Ion beam deposition of nitrogen doped diamond-like carbon thin films for enhanced biological properties

Abstract

Artificial cardiovascular implants are now made mainly from extruded polytetrafluroethylene (PTFE). However, the limited haemocompatibility of PTFE causes blood clotting and results in early replacement. Many techniques are being developed to improve the haemocompatibility of such devices. One of the most promising techniques is to coat the devices with nitrogen-doped diamond-like carbon (NDLC) thin films. However, the structure of NDLC and its effect on the haemocompatibility of the coated devices have not been fully investigated as required for practical applications. In this thesis, ion beam deposited DLC and Nitrogen doped thin films on PTFE were investigated in order to have a better understanding of the relationships between the structure and biomedical properties of the DLC thin films.

DLC and NDLC thin films were synthesized using ion beam deposition. Commercially available PTFE sheets, which are similar to the material used for vascular grafts, were used as substrates for the DLC thin films. Silicon wafers were also utilized as substrates for condition optimization and property comparison. Raman spectroscopy, atomic force microscopy, X-ray photo emission spectroscopy and scanning electron microscopy were used to study the structural and morphological properties of the coated surface. The results show that the ion beam deposited thin films have a very smooth surface and exhibit low coefficient of friction and high adhesion to the substrate. Low concentration of nitrogen doping in DLC improved surface hardness and reduced surface roughness. Higher concentration of sp3 hybridized bonds was observed in the DLC thin films on Si than those on PTFE. DLC coating decreased the surface energy and improved the wettability of PTFE films.

The haemocompatibility of the pristine and DLC coated PTFE sheets were evaluated by platelet adhesion technique. The platelet adhesion results showed that the haemocompatibility of DLC coated PTFE, especially NDLC coated PTFE, was considerably improved as compared with uncoated PTFE. SEM observations showed that the platelet reaction on the coated PTFE was minimized as the platelets were much less aggregated and activated.