Blood interface biomaterials - Biomaterials and Devices for the Circulatory System - page 27

statements, such as that protein adsorption is indeed important in the blood
compatibility process and that any simplistic hypothesis and mechanism are
generally not very applicable.
However, Pitt et al. (1986) found that certain hydrophobic surfaces, which
possessed a high adsorption, and low desorption rates of fi brinogen, showed
better compatibility. Horbett et al. (1986) postulated that this was due to
the rapidly forming fi brin fi lm from fi brinogen and they thought this might
be another approach for designing blood compatible materials.
Ito et al. (1989) developed the previous 'concept of correspondence' into
a 'concept of complementarity', i.e. for a high blood-compatible biomate-
rial, the 'complementarity' between hydrophobic and hydrophilic regions
of the surface should be satisfi ed. In other words, ideal blood-compatible
materials should possess an amphiphilic surface.
By simulating the external surface of blood cells, which is inert in coagula-
tion assays, Hayward & Chapman (1984) proposed the development of new
biomaterials with a biomembrane-like surface composed of polymer and
phospholipids. Watanabe et al. (1989), however, hypothesised that if a
polymer surface possesses phospholipid-like structure, then a larger amount
of natural phospholipids in plasma can be adsorbed on the surface by their
self-assembling character. Thus a well-structured liposome will form on the
surface. This might be able to simulate blood cell membrane properties.
Based on this idea, Nakabayashi designed a methacrylate monomer with a
phosphorylcholine (MPC) and synthesised for the fi rst time and Ishihara et
al. (1992) developed an improved method to prepare MPC and perfected
the 'biomembrane-mimetic hypothesis'.
Okkema et al. (1991) utilised sulphonated PEO to modify polyurethane.
Based on the low platelet adhesion and other blood compatibility results,
they postulated a 'fi brinogen retention hypothesis', i.e. the sulphonic ions
of the surface could inactivate fi brinogen, making it unrecognisable by
platelets. Han et al. (1993) also proposed a similar mechanism to explain
how the blood compatibility of fi brinogen adsorbed sulphonated surfaces
could be improved. These concepts were similar to the suggestion of
Horbett, discussed previously, that the conformational change of fi brinogen
due to adsorption might be an approach for designing blood-compatible
surfaces.
So far, various basic concepts and hypotheses for the development of
blood-compatible surfaces have been described. It is not surprising to fi nd
different views and contradictory results in the literature due to the multi-
variable nature of the blood compatibility of biomaterials. It is also diffi cult
to regulate blood-foreign surface interaction by any simple hypothesis.
It is believed that many new concepts will emerge in the future for the
development of new surface-modifi ed biomaterials with improved blood
compatibility.

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