Alginic acid
Alginic acid is consist of β-D-mannuronic acid and α-L-glucuronic acid residues joined by 1,4-glycosidic linkages it is ia linear block copolymer polysaccharide. The proportion of each block and the arrangement of blocks along the molecule differ depending on the algal source. Dilute aqueous solutions of alginates form firm gels on addition of diand trivalent metal ions by a cooperative process involving consecutive glucuronic residues in the α-Lglucuronic acid blocks of the alginate chain163. Alginic acid can be selected as a vehicle for ophthalmic formulations, since it exhibit favorable biological properties such as biodegradability and nontoxicity. A prolonged pre-corneal residence of formulations containing alginic acid was…show more content… And chemically, it is polysaccharide composed of a chain of (1-4)- -D-glucan having (1-6)- -D xylose units as branches which have partial (1-2)- -D-galactoxylose substitution. Xyloglucan, itself, does not undergo gel formation but dilute solutions partly degraded by galactosidase exhibit gelling properties on heating (temperature dependent gelformation). Besides the use in oral drug delivery, it is also being used for ocular and rectal drug delivery. Xyloglucan has shown a very little gelation time of up to few minutes. Xyloglucan is a polysaccharide derived from tamarind seeds and is composed of a (1-4)-β-D-glucan backbone chain, which has (1-6)-α-D xylose branches that are partially substituted by (1-2)-β-D-galactoxylose. Xyloglucan is composed of octasaccharide, heptasaccharide and nona-saccharide oligamers, which differ in the amount of galactose side chains. Although xyloglucan itself does not gel, dilute solutions of xyloglucan which has been partially degraded by galactosidase exhibit a thermally reversible sol–gel transition on…show more content… pH