Formation of dextran hydrogels by crystallization

In this paper, a novel method is presented for the preparation of dextran h ydrogels and microspheres, based on crystallization. Although dextrans are known to be well soluble in water, precipitation was observed in concentrat ed aqueous solutions of low molecular weight dextran (dextran 6000), wherea s for solutions of dextran with higher molecular weights (dextran 40,000 an d 220,000) no precipitation was observed in the time-frame studied. The kin etics of the precipitation process were studied and showed that precipitati on was faster when more concentrated dextran solutions were used. Furthermo re, the precipitation process was accelerated by stirring and by the presen ce of salts. Depending on the precipitation time, microspheres or gels were obtained. The precipitates were insoluble in water at room temperature, bu t readily dissolved in boiling water or DMSO. IR spectroscopy and (modulate d) differential scanning calorimetry ((M)DSC) demonstrated that the precipi tates were crystalline. We hypothesize that crystallization is due to assoc iation of the chains through hydrogen bonding, induced by the large polymer /water ratio in concentrated dextran 6000 solutions. (C) 2001 Elsevier Scie nce Ltd. All rights reserved.