Blood interface biomaterials - Biomaterials and Devices for the Circulatory System - page 24

2.2.1 Hypothesis on the correlation of blood compatibility
with polymer surface characteristics

The hypothetical correlation of blood compatibility with surface proper-
ties can be traced back to 1863 when Lister (1863) fi rst attempted a
jugular vein bypass in sheep, using rubber and glass tubes. He found that
blood clotted more slowly in rubber than in glass. Freund (1885) found
that glassware coated with petroleum jelly, such as Vaseline, delayed the
blood clotting time. Bordet & Gengou (1903) discovered that the blood
clotting time was increased when glass was covered with paraffi n wax.
These above observations and experiments have led to the conclusion that
the nature of the polymer surface affects the clotting process. Since the
early studies, numerous hypotheses attempting to correlate polymer sur-
faces with blood compatibility have been proposed. Neubauer & Lampert
(1930) were the fi rst to outline a rule to describe the inverse relationship
between blood clotting time and surface wettability: the Lampert rule of
blood clotting time.
Sawyer and Pater (1953) pointed out that a blood-compatible surface
should be of a net negative charge and that negatively charged surfaces
tend to be non-thrombogenic. This hypothesis was supported by the fact
that heparin, a common anticoagulant, and many sulphonated carbohydrate
heparin-like substances were highly negatively charged, and both the vein
inner walls and the formed bodies of the blood, under physiological condi-
tions, are of a net negative charge. Indeed, early studies by Lovelock &
Porterfi eld (1951) on the sulphonation of polystyrene to produce sulphonic
acid groups analogous to those on heparin showed that such surfaces
increased static blood coagulation times.
Gott et al. (1963) fi rst reported that a heparinised artifi cial surface is
thromboresistant. This fi nding stimulated the development of non-throm-
bogenic polymer surfaces based on the use of antithrombotic agents.
Zisman (1964) proposed that a material with minimal critical surface
tension will be blood compatible (

￿ ￿ ￿ ￿ ￿

15 mN m -1 ) and Lyman et al.
(1965) suggested a relationship between surface free energy and blood
compatibility, i.e. the lower the surface free energy or critical surface tension,
the better the blood compatibility of the material. Baier (1972) eventually
led to the hypothesis that surfaces with a critical surface tension in the range
of 20

γ c → 0, 10 ∼

25 mN m -1 have optimal blood compatibility. Nyilas et al . (1975),
however, hypothesised that thrombogenicity increases as the polar contri-
bution to the surface free energy increases, which might cause protein
conformational change. This was the fi rst mention of the possible confor-
mational change due to surface adsorption.
With a different opinion from that of the surface energy concept, Andrade
(1973) postulated that a blood-compatible biomaterial must have minimal

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