Enhanced bioactivity of biomedical NiTi through surface plasma polymerization

Plasma polymerization of propylene amine was carried out to produce a polymeric layer with a thickness of 100∼500 nm on the surface of biomedical NiTi shape memory alloys. Nitrogen plasma immersion ion implantation (N-PIII) was carried out prior to the polymerization of allylamine in order to prepare a ceramic transition layer of TiN. Atomic force microscopy (AFM) and Fourier infrared spectrum (FTIR) were used to examine the surface characteristics of NiTi alloys such as surface topologies, functional structure and chemical compositions. Cell culture results showed that the osteoblasts exhibited better adhesion and proliferation behaviors on the surface of modified NiTi than on the untreated samples, which was possibly ascribed to the formation of amino functional groups after allyl amine polymerization, thus favoring the improvement of surface bioactivity and consequently promoting the growth of bone cells. The immersion tests and contact angle measurement revealed that the combined treatment of N-PIII and allylamine polymerization was beneficial to the improvement of surface hydrophilicity and the suppression of nickel leaching from NiTi substrate into simulated body fluid.