Blood interface biomaterials - Biomaterials and Devices for the Circulatory System - page 33

A PEO-linked surface is usually considered to be a protein-resistant
surface. However, some PEO derivatives, such as sulphonated PEO, have
been found to show a very strong affi nity to fi brinogen and cause a confor-
mational change. A PU surface grafted with sulphonated PEO has achieved
an improved blood compatibility due to this possible inactivation of fi brino-
gen (Han et al. , 1998). Nelson et al. (1996) also investigated the high affi nity
for albumination due to PEO attachment.
Polymer blending has always been considered to have industrial rele-
vance. Surface modifi cation by this approach can be achieved on the basis
of segregation phenomenon, i.e. surface active additives prefer to accu-
mulate at surface. Wesslin et al. (1994) modifi ed a segmented PU surface
through the use of PEO-containing block copolymers as additives. They
showed that adsorption of fi brinogen is signifi cantly reduced by these
additives to levels similar to those obtained for PU surfaces grafted with
PEO. In addition, PEO has been reported to blend with other polymers,
such as PE and PVC, by melting to achieve a PEO-rich surface (Ding
et al. , 1996).
Zhao & Courtney (2009) proposed an 'anchor modifi cation' approach for
improving the blood compatibility of the polymeric surfaces. The concept
of anchor modifi cation is the formation of an inclusion complex between a
cyclodextrin and a suitable material and the incorporation of this complex
into a polymer by blending. -Cyclodextrin (BCD) was used to prepare two

inclusion complexes: BCD with PEO-PPO-PEO copolymer (CIC1) and
BCD with PPO-PEO-PPO copolymer (CIC2). The complexes were incor-
porated into medical grade DEHP-plasticised PVC compound on a two-roll
mill. PVC batches incorporating mixtures of BCD and copolymer were
prepared for comparison. PVC compound without addition served as a
control. Flat sheets were obtained by moulding. Fibrinogen adsorption was
measured and surface characterisation performed by ATR-FTIR analysis.
The conclusions are listed below.

β

￿ ￿ ￿ ￿ ￿

• With respect to fi brinogen adsorption, incorporation of CIC1 was clearly
superior to incorporation of CIC2 in terms of reduction because of
enriched PEO surface.
• CIC1 incorporation promoted movement of BCD to the surface.
• Fibrinogen adsorption on PVC modifi ed by incorporation of CIC1 was
lower than that of unmodifi ed PVC and PVC modifi ed by incorporation
of BCD alone.
• In comparison with PVC modifi ed by the incorporation of a BCD/
copolymer mixture, incorporation of CIC1 enhances consistency and
avoids the leaching of free cyclodextrin or copolymer.

• The change in surface chemistry of the PVC induced by the incorpora-

tion of CIC1 suggests that modifi cation will reduce DEHP extraction.