Diamond-like carbon films for polyethylene femoral parts: Raman and FT-IR spectroscopy before and after incubation in simulated body liquid.

In artificial prosthetics for knee, hip, finger or shoulder joints, ultrahigh molecular weight polyethylene (UHMW-PE) is a significant material. Several attempts to reduce the wear rate of UHMW-PE, i.e. the application of suitable coatings, are in progress. A surface modification of polyethylene with wear-resistant hydrogenated diamond-like carbon is favourable, owing to the chemical similarity of polyethylene (-C-H(2)-)(n) and C:H or amorphous C:H (a-C:H) coatings with diamond-like properties. In the present study, the microstructure of a-C:H coatings on UHMW-PE substrates was investigated by Raman and Fourier transform infrared (FT-IR) spectroscopy. FT-IR spectroscopy shows very broad absorption lines, which point to the disorder and diversity of different symmetric, asymmetric aromatic, olefin sp(2)-hybridized or sp(3)-hybridized C-H groups in the amorphous diamond-like carbon coating. Following a long incubation of 12 months in a simulated body liquid, the structural investigations were repeated. Furthermore, fractured cross-sections and the wetting behaviour with polar liquids were examined. After incubation in simulated body liquid, Raman spectroscopy pointed to a reduction of the C-H bonds in the diamond-like carbon coatings. On the basis of these findings, one can conclude that hydrogenated diamond-like carbon is able to interact with salt solutions by substituting the hydrogen with appropriate ions.