No abstract

No abstract

Surface thrombus formation on implantable biomaterials such as polyurethane is a major concern when utilizing these materials in the clinical setting. Thrombin, which is responsible for thrombus formation and smooth muscle cell activation, has been the target of numerous surface modification strategies in an effort to prevent this phenomenon from occurring. The purpose of this study was to covalently immobilize the potent, specific antithrombin agent recombinant hirudin (rHir) onto a novel polyurethane polymer synthesized with carboxylic acid groups which served as protein attachment sites. The in vitro efficacy of thrombin inhibition by this novel biomaterial surface was then evaluated. Bovine serum albumin (BSA), which was selected as the basecoat protein, was reacted with sulfo-SMCC in a 1:50 molar ratio. This BSA-SMCC complex was then covalently linked to the carboxylated polyurethane (cPU) surface via the crosslinker EDU (cPU-BSA-SMCC). This cPU-BSA-SMCC surface was then reacted with Traut's-modified 125I-rHir, a procedure which created free sulfhydryl groups on rHir (cPU-BSA-SMCC-S-125I-rHir). Using these crosslinking procedures, the cPU-BSA-SMCC-S-125I-rHir segments bound 188 +/- 40 ng/cm2 (n = 60) whereas the controls with non-specifically bound 125I-rHir (Mitrathane + EDC + BSA + 125I-rHir-SH and cPU-BSA + 125I-rHir-SH) bound 13 +/- 8 ng/cm2 and 4 +/- 8 ng/cm2, respectively. Evaluation of these cPU-BSA-SMCC-S-125I-rHir segments for 131I-thrombin inhibition using a chromogenic assay for thrombin showed that a maximum of 2.64 NIHU thrombin was inhibited in contrast to the controls which inhibited bound 0.76 and 0.70 NIHU. Controls with nonspecifically bound 125I-rHir also had 0.31 and 0.76 NIHU 131I-thrombin adherent to their respective surfaces whereas the maximum 131I-thrombin binding to the cPU-BSA-SMCC-S-rHir segments was 1.51 NIHU. Exposure to 131I-thrombin did not result in any release of covalently bound 125I-rHir from the cPU-BSA-SMCC-S-125I-rHir segments. Thus, these results demonstrate that rHir can be covalently bound to this novel polyurethane surface and still maintain potent antithrombin activity.

A major complication which occurs with implantable polyurethane biomaterials is bioincompatibility between blood and the biomaterial surface. Development of a novel biodurable polyurethane surface to which biological agents, such as growth factors or anticoagulants could be covalently bound, would be beneficial. The purpose of this study was to synthesize a novel poly(carbonate urea) urethane polymer with carboxylic acid groups which would serve as "anchor" sites for protein attachment. Physical characteristics such as tensile strength, initial modulus, ultimate elongation, tear strength, water/alcohol uptake and water vapor permeation were then evaluated and compared to other biomedical-grade polyurethanes. Covalent linkage of the blood protein albumin to this novel surface was then examined. A biodurable polycarbonate-based polyurethane containing carboxylic acid groups (cPU) was synthesized using a two step procedure incorporating the chain extender 2,2-bis(hydroxymethyl)-propionic acid (DHMPA). Tensile strength of this cPU film was 2.7 and 2.6 fold greater than both a polycarbonate-based polyurethane synthesized with a 1,4-butanediol chain extender (bdPU) and Mitrathane (Mit) controls, respectively. The cPU polymer also possessed 7.8 and 31 fold greater structural rigidity upon evaluation of initial modulus as compared to the bdPU and Mit, respectively. Ultimate elongation for the bdPU films was slightly higher than the cPU and Mit films, which had comparable elongation properties. The force required to tear the bdPU film was 1.9 and 32 fold greater than the cPU and Mit films, respectively. Alcohol solution uptake by all of the polyurethane segments increased with increasing alcohol concentrations, with the cPU having the greatest uptake. Water uptake was minimal for all the polyurethanes examined and was not affected by altering pH. Water vapor permeation was lowest for the cPU films as compared to both bdPU and Mit. Swelling the cPU in 50% ethanol prior to evaluation slightly increased water vapor permeation through the films. Covalent linkage of the radiolabelled blood protein albumin (125I-BSA) to the cPU segments incubated with the heterobifunctional crosslinker 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) was greatest in the higher percent of ethanol as compared to controls. These results serve as foundation for developing a novel poly(carbonate urea) urethane with physical characteristics comparable to other medical-grade polyurethanes while having protein binding capabilities.

No abstract