Chemical and biological characteristics of low-temperature plasma treated ultra-high molecular weight polyethylene for biomedical applications

Several low-temperature radio-frequency (RF) plasma surface treatments were performed on ultra-high molecular weight polyethylene (UHMWPE) used in biomedical applications. Process gases included Ar, C3F6, CH4, hexamethyldisiloxane (HMDSO), and NH4. These treatments were carried out at pressures in the range of 64-400 mTorr, RF powers of 240-1200 W, and temperatures well below the melting point of UHMWPE. X-ray photoelectron spectroscopy (XPS) was used to obtain information about the surface characteristics of UHMWPE treated with the HMDSO, C3F6, and CH4 gases as a function of treatment conditions. XPS spectra of UHMWPE treated with C3F6 and CH4 and exposed to a laboratory environment for different time periods were examined in order to assess the stability of these treatments. It was found that for the C3F6 process gas the amount of fluorine at the surface decreased over time, whereas the oxygen content of the CH4 treated samples increased as a function of time. In vitro cytotoxicity of Ar, C3F6, CH4, and NH4 plasma treated samples was studied in light of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) test results. The hemolytic nature of the various plasma treatments was evaluated using standard hemolysis tests. All of the samples tested in this study exhibited no cytotoxic and negligible hemolytic effects. The process parameters for several low-temperature plasma treatments demonstrating chemical and structural stability and good biocompatibility are discussed in conjunction with the broad applicability to other biomedical polymers. (C) 2001 Kluwer Academic Publishers.