Properties and drug release behaviour of poly(3-hydroxybutyric acid) and various poly(3-hydroxybutyrate-hydroxyvalerate) copolymer microcapsules

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Abstract
Microcapsules of poly(3-hydroxybutyric acid) [PHB] and its copolymers with hydroxyvalerate [HV] were prepared by the solvent evaporation technique and loaded with a model drug, 2,7-dichlorofluorescein. Microcapsules were also prepared from the same polymers by incorporating a polyphosphate-Ca+2 complex into the membrane. The morphology of the microcapsules varied by the change in the type of polymer used, by the introduction of drug and by the incorporation of the complex. Drug release behaviour, encapsulation efficiency and loading were all found to be influenced by the polymer type. The DSC results revealed that upon incorporation of valerate as the co-monomer, the crystallinity of the polymer decreased, leading to a material with more segmental mobility. This probably was the reason why the loading and encapsulation efficiency of the homopolymer were lower than those of the copolymers. DSC also indicated that the complex became an integral part of the membrane.