Industrial coatings used in the orthopaedic industry to reduce wear

This paper describes some of the findings from tests which look at the protection offered by surface coating both the metal and plastic surfaces of prostheses. All joints experience some form of wear and consequently produce debris. Accumulation of debris can cause adverse cellular reactions resulting in loosening of the prosthesis through bone resorption. Suitable treatments and coatings include titanium nitriding (TiN), implantation of ions into the surface by beam bombardment (nitrogen ion-implantation), and the application of amorphous diamond-like carbon coatings (DLC). The durability and osseous response to coatings and surface treatments applied to prostheses at the bone-implant interface is of great interest if, by such application, the interface can limit wear and increase osseointegration. The greatest flexibility would be offered if such treatments could be applied to both the metal and polymer surfaces. However, some physical methods of application may well restrict the treatment of plastics because of the temperatures involved. Initial investigations indicate that minimum damage occurs to the metal element of the joint combination if a coating of DLC is applied at the optimum thickness. This is evidenced by the lack of transfer film observed by SEM examination and absence of scuffing marks on the surface. Nitrogen ion-implantation of the metal surface appears to have a beneficial effect for potential use in total knee replacements.