Antibiotic-directed polymerization enables tunable antibacterial polydopamine coatings

Polydopamine (PDA) is a nature-inspired coating material due to its strong adhesion, excellent biocompatibility, and rich surface chemistry; however, pure PDA generally exhibits limited intrinsic antibacterial activity. In this study, PDA coatings containing structurally distinct antibiotics, gentamicin (an aminoglycoside), imipenem, and meropenem (carbapenems), were prepared to investigate how the molecular structure and concentration of the antibiotic affected PDA polymerization, surface properties, and antibacterial performance. The coatings were deposited on glass substrates via oxidative self-polymerization of dopamine under mild alkaline conditions. The surface and physicochemical properties were characterized using FTIR, UV-Vis spectroscopy, water contact angle measurements, colorimetry, FESEM, and AFM. The addition of antibiotics significantly altered the coating morphology, roughness, wettability, and optical appearance in an antibiotic-specific manner. Gentamicin and imipenem loaded PDA coatings generally exhibited lower coating thickness and greater surface heterogeneity, whereas the addition of meropenem increased the polymerization of PDA, resulting in thicker, more homogeneous, and more hydrophilic coatings. Antibacterial evaluation using zone of inhibition and colony count assays revealed that the pure PDA exhibited negligible antibacterial activity. Gentamicin-loaded PDA coatings exhibited potent antibacterial activity against Escherichia coli, while meropenem-loaded PDA coatings exhibited significant activity against Staphylococcus aureus. In contrast, imipenem- loaded PDA coatings did not exhibit significant antibacterial activity against any of the bacterial strains. These results indicate that antibiotic molecular structure is a key parameter for tailoring PDA-based coatings with selective antibacterial performance.