Hydrogels are three-dimensional, hydrophilic, polymeric networks, with chemical or physical cross-links, capable of imbibing large amounts of water or biological fluids. Among the numerous macromolecules that can be used for hydrogel formation, polysaccharides are extremely advantageous compared to synthetic polymers being widely present in living organisms and often being produced by recombinant DNA techniques. Coming from renewable sources, hydrogels also have frequently economical advantages over other drug delivery systems. Hydrogels are usually non-toxic, biocompatible and show a number of peculiar physico-chemical properties that make them suitable for different applications in drug delivery systems. Chitosan hydrogels are attractive systems for drug delivery and tissue engineering that combine biodegradability, biocompatibility and the ability to form in situ gel-like implants. Chitosan from two different sources were added with several phosphate-free polyols or polyoses as gelling agents. Design of alginate–guar gum hydrogel crosslinked with glutaraldehyde was done for the controlled delivery of drugs. Alginate is a non-toxic polysaccharide. Drug leaching during hydrogel preparation and rapid dissolution of alginate at higher pH are major limitations, as it results in very low entrapment efficiency and burst release. To overcome these limitations, another natural polysaccharide, guar gum was included in the alginate matrix along with a cross linking agent to ensure maximum encapsulation efficiency and controlled drug release. The crosslinked alginate–guar gum matrix is novel and the drug loading process used in the study was mild and performed in aqueous environment. We review here a selection of the most important hydrogels that have been studied and exploited in several fields related to pharmaceutics. Particular attention has been focused on the polymers used to prepare the hydrogel network preparation.
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