Biomedical Engineering Reference
In-Depth Information
thrombin by catalyzing the inactivation of enzymes i.e. thrombin and Factor X
a
,
and (2) reducing/selective plasma protein adsorption (Oeveren, 2005).
Roller and centrifugal pumps with and without heparin coating were com-
pared in vivo in order to measure blood activation potentials (Moen et al., 1996).
The results showed that the heparin-coated surface performed well in terms of
reduction of blood activation compared with non-coated surfaces. In addition,
less haemolysis was observed with heparin-coated centrifugal pump over axial
pump.
BerlinHeart is another commercial application which utilizes heparin coating.
Even though cannulas of BerlinHeart are made of silicon rubber (high flow rate
on extreme smooth surface) which does not need any coating, the inner blood
contact surfaces are completely deposited with heparin. Carmeda BioActive
Surface (Carmeda AB) technology was used for coating in which heparin is
attached by covalent bonding (Drews et al., 2000). Evaluation of heparin effects
on occurrence of heparin/platelet factor 4 antibodies (HPF4/A) was studied by
Koster et al. (2001). No effect of heparin coating was observed on incidence of
HPF4/A which is associated with thromboembolic complications.
In another study, heparin coating was investigated in a blood pump made of
polycarbonate substrate (Muramatsu et al., 2001). In vitro observation showed
that heparin coatings show anticoagulant activity. Christensen et al. (2001)
performed an investigation on platelet and coagulation activation within the
heparin-coated stent StentGraft
TM
(JomedImplantate GmbH, Germany). The
experiments indicated the occurrence of significant activation of platelets and
coagulation without coatings. However, heparin-coated stent grafts functioned
well in terms of blood compatibility as proved by SEM.
Reduction of fibrinogen adsorption was reported when the heparin coating
present on the polymer substrate for particular situations (Vroman and Adams,
1969). Heparin coating has been used for extracorporeal systems as well.
Wendel and Ziemer (1999) investigated a heparin-coated surface in order to
decrease the intensity of unspecific post-perfusion syndrome. A comparison
study of coated and non-coated surfaces showed that heparin coating performed
well in terms of reduction of humoral and cellular activation, platelet protection
and total cost savings.
Owing to the above properties of heparin, titanium alloy blood-contacting
surfaces of the magnetically suspended third generation blood pump, Incor
(BerlinHeart, Germany), are coated with heparin (Hetzer et al., 2004). The
Carmeda process, covalent binding of heparin, is used for titanium alloy surface.
Other commercial methods for heparin coatings are Duraflo technology
(Baxter International, Inc., Deerfield, IL) and PhotoLink photo heparin coatings
(SurModics) and Medi-Coat hydrogels (STS). The implications of these coating
methods are out of the scope of the chapter.
On the other hand, as a disadvantage, it is important to consider the lifetime
of heparin coatings, which is limited due to its biodegradable nature. The
