Osseointegration of hydroxyapatite coatings doped with silver nanoparticles: scanning electron microscopy studies on a rabbit model.

Modern joint arthroplasties rely on osseointegration of metal components through bone ingrowth into hydroxyapatite (HA) layers. However, such surfaces are prone to colonisation by bacteria and formation of biofilms. Application of silver nanoparticles (SN) to hydroxyapatite coatings could reduce the risk of infection, however little is known about how this would affect the process of bone ingrowth. This study examined osseointegration of conventional and SN doped HA coatings in a rabbit model. In this study, twelve cylindrical implants coated with conventional and SN doped HA were implanted into New Zealand white rabbit femora, with each animal receiving both types of implants. After 12 weeks, rabbits were sacrificed, their femora were harvested and implants removed during pull-out testing. Retrieved samples were dehydrated, sputter coated and observed using a scanning electron microscope (SEM) to verify bony ingrowth and retention of SNs. The percentage of implant in direct contact with bone was measured in cross-sections of implants. The SEM analysis demonstrated that osseointegration of the SN doped coatings was similar to the conventional HA samples. A similar morphology of newly formed trabecular bone was observed in both implants, with silver doped HA-coated implants retaining multiple nanoparticles in areas which were not overgrown by bone. Analysis of the bone-implant contact area revealed comparable results for both types of coatings. These finding indicated that SN doped HA coatings are characterised by good osseointegrative properties. Since SNs were found in areas not covered by mineralised bone, it is assumed that the antimicrobial properties of the modified coating may be retained for 12 weeks after implantation. Additional studies are required to fine-tune the composition of HA coatings with silver nanoparticles, to ensure optimal osseointegrative and antimicrobial properties.