Table 2.

Normal natural hydrogels for liver tissue engineering

Type	Origin	Constituents	Crosslinking	Fabrication	Features	References
Alginate	From cell walls of algae/seaweed	Guluronic acid and mannuronic acid	Ionic (Ca2+, Ba2+, Mg2+)	Extrusion-based bioprinting; Inkjet-based bioprinting	With shear thinning properties, abundant sources, easy to crosslink	[125–127]
Agarose	Marine seaweed	3,6-anhydro-L-galactopyranose and D-galactose	Temperature	Extrusion-based bioprinting	High propensity to gelation	[128]
Chitosan	Insects and crustacean exoskeleton	N-deacetylation of chitin and glycosaminoglycans	Ionic and covalent cross-link	Extrusion-based bioprinting	High viscosity fluids, resistant to bacteria and fungi and analgesia	[129, 130]
Hyaluronic Acid (HA)	ECM, all over the body	β1, 4D glucosamine and N-acetyl-D-glucosamine	Physical, light-controlled chem	Extrusion-based bioprinting	Hydrophilicity and biocompatibility, faster healing	[131]
Gelatin	Cow skin, pig skin, fish skin	Glycosaminoglycans	Covalent, enzymatic, temperature, physical	Extrusion-based bioprinting	It is sensitive to thermal environment, effective cell bonding	[132]
Gelatin MA	Semi-natural polymer	Gelatin and acrylates	Light (UV)	Digital light processing (DLP)-based 3D bioprinting; Extrusion-based bioprinting; Inkjet-based bioprinting	Facilitate attachment of cells with scaffold promoting adhesion and cell activity, have great mechanical properties	[133, 134]
Collagen	Nature-derived ECM, the tendon of rat tail, fish skin	Chains of polypeptide	pH, ionic cross-link, temperature, protein riboflavin	Extrusion-based bioprinting; Inkjet-based bioprinting	Enzyme catalyzed degradation, poor printability	[135, 136]
Fibrin	Distributed in plasma	Fibrous and non-globular glycoproteins	Enzymatic Crosslinking (Factors IIa, XIIIa and IV)	Extrusion-based bioprinting	Biodegradable with cell adhesion sites	[137, 138]
Decellularized extracellular matrix (dECM)	Extracellular matrix	Collagen, fibrin, gelatin	Light (UV), enzymatic	Digital light processing (DLP)-based 3D bioprinting; Extrusion-based bioprinting;	With complex natural ingredients and biomimetic structure	[139]