Hydrogels are solid and network-structured systems consisting of crosslinked hydrophilic macromolecules, which refer to materials that absorb high amounts of water, and turn into a flexible and soft jelly consistency. In aqueous environments, they can absorb water at 20–95% of their own dry weight. Although hydrogels like water, they generally do not dissolve in water due to their crosslinked structure, but they swell and get larger in volume. They are widely used in the medical field, as scaffolds in tissue engineering applications, as carriers in drug delivery systems, as water-retaining components of wound and burn dressings, and in cosmetics. Their first application was in contact lens production. Since their structure is soft, they adapt well to natural tissues, and when used inside the body, they do not disturb the patient and do not give frictional damage to the tissues. Some hydrogels are able to adhere to tissues or mucosal surfaces.