Deposition of a-C:H films on UHMWPE substrate and its wear-resistance

Abstract

In prosthetic hip replacements, ultrahigh molecular weight polyethylene (UHMWPE) wear debris is identified as the main factor limiting the lifetime of the artificial joints. Especially UHMWPE debris from the joint can induce tissue reactions and bone resorption that may lead to the joint loosening. The diamond like carbon (DLC) film has attracted a great deal of interest in recent years mainly because of its excellent tribological property, biocompatibility and chemically inert property. In order to improve the wear-resistance of UHMWPE, a-C:H films were deposited on UHMWPE substrate by electron cyclotron resonance microwave plasma chemical vapor deposition (ECR-PECVD) technology. During deposition, the working gases were argon and acetylene, the microwave power was set to 800 W, the biased pulsed voltage was set to −200 V (frequency 15 kHz, duty ratio 20%), the pressure in vacuum chamber was set to 0.5 Pa, and the process time was 60 min. The films were analysed by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, nano-indentation, anti-scratch and wear test. The results showed that a typical amorphous hydrogenated carbon (a-C:H) film was successfully deposited on UHMWPE with thickness up to 2 μm. The nano-hardness of the UHMWPE coated with a-C:H films, measured at an applied load of 200 μN, was increased from 10 MPa (untreated UHMWPE) to 139 MPa. The wear test was carried out using a ball (Ø 6 mm, SiC) on disk tribometer with an applied load of 1 N for 10000 cycles, and the results showed a reduction of worn cross-sectional area from 193 μm 2 of untreated UHMWPE to 26 μm 2 of DLC coated sample. In addition the influence of argon/acetylene gas flow ratio on the growth of a-C:H films was studied.