Blood interface biomaterials - Biomaterials and Devices for the Circulatory System - page 29

More recent forms of PVC include PVC plasticised with triethylhexyl
trimellitate (TEHTM) (Kambia et al. , 2001) and butyryl trihexylcitrate
(BTHC) (Kevy et al. , 1985). Both of these have been shown to leach from
plastic and into blood components to a lesser extent than DEHP (Flaminio
et al. , 1988; Seidl et al. , 1991).
The blood compatibility of PVC-P is strongly dependent on the plasti-
ciser selection. PVC-TEHTM was found to be unsuitable for red cell
storage because it had no stabilising effect on red cell membranes (Estep
et al. , 1984; Rock et al. , 1984) and reduced in vivo survival time, while PVC-
DEHP was shown to confer stability on red cell membranes, reducing
haemolysis and increasing in vivo survival (Estep et al. , 1984; Rock et al. ,
1984; AuBuchon et al. , 1988).
PVC-BTHC has been shown to have a stabilising effect on red cell mem-
branes similar to that of DEHP (Buchholz et al. , 1989) and has proved to
be an excellent platelet storage polymer for high concentrations of machine-
derived platelets (Simon et al. , 1991).
The content of plasticizer (P) in PVC-P formulation also infl uences the
blood compatibility. Bowry (1981) compared extra-soft (48% DEHP) and
standard PVC (39% DEHP) and found an enhanced platelet adhesion and
aggregation with extra-soft PVC. Protein adsorption was found to be
dependent on the DEHP concentration either at the PVC surface (Kim
et al. , 1976) or in the total formulation (Kicheva et al. , 1995).
It was also found that plasticiser surface distribution had pronounced
effects on blood compatibility (Yin et al. , 1999). Blood compatibility has
been found to be correlate with the surface plasticiser level and the higher
plasticiser level tends to have the higher fi brinogen adsorption which leads
to a less blood-compatible surface (Zhao & Courtney, 1999, 2003).

2.3.2 Surface modifi cation of poly(vinyl chloride)

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Options for altering the infl uence on blood of a polymer are polymer syn-
thesis, polymer formulation and polymer modifi cation (Courtney et al. ,
1994). Most approaches to polymer modifi cation focus on surface modifi ca-
tion. Techniques include physical, chemical, biological and pharmaceutical
modifi cation. Generally, surface modifi cation of PVC biomaterials can be
either by removal of material, addition of material or changing the material
already present at the surface.
Kim et al. (1976) reported that a methanol-extracted PVC-DEHP surface
exhibited lower platelet adhesion and aggregation compared with non-
cleansed samples. Anticoagulants such as prostaglandin have been incorpo-
rated into PVC in order to enhance the blood compatibility (Kim, 1980).
Lakshmi and Jayakrishnan (1998) grafted polyethylene glycol (PEG) onto
PVC-DEHP to obtain an increased hydrophilicity at the surface which led