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.