Hydrogels are water-based biomaterials developed specifically for human use, according to a 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.
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.