Biomedical Engineering Reference
In-Depth Information
investigated TiN coating based on the principle of the Maillard-Wankel rotary
pump. The report indicates that TiN coating performed well with respect to
blood interaction. However, SEM observations showed irregularities on its
surface. MontiÁs et al. (1997) investigated TiN coating on graphite substrate for
long-term and permanent implantable LVAD. They reported a low roughness
and good blood compatibility on its surface.
On the other hand, the enormous use of DLC coatings for VADs eliminates
the use of TiN coatings due to advances on haemocompatibility of DLC
coatings.
DLC coatings (inorganic)
DLC, known as amorphous hydrogenated carbon (a-C:H), consists of 50±70%
carbon and 50±30% hydrogen. DLC can be deposited easily by several methods,
including chemical vapour deposition, cathodic arc deposition, pulsed laser
deposition, direct ion beam deposition, ion beam conversion of condensed
precursor, magnetron sputtering, plasma source ion deposition and direct
current/radiofrequency sputtering (Dearnaley and Arps, 2005). A wide range of
substance materials, e.g. Ti (Krishnan et al., 2002), NiTi (Sui and Cai, 2006; Sui
et al., 2007), Ti-6Al-4V (Dion et al., 1993c), polymeric materials (Alanazi et al.,
2000; Ohgoe et al., 2004; Igarashi et al., 2006) are suitable for DLC coating. It
has received considerable attention as a coating material due to its advantages
such as very smooth surface state, good wear resistance, low frictional coeffi-
cient, inertness, excellent biocompatibility and haemocompatibility over other
coatings. Several studies of DLC coating with respect to blood compatibility
indicated a considerable reduction of platelet adhesion to titanium (Jones et al.,
2000; Krishnan et al., 2002).
Comparison of platelet attachment on Ti substrate and DLC coating is
depicted in Fig. 8.1. In the case of DLC coating, disk-shaped platelets at the end
of incubation period of 15min remain the same for 60min. This indicates that
the DLC coatings prevent activation of platelets. However, morphology of the
widely spread platelets is different after 60 min on Ti substrate without any
coatings.
The clear thrombus formation on TiN coating can be seen in Fig. 8.2(a). The
same results were reported for titanium and TiC surfaces. However, no thrombus
was observed on the SEM micrograph of the DLC surface as depicted in Fig.
8.2(b).
Despite the fact that the DLC coating provides excellent haemocompatibility
and biocompatibility, DLC coating on Ti-6Al-4V presented double the platelet
retention than on silicon elastomer (Dion et al., 1993c). One of the other
disadvantages of this coating is the chance of micro-cracks on the surface. In
fact, this can cause serious problems after implantation of a DLC-coated device
(Sin et al., 2009). Therefore, this limitation deserves serious attention that the
