Preparation and characterization of native poly(3-hydroxybutyrate) microspheres from Ralstonia eutropha

An efficient process for the preparation of poly(3-hydroxybutyrate) (PHB) m icrospheres with a narrow size distribution was developed. PHB was produced by a fed-batch culture of Ralstonia eutropha using fructose syrup as the s ole carbon source. After autoclaving the bacteria, PHB granules, which accu mulated in the cells, were isolated by a detergent/hypochlorite treatment a nd then spray-dried to obtain the microspheres. The diameters of the PHB mi crospheres ranged from 0.6 to 1.1 mu m and the weight-average molecular wei ghts were approximately 50 000 with polydispersity indexes of 5.0. The micr ospheres had a porous internal structure with an average porosity value of 72% and efficiently blocked UV light shorter than 220 nm. When isosorbide d initrate was used as a model drug, the optimal drug loading concentration o f the microspheres for controllable retardation was 3% (w/w). Almost 80% of the loaded drug (3%, w/w) was released within 12 h with typical sustained drug release behaviors.