PolyDL-lactide (PDLLA) and the block copolymer

polyDL-lactide-b-poly(ethylene glycol)-b-polyDL-lactide(PELA) were used as the microsphere matrix to encapsulate plasmid DNA. The PDLLA

PELA

pBR322-loaded PDLLA and pBR322-loaded PELA microspheres were prepared by solvent extraction method based on the formation of multiple w1/o/w2 emulsion. The microspheres were characterized by surface morphology

mean particle size

particle size distribution and loading efficiency. The integrity of DNA molecules after being extracted from microspheres was determined by agarose gel electrophoresis. The result suggested that plasmid DNA molecules could retain their integrity after being encapsulated by PELA. The PELA microspheres could prevent plasmid DNA from being digested by DNase. The in vitro degradation and release profiles of plasmid DNA-loaded microspheres were measured in pH = 7.4 buffer solution at 37 ℃. The in vitrodegradation profiles of the microspheres were evaluated by the deterioration in microspheres surface morphology

the molecular weight reduction of polymer

the mass loss of microspheres

the changes of pH values of degradation medium

and the changes of particle size. The in vitro release profiles of the microspheres were assessed by measurement of the amount of DNA presented in the release medium at determined intervals. The release profiles were correlation with the degradation profiles. The release of plasmid DNA from PELA microspheres showed a similar biphasic trend

that is

an initial burst release was followed by a slow

but sustained release.