TABLE 1.

A summary of cross‐linking methods of silk fibroin hydrogels

Classification	Methods	Advantages	Disadvantages	Ref
Physical cross‐linking	Temperature	Mild and easy condition No toxic agents	Slow gelation	48 , 49 , 51 , 52
	Shear forces	Simple operation No toxic agents Directional gel structures	Relatively high gelation concentration	53 , 54 , 55
	Ultrasound	Rapidity and controllability Environmental protection No toxic agents	High ultrasonic intensity	56 , 57 , 58 , 59
	Polar reagents	Rapid and easy processing	Cytotoxicity	60 , 61 , 62 , 63
	pH	Promoted gelation process	Acid condition Cytotoxicity	48
	Carbon dioxide	Directional gel structures No toxic agents	Slow gelation	65 , 66
	Electric field	Free of residual acids or chemical cross‐linkers	Long processing time Stiff gel	67 , 68
	Surfactants	Accelerated gelation	Release of surfactants	70 , 71
Chemical cross‐linking	Enzymatic cross‐linking	Moderate reaction Biocompatibility Elastic gel structures	Time‐consuming	72 , 73 , 74 , 75
	Chemical agents	Rapid gelation	Cytotoxicity (some agents)	76 , 77 , 78 , 79 , 80 , 81 , 82
	Photo cross‐linking	Efficient, rapid and, mild process	Cytotoxicity	83 , 84 , 85 , 86
	Irradiation	Satisfactory rapidity	High energy consumption	91 , 92