Biomedical Engineering Reference
In-Depth Information
2.3
Factors infl uencing the blood compatibility of
plasticised poly(vinyl chloride)
In terms of volume, PVC resin is the most widely used polymeric biomate-
rial for single-use, pre-sterilised medical devices (Blass, 1992). Plasticised
PVC-based fi lms, sheets and tubing are used in numerous medical products.
Most of them are relevant to blood-contacting application, as
summarised:
• cannulae;
• devices for the collection of blood;
• devices for the storage and administration of blood products, e.g. tubing
and bags;
• catheters;
• haemodialysis sets;
• cardiopulmonary bypass systems;
• extension sets.
From the material point of view, the blood compatibility of plasticised
PVC is infl uenced by the PVC formulation (plasticiser selection and utili-
sation of other additives or modifi ers) and PVC surface modifi cation
(alteration of plasticiser surface distribution, plasticiser surface level and
other surface properties). PVC formulation determines the properties of
both bulk and surface while surface modifi cation only infl uences the
surface properties.
2.3.1 Plasticiser selection
PVC is a very hard and rigid substance, which is also very sensitive to heat.
It needs the addition of plasticiser to provide fl exibility and a stabiliser to
prevent degradation at high temperature. In the formulation, plasticiser
selection is critical in the medical application of PVC. Diethylhexyl phthal-
ate (DEHP) is the most commonly utilised plasticiser which comprises
30-40% of fi nal polymer weight mass (Ljunggren, 1984). Also, DEHP is the
only plasticiser mentioned in any European pharmacopoeia monograph. It
remains by far the largest tonnage plasticiser used in medical products
(Wilson, 1995). It is probably one of the most studied substances in the
world and it is estimated that over 3000 scientifi c papers on its biological
activity have appeared (Van Dooren, 1991).
Since DEHP is not covalently bound within the PVC-DEHP matrix, it
might leach from the material into the contacting physiological medium
(Rubin & Ness, 1989). The migration problem of DEHP spurred the research
and development of new generation plasticisers as alternatives to DEHP
or PVC alternatives.
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