SUPPORTED CELL MIMETIC MONOLAYERS AND THEIR COMPATIBILITY - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 662

the thrombosis may get mediated through the direct interaction between the
exposed surface groups and the receptors of the blood cells. Therefore, the authors
have studied the blood cell interaction to these surfaces from washed blood cells.
20.6 BLOOD CELL ADHESION STUDIES
Figure 20.5(V) shows the data of blood cell adhesion using washed platelets,
erythrocytes and the leukocytes to the bare PC and the modifi ed surfaces. The
results show an overall decrease in cell adhesion on to modifi ed surfaces as
compared to the bare polymer surface. The orientation as well as packing of the
exposed monolayer infl uences the observed difference in cell adhesion. Further-
more, the optimized surface, PC modifi ed with (PTC : Chol : GalC) (1 : 0.35 : 0.125)
have been evaluated towards the platelet activation from platelet rich plasma to
confi rm the anti-thrombogenecity of the surface.
20.7 PLATELET ADHESION AND ACTIVATION STUDIES
Platelet adhesion and activation are two important steps that regulate the forma-
tion of the thrombus and medical device rejection. During the initial stage of
surface activation, the change in conformation of the adsorbed proteins exposes
RGD sequences that are sensitive to the platelet GPIIb/IIIa receptor. When
platelets are surface activated, they progress through a sequence of morphologi-
cal changes. This can be evaluated by using SEM. The surface activation contrib-
utes to the change in the organization of the cytoskeleton, in turn increases the
surface area of the platelets by the formation of pseudopods. The adhered and
activated platelets go through a sequence of cytoskeletal events and rise in endo-
plasmic Ca++ concentration, polymerization of actin fi laments, thrombin activa-
tion, release of the cytoskeletal granule contents, and platelet aggregation. The
extent of shape change and the spread area have been related to the surface ener-
getic of the polymer materials. Therefore the platelet activation studies are essen-
tial to prove the blood compatibility of the surface. The shape change could be
correlated with the activation.
The studies were done for two hours with PRP under static conditions.
Usually one hour is suffi cient to establish the activation of the platelets 18 . The
authors' studies show that the platelet activation to the modifi ed surface has been
signifi cantly reduced as compared to the bare polycarbonate surfaces (Figure
20.5 (II) 16 . The surface mediated shape change of the cells has been related to the
physical (interfacial energy) and the chemical (due to specifi c groups) interac-
tions. More than half of the platelets adsorbed to the bare polymer surface were
fully spread and the other platelets were on the verge of spreading. The extended
pseudopods of the activated platelets on the bare polymer surface indicate that
these platelets can recruit the other platelets still in suspension. (Form surface
bound aggregates with time.)