A 2-PHASE MODEL FOR CONTROLLED DRUG-RELEASE FROM BIPHASIC POLYMER HYDROGELS

A comprehensive two phase model is developed to describe the sustained release of a solute or drug from a biphasic hydrogel substrate. Such a material consists of a continuous hydrophilic phase (polymer backbon e in water) and a dispersion of spherical microdomains made of the hyd rophobic side chains of the polymer organised in a micelle like fashio n. The solute or drug is assumed to be encapsulated within the dispers ed microdomains, and to diffuse from the interior to the surface of th e microdomain where it exchanges following a Langmuir isotherm. Mass t ransfer to the bulk phase occurs by desorption of the drug from the su rface through a driving force that is proportional to the difference o f surface and bulk concentration. Accordingly the drug is released to the surroundings by diffusion through the bulk. Depending on the value s of the Langmuir constant and assuming well stirred behaviour in the interior of the microdomain, the present model results in either of th e two asymptotic models developed in previous studies. The results of a parametric study show that the desired steady state flux of a specif ic drug to the surroundings may be obtained given appropriate values o f structural properties of the material. This conclusion is further su pported when using this model to simulate earlier experimental results . The polymer structural properties can be manipulated easily during t he fabrication of dispersed-phase networks, as indicated by preliminar y experiments. (C) 1998 Elsevier Science B.V.