ZERO-ORDER RELEASE FROM BIPHASIC POLYMER HYDROGELS

This is the first controlled release study performed using a new material, namely, biphasic polymer hydrogels. The uptake and release of tryptophan and theophylline were investigated. Dried gels were reswollen to constant volume in an excess of saturated aqueous drug solution. They were found to contain 70 +/- 6% (N = 3) or 50 +/-: 10% (N = 3) more drug than the equivalent volumes of saturated water solutions for tryptophan and theophylline, respectively. The release of drug from the gels was investigated in both batch mode, in which the gel was immersed in a single water bath and the efflux of drug was monitored with time, and semi-batch made, in which the water bath was changed hourly. In both modes, drug exited with zero- or near zero-order kinetics until approximately 67-88% of the excess drug in the gel was released. Thereafter a time-dependent release rate was observed. Mathematical models of different mechanisms of release from two-phase networks were developed to explain the observed profiles.