Antibacterial tannic acid/polydopamine hybrid coatings for titanium implants

Bacterial infections pose a significant threat to the longevity of titanium (Ti) implants, often leading to implant failure and peri-implantitis. This study aimed to improve the antibacterial properties of Ti implants by modifying their surfaces with tannic acid (TA) and polydopamine (PDA) as an antibiotic-free strategy. Four different concentrations of TA (2, 4, 8, and 16 mg/mL) in Tris buffer served as the deposition solution. TA-based coatings, both with and without the addition of PDA, were applied to Ti substrates via a simple drop-coating approach. The phase composition and microstructure of the coated samples were examined. The antibacterial performance of the coatings against E. coli and S. aureus was evaluated using various assays. Additionally, the cytotoxicity of the samples was also assessed using L929 cells. The surface characterization confirmed the successful formation of the coating; however, high concentrations of TA resulted in surface cracking. Importantly, incorporating PDA improved the structural integrity of the hybrid coating without compromising its antibacterial efficacy. Coatings with higher TA loading, specifically 8 mg/mL and 16 mg/mL, effectively eliminated both bacterial strains, achieving a bacteriostatic ratio exceeding 90 %. Furthermore, cytotoxicity assays demonstrated good cytocompatibility for all coatings, although a slight decline in cell viability was observed with increasing TA concentration. This study highlighted that the coating formulated with 8 mg/mL TA in combination with PDA provided an optimal balance between antibacterial efficacy, structural integrity, and cytocompatibility. This cost-effective and straightforward coating showed promising potential for use in antibacterial titanium implants.