Polycrystalline Diamond Coating on Orthopaedic Implants: Realization, and Role of Surface Topology and Chemistry in Adsorption of Proteins and Cell Proliferation

Polycrystalline diamond has the potential to improve the osseointegration of orthopaedic implants compared to conventional osteo-implant materials such as titanium. However, despite the excellent biocompatibility and superior mechanical properties, the major challenge of using diamond for implants such as those used for hip arthroplasty is the limitations of microwave plasma chemical vapor deposition (CVD) techniques to synthesize diamond on complex-shaped objects. Here, for the first time we demonstrate diamond growth on titanium acetabular shells using surface wave plasma CVD method. Polycrystalline diamond coatings were synthesized at low temperatures (~400 °C) on three types of acetabular shells with different surface structure and porosity. We achieved diamond growth on highly porous surfaces designed to mimic the structure of the trabecular bone and improve osseointegration. Biocompatibility was investigated on nanocrystalline diamond (NCD) and ultrananocrystalline diamond (UNCD) coatings terminated either with hydrogen or oxygen. To understand the role of diamond surface topology and chemistry in attachment and proliferation of mammalian cells we investigated adsorption of extracellular matrix (ECM) proteins, and monitored metabolic activity of fibroblasts, osteoblasts, and bone marrow-derived mesenchymal stem cells (MSCs). The interaction of bovine serum albumin (BSA) and Type I collagen with diamond surface was investigated by confocal fluorescence lifetime imaging microscopy (FLIM). We found that proliferation of MSCs was better on hydrogen terminated UNCD than on oxygen terminated counterpart. These findings corelate to the behaviour of collagen on diamond substrates observed by FLIM. Hydrogen terminated UNCD provides better adhesion and proliferation for MSCs, compared to titanium, while growth of fibroblasts is poorest on hydrogen terminated NCD and osteoblasts behave similarly on all tested surfaces. These results open new opportunities for application of diamond coatings on orthopaedic implants.