Effect of polymer microstructure on the docetaxel release and stability of polyurethane formulation

PurSil (R) AL20 (PUS), a copolymer of 4,4'-dicyclohexylmethane diisocyanate (HMDI), 1,4-butane diol (BD), poly-tetramethylene oxide (PTMO) and poly-dimethyl siloxane (PDMS) was investigated for stability as a vehicle for Docetaxel (DTX) delivery through oesophageal drug eluting stent (DES). On exposure to stability test conditions, it was found that DTX release rate declined at 4 and 40 degrees C. In order to divulge reasons underlying this, changes in DTX solid state as well as PUS microstructure were followed. It was found that re-crystallization of DTX in PDMS rich regions was reducing the drug release at both 4 degrees C and 40 degrees C samples. So far microstructural features have not been correlated with stability and drug release, and in this study we found that at 40 degrees C increase in microstructural domain sizes and the inter-domain distances (from 85 A to 129 A) were responsible for hindering the DTX release in addition to DTX re-crystallization.