ABSTRACT
Hydrogel is a linkage of 3D chains which are insoluble in water, hydrophilic, and occasionally can be observed as colloidal gel. Hydrogels are natural or synthetic and highly absorbent cross-linked polymers that absorb considerable amounts of aqueous solutions and can contain over 99.9% of water. The network is composed of homopolymers or copolymers and is insoluble due to the presence of chemical or physical cross-links such as entanglements or crystallites. These hydrogels possess a thermodynamic compatibility with water which allows them to swell in aqueous media. Entrapment of microbial cells within hydrogel beads has the advantage of low toxicity. Environmentally sensitive hydrogels have the ability to sense changes of pH, temperature, or the concentration of metabolite and release their load as a result of such a change. Hydrogels are biocompatible, further, and can be used in biomedical fields such as drug delivery, wound healing, and tissue engineering.
