Hydrogels are three-dimensional structures of hydrophilic polymers that do not dissolve in water, but swell in the presence of water. The tendency of these compounds to absorb water is due to the presence of hydrophilic groups such as OH, COOH, CONH and HSO in the polymers that form the hydrogel structure. The common point among all hydrogels is swelling, but these materials have unique properties depending on the type of polymer and synthetic methods used. High amounts of water in the structure of hydrogels give these materials biocompatible properties suitable for use in biological research, so that hydrogels are the first materials designed for use in the human body. Today, hydrogels are used in the field of drug delivery, tissue engineering and biosensors. Hydrogels are divided into different types, one of which is smart hydrogels, among this categories, self-healing hydrogels are a new and attractive branch today.

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