Blood interface biomaterials - Biomaterials and Devices for the Circulatory System - page 36

• Incorporation of cyclodextrins by blending can achieve surface
modifi cation.
• Fibrinogen adsorption was dependent on the type and quantity of cyclo-
dextrin incorporated.
• Modifi ed PVC surfaces induced less fi brinogen adsorption than stan-
dard PVC.

• Fibrinogen adsorption was markedly reduced by the combined incor-

poration of cyclodextrin and PEO-PPO-PEO.

• Reduced DEHP extraction could be achieved.

Hydrogel-modifi ed surface

Hydrogels are water-swollen, crosslinked polymeric materials produced by
the single reaction of one or more monomers or by association bonds such
as hydrogen bonds and strong van der Waals interaction between chains
(Peppas, 1987). Hydrogels can be derived from natural biopolymers or
synthetic hydrophilic polymers. The most widely used synthetic hydrogels
are crosslinked poly(hydroxyethylmethacrylate) (PHEMA), poly(vinyl
alcohol) (PVA), polyacrylamide (PA), poly(vinyl pyrrolidone) (PVP),
poly(methacrylic acid) (PMAA) and copolymers of these (Ratner et al. ,
1996). Natural biopolymers, such as collagen, albumin, alginate, chitosan,
and many other polysaccharides, have also been employed to produce
hydrogels for biomedical applications.
The utilisation of hydrogel to modify a polymer surface can achieve an
oily surface with reduced frictional resistance or increased slipperiness due
to the high water content of hydrogels (Ikada, 1994). Additionally, hydogels
provide the basement for improving blood compatibility in active ways by
incorporation of bioactive substances or cell seeding. The molecular design
of a surface by utilisation of hydrogels is shown in Fig. 2.2.
With respect to short-term blood-contacting applications, it is important
only that the device repels platelets, proteins, cells and other fouling materi-
als. A coating of hydrogel is able to provide such a blood-compatible surface
for medical devices, such as catheters, which also require an oily surface.
Hydrogel can be achieved by photo-initiated polymerisation of a hydro-
philic monomer at the catheter surface. Studies have shown that platelet
aggregation and clot formation through adherence of blood components to
the coated catheters is less than with uncoated catheters (Anderson et al. ,
1996). Albumin or photoactivated albumin can be coated on to a hydropho-
bic surface, followed by crosslinking with glutaraldehyde (Kottke-Marchant
et al. , 1989) or by photo-initiated crosslinking (Matsuda & Inoue, 1990).
PVP crosslinked with an isocyanate has been employed for coating poly-
urethane catheter surfaces. The PVP coating induced a hydrophilic surface
with non-adhesive surface properties, which would minimise diffi culties

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