Alginic acid gelation

Alginic acid, also called algin or alginate, is an anionic polysaccharide distributed widely in the cell walls of brown algae. It binds with water to form a viscous gum. It absorbs water quickly and is capable of absorbing 200-300 times of water by its weight [142]. It is biocompatible and less toxic with relatively low cost and forms mild gelation by the addition of cations such as Na+ and Ca + [143]. 

Yotsuvanagi, T., T. Ohkubo, T. Ohhashi and K. Ikeda, Calcium-induced gelation of alginic acid and pH-sensitive reswelling of dried gels, Chem. Pharm. Bull., 35 (1987) 1555-1563. 

Organic polymer gels used for sensors include alginic acid gel, alginic acid/chitosan complex gel, acrylamide gel, and N-isopropyl acrylamide (hereinafter abbreviated as NIPAAm) gel. Basically, a sensing material is dissolved in the sol, followed by gelation to form a thin sensor film. On the other hand, in one example, a Nafion gel film that had already been formed into a film was used. 

Pectins are generally classed according to their ester content as high methoxyl pectins (>50% of the carboxyl groups esterified) or low methoxyl pectins (<50% of carboxyl groups esterified) (pectic acid, methyl ester [9049-34-1]). Low methoxyl pectins, like algins, require calcium for gelation. 

Propyleneglycol alginates do not precipitate from acidic media and their acid stability increases in proportion to the propyleneglycol content. Additionally, those esters with DS > 60% are not precipitated by Ca2 +, because the bulky propyleneglycol substituent hinders the prerequisite alignment for gelation and precipitation. These esters are more tolerant of alcohol than the unesterified alginate. 

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