Haemocompatibility of DLC and TiC–TiN interlayers on titanium

Abstract

An interlayer approach was adopted to achieve adequate adhesion between a DLC coating deposited by plasma-assisted CVD and a titanium substrate as part of a study to coat a bi-leaflet heart valve prosthesis. The interlayers (TiC and TiN) were deposited by d.c. ion plating. TiN was also deposited by reactive r.f. sputtering. The substrate, interlayers and DLC were assessed for haemocompatibility and thrombogenicity using a dynamic blood method and interactions with rabbit blood platelets, respectively. The adhesion, activation and morphology of the platelets were determined by stereological techniques using SEM. All surfaces were assessed topographically by stylus profilometry and AFM. Surface energies were compared by liquid drop goniometry. The structure and crystallographic orientation of the TiN interlayers were determined using XRD. The coatings produced no haemolytic effect, except in the case of TiN deposited by reactive r.f. sputtering, which showed a significant effect after longer assessment periods. In contrast to the DLC coating, all of the interlayers showed a slight tendency towards thrombus formation during the later stages of incubation. Platelet spreading correlated with the surface energy of the coatings.