Incorporation of ionic ligands accelerates drug release from LDI–glycerol polyurethanes

This study seeks to determine the effect of ionic ligands on the drug delivery characteristics of biodegradable polyurethane materials synthesized from lysine diisocyanate (LDI) and glycerol. Two naturally occurring, structurally related ionic species, choline chloride (CC) and isethionic acid (ISE), along with 3,3-dimethyl-butanol (DMB), their neutral carbon analog, were covalently incorporated into LDI-glycerol polyurethane materials. Selected organometallic and tertiary amine catalysts were used to fashion films and foams, respectively. The potent anticancer compound DB-67, a fluorescent camptothecin derivative, was also covalently linked to the polyurethane constructs. It was first determined that the sulfonate functional group on ISE does not react to a significant degree with isocyanate. The morphological characteristics of the polyurethane films and foams were assessed via scanning electron microscopy, showing significant differences related to the ionic ligands. The ionic materials displayed increased swelling in aqueous media over the neutral control materials. Differences in the distribution of DB-67 throughout the films and foams were then detected by fluorescence microscopy. The drug delivery characteristics of the materials were then evaluated in vitro, revealing accelerated release from ionic materials. The results of this study demonstrate the unique effects that incorporation of ionic ligands into LDI-glycerol polyurethanes have on the morphology and drug distribution of the materials. These differences have a significant impact on the drug delivery characteristics of the materials, and this information should prove useful in the design and synthesis of biodegradable controlled release systems.