Chemical Modifications of Alginates for Biomedical Applications-A Review

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In current pharmaceutical developments biopolymers have earned a unique position as a choice of excipient not only by affecting formulation developments but also imparting biocompatibility, degradability and stimuli responsiveness for controlled drug release in living systems. Alginate (Alg) is a versatile, flexible, bioactive, non-toxic and inexpensive biopolymers obtained from brown seaweeds and some exo-polysaccharide producing bacteria. Native Alg is susceptible to faster degradation, dimensional instability, de-polymerization at high temperature and low pH precipitation. Therefore, its chemical modifications attracted researcher in order to improve biological, chemical and physicochemical properties by tailoring its hydroxyl and carboxylic functional groups via oxidation, reductive amination, acetylation, phosphorylation, sulfation, esterification, amidation and Ugi reactions.  These modifications are carried out by blending, cross-linking and grafting to enable the use of Alg to improve cell affinity, gelation, mechanical strength, structural, functional flexibility and encapsulation for drug delivery, wound healing, tissue engineering, cancer treatments, food packaging, metal adsorption, wastewater treatment and cosmetics. The active sites in the Alg are generated by the use of initiator, cross-linker or irradiation. In this review, sources, properties and different chemical reactions used for making alginate derivatives are summarized. In the end, applications of modified Alg in medico-biological, environmental and food industry are briefly stated.