The thrombogenicity of radiation grafted polymers as measured by the vena cava ring test.

Radiation grafted hydrogels on silicone rubber with water contents ranging from 10--90% have been evaluated by the vena cava ring test. All hydrogel grafted materials were found to accumulate less thrombus than ungrafted silicone rubber, and graft level was found to have little effect on thrombus accumulation. Acrylamide grafts demonstrated superior thromboresistance by this test. Poly (2-hydroxyethyl methacrylate-ethyl methacrylate (HEMA/EMA) copolymers were examined along with pure HEMA and EMA grafts. At two weeks implantation, intermediate HEMA/EMA copolymers were found to have the least thrombus accumulation of any of the polymers in this series. EMA grafted rings were highly thrombogenic. The results from these studies indicate that the sensitivity of the vena cava ring test for detecting certain differences in polymer structure is poor. Also, the significance of the vena cava ring test for evaluating materials for use in contact with flowing human blood is questionable, based upon comparisons of results for similar materials tested in other blood compatibility evaluation systems.