Coextruded PVC Tubes for Biomedical Application

The use of PVC in biomedical applications is often questioned, owing to the possible adverse effects that this material may have on human health. Blood is transported in dialysis devices through flexible plastic tubes that are usually made of PVC. The most common plasticizer, even for such biomedical applications, is dioctyl phthalate (DOP). It improves the processability of the blend, thus reducing the viscosity, and improves the characteristics of the product by increasing its flexibility at low temperatures. However, the DOP migration to the tube surface may cause thrombogenic reactions, and for this reason, the medical use of PVC implies the addition of heparin to blood as an anticoagulant and is, however, limited to short-term applications. In this work the production of coextruded PVC tubes was explored. These two-layer tubes are characterized by an internal layer, in contact with the patient blood, which has a DOP content distinctly lower than that of the external layer. This difference can reduce the amount of released plasticizer harmful to the organism. On the other hand, the inner layer reduces the overall mechanical flexibility of the tube. A complete characterization, therefore, was carried out in order to evidence the advantages and drawbacks of such products. Extraction tests were conducted to evaluate the release rate of PVC in comparison to that of traditional tubes. Thermal and rheological analyses were performed to estimate material processability. Mechanical and dynamic-mechanical testing were done to determine performance. The results showed that the biocompatibility characteristics are significantly improved, while keeping acceptable levels of mechanical properties and of additional product cost.