 Hydrogels are a class of biomaterials that are chemically or physically cross-linked water-soluble polymers.They can be either degradable or non-degradable as determined by their chemistry, but degradable is more desirable whenever possible.There has been great interest in hydrogels for tissue engineering purposes, because they generally possess high biocompatibility, mechanical properties similar to soft tissue, and the ability to be injected as a liquid that gels.