Improvement of titanium alloy for biomedical applications by nitriding andcarbonitriding processes under glow discharge conditions

Although titanium alloys are used in medicine, they present low wear resist ance. In this paper we present the results of studies on surface layers pro duced by nitriding at three different temperatures, and by carbonitriding u nder glow discharge conditions in order to improve wear resistance, hardnes s, and to modulate microstructure and chemical composition of surface layer s. A cell culture model using human fibroblasts was chosen to study the eff ect of such treatments on the cytocompatibility of these materials. The res ults showed that nitrided and carbonitrided surface layers were cytocompati ble. Modulation of surface microstructure by temperature in the nitriding p rocess and chemical composition of surface layers by carbonitriding led to differences in cellular behaviour. Cell proliferation appeared to be slight ly reduced from the 6th day of culture on nitrided surfaces produced at 730 degrees C and 1000 degrees C, however after 12 days of culture, the best g rowth was on surface layers produced at 850 degrees C. The best viability w as observed on the carbonitrided layer. The orientation and shape of the ce lls corresponded to surface topography. Nitriding and carbonitriding under glow discharge conditions may constitute interesting techniques allowing th e formation of surface layers on parts with sophisticated shapes. They may also permit modulating surface topography in a way improving the features o f titanium alloys for various applications in medicine. (C) 2000 Kluwer Aca demic Publishers.