Development and Validation of Anticoagulant Peptide for Bonding Onto

Polymeric biomaterials used for applications such as coronary and vascular bypass grafting have demonstrated poor patency due to their surface thrombogenicity, initiation of chronic inflammation and unfavourable host tissue responses. The aim of this thesis has been to develop a peptide which would demonstrate an inhibitory effect on blood coagulation and/or improved endothelial cell adhesion. Employing the RGD (Arginine-Glycine-Aspartate) peptide as a base, GRGD, GRGDS and GRGD(AhxGRGD)3 were produced. In order to allow incorporation of the peptide into the polymer matrix the corresponding lauric acid (LA) conjugated peptides were synthesised. In vitro determination of blood clotting time and tissue factor activity was utilised to determine the optimum peptide concentration for an anti-thrombogenic effect. Cytotoxicity and cell adhesion were assessed on endothelial cells. The results obtained suggest that LA-GRGD offered the best anti-thrombogenic effect whilst LA-GRGDS had the most improved cell adhesive effect. These two peptides were then used to investigate the surface modification of poly(carbonate-urea)urethane (PCU). The PCU surface was modified by passive peptide coating or peptide incorporation into the polymer matrix. Cell adhesion and activity studies showed that the incorporated LA-GRGDS peptide produced a significant (P<0.05) improvement. Biocompatibility studies demonstrated no adverse effects with respect to either platelet adhesion or haemolysis. The inhibition of platelet factor 4 obtained with coated GRGD, GRGDS and incorporated LA-GRGD was comparable to that obtained with heparin coating. An in vitro flow study showed that significantly (P<0.005) more incorporated peptide (42.6%) was retained on the surface of the polymer after 8 hours flow compared to coated (20%). In conclusion the direct incorporation of an LA conjugated peptide into the matrix of the polymer was successful with the peptide retaining its activity. This process of incorporation by solvent casting is attractive from a commercial viewpoint and shows the potential for future development and use in a clinical situation to produce a surface modified PCU polymer.