Haemocompatibility and charactersation of candidate coatings for heart valve prosthesis.
Prosthetic cardiac valve surgery is a well-established technique, but the search
continues for engineering materials with sup..e rior mechanical characteristics in order
to extend the service life of the implant. The introduction of pyrolytic carbon was
seen as a breakthrough in the development of wear resistant, non-thrombogenic
materials for such applications. However, thrombo-embolic phenomena and the
need for anticoagulation treatment following valve insertion remain the main
problems associated with artificial materials in this application.
The work carried out in this research has studied the haemocompatibility of a
commercially available, wear resistant TiffiN/TiCfDLC multilayer structure, and a
second TiN coating deposited by RF reactive sputtering of a titanium target in a
ArIN2 environment, as candidate materials for a heart valve prosthesis. The structure
of the RF deposited tiN coating was assessed as a function of deposition conditions,
and was seen to develop a particular preferred crystallographic orientation. The
nature of this texture was influenced by the condition of the underlying substrate.
The effect of substrate condition on the biocompatibility of the tiN coating was
studied by assessment of fibroblast attachment and spreading, and by haemolytic
analysis of released haemoglobin. The results showed that the initial attachment and
orientation of fibroblast cells was influenced by the substrate condition, but no
influence on the degree of spreading and haemolytic nature was observed.
Characterisation of the TiN coating and the components of the multilayer structure
was carried out by Atomic Force Microscopy (AFM), X-ray Photoelectron
Spectroscopy (XPS), stylus profilometry and contact angle measurement.
Haemocompatibility was studied by the interaction of the surfaces with plasma
proteins, blood platelets and red blood ceUs. Cytotoxicity was studied using the
The degree of platelet activation on the surfaces correlated with their surface energy.
The greatest degree of platelet spreading was observed on the more hydrophilic
coatings. The lack of platelet activation seen on the DLC coating is attributed to its
smooth surface and hydrophobic nature, resulting in higher levels of adsorption of
The RF sputtered TiN coating caused significant levels of haemolysis and fibroblast
cell death. None of the components of the multilayer structure caused such effects,
although thrombus formation was observed to a degree on the Ti, TiN and TiC
components of this structure. The toxic nature of the RF deposited TiN coating was
not attributed to surface chemistry or roughness, but rather to a combination of the
hydrophilic nature and the defect state of the surface.