Blood interface biomaterials - Biomaterials and Devices for the Circulatory System - page 23

structures of the surfaces, the blood condition and the manner in which the
interaction occurs. In this chapter, the blood response to the biomaterial is
reviewed, together with hypotheses on designing an ideal blood-compatible
biomaterial. These hypotheses are used to assess different approaches
for the modifi cation of biomaterial surfaces to achieve improved blood
compatibility.

2.2 Factors infl uencing blood compatibility

The selection of biomaterials for use in medical devices and artifi cial
organs involves consideration of both surface and bulk property require-
ments. The bulk properties, mainly mechanical properties, such as
strength, toughness, fatigue resistance and stability, often infl uence the
durability of biomaterials for long-term applications. In addition, the bulk
properties have a strong infl uence on the surface properties. For instance,
the migration and leaching of surface-active additives from the bulk
phase or reorientation of bulk molecules will dramatically change the
surface properties.
Obviously, the surface plays a very important role in determining its
blood compatibility, since, as a blood-contacting biomaterial, only the
surface contacts blood. The blood-foreign surface interaction determines
the blood compatibility, which is strongly correlated to the surface charac-
teristics. It is well recognised that understanding the nature of the surface
of a biomaterial is essential both for understanding the interaction between
materials and blood and for fabricating biomedical and medical devices
(Ratner et al. , 1992).
The rationales for developing a new biomaterial can be grouped as
polymer synthesis, polymer formulation and polymer surface modifi cation
(Courtney et al. , 1999). During the last 50 years, many polymeric bioma-
terials have been investigated for biomedical applications because of their
favourable mechanical and processing properties, such as polyurethane,
silicone rubber, ethylene vinyl acetate (EVA), poly(vinyl chloride) (PVC),
polycarbonate, polyester, polyacrylonitrile, cellulose acetate, hydrogels
and biodegradable polymers. Owing to the diffi culties of fi nding a novel
synthetic polymeric biomaterial, many researchers have been focusing
on maintaining the bulk properties of those conventional materials,
while modifying the surface of the polymer and/or the blood-polymer
interface.
This section will present an overview of the hypotheses, which have been
applied to correlate the surface properties with blood compatibility. Based
on these hypotheses, numerous blood-compatible surfaces have been
designed. As an example, the infl uence on blood of plasticised PVC as a
blood-contacting biomaterial is discussed in detail.

￿ ￿ ￿ ￿ ￿