Blood interface biomaterials - Biomaterials and Devices for the Circulatory System - page 30

to no platelet adhesion to the modifi ed surface, whereas the unmodifi ed
PVC-DEHP surface promoted extensive adhesion of platelets. Polymer
blending modifi cation of PVC-P with PEO has been shown capable of
producing a PEO-enriched surface, resulting in a protein-resistant surface
(Ding et al. , 1996). Attachment of heparin onto a PVC surface is one of the
most widely accepted techniques for improving the blood compatibility of
PVC. Heparinised PVC-DEHP and PVC-TEHTM tubing prepared accord-
ing to the Carmeda end-point attachment method have demonstrated an
improved blood compatibility (Yin, 1996; Zhao et al. , 2008).
It has been shown that surface contamination or cleanness of a bioma-
terial has a strong infl uence on the blood compatibility (Kasemo &
Lausmao, 1988). Also, Kim et al. (1976) discovered that protein adsorption
on PVC-DEHP was affected by surface methanol extraction. With the
cleansed PVC-DEHP surface, there was a reduced fi brinogen adsorption
and increased albumin adsorption compared with non-cleansed PVC-
DEHP. For correlation of blood compatibility with plasticiser surface
level, surface modifi cation of PVC has been achieved using surface metha-
nol extraction to produce a reduced surface plasticiser level (Zhao &
Courtney, 2003).
Since the interaction between blood and material takes place on the
outermost surface within only a few molecular layers, information on the
surface, such as physicochemical properties, and chemical composition, is
crucial to the interpretation of the blood response. Numerous surface char-
acterisation techniques have been developed, among which X-ray photo-
electron spectroscopy (XPS), electron spectroscopy for chemical analysis
(ESCA) and attenuated total refl ectance/Fourier transform infrared spec-
troscopy (ATR-FTIR) are the most common.
The fi rst event when a foreign surface comes into contact with blood is
protein adsorption and the protein layer adsorbed onto the surface deter-
mines the following coagulation reaction and cellular responses (Forbes &
Courtney, 1994).

￿ ￿ ￿ ￿ ￿

2.4 Molecular design of surfaces for improved
blood compatibility
The prediction that surface properties are related to blood compatibility
has long been made (Lyman, 1975). Ideally, the properties of an artifi cial
surface designed for blood-contacting application should be as similar as
possible to those of a natural blood vessel surface. This natural surface has
physical characteristics such as highly hydrated, multiphase and fl exible in
structure, functioning biologically with response, secretion and metabolism
due to the presence of endothelial cells on the inside surface (Gebelein,
1985).