Table 3.

Dynamic cross-linked hydrogel systems for potential and recent hydrogel-based extrusion bioinks

	Crosslinking mechanism		Hydrogels	Testing status			Ref.
				Shear- thinning	Injectabilitya	Printabilityb
Physical interaction	Hydrogen bonding	Phenolic compound-based interaction	Gallol-containing hydrogels	○	○ (26 or 25 G)	○	136,138
			Catechol-functionalized ABA triblock copolymer hydrogels	○	○ (23 G× 3/4”)	✖	140
		Ureidopyrimidinone self-complementary dimerization	UPy-containing thermosensitive ABA triblock copolymer hydrogels	○	○ (20 G)	✖	453
	Host-guest interaction	Cyclodextrin-mediated supramolecular interaction	poly-β-cyclodextrin (Pβ-CD)/ poly(3,4-ethylenedioxythiophene)(PEDOT):adamantyl-modified sulfated alginate (S-Alg-Ad) hydrogels	○	○ (27 G)	✖	157
		Cucurbit[n]uril-Mediated supramolecular interaction	highly branched CB[n]-threaded polyrotaxane (HBP-CB[n])/naphthyl-functionalized hydroxyethyl cellulose (HECNp) hydrogels	○	✖	✖	178
	Metal-ligand coordination	Bisphosphonates	bisphosphonate-modified hyaluronic acid/metal ion hydrogels	○	○ (21 G)	O	141,190,199
		Carboxylates	folate/Zn2+ hydrogels	○	○	✖	207
			Fe3+-carboxylate in UPy-functionalized gelatin hydrogels	○	✖	✖	147
		Catechols	DOPA-conjugated chitosan/Fe3+ ion hydrogels	✖	○	✖	227
		Histidine	histidine-bearing acrylamide/acrylate copolymer hydrogels crosslinked with Zn2+ ions	✖	✖	✖	242
Dynamic covalent bond	Imine bond		Chitosan/dibenzaldehyde-functionalized PEG hydrogels	○	○ (22 G, 26 G, or 32 G)	✖	271,273,274
	Hydrazone bond		hydrazine-modified elastin-like protein/ aldehyde-modified hyaluronic acid hydrogels	○	○ (28 G)	✖	282
			hydrazide-modified hyaluronic acid/benzaldehyde terminated F127 triblock copolymers hydrogels	○	○	✖	285
	Oxime bond		poly(n-hydroxyethyl acrylamide-co-methyl vinyl ketone) hydrogels crosslinked with a bifunctional hydroxylamine.	○	○ (0.6 mm)	○ (400 μm, 3.0 bar, and 12 mm/s)	294
	Disulfide bond		thiol functionalized F127/dithiolane modified PEG hydrogels	✖	○ (23 G× 3/4”)	✖	299
	Boronic ester bond		glycopolymer chain-containing copolymer/benzoxaborole-containing copolymer hydrogels	○	○ (21 G)	✖	327,328
Nanocomposite hydrogels	Nanocarbon-based hydrogels	Carbon nanotubes	Single-walled carbon nanotube (SWCNT)/DNA supramolecular hydrogels	○	✖	✖	346
		Graphene-based nanomaterials	aminated-graphene oxide/sodium alginate/polyacrylamide/ nanocomposite hydrogel	○	✖	○ (1.2 bar and 500 mm/min)	352
			phenyl boronic acid-containing copolymer/polydopamine-coated graphene oxide hydrogels	○	○ (19 G)	✖	335
	Metal carbonate-based hydrogels	Calcium carbonates	Poly(acrylic acid)/amorphous CaCO3 hydrogels	○	✖	✖	394
		Other alkaline earth metal (except for Ca2+ ions) and transition metal carbonates	Poly(acrylic acid)/alkaline earth or transition metal carbonate hydrogels	○	✖	✖	397
	Nanoclay and silica-based hydrogels	Laponites	κ-carrageenan/laponite nanosilicate-based hydrogels	○	✖	○ (400 μm or 23 G and 20 or 0.5~8 mm/s)	330,413
			DNA/laponite nanosilicate hydrogels	○	○ (22 G)	○ (feedrate: 39 mm/s and flowrate: 10 mm/s)	15
		Silica nanoparticles	anionic alginate/gellan polymer mixture/cationic silica nanoparticle composite hydrogels	○	✖	○ (400 μm, 40-50 kPa, and 10~20 mm/s)	431
	Metal-based Hydrogels	Gold nanoparticles	poly(N-isopropylacrylamide)/gold nanoparticle composite hydrogels	○	○ (20 G)	✖	440
		Silver nanoparticles	α-CD/PEG polypseudorotaxane/siliver nanoparticle composite hydrogels	○	✖	✖	338

^aInformation for the hydrogels subjected to the injection through syringe needles. The sizes of needle gauges are presented in the parenthesis; in case the information was provided.

^bThe hydrogels were tested by 3D printing are marked with open circles. The printing parameters are presented; in case the information was provided.