Crystallization Behavior and Drug Release from Bacterial Polyhydroxyalkanoates: Polymer

S. Akhtar, C. W. Pouton, L. J. Notarianni

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Crystalline polyhydroxyalkanoates (PHAs) such as poly-D(-)3-hydroxybutyrate (PHB) and its copolymers with poly-3-hydroxyvalerate (P(HB-HV)) are produced by a wide variety of bacteria and have uses in controlled drug delivery systems. The crystallization kinetics and morphology of P (HB-HV) polyesters both with and without the incorporation of a model drug, Methyl Red, have been investigated, as they are thought to influence drug release characteristics. The influence of copolymer composition and incorporation of Methyl Red on radial growth rates, G, of PHB and P (HB-HV) copolymer spherulites were investigated using polarized light video-microscopy. Growth curves could be obtained over a wide range of undercoolings for all the copolymers studied. At a given crystallization temperature, G decreased with increasing HV content and with increasing drug concentration in polymer spherulites. Spherulite morphology appeared to be a complex function of polymer molecular weight, copolymer composition, drug loading and crystallization temperature (T(c)). Release of Methyl Red from melt-crystallized matrices of these PHAs was a function of T(c) and copolymer composition. Drug release from isothermally crystallized copolymer films occurred progressively more rapidly with increasing HV content. This could be explained by the progressively poorer drug entrapment within copolymer matrices with increasing HV content. In PHB, Methyl Red was thought to be largely entrapped within spherulites (interlamellar regions) but for copolymers with increasing HV content, progressively greater amounts of drug were excluded at the spherulite surface and at interspherulitic boundaries.
Original languageEnglish
Pages (from-to)117-126
Number of pages10
Publication statusPublished - 1992


  • poly-d(-)-3-hydroxybutyrate poly-3-hydroxyvalerate crystallization kinetics crystalline morphology drug distribution drug delivery copolymers polymers poly(beta-hydroxybutyrate-co-beta-hydroxyvalerate) crystallinity blends melt

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