Polymeric Biomaterials - Biomaterials - page 71

biodegradability (Lee et al., 1990b, 1997b). Recently, plasma gas discharge (Khang et al., 1997a) and
corona treatment (Khang et al., 1996d) with reactive groups introduced on the polymeric surfaces have
emerged as other ways to modify biomaterial surfaces (Lee et al., 1991, 1992).
Hydrophobic coatings composed of silicon- and fluorine-containing polymeric materials as well
as polyurethanes have been studied because of the relatively good clinical performances of Silastic ® ,
Teflon, and polyurethane polymers in cardiovascular implants and devices. Polymeric fluorocarbon
coatings deposited from a tetrafluoroethylene gas discharge have been found to greatly enhance resis-
tance to both acute thrombotic occlusion and embolization in small-diameter Dacron ® grats.
Hydrophilic coatings have also been popular because of their low interfacial tension in biological
environments (Hoffman, 1981). Hydrogels as well as various combinations of hydrophilic and hydro-
phobic monomers have been studied on the premise that there will be an optimum polar-dispersion
force ratio which could be matched on the surfaces of the most passivating proteins. The passive surface
may induce less clot formation. PE oxide-coated surfaces have been found to resist protein adsorption
and cell adhesion and have therefore been proposed as potential “blood-compatible” coatings (Lee et al.,
1990a). General physical and chemical methods to modify the surfaces of polymeric biomaterials are
listed in Table 3.7 (Ratner et al., 1996).
Another way of making antithrombogenic surfaces is the saline perfusion method, which is designed
to prevent direct contacts between blood and the surface of biomaterials by means of perfusing saline
solution through the porous wall which is in contact with blood (Park and Kim, 1993; Khang et al.,
1996a, b). It has been demonstrated that the adhesion of the blood cells could be prevented by the
saline perfusion through PE, alumina, sulfonated/nonsulfonated PS/ styrene butadiene rubber (SBR),
expanded PTFE, and polysulfone porous tubes.

TABLE 3.7 Physical and Chemical Surface Modification Methods
for Polymeric Biomaterials
To modify blood compatibility Octadecyl group attachment to surface

Silicon containing block copolymer additive
Plasma fluoropolymer deposition
Plasma siloxane polymer deposition
Radiation-grafted hydrogels
Chemically modified PS for heparin-like activity

To influence cell adhesion and
growth

Oxidized PS surface
Ammonia plasma-treated surface
Plasma-deposited acetone or methanol film
Plasma fluoropolymer deposition

To control protein adsorption Surface with immobilized polyethyelene glycol

Treated enzyme-linked immunosorbent assay dish
surface
Affinity chromatography particulates
Surface cross-linked contact lens

To improve lubricity Plasma treatment

Radiation-grafted hydrogels
Interpenetrating polymeric networks

To improve wear resistance and
corrosion resistance

Ion implantation
Diamond deposition
Anodization

To alter transport properties Plasma deposition (methane, fluoropolymer, siloxane)

To modify electrical characteristics Plasma deposition

Solvent coatings
Parylene coatings

Source: Adapted from Ratner, B.D. et al. 1996. Biomaterials Science: An Introduction to
Materials in Medicine , Academic Press, New York, p. 106.