Progress in Wear Resistant Materials for Total Hip Arthroplasty

Total joint replacement, although considered an excellent surgical procedure, can be complicated by osteolysis induced by implant particles and subsequent aseptic loosening of the implant. The pathogenesis of implant-associated osteolysis includes inflammatory and osteolytic processes. The sustained chronic inflammatory response initiated by particulate debris at the implant-bone interface is manifested by recruitment of a wide array of cell types. These cells include macrophages, fibroblasts, giant cells, neutrophils, lymphocytes, and – most importantly – osteoclasts, which are the principal bone resorbing cells. The 'cellular response' entails secretion of osteoclastogenic and inflammatory cytokines that favor exacerbated osteoclast activity and enhanced osteolysis. An appreciation of the complex network that leads to these cellular and inflammatory responses will form a foundation on which to develop therapeutic interventions to combat inflammatory periprosthetic bone loss.

Bacterial infection after implant placement is a significant rising complication. In order to reduce the incidence of implant-associated infections, several biomaterial surface treatments have been proposed. In this study, the effect of in vitro antibacterial activity and in vitro cytotoxicity of co-sputtered silver (Ag)-containing hydroxyapatite (HA) coating was evaluated. Deposition was achieved by a concurrent supply of 10 W to the Ag target and 300 W to the HA target. Heat treatment at 400 degrees C for 4 h was performed after 3 h deposition. X-ray diffraction, contact angles measurements, and surface roughness were used to characterize the coating surfaces. The RP12 strain of Staphylococcus epidermidis (ATCC 35984) and the Cowan I strain of Staphylococcus aureus were used to evaluate the antibacterial activity of the Ag-HA coatings, whereas human embryonic palatal mesenchyme cells, an osteoblast precursor cell line, were used to evaluate the in vitro cytotoxicity of the coatings. X-ray diffraction analysis performed in this study indicated peaks corresponding to Ag and HA on the co-sputtered Ag-HA surfaces. The contact angles for HA and Ag-HA surfaces were observed to be significantly lower when compared to Ti surfaces, whereas no significant difference in surface roughness was observed for all groups. In vitro bacterial adhesion study indicated a significantly reduced number of S. epidermidis and S. aureus on Ag-HA surface when compared to titanium (Ti) and HA surfaces. In addition, no significant difference in the in vitro cytotoxicty was observed between HA and Ag-HA surfaces. Overall, it was concluded that the creation of a multifunctional surface can be achieved by co-sputtering the osteoconductive HA with antibacterial Ag.

New promising techniques for depositing hydroxyapatite (HA) and calcium phosphate (CaP) coatings on medical devices are continuously being investigated. Given the vast number of experimental deposition process currently available, this review will focus only on CaP and/or HA coatings produced using the sputtering process. This review will discuss the characterization of sputtered CaP coatings before and after post-deposition treatments and tissue responses to some of the characterized coating surfaces. From the studies observed in the literature, current research on sputtered CaP coatings has shown some promises that may eliminate some of the problems associated with the plasma-spraying process. It has been generally accepted that sputtered HA and CaP coatings improve bone strength and initial osseointegration rate. However, optimal coating properties required to achieve maximal bone response are yet to be reported. As such, the use of well-characterized sputtered CaP and/or HA surfaces in the evaluation of biological responses should be well documented to avoid controversial results. In addition, future investigations of the sputtering process should include clinical trials, to continue the understanding of bone responses to coated-implant surfaces of different properties, and the possibility of coupling sputtered HA and CaP coatings with growth factors.