Comparison of haemocompatibility improvement of four polymeric biomaterials by two heparinization techniques.

Two surface heparinization procedures, introduced by Bamford and Al-Lamee (Polymer 22 (1996) 4885; 13 (1994) 2844) and Seifert et al. (J. Mater. Sci.: Mater. Med. 7 (1996) 465), respectively, were applied to four commercially available biomaterials (silicone rubber, polyethylene, polypropylene and polyvinylchloride) in order to compare their efficiency in improving haemocompatibility. The indirect method (Bamford and Al-Lamee) produced a much better heparinization yield-10.5% maximum, compared to the direct one (Seifert et al.), of only 0.20% maximum. Both methods provided a better response of the heparinized biomaterials compared to the uncoated ones in terms of platelet retention and a significantly better response in terms of activation of the coagulation system, suggesting that heparin molecules remained biologically functional in both cases. The results were particularly interesting in the case of polyvinylchloride where the maximum immobilization yield was obtained by the indirect method resulting also to a pronounced haemocompatibility improvement. Scanning electron microscopy studies confirmed adhered platelet morphology whereas atomic force microscopy was used to examine surface morphology of heparinized and reference materials surface.

Influence of test protocol in determining the blood response to model polymers.

A multi-parametric, multi-center evaluation of three polymers was performed measuring their response to blood contact. The purpose of this study was to pinpoint differences in tests performed for assessing "basic" hemocompatibility on identical materials at different centers and attempt to rationalize. Assays for platelet adhesion, activation, aggregability and activation of the coagulation system in addition to an ex vivo patency assay were performed at four centers across Europe, using protocols favored by each center for determining the blood-contacting performance of a biomaterial. Three polymers were chosen for their expected blood response spanning the range of undesirable to desirable: ethylenevinylacetate (EVA), polyvinylchloride (PVC) and PVC modified with polyethylene oxide (PEO). The assays were ranked in terms of their efficacy compared to cost and simplicity. A correlation between assays was calculated, indicating the ability of one test to correctly determine the blood response compared to another. Some assays were unable to distinguish between materials, but of the assays which could, the materials were ranked in the following order: EVA; PVC; PVC-PEO, EVA producing the most undesirable response. It is concluded that many commonly used assays for determining hemocompatibility are inappropriate, but there are simple and reliable test methods available which correlate well with the more sophisticated protocols.