The use of aqueous PEG dextran phase separation for the preparation of dextran microspheres

A novel procedure to prepare dextran microspheres, without the use of organ ic solvents was developed. The method is based on phase separation which oc curs in aqueous solutions of PEG and methacrylated dextran (dexMA). After s tirring this two phase system a water-in-water emulsion is formed. When dex MA forms the discontinuous phase, dextran microspheres can be obtained by p olymerization of the methacryloyl groups attached to dextran. The aim of th is study was to gain insight into the formulation parameters that affect th e particle characteristics. Therefore, it was necessary to establish dexMA/ PEG/water phase diagrams. Lower polymer molecular weights and higher degree s of MA substitution resulted in less pronounced phase separation (binodal shifts to higher concentrations). The volume weight mean microsphere diamet er varied between 2.5 and 20 mu m, depending on the viscosities of both pha ses and the PEG/dexMA volume ratio. A more viscous continuous phase and/or a less viscous discontinuous phase resulted in smaller microspheres. Furthe rmore, the particle size increased with decreasing PEG/dexMA volume ratios. The particle characteristics, like cross-link density, initial water conte nt and size can be tailored by adjusting the formulation parameters. (C) 19 99 Elsevier Science B.V. All rights reserved.