Ex-vivo blood compatibility of silicone-containing biomaterials

The acute blood-contacting properties of five silicone-containing elastomers and a poly(vinyl alcohol) coated silicone elastomer were assessed using a canine ex vivo shunt model. The silicone-containing elastomers studied included two thermoset amorphous silica reinforced dimethyl methylvinyl siloxane-based polymers which were extruded as Silastic^® RX-50 Medical Grade Tubing (RX-50) and Silastic^® Medical Grade Tubing H.P. (HP). They also included three experimental thermoplastic silicone-urea urethane copolymers received as X7-4074 (SP-1), X7-4037 (SP-2), and X7-4943 (SP-3). The RX-50 tubing material showed less thrombus deposition compared to the silicone-urea urethane copolymers. This suggests that the blood-contacting response of a silicone elastomer is strongly affected by the incorporation of the urea urethane segments. Among the silicone-urea urethane copolymers, the SP-3 material showed higher levels of platelet and fibrinogen deposition than the SP-1 and SP-2 materials, whereas the SP-1 and SP-2 samples had similar levels of deposition. These results indicate that the blood-contacting properties of the silicone-urea urethane copolymers were influenced more by the molecular weight of the polydimethylsiloxane than by the type of diol used in the urea urethane segments. The maximal platelet deposition on the poly vinyl alcohol-coated silicone was approximately an order of magnitude greater than those on the silicone-containing elastomers indicating that the PVA coating was more thrombogenic.