In vitro degradation and dissolution behaviours of microspheres prepared by three low molecular weight polyesters

Three low-molecular weight polyesters, poly( L-lactic acid) (PLA), copoly( lactic acid/glycolic acid) (PLGA) and poly(delta-valerolactone) (PV), were used to prepare water-soluble sodium diclofenac-loaded microspheres by usin g the oil-in-oil (o/o) emulsircation-solvent evaporation method. Their micr omeritic and physicochemical properties, and degradation and dissolution be haviours were determined in vitro. The results indicate that high encapsula tion efficiency and better monodispersity might be achieved by the o/o emul sification-solvent evaporation method, depending on the amount of drug load ing used. The slower evaporation of organic solvent from the system during microencapsulation seemed to modify the crystallinity of drug and polyester in the microspheres, determined by powder x-ray diffractometry and differe ntial scanning calorimetry. The in vitro degradation rate of all the micros pheres in pH 7.4 phosphate buffer solution showed first-order kinetics and ranked in the order of PLGA> PLA> PV microspheres. Furthermore, the first-o rder release rate was also found in all the microspheres after an initial d rug burst and ranked in the order of PLGA> PLA> PV microspheres, too. The r elationship between degradation and dissolution behaviours of these microsp heres is discussed.