Crosslinked poly(alkylene oxides) for the preparation of controlled release micromatrices

Poly(ethylene oxides) and block copolymers of ethylene oxide and propylene oxide were crosslinked by diisocyanates and multifunctional branching agents to form water-swellable, partially crystalline networks. The equilibrium weight swelling ratio of the samples was determined in water and benzyl alcohol. Solvent fractional uptake varying from about 0.2 to 19, relative to the dry material, was achieved. This wide sorption range allowed incorporation of large amounts of active agents with different solubility characteristics. Proxyphylline, theophylline and methylcatechin were incorporated into the hydrogels by soaking in benzyl alcohol solutions. The final systems were reduced to a particle size of 400–630 μm and their release behavior studied. Various preparation parameters, such as the molecular weight of the initial poly(ethylene oxide), the copolymer composition and the interlinking degree, influenced the delivery rate by means of a modified effective mesh size of the network. In addition, drug characteristics greatly affected their release, possibly due to drug-polymer interactions. Fickian drug delivery was observed from these micromatrix systems.