Page 91 - Demo

Biomaterials in TMJ replacement893Another form of surface modification that can be used involves carbon. When carbon is applied to Ti’s surface, both TiC and graphite (C-C) can be formed. The bonds that are formed depend on the amount of carbon applied to the metal’s surface.(76) The use of carbon increases hardness and resistance to wear and corrosion, and it also improves adhesion, growth, and maturation of bone-derived cells.(19,48,76) However, if the concentration of carbon is too high, a decrease in hardness will occur.(76) Another suitable coating material is DLC, a metastable form of amorphous carbon with both tetrahedrally bonded (sp3) carbon atoms, as in diamond, and trigonal planar bonded (sp2) carbon atoms, as in graphite. With increasing diamond-like bonds, DLC-coatings typically exhibit more diamond-like properties, such as a low friction coefficient and high hardness.(76,81–83) Moreover, DLC-coatings are chemically inert and exhibit high bio- and hemocompatibility, as well as corrosion resistance.(48,82–84) Besides a high hardness, a very smooth surface can also be obtained with DLC, resulting in excellent wear resistance. (83,84) Jiang et al.(82), Kim et al.(84), and Firkins et al.(85) reported that when in contact with UHMWPE, DLC-coated stainless steel and Ti produced less wear than the pristine substrate materials. Jiang et al.(82) noted that while UHMWPE initially forms more debris when combined with DLC-coated Ti6Al4V, the amount of debris decreased as the amount of total movement increased. As a result, after a total sliding distance of 500 m, a higher total amount of UHMWPE debris was formed when combined with untreated Ti6Al4V than with DLC-coated Ti6Al4V. DLC-coating can be applied via several different techniques, such as magnetron sputtering, ion beam deposition, and plasma-enhanced chemical vapor deposition (CVD).(83) However, care must be taken when selecting the appropriate processing route. Because of the difference in the thermal expansion coefficient and structure between the coating and Ti, as well as a high intrinsic stress, adhesion between the two surfaces is relatively poor.(76,81–83,86) As a result, when a coated Ti implant is subjected to higher forces, plastic deformation of the softer Ti can occur, resulting in insufficient support of the harder DLC coating.(83,84,86) This can cause chipping, fractures, and even delamination of the coating, Nikolas de Meurechy NW.indd 89 05-06-2024 10:14