cycles. Complex clinical bacteria: Subgingival plaque from peri-implantitis patients incubated under anaerobic and aerobic conditions for 24 h on samples; quantified by crystal violet OD595 for biofilm biomass and LIVE/DEAD CLSM (red fluorescence ratio by ImageJ). Biocompatibility in vitro: MC3T3-E1 preosteoblast proliferation (CCK-8 OD450 at 1, 3, 7 d), adhesion morphology (DAPI/Actin CLSM), osteogenic function: ALP activity (7, 14 d), Alizarin Red S staining and calcium quantification (21 d), and osteogenic protein (OCN, OPN, RUNX2 by Western blot) and gene expression (RT-qPCR) at 3, 7, 14 d. In vivo biocompatibility: Subcutaneous implantation of Ti–OH and Ti–PAA–NCl disks in BALB/c nude mice for 4 weeks; assessed by HE staining and CD68 immunofluorescence. Rabbit mandible model: Custom titanium mini-implants with Ti–OH or Ti–PAA–NCl surfaces implanted bilaterally in New Zealand rabbits. After 4 weeks, osseointegration assessed by Van Gieson staining. Ligature-induced peri-implantitis: silk ligatures placed for 8 weeks, then removed for 4 weeks re-osseointegration; micro-CT (bone height, BV/TV within 0.15 mm ROI) and removal torque measured. Human intraoral assessment: Tiny titanium disks (3 mm × 0.2 mm) with Ti–PAA–NCl bonded to molars in volunteers; contralateral Ti–OH controls. Exposure for 4 or 12 weeks under daily oral activities. LIVE/DEAD CLSM quantified covering area and fluorescence intensity; 3D biofilm morphology imaged. Rechlorination in situ performed with 5% NaOCl (pH 7) for 15 min under rubber dam; reassessed after 48 h. Statistics: Student’s t test, ANOVA with Bonferroni, Wilcoxon for heteroscedastic data; significance at P<0.05.

- Coating structure and stability: Porous N-halamine polymeric coating (Ti–PAA–NCl) uniformly grafted on titanium with chlorine loading 49.57 ppm; preserved porous morphology (pore size ~100–300 nm), contact angle 43.12°, Young’s modulus 261 MPa. Thermally stable through 121 °C sterilization hold. Available Cl+ remained nearly unchanged over 8 weeks storage; dechlorinated samples could be rechlorinated to original levels; 5% NaOCl irrigation for 15 min achieved 88% of immersion rechlorination effectiveness. - Antibacterial efficacy (single species): Release killing reduced S. aureus by 64% and P. gingivalis by 42%. Contact killing wiped out 96% of S. aureus and 91% of P. gingivalis. SEM and LIVE/DEAD imaging showed disrupted morphology and predominantly dead cells on Ti–PAA–NCl. - Long-lasting action: Against P. gingivalis, antibacterial rate decreased from 96% initially to 89% at 4 weeks and 79% at 12 weeks (after PBS storage). In cyclic exposure, antibacterial rate declined from 96% (cycle 1) to 88% (cycle 10) and 68% (cycle 20). - Renewability: After 12 weeks storage, rechlorination restored antibacterial rate from 78% to 91%. After 27 cycles (down to 33%), rechlorination recovered to 76%. Incomplete recovery in cyclic tests attributed to ultrasonic damage to grafted chains. - Complex clinical bacteria: Biofilm biomass reduced by 56% (anaerobic) and 62% (aerobic) relative to Ti–OH. LIVE/DEAD red fluorescence (dead fraction) increased to 63% (anaerobic) and 54% (aerobic) on Ti–PAA–NCl vs 13% and 19% on Ti–OH. - Biocompatibility and osteogenesis: No significant differences vs Ti–OH in MC3T3-E1 proliferation (1, 3, 7 d), adhesion morphology, ALP activity (7, 14 d), mineralization (21 d), and OCN/OPN/RUNX2 protein and gene expression. In vivo subcutaneous implantation showed similar fibrotic capsule thickness and macrophage (CD68) distribution without significant inflammation. - Rabbit model: Both surfaces achieved satisfactory osseointegration at 4 weeks. After ligature-induced peri-implantitis (8 weeks), bone height and BV/TV decreased around both groups, confirming disease. After 4 weeks post-ligature, Ti–PAA–NCl implants recovered bone height and BV/TV nearly to original osseointegration levels, with greater improvement and higher removal torque compared to Ti–OH. - Human intraoral performance: After 4 weeks, covering area and fluorescence intensity on Ti–PAA–NCl were 18% and 7% of Ti–OH; after rechlorination, 3% and 2%. After 12 weeks, 53% and 22% of Ti–OH; after rechlorination, 12% and 14%. Biofilms were sparse or barely visible on Ti–PAA–NCl, especially post-rechlorination.

The study addresses the need for durable antibacterial protection during the vulnerable osseointegration period and for renewable antibacterial function to manage peri-implantitis. By engineering a porous, covalently grafted N-halamine polymer containing both amide (moderate stability, faster release) and amine (higher stability, durable contact) N–Cl functionalities, the coating delivers a synergistic combination of contact and release killing. This dual mechanism provides immediate and sustained antibacterial activity against key peri-implant pathogens and patient-derived complex biofilms, while maintaining biocompatibility and osteogenic capacity. The long-lasting efficacy spans the typical 3-month osseointegration window in vitro and in vivo, and the coating’s active chlorine can be rapidly regenerated in situ via simple NaOCl irrigation, enabling treatment of established peri-implantitis and promoting bone recovery around implants. The nonspecific oxidative mechanism suggests broad-spectrum action with low propensity for resistance development, making the renewable N-halamine approach a promising strategy for implant infection prevention and therapy.

A porous N-halamine polymeric coating (Ti–PAA–NCl) was developed on titanium via alkali-heat pore formation, PAA grafting, amination, and chlorination. The coating achieves high antibacterial activity (up to 96% contact killing), sustained efficacy over 12 weeks and multiple bacterial exposure cycles, and simple renewability by rechlorination. It is biocompatible, preserves osteogenic functions, exhibits prolonged anti-infection performance in a rabbit peri-implantitis model with improved bone recovery and bonding strength, and shows long-lasting and renewable antibacterial effects against human intraoral biofilms. These contributions introduce a renewable antibacterial coating concept for dental implants, offering both prevention and treatment of peri-implant infection and potentially improving implant success rates.

Incomplete restoration of antibacterial efficacy after many in vitro cycles was observed, likely due to ultrasonic vibration mechanically damaging grafted polymer chains during repeated testing, suggesting that extreme mechanical stresses may reduce renewability. The study did not report long-term clinical outcomes beyond biofilm metrics in a limited number of volunteers (n=8 for 4 weeks, n=3 for 12 weeks), and animal sample sizes were modest, which may limit generalizability of in vivo findings. The rechlorination used NaOCl; potential effects of repeated clinical rechlorination on surrounding tissues and long-term coating integrity were not fully evaluated within this study.