Dextran is a biocompatible and nontoxic polysaccharide which is widely used in pharmaceutical and biomedical applications. Even at concentrations above 20 wt%, dextran forms low-viscosity solutions in water. Chemical modifications can introduce aldehydes, (meth)acrylate, thiol, phenol, maleimide, and vinyl sulfone groups in dextran. Dextran suffers disadvantages of high cost and nonavailability. Applications of dextran include sustained protein and drug delivery, in tissue-engineered scaffolds, as an antithrombolytic agent, and as a bioadhesive. Dextran-based injectable hydrogels are also developed as a site-specific, trackable, chemotherapeutic devices.
Dextrans have nonfouling properties (i.e., protein rejection, high enzyme degradability) and are also biocompatible, making them ideal for use as ECM hydrogels in tissue engineering applications (Yahia et al., 2015). Dextran-based hydrogels can be fabricated by both physical and chemical crosslinking. Synthesis of glycidyl methacrylate (or acrylate) dextran derivative hydrogels has been reported using free radical polymerization (van Dijk-Wolthuis et al., 1995; Chiu et al., 2001). van Dijk-Wolthuis et al. (1995) reported the preparation of glycidyl methacrylate derivatized dextran with ammonium peroxydisulfate and N,N,N′,N′-tetramethylethylenediamine as initiators followed by radical polymerization. Also, dextran hydrogels prepared by crosslinking with 1,6-hexamethylenediisocyanate have been extensively reported (Hennink and Van Nostrum, 2012).
Physically crosslinked dextran hydrogels are made by electrostatic interactions. Dextran hydrogel microspheres have been developed that have both positive and negative charges, generated using dimethylaminoethyl methacrylate and MAA, respectively (Schillemans et al., 2011). The viscosity of the physically crosslinked dextran hydrogels can be reduced by applying sufficient shear, thus making them into injectable solutions. Upon removal of shear after injection, the hydrogel is formed again (Hennink and Van Nostrum, 2012). PEGylation of dextran (Moriyama et al., 1999) and photo-polymerization are other methods to fabricate dextran hydrogel. Kim et al. (1999) developed dextran hydrogel by first employing bromoacetylation of dextran followed by reacting it with sodium acrylate. The acrylated dextran is then photo-crosslinked using a long-wave UV lamp.
Co-polymerization of dextran with other polymers has also been studied extensively and is found to enhance the properties of the hydrogel. Liu et al. (2008) developed a co-polymer of methacrylate-aldehyde-bifunctionalized dextran (Dex-MA-AD) and gelatin. Methacrylate groups on Dex-MA-AD and the aldehyde groups were crosslinked by UV radiation, which facilitated the insertion of gelatin into matrix, which enhanced the enzymatic degradation. This co-polymerization also increased the cell adhesion properties of the hydrogels—in particular, it was found to support the adhesion of vascular endothelial cells.