Blood interface biomaterials - Biomaterials and Devices for the Circulatory System - page 31

In this section, the molecular design of a polymeric surface for improved
blood compatibility focuses on increased hydrophilicity, increased hydro-
phobicity, microphase separated (microdomain) structure (balance of
hydrophobicity and hydrophilicity), and biomimetic surface design, includ-
ing bioactive surfaces.

2.4.1 Increase in hydrophilicity

Minimal protein adsorption on surfaces is important for blood-contacting
devices and this supports the approach of an increase in hydrophilicity
(Engbers & Feijen, 1991; Amiji & Park, 1992; Courtney et al. , 1994). In this
section, three types of surface with increased hydrophilicity are reviewed,
namely, PEO-modifi ed surfaces, non-ionic surfactant-modifi ed surfaces and
hydrogel-modifi ed surfaces.

Polyethylene oxide-modifi ed surfaces

A PEO-modifi ed surface is considered capable of simulating the natural
blood vessel surface in terms of the hydrophilic nature and high mobility.
For reducing protein adsorption onto the polymeric surface, utilisation of
PEO is effective. There are many possible factors involved in the protein-
resistant character of PEO surfaces in aqueous media. These can be sum-
marised as: minimum interfacial free energy with water (Andrade, 1973;
Coleman et al. , 1982), steric stabilisation effect (Lee et al. , 1995) and PEO's
unique solution properties, which differ from those of other hydrophilic
polymers. PEO shows complete water solubility among the related
polyethers because its segments fi t in the water structure without any
distortion of water lattices. PEO-modifi ed surfaces in aqueous media
would exhibit considerable fl exibility or mobility due to this unique water
solubility.
The high miscibility of PEO with water causes a large excluded volume
in water and thus is very effective for steric repulsion of any protein. Mean-
while, the surface mobility of the PEO chains is very effective in preventing
stagnation of the proteins on the surface, probably because the contact time
is shortened. The longer PEO chains are more effective than shorter chains
(Nagaoka et al. , 1984). The molecular design of a PEO-modifi ed surface is
schematically described in Fig. 2.1.
Methoxy-poly(ethylene glycol)methacrylate is the most commonly used
PEO macromonomer with controlled chain length. Fujimoto et al. (1993)
grafted it on to PU by a glow discharge technique to obtain a PEO-modifi ed
surface with a decreased protein adsorption to the surface. Yamada-Nosaka
et al. (1990) grafted PEO-macromonomer on to PVC with PEG as a
side chain. In vitro evaluation indicated that the PEO-modifi ed surface

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