In vitro release behavior of insulin from biodegradable hybrid hydrogel networks of polysaccharide and synthetic biodegradable polyester.

The controlled release of insulin from a series of biodegradable hybrid hydrogel network containing dextran derivative of allyl isocyanate (dex-AI) and poly (D,L) lactide diacrylate macromer (PDLLAM) over a wide range of composition ratio was investigated. Laser confocal scanning microscope was used to understand the insulin dispersion and release mechanism in the hydrogels. We found that the dispersion of insulin in the hydrogel network appeared to become less homogeneous as the PDLLAM composition in the hydrogel increased. The increase in hydrogel degradability imparted by PDLLAM incorporation shifted the hydrogel to a more open structure at a later release time, which facilitated the release rate and extent of insulin. From the result of release kinetics study (i.e., diffusion coefficient), insulin release occurred through diffusion and degradation controlled mechanisms. In addition, a comparison of the release characteristics of indomethacin, insulin and bovine serum albumin from the hydrogel network showed that the following parameters determined the release kinetics: drug molecular weight and size, hydrogel swellability and degradability, drug solubility in water and the hydrophobic interaction between drugs and the hydrogel network.