In vitro and in vivo investigations of a-C/a-C:Ti nanomultilayer coated Ti6Al4V alloy as artificial femoral head.

Hydrogen-free a-C/a-C:Ti nanomultilayer (a-C NM) films were deposited on medical Ti6Al4V by the magnetron sputtering technique under bias-graded voltage. Cell tests and implantations were performed for the a-C NM films coated Ti6Al4V with the uncoated Ti6Al4V as the control. The canine total hip arthroplasty (THA) surgeries were conducted for 12 dogs using the coated femoral heads, with the CoCr heads as the control. Results of cell tests showed that the coated Ti6Al4V had no cytotoxicity, and there was no statistical difference of the cell attachment rates between the coated and uncoated sample (P = 0.091). No significant difference of the tissue response around the coated and uncoated implants were observed after the intramuscular (P = 0.679) and intraosseous implantations (P = 0.122). After two years of successful canine THA, the polyethylene wear particles isolated from periprosthetic soft tissue showed similar sizes, shapes and counts in the two groups (all of the P values >0.05). The retrieved femoral heads showed slightly change of the surface roughness, but no statistical differences between groups (P = 0.696). However, the systemic metal ion analysis indicated that the content of Co and Cr ions released in the coated group (Co: 0.71 ± 0.06 μg/L, Cr: 0.52 ± 0.05 μg/L) were significant lower than that in the control (Co: 1.98 ± 0.16 μg/L, Cr: 1.17 ± 0.19 μg/L) (both P < 0.005). Histological analysis of the periprosthetic tissue in CoCr group showed a severer histiocyte response than that in the coated group (P = 0.029). The head-taper interfaces showed galvanic corrosion attack in the CoCr group, but not in the coated Ti6Al4V group. Therefore, the a-C NM films coated Ti6Al4V exhibited good biocompatibility as an implant material. Compared with the CoCr, the coated Ti6Al4V femoral head could provide comparable in vivo wear properties, release less harmful metal ions and reduce the inflammatory response in periprosthetic tissue, which may help to prolong the longevity of prostheses.