DLC Films in Biomedical Applications

Diamond-like carbon (DLC) has outstanding tribological properties and is, additionally, tolerated well by the body. Due to this advantageous combination of properties, research and development efforts have been made toward the use of DLC coatings in biomedical applications. It has been demonstrated that DLC coatings do not trigger any adverse effects on attached cells and that DLC can be considered to be biocompatible by in vivo and also many in vitro experiments. DLC surfaces also have an excellent haemocompatibility and DLC-coated cardiovascular implants such as artificial heart valves, blood pumps, and stents are already commercially available. The different studies presented demonstrate that DLC has the ability to reduce wear, more or less independently of the lubricant used, in load-bearing implants when sliding against metals or against DLC. However, it seems that when DLC slides against ultra high molecular weight polyethylene (UHMWPE) in the presence of body fluids, the good tribological properties that DLC shows in air could not be obtained. The in vitro experiments of DLC sliding against UHMWPE apparently showed different results, due to variations in experimental setups (ball-on-disk, hip or knee simulator, surface roughness) and especially the different liquids used as lubricants. In some medical applications such as guidewires, urinary tract catheters, and orthodontic archwires, the in vitro and in vivo experiments on DLC-coated parts showed an improved tribological performance. When implanting a DLC-coated material, it has to be considered that the reaction layer at the DLC/substrate interface has to have a high chemical durability under in vivo conditions to guarantee lifetime adhesion.