Polymer brush grafted antimicrobial peptide on hydroxyapatite nanorods for highly effective antibacterial performance

Serious bacterial infection induces the failure of artificial implants. Covalent bonding of antimicrobial peptides (AMPs) on implant surfaces can avoid the main shortcoming (blast releasing) by physisorption, but the low grafting yield, mobility, and stability of bonded AMPs limit their antibacterial efficiency. In this study, hydroxyapatite (HA) nanorods co-doped with Fe and Si were fabricated on Ti based on previous work, and the antimicrobial peptide HHC-36 was chemically bonded on the nanorods with and without polymer brushes as a spacer. The microstructures and physicochemical properties of coating surfaces were observed; Staphylococcus aureus (S. aureus), Escherichia coli (E. coli), and hFOB1.19 behaviours in the presence of in vitro antibacterial activity, and the immunization response in vivo on various surfaces were evaluated. The results show that the grafting of polymer brushes and HHC-36 did not substantially change the microstructure of the nanorods, but the brushes efficiently increased the load and stability of the HHC-36. The HA nanorods did not kill bacteria, but with the assistance of HHC-36, physical puncturing by nanorods worked efficiently in killing S. aureus. In contrast with Ti, in phosphate-buffered saline and suppressed biofilm formation in a nutrient-rich medium, HA nanorods with polymer-brush-grafted HHC-36 killed 99.5% of S. aureus and 99.9% of E. coli. This outstanding antibacterial activity was attributed to the synergistic effect of AMP-derived destruction and the physical puncturing by HA nanorods. Also, HA nanorods with polymer-brush-grafted HHC-36 showed cytocompatibility in vitro, and in vivo they inhibited bacterial infection and reduced the inflammatory response, indicating that polymer-brush-grafted HHC-36 on HA nanorods has great potential application in surface modification of Ti implants, especially in infected cases.