Development of poly(propylene fumarate-co-ethylene glycol): An injectable, biodegradable implant for cardiovascular applications

A novel block copolymer consisting of poly(propylene fumarate), PPF, and poly(ethylene glycol), PEG, was fabricated and evaluated for use as a cardiovascular stent to prevent reclosure of the vessel lumen following balloon angioplasty. This copolymer has been fabricated in a block configuration with two to three homopolymer units in series through a transesterification reaction between the linear polyester and the terminal hydroxyl functionalities of the PEG. This material has been characterized in terms of structure and composition as well as thermal properties and solubility behavior. We described the preparation and bulk characterization of crosslinked P(PF-co-EG) hydrogels. The extent of the crosslinking reaction and the degree of swelling in aqueous solution were determined on several different copolymer formulations. Mechanical properties were evaluated and were shown to increase with increasing PPF molecular weight and decrease with increasing PEG content. The degradation behavior was examined in vitro at pH 7.4 and in vivo in a subcutaneous rat model, in terms of mass loss, dimensional changes, mechanical properties, morphology, and biocompatibility over a twelve week time course. The P(PF-co-EG) hydrogels demonstrated a pattern typical of bulk degradation. They retained at least a 20% of their initial ultimate tensile stress after three weeks with no apparent changes in morphology. Platelet adhesion and aggregation on P(PF-co-EG) hydrogels was examined under both static and flow conditions. We demonstrated a significant decrease in platelet attachment on the copolymer hydrogel films relative to PPF. In addition, there were also reductions in attachment resulting from an increase in PEG weight percent or molecular weight. The copolymer surfaces showed no thrombus formation or platelet spreading