They have shown the ability to regrow bones and illuminate when exposed to certain chemicals on the skin. Recently, researchers even built a robot out of hydrogels.
Biomaterials journal article. They are a water-swollen polymeric material that doesn’t change its distinct 3D structure. They are formed from super-absorbent, chain-like polymers and are not soluble in water. However, their porous surface allows for nutrients and cell waste to pass through.