Table 1.

Differences in mechanical properties of hydrogels prepared by different cross-linking methods.

Cross-Linking Method	Hydrogel Name	First Network	Second Network	Tensile Strength	Ref.
Physical cross-linking	Agar/Hydrophobic associated polyacrylamide hydrogels	Agar hydrogel network	Hydrophobically associated polyacrylamide gel network	0.267 MPa	[15]
	Gelatin/Polyacrylic acid/Tannic acid/Aluminum chloride hydrogels	Gelatin, polyacrylic acid, tannic acid hydrogen bonding network	Al3+ ligand bonding network with polyacrylic acid	216 KPa	[16]
	Chitosan/Polyacrylic acid/Ag+ hydrogels	Chitosan/Ag+ cross-linking network	Polyacrylic acid network	24 MPa	[17]
Chemical cross-linking	Poly(2-acrylamido-2-methylpropanesulfonic acid)/Poly (N-isopropyl acrylamide-co-polyacrylamide) hydrogels	Poly(2-acrylamido-2-methylpropane sulfonic acid) network	poly(N-isopropyl-acrylamide-co-acrylamide) network	25 MPa	[18]
Physical-chemical cross-linking	Polyacrylamide/Gelatin hydrogels	Gelatin network	Polyacrylamide network	0.57 MPa	[19]
	Xylan/PVA/Borax hydrogels	PVA chain with Xylan first physical network, PVA crystal domain second physical network	PVA chain and borax chemical network	81 KPa	[20]
Radiation Crosslinking	N-Acryloyl glycinamide/PVA-borax hydrogels	PVA/Dynamic boronic acid lipid bond	poly(N-acryloyl glycinamide)/PVA network	200 KPa	[21]