P.J. Martin

The deposition of TiN thin films by nitrogen ion assisted deposition of Ti from a filtered cathodic arc source

Abstract TiN films are synthesised on ambient temperature substrates by condensing Ti+ ions from a filtered cathodic arc source beam under 500 eV N+2 nitrogen ion bombardment. The film stoichiometry was varied from a N:Ti ratio of 0.8 to 1.2 by controlling the relative arrival rates of Ti and nitrogen ions. The compressive stress in 120 nm thick films deposited onto Si was found to decrease from a maximum of 10 GPa under no ion bombardment to a minimum of 6 GPa for an arrival ratio of 1.0. In the absence of ion bombardment the composition of the films was found to depend on the partial pressure of nitrogen over the range 0.6–2 Pa where the N:Ti ratio changed from 0.3 and saturated at approximately 0.8. Collision cascade models are used to describe the evolution of compressive stress as a function of arrival ratio, the damage depth distribution due to Ti+ ions and N+ ions and the composition of the TiN films.

Biomineralization of osteoblasts on DLC coated surfaces for bone implants

Diamond like carbon (DLC) films were deposited onto Ti6Al4V and Si wafer substrates by RF plasma enhanced chemical vapor deposition. The influence of dopants such as fluorine (F), silicon (Si), and nitrogen (N) on composition, structure, and biocompatibility was investigated. Ion scattering spectroscopy analysis revealed the presence of dopant atoms in the outer-most layers of the films. Raman studies showed that the position of the G-band shifts to higher frequencies with the fluorine and nitrogen content in the DLC film, whereas the incorporation of Si into DLC induces a decrease of the position of the G peak. The corrosion behavior was studied in simulated body fluid. A higher charge transfer resistance (Rct) was observed for the doped DLC films. The indirect cytotoxicity was performed using L929 fibroblast cells. The coated surfaces were hemocompatible when tested with red blood cells. DLC films were noncytotoxic to L929 cells over a 24 h exposure. Saos-2 osteoblast cell response to the doped and undoped DLC coated surfaces was studied in adhesion, proliferation, differentiation, and mineralization assays. The production of calcium and phosphate by cells on doped DLC, particularly, nitrogen doped DLC, was higher than that on undoped DLC.

Biomineralisation with Saos-2 bone cells on TiSiN sputtered Ti alloys

Surface modifications of metallic implants are important in order to protect the underlying metals from the harsh corrosive environment inside the human body and to minimize the losses caused by wear. Recently, researches are carried out in developing bioactive surfaces on metallic implants, which supports the growth and proliferation of cells on to these surfaces. Titanium silicon nitride (TiSiN) hard nanocomposites thin films were fabricated on Ti alloys (Ti-6Al-4V) by pulsed direct current (DC) reactive magnetron sputtering. The films were characterized for its microstructural and electrochemical behavior. The higher charge transfer resistance (Rct) and positive shift in Ecorr value of TiSiN/Ti alloys than the bare Ti-alloys indicates a better corrosion resistance offered by the TiSiN thin films to the underlying substrates. The biological response to TiSiN/Ti alloys and control bare Ti-alloys was measured in vitro using cell-based assays with two main outcomes. Firstly, neither the Ti alloy nor the TiSiN thin film was cytotoxic to cells. Secondly, the TiSiN thin film promoted differentiation of human bone cells above the bare control Ti alloy as measured by alkaline phosphatase and calcium production. TiSiN thin films provide better corrosion resistance and protect the underlying metal from the corrosive environment. The thin film surface is both biocompatible and bioactive as indicated from the cytotoxicity and biomineralization studies.