Blood interface biomaterials - Biomaterials and Devices for the Circulatory System - page 34

• Anchor modifi cation could improve DEHP-plasticised PVC, while
maintaining acceptable processability.

Surfactant-modifi ed surface

Amphiphilic polymers and surfactants containing PEO have been used
to render surfaces hydrophilic (Lee et al. , 1989; Amiji and Park, 1992).
Among these, the commercially available surfactant poly(oxyethylene)-
poly(oxypropylene) (PEO-PPO), e.g. Pluronic, is the most widely studied
biocompatible surfactant. It has been investigated for use in biomedical
applications for reduction of the adsorption of proteins (Lee et al. , 1989)
and adhesion of cells (Amiji & Park, 1992). It has been applied as a stabi-
liser of fl uorocarbon emulsions for use in in vivo oxygen delivery during
percutaneous transluminal coronary angioplasty (PTCA) (Lowe, 1997), and
as a pharmaceutical stabiliser for formulating applications (Sweetana &
Akers, 1996).
The effect of surfactant on haemolysis of human red blood cells has been
extensively investigated. The amount of haemolysis induced by non-ionic
surfactant formulations has been shown to be relatively low and to increase
only slightly with contact time (Ai-Assadi et al. , 1989; Lowe et al. , 1995).
The effect on platelet aggregation in human whole blood of Pluronic ® F-68,
a commonly utilised PEO-PPO surfactant, has been studied. It was found
that the surfactant inhibited platelet aggregation signifi cantly.
Physical adsorption, polymer blending and physical adsorption/chemi-
cally binding can be used to achieve a PEO-PPO-PEO surfactant-modifi ed
surface.
The hydrophobic nature of PPO is responsible for the modifi cation
involving physical adsorption. The adsorption of a segment of the hydro-
phobic middle PPO block will promote the adsorption of the neighbour-
ing segments, and fi nally the whole PPO block will be attached at a
hydrophobic surface (Freij-Larsson et al. , 1996). The block copolymer
may adsorb in more regular tail-train-tail conformations (Takahashi &
Kawaguchi, 1982).
The infl uence of the Pluronic pre-adsorbed surface in suppressing protein
adsorption is related to PEO block length, when the PPO block is kept
nearly constant in length and the adsorbed layer is thin. Although increas-
ing the PEO block length increases the protein resistance of the modifi ed
surface, a surfactant with a given PEO block size appears to be more effec-
tive as a protein repellent when a less concentrated and thin surface layer
is formed (Li et al. , 1996).
The adsorption of albumin and fi brinogen at the surface pre-adsorbed
with this surfactant was signifi cantly reduced in comparison with the bare
hydrophobic surface at a 10-fold reduction rate (Freij-Larsson et al. , 1996).

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