Abstract

Carbon-based materials, for example pyrolytic carbon, have been successfully applied as artificial clinical heart valve coatings but due to ease of availability, processing, increased hardness, corrosion and scratch resistance, DLC has recently attracted attention for biomedical applications. Although often cited as having bio-compatible properties there has been little systematic study of DLC and how film structure may affect such properties. RF PECVD a-C:H and Si-doped a-C:H:Si films were deposited and in-vitro blood compatibility (haemocompatibility) investigated by the use of human microvascularendothelial cells (HMEC) on one end of the scale and platelets on the other, in order to assess the potential of DLC in biomedicine and surgical applications. Increased electronic conduction, decreased work function and decreased surface bond energy (with a high dispersive component) in the absence of graphitisation improved the blood compatibility of a-C:H and a-C:H:Si thin films. Changes in the nanostructure, surface energy and electrical properties was observed with silicon doping while thermal annealing also altered the electrical properties, reduced intrinsic compressive stress and at higher temperatures (> 400 degreesC) induced graphitisation. Increased HMEC adhesion (approx. 6x) and/or decreased platelets aggregation (approx. 6x) is associated with lower resistivity, work function and surface energy in the thin films where there is no graphitisation. Graphitisation, however, despite the lower resistivity and work function, leads to lower HMEC adhesion and increased platelets aggregation. Si-doped a-C:H coatings deposited under optimal conditions are a significant factor in developing haemocompatible medical implants and devices. (C) 2003 Elsevier B.V. All rights reserved.