1.1.1. Alginate:
Alginates are components of the cell wall of seaweeds includingLaminaria, Macrocystis, Ascophyllum, Eclonia, Lessonia, Durvellia, Sargassum as magnesium, calcium and sodium salts of alginate. These are anionic, nontoxic, biocompatible, biodegradable, polysaccharides with controlled porosity (Gomez et al., 2009). Algin is formed by copolymerization of β-D- mannuronate and α-1-guluronate (1→4′)-linkage and gelation is affected by pH. Alginates drawn out from various sources have different lengths and varying compositions of monosaccharides. Purified alginates may be applied to form different structures like fibers, beads, hydrogels or films.
Alginate hydrogels are formed by various cross-linking associations of anionic and multivalent inorganic cationic alginates. Hydrogels have a structural resemblance to extracellular matrices of living tissues and are widely studied as a scaffold. The mechanical toughness of hydrogels helps in maintaining their structure in membranes, avoids breaking when in use, and after tissue adherence. Drug delivery through alginate hydrogels is pH sensitive and in acidic conditions, gel deters the drugs tight and in neutral conditions, carboxylic group on alginate deprotonates leading to network swelling and drug release (Silva et al., 2008). Some limitations of alginate hydrogels are low porosity, swelling, degradation, mechanical rigidity, cell attachment or detachment of bio-active molecule by physical or chemical modification. Alginate biomaterial has an application in the biomedical field (Rossi et al.,2018), tissue regeneration, wound healing (Campiglio et al., 2020), three dimensional (3D) printing (Wang et al., 2018), in vitro  modeling (Chu et al., 2018), and biosensing (Sun et al., 2020) .