Sodium alginate is one of the best-known members of the hydrogel group. The hydrogel is a water-swollen, and cross-linked polymeric network produced by the simple reaction of one or more monomer . The ability of hydrogels to absorb water arises from hydrophilic functional groups attached to the polymeric backbone, while their resistance to dissolution arises from cross-links between network chains.

Sodium alginate is a naturally occurring anionic polymer typically obtained from brown seaweed, it consists of mannuronic (M) and guluronic (G) acids arranged in different combinations (fig. 1) such as blocks rich in either M or G units, or blocks of alternating G and M units . In the presence of divalent Ca²⁺ cations, the guluronic acids from nearby chains form ionic crosslinks resulting in alginate hydrogel. The ratio of M and G units defines the physicochemical properties of the hydrogel.

Alginate-based hydrogels are highly promising candidates for use as drug delivery systems  and as biomedical implants as they are structurally similar to the macromolecular-based components in the body, and can often be delivered into the body via minimally invasive administration. Alginate is an excellent candidate for delivery of protein drugs, since proteins can be incorporated into alginate-based formulations under relatively mild conditions that minimize their denaturation, and the gels can protect them from degradation until their release .