Controlled Release of Model Drug from Biodegradable Segmented Polyurethane Ureas: Morphological and Structural Features

Segmented polyurethane ureas (SPUUs), which are being used in implant devices, were evaluated as drug delivery matrices using theophylline as a model drug without much sacrificing the mechanical properties of films after drug doping. SPUUs were synthesized from aliphatic diisocyanate (lysine methyl ester diisocyante (LDI)), poly(caprolactone) diol with molecular weights 530, 1250 and 2000 and 1,4-butanediamine. Three series of segmented SPUUs were prepared with various soft segment lengths and were characterized by Fourier transform infrared spectroscopy, dynamic viscoelastic measurements and tensile testing. A single tanδ peak was observed in dynamic viscoelastic measurements, which revealed phase mixing of hard and soft segments. Low elongation at break was observed in case of PCL 2000 based SPUUs, may be due to partial cystallization of PCL segment. The degradation of SPUUs in alkaline solution and in vitro drug release of theophylline in pH 7.4 buffer were also investigated. The drug release behavior from these films were analyzed by the exponent relation M_t/M_∞ = ktⁿ, where k and n are constants and M_t/M_∞ is the fraction of drug released until time, t. The constant n was found to be close to 0.5 in all samples, which suggests the release of drug from these polymers can be explained by the Fickian diffusion model.