Surface chemical modification of poly(phthalazinone ether nitrile ketone) through rhBMP-2 and antimicrobial peptide conjugation for enhanced osteogenic and antibacterial activities in vitro and in vivo

Failure of poly(aryl ether ketone) (PAEK) bone implants results mainly from poor osteogenesis and bacterial infection. One promising strategy for enhancing osteointegration involves developing a bioactive surface of PAEK implants through chemical modification. Poly(phthalazinone ether nitrile ketone) (PPENK) is considered a potential PAEK bone implant because it possesses mechanical properties similar to those of natural bone and its cyano group has high reactivity which provides a surface modification strategy. In this work, recombinant human bone morphogenetic protein-2 (rhBMP-2) and newly synthesized cationic antimicrobial polypeptides (AMPs) were chemically conjugated to a PPENK substrate surface to enhance osteogenic and antibacterial activities. The molecular structures of AMP-1 and AMP-2 containing PEG segments were confirmed by nuclear magnetic resonance spectroscopy. The surface roughness of each substrate was reduced by rhBMP-2 and AMP immobilization. In situ, real-time quartz crystal microbalance with dissipation studies revealed that the loading amount increased with the successive immobilization of rhBMP-2 and AMPs. In vitro antibacterial assay confirmed that the AMP-modified PPENK surfaces provided an effective antibacterial effect and the number of residential bacteria remaining on the substrate was reduced by the PEG segments in AMP-2. In vitro osteogenic properties of the rhBMP-2-modified PPENK surface presented favorable cytocompatibility and osteo-inductive activity. In vivo studies confirmed that the rhBMP-2 and AMP immobilization led to decrease amounts of fibrous tissues around the implant and improved bone regeneration. This study provides a strategy for surface modification that enhances the antibacterial and osteogenic activities to develop a bone implant material with considerable potential for clinical application.