“…These hydrogels can be produced with a variety of cross-linking methods based on using chemical agents (e.g., glutaraldehyde [ 41 , 59 ], sodium trimetaphosphate [ 69 ], genipin [ 60 ], and microbial transglutaminase [ 58 ]) or physical processes, such as irradiation [ 61 , 63 ] and repeated freeze-thaw cycles [ 58 , 59 , 64 , 65 , 68 ]. Furthermore, they can be obtained in the form of thin films [ 58 , 63 , 64 , 66 , 69 ], membranes [ 67 ], and three-dimensional porous constructs [ 41 , 59 , 60 , 61 , 65 , 68 , 69 ]. Gelatin/PVA hydrogel blends can be based mainly on PVA with a small amount of gelatin [ 58 , 59 , 61 , 63 , 64 , 65 , 66 , 67 , 68 , 69 ] as well as quite the opposite, with gelatin as the major component with the addition of a small amount of PVA [ 41 , 59 , 63 ].…”