Effect of polymer foam morphology and density on kinetics ofin vitro controlled release of isoniazid from compressed foam matrices

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Abstract
The purpose of this study was to compare the effect of polymer foam morphology and density prior to compaction on the kinetics of isoniazid (INH) release from the final high-density extruded matrices. The feasibility of preparing low density foams of several biopolymers, including poly(L-lactide) (PLLA), poly(glycolide) (PGA), poly(DL-lactide-co-glycolide) (PLGA), poly(γ-benzyl-L-glutamate) (PBLG), and poly(propylene fumarate) (PPF), via a lyophilization technique was investigated. Low-density foams of PLGA, PBLG, and a mixture of PLGA and PPF were successfully fabricated by lyophilization of the frozen polymer solutions either in glacial acetic acid or in benzene. The morphology of these foams depends on the polymer as well as the solvent used in the fabrication process. Thus, PLGA produces a capillary structure when lyophilized from benzene solution and a leaflet structure from glacial acetic acid, but PBLG yields a leaflet structure from benzene. Matrices were prepared by impregnating these foams with aqueous solutions of INH, removing the water by a second lyophilization, and then compressing the low-density INH containing foams by compaction and high-pressure extrusion. The resulting nonporous matrices had densities of approximately 1.30 g/cm3. In vitro kinetics were in accord with the Roseman-Higuchi diffusion model and demonstrate that release rates depend on the initial foam density, while foam structure has little influence on the release kinetics. © 1997 John Wiley & Sons, Inc.