Biomedical Engineering Reference
In-Depth Information
2-methacryloyloxyethyl phosphorylcholine (MPC) polymer coatings (organic)
Copolymer MPC coatings are also used for VADs owing to their excellent
haemocompatibility. MPC coatings offer the elimination of thrombus deposi-
tion. They were designed as a non-thrombogenic surface approximately 20 years
ago. The idea was to create a non-thrombogenic surface by having phospholipid
membranes, which are accumulated from the bloodstream on the blood-
contacting surface. In other words, the non-thrombogenic surface is achieved by
the reduction of protein adsorption as a consequence of accumulation of free
water in the MPC hydrogels (Nakabayashi and Iwasaki, 2004; Sin et al., 2009).
The relative amount of protein adsorption depends on the MPC units in the
polymer (Trevor et al., 2007). The intensity of protein adsorption can be
decreased by increasing MPC units which also leads to an increase in surface
phospholipid levels (Nakabayashi and Williams, 2003).
It has been reported that MPC surface coatings can suppress platelet
adhesion, complement activation and protein adsorption. They offer minimum
thrombus formation without anticoagulants (Ishihara, 2000).
Comparison of thrombogenicity and biocompatibility of MPC and DLC
coatings was conducted on pure titanium substance by Kihara et al. (2003). In
this, blood compatibility of the SunMedical EVAHEART LVAS (SunMedical
Technology Research Corporation, Nagano, Japan) system was evaluated with
the coatings. There were no major differences between MPC and DLC surface
coatings in terms of thrombogenicity and biocompatibility. On the other hand,
MPC polymer surface coating offers reduction of anticoagulation in the acute
postoperative period. It is also less expensive and easy to apply over DLC
surface coatings. On the other hand, DLC coating is an expensive technology
and hard to deposit on a complex featured surfaces. However, the study showed
that low thrombogenicity occurred after around one month without
anticoagulation. This indicates that MPC coatings may not offer the above
advantages over a long period.
One of the major drawbacks of MPC surface coatings is that they last for a
limited period of time because of their biodegradability (Yamazaki et al., 2002).
This characteristic of MPC leads to the use of anticoagulants after the coating
diminishes (Sin et al., 2009). In addition, compared to other coatings for blood
circulatory devices (i.e. TiN and DLC), MPC coating seems weak and not stable
on polymeric and metallic bulk materials.
Heparin coatings (bioactive)
Biological active coatings are used to improve haemocompatibility of the device.
Heparin is one of the agents used to create bioactive surface. The most important
characteristic of heparin coatings is the effective inhibition of thrombus over
other repellent surface coatings. There are two different hypotheses on how
heparin coating leads to reduction in thrombogenicity: (1) by the inhibition of
