A hydrogel is a class of polymer that can absorb large amounts of water without dissolving. This is due to the physical and chemical cross-hydrophyllic linkages that contain 99% water and are highly flexible, hence they can store such large quantities of water. These hydrogels mimic many of the properties of natural tissue in humans and because of this, they are highly biocompatible, or can basically be used to even replace human tissue with a bit of tweaking. These can also be modified to be made porous or dense. These properties of hydrogels allow it to be a very good material for contact lenses to be made from, as they are flexible and can adapt to the shape of the eye for maximum comfort and are biodegradable.