Blood interface biomaterials - Biomaterials and Devices for the Circulatory System - page 41

Other anticoagulant or platelet aggregation inhibitor-modifi ed surfaces

Surface immobilisation or incorporation of other bioactive substances with
antithrombogenic activities is another approach. Active substances, such as
urokinase (Oshiro & Kosaki, 1980), lumbrokinase (Ryu et al. , 1993), hirudin
(Phaneuf et al. , 1998) and human thrombomodulin (Kishida et al. , 1994,
1995) or inhibitors for activation and aggregation of platelets such as pros-
tacyclin (Ebert et al. , 1982; McRea & Kim, 1983) or inhibitor of complement
activation such as human decay accelerating factor (hDAF) (Watkins et al. ,
1997) have been used to modify polymeric surfaces. The bioactive sub-
stances are either tightly bound to the surface or simply blended into the
polymer system for controlled release. Nitric oxide (NO) has been found
to show a strong inhibitory activity of platelet aggregation (Yin et al. , 1995;
Sly et al. , 1995). Several nitric oxide-releasing polymers have been devel-
oped to coat medical devices and deliver nitric oxide in vivo to treatment
sites (Stamler et al. , 1998) or for incorporation into vascular grafts (Pulfer
et al. , 1997).

Surfaces containing phosopholipid polar groups,
oligosaccharides and peptides

Modifying polymeric surfaces by introducing phospholipid polar groups,
oligosaccharide chains, and specifi c oligopeptides for promotion of cell
growth has been successful in developing new biomimetic biomaterials.
Ishihara et al. (1992, 1993) have studied blood-compatible surfaces with
phospholipid polar groups. Their approach was to synthesise a polymer
possessing a strong affi nity for phospholipids from blood, which could be
organised to form a biomembrane-like assemblage on the polymer surface.
Based on this idea, many phosphorylcholine (PC) modifi ed surfaces have
been developed, including poly(MPC-CO-BMA) (2-methacryloyloxyethyl
phosphorylcholine-co-butyl methacrylate) (Ueda et al. , 1992). MPC-
co-cyclohexyl methacrylate and MPC-co-2-ethylhexyl methacrylate (Ishi-
hara et al. , 1996). The incorporation of phosphorylcholine-containing moi-
eties to polymer is an effective method for imparting non-thrombogenicity
(Yu et al. , 1994; Ishihara et al. , 1996; Zhang et al. , 1998). In addition, some
other phospholipid-containing materials have been investigated using phos-
phatidylcholine analoges as chain extenders for polyurethane synthesis.
Polysaccharides such as dextrin sulphate have been used as anionic modi-
fying agents to modify haemodialysis membranes. The modifi ed membranes
resist complement activation and platelet adhesion and activation (Amiji,
1996). The surface modifi ed with dextrin demonstrated a glycocalyx-like
interface in an aqueous environment. It was claimed that this biomimetic
surface was effective in suppressing protein adsorption from human plasma
protein solution (Holland et al. , 1998).

￿ ￿ ￿ ￿ ￿