Microspheres based on a poly(hydroxybutyrate-hydroxyvalerate) copolymer (PHBV) (Mw = 630kD, 21% mol HV) were loaded with diazepam using different emulsion-solvent evaporation processes. Gelatin was used as a strategy to alter the release profile of the incorporated drug. The mean diameter of microspheres was from 30-40 micron. Drug-release from the microspheres over a 30-day period showed a characteristic triphasic release pattern with an initial burst effect, but was linear over the same period and without a burst effect when gelatin was used as a coating agent. Scanning electron microscopy revealed that the microspheres had different structures depending upon their method of preparation.
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Chen et al. (2002) studied this question.