Biocompatibility evaluation of DLC-coated Si 3 N 4 substrates for biomedical applications E. Salgueiredo a , M. Vila a , M.A. Silva b , M.A. Lopes b,c , J.D. Santos b,c , F.M. Costa d , R.F. Silva a, ⁎ , P.S. Gomes e , M.H. Fernandes e a CICECO, Glass and Ceramics Eng. Department, University of Aveiro, 3810-193 Aveiro, Portugal b Instituto de Engenharia Biomédica (INEB), Lab. Biomateriais, Porto, Portugal c Dep. Eng. Metalúrgica e Materiais, Fac. Engenharia, Univ. do Porto, Portugal d Physics Department, University of Aveiro, Portugal e Lab. Farmacologia e Biocompatibilidade Celular, Fac. Medicina Dentária, Univ. do Porto, Portugal Available online 23 August 2007 Abstract DLC coatings are of enormous interest for biotribological applications due to their biocompatibility, auto-lubricious, and non-stick properties. The most demanding implant is the hip joint. Alternative materials to metal alloys are being increasingly investigated aiming low wear debris volume, in any case innocuous wear particles. Silicon nitride (Si 3 N 4 ) ceramics are light, tough, mechanical resistant, inert materials, turning them suitable for high-load medical applications. In this study, Si 3 N 4 polished substrates were coated with adherent DLC coatings grown by DC magnetron sputtering to reduce of the friction forces against any antagonist material. Surface characterization results showed that the developed material is quite hydrophobic, with a total surface tension of 45.7 mN/m (polar component: 9.1 mN/m; dispersive component: 36.6 mN/m), and a zeta potential of - 35.0±1.3 mV. In vitro testing using an acellular simulated body fluid (SBF) showed no apatite layer formation ability, as confirmed by SEM observation and analysis of the solution ions concentration with immersion time. MG63 osteoblast-like cells showed poor adhesion on the DLC films but the adherent cells displayed a normal morphology and, as compared to standard polystyrene tissue culture plates, exhibited a higher cell growth rate, suggesting no indication of cytotoxicity. Results suggested that the novel DLC-coated Si 3 N 4 biomaterial should be adequate to be used for articular prostheses medical application. © 2007 Elsevier B.V. All rights reserved. Keywords: DLC coatings; Biomedical applications; Cell cultures 1. Introduction Some medical applications require materials with a non cell- adhesive surface, such as devices in contact with human blood (e.g., artificial heart valves), while others need a cell-adhesive surface to assure complete tissue integration of the implanted material in the human body. In orthopaedic applications, the osteointegration is promoted by the formation of an apatite layer on the surface of the biomaterial upon implantation. The biomaterial surface properties can be defined aiming to control its bioactivity and biocompatibility. For applications such as replacement of the hip joint, which is composed of a stem, a femoral head and an acetabulum, the formation of an apatite layer is desired on the stem, but not at femur head or acetabulum surface since it would compromise the tribo-system perfor- mance. There are many different shapes, sizes, and designs of artificial components of the hip joint, made of several materials such as chrome, cobalt, titanium, polymeric or ceramic materials. Nevertheless, on going problems with wear and particulate debris still exist, causing metallosis, and eventually periprosthetic osteolysis and aseptic loosening [1]. Silicon nitride (Si 3 N 4 ) based ceramics are well known for their superior combination of fracture toughness and hardness [2]. These are key properties for an excellent wear resistance, which, combined with Si 3 N 4 chemical inertness, turns this material a suitable candidate for high-load medical applications, namely for metal prostheses replacement. In order to diminish the friction forces in such kind of bio-tribological systems, the Si 3 N 4 surfaces must be modified. Diamond-like carbon (DLC) Available online at www.sciencedirect.com Diamond & Related Materials 17 (2008) 878 – 881 www.elsevier.com/locate/diamond ⁎ Corresponding author. Tel.: +351 234370243; fax: +351 234425300. E-mail address: rsilva@cv.ua.pt (R.F. Silva). 0925-9635/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2007.08.019