| Description |
Several approaches have been described to improve the blood compatibility of polymers. This dissertation examines the feasibility of covalently attaching prostaglandin Ei (PGEi) to agarose beads via a spacer arm. The overall goal of attaching this antiplatelet drug to the surface is to reduce platelet adhesion, aggregation and activation that can result in thrombus formation at the blood/polymer interface. Agarose and cross-linked agarose (CL-agarose) were characterized by investigating the dissolution of the agarose matrices and the leakage of PGEi ^rom the PGEi coupled beads. CL-agarose was found to be more suitable because of the increased stability of the matrix. The stability of the diaminoalkane spacers coupled to cyanogen bromide activated CL-Sepharose beads and to 1,1'-carbonyldiimidazole activated Reacti-Gel (CL-agarose) beads was evaluated using methyl-amine-C^. It was found that 1,1'-carbonyldiimidazole activated Reacti-Gel was superior to cyanogen bromide activated beads because of greater bond stability and low nonspecific adsorption of PGE]. PGEi was coupled to Reacti-Gel via three different length spacers, diaminoethane (C2), 1,6-diaminohexane (Cg) and 1,12-diaminododecane (C12). All three PGEi-spacer-Reacti-Gel systems showed acceptable low levels of PGEi leakage. The coupling yield was to be 1.5 umoles PGEi/ml PGEi-C2-Reacti-Gel, 1.1 umoles PGEi/ml PGEi-C6-Reacti-Gel, ana1 2.0 unoles PGEi/ml PGEi-Ci2-Reacti-Gel. PGE-j covalently coupled to Reacti-Gel via different length spacer arms (C2-, C6~ and C^-) was tested for its inhibitory effect on platelet activation. Platelet activation was determined by evaluating platelet retention on columns packed with the test beads, and by adenosine diphosphate (ADP) induced platelet aggregability of dog platelets exposed to test beads packed in the column. The various length spacer arms were evaluated to see whether there was any difference in the degree of accessibility of the immobilized PGEi to the platelets. Prostaglandin F2« (PGF2ah which is known to be pharmacologically inactive in platelet function, was also immobilized on the Reacti-Gel via C2-, C6- and Ci2-spacer arms and was used as a control. The platelet retention results showed reduction in the % platelet retention for C2- and C6~PGEi coupled beads as compared to their respective PGE-j uncoupled beads (i.e, C2- and Cs-Reacti-Gel). However, a similar reduction was obtained for PGF2(x coupled beads, indicating that the % reduction in the platelet retention was due to some factor other than the PGEi, perhaps the plasma albumin adsorbed on the immobilized prostaglandins. A comparison of the platelet aggregation curves obtained using immobilized PGEi and immobilized PGF2a showed no differences and there was no inhibitory effect of immobilized PGEi on platelet aggregation. |
