N+ ion implantation of Ti6Al4V alloy and UHMWPE for total joint replacement application.

Multidirectional pin-on-plate tribological wear tests were performed to evaluate and compare the tribological behavior of N+ ion-implanted and unmodified Ti6Al4V/ultra high molecular weight polyethylene (UHMWPE) sliding couples, for total joint replacement (TJR) applications. Knoop microhardness indentations were measured and an increase in surface hardness of more than twofold and up to four times, respectively, was observed for the Ti6Al4V alloy and UHMWPE after N+ ion implantation, at a load of 1 gf. Increase in hardness was attributed to the formation of TiN precipitates and cross-linking in the alloy and polymer, respectively. Wear test results showed that N+ ion implantation reduced surface wear of the Ti6Al4V alloy and, in turn, significantly reduced the wear of the mating UHMWPE. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), non-contacting interferometry and optical microscopy were used to characterize both modified and unmodified material surfaces prior to and after tribological wear tests. The results indicated that N+ ion-implanted Ti6Al4V/UHMWPE sliding couples were distinctly superior to the unmodified sliding couples, and demonstrated a definite potential for the use of N+ ion-implanted Ti6Al4V and implanted UHMWPE as load bearing surfaces in TJR prostheses