Table 1.

Properties of crosslinking reactions of hydrogels.

Hydrogel	Principle	Cross-linking method	Reversible or not	Forming efficiency
Alginate [37]	Linking between calcium ion and alginate	Chemical cross-linking	Irreversible	High-speed
Gelatin [38]	Thermosensitive cross-linking	Physical cross-linking	Reversible	Low-speed
GelMA [39]	Thermosensitive cross-linking	Physical cross-linking	Reversible	Low-speed
GelMA [40]	Photo-crosslinking	Chemical cross-linking	Irreversible	High-speed