A review of modified DLC coatings for biological applications

Diamond-like carbon (DLC), also known as amorphous hydrogenated carbon (a-C:H), is a class of materials with excellent mechanical, tribological and biological properties. By the addition of other elements into the DLC all of these properties can be changed within a certain range. It will be shown that the ratios of the different proteins adsorbed on the surface can be influenced by the addition of different elements into the DLC film. These proteins will then subsequently influence cell attachment, cell proliferation and cell differentiation. Certain toxic elements such as Cu, Ag, V, embedded in the DLC will, when exposed to a biological media, be released and cause toxic reactions. This allows the preparation of surfaces with a tunable antibacterial effect. DLC has proven its outstanding tribological properties in many technical applications due to the transformation of DLC into graphite (a solid lubricant) and the build up of a transfer layer on the counterpart. However, it is questionable if this effect takes place in artificial joints. Contradicting results on DLC coated hip joints are found in the literature, some indicating an improvement and some a change for the worse. DLC coatings have an excellent haemocompatibility, which is expressed in a decreased thrombus formation. When exposed to blood, an increased ratio of albumin to fibrinogen adsorption as well as decreased platelet activation is observed on coated surfaces. DLC coated cardiovascular implants such as artificial heart valves and stents are already commercially available.