Blood interface biomaterials - Biomaterials and Devices for the Circulatory System - page 26

Since the early 1980s, it has been realised that a surface with a microphase
structure might be benefi cial for the preferential adsorption of albumin.
Okano et al. (1981) fi rst explained that within the microphase system, the
high affi nity for serum albumin is due to the hydrophilic phase, while the
hydrophobic phase refers to fi brinogen and -globulin.

In addition, Barenberg et al. (1981) proposed that the surface mobility of
the hydrophilic segment could be correlated with blood compatibility. In
contrast, Yeh et al. (1988) hypothesised that a stable surface confi guration
is required for good blood compatibility, which is supported by the observa-
tions that those polymers which are rather well behaved towards to blood
are constituted by rotationally symmetric macromolecules, and thus their
confi guration is stable even if their polymer chains are mobile. This hypoth-
esis was also supported by the observation of a substantial reduction in
thrombus accumulation when side-chain motions at the polymer-blood
surface were restricted by irradiation.
Ikada (1984) proposed that a polymer surface that does not adsorb any
plasma protein must be a blood-compatible surface, and this could be
achieved by introducing a super-hydrophilic diffuse surface. The claim was
that this type of surface appears to be more promising for long-term blood
compatibility.
Ruckenstein & Gourisankar (1984) believed that a compromise between
adhesive and non-adhesive properties of the surface is required for blood
compatibility, and that while the driving force for the adsorption of blood
components should be minimised, a certain degree of mechanical stability
of the interface is also required. They postulated that an interfacial tension
of 1

γ

3 mN m -1 will satisfy blood compatibility.
Based on the well-accepted concept that the conformational change of
adsorbed protein will alter the subsequent blood response of material
surface, Lin and coworkers (Lin et al. , 1984; Lin, 1985) proposed a hypoth-
esis of maintaining the protein's normal conformation for blood compatible
biomaterials. This hypothesis was supported by evaluation of the blood
compatibility of a novel segmented polyurethane-siloxane copolymer and
polyimide-siloxane copolymer (Lin et al. , 1992, 1994).
With the discovery of a surface with polyethylene oxide (PEO), which
can act repelling macromolecules such as proteins from the interface by
steric exclusion and interface entropy methods, Nagaoka et al. (1984) have
studied the effect of PEO side-chain length and surface mobility on platelet
adhesion minimisation. They concluded that the longer PEO side chain
shows a better blood compatibility.
In 1987, Andrade et al. summarised that a hydrated dynamic surface
formed by grafting of longer chains of PEO onto the surface is blood com-
patible. However, when summarising the hypothesis and mechanism sug-
gested for blood compatibility, Andrade & Hlady (1986) made only general

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