Antibacterial and Anti-biofilm Properties of Hydroxyapatite Nanoparticles Enhanced by Dopamine Functionalization

Biofilm-associated infections on biomaterial surfaces represent a major clinical challenge, particularly in orthopedic and dental fields. Here, dopamine functionalized hydroxyapatite (HA-DOPA) particles were prepared and their antibacterial properties against E. coli were investigated. Material characterizations reveal B-type carbonated hydroxyapatite with thin polydopamine film, nano-sized grains (20-50 nm) with aggregation, negative zeta potential and low water contact angle of HA-DOPA (-13.9 mV, 42.3±1.6 ° ) and HA (-21.2 mV, 47.5±1.2 ± ). HA-DOPA demonstrates superior antibacterial activity with minimum inhibitory concentration of 300 μg/mL and minimum bactericidal concentration of 500 μg/mL (≥99.9% bacterial killing), while HA fails to achieve bactericidal effects at the tested concentrations. HA-DOPA significantly increases bacterial membrane permeability (2.5-fold higher ONPG uptake), induces elevated intracellular reactive oxygen species generation (1.2~2.7-fold increase), and reduces β-galactosidase activity (by up to 32.7%), indicating metabolic disruption. HA-DOPA exhibits the concentration-dependent biofilm inhibition, achieving 79.8% inhibition at 500 μg/mL compared to 46.3% for HA. Furthermore, HA-DOPA effectively degrades the established biofilm by reducing extracellular polymeric substances, with 1.7-fold lower protein and 2-fold lower carbohydrate content compared to HA. HA-DOPA exhibits excellent cytocompatibility with MC3T3-E1 cells (viability >90%). The dopamine functionalization is a facile and effective method to enhance antibacterial properties of hydroxyapatite nanoparticles for their biomedical applications.