Table 1. Comparison of SF hydrogels.

Ref.	Method	Shortest gelation time	Modulus (kPa)	Main conformation	SF concentration
16	Storing SF solution at 4 °C	~3 days	—	β-sheet	2 wt.%
16	Addition of glycerol in SF solution	~2 days	—	β-sheet	2 wt.%
44	Addition of citric acid in SF solution and storing at 50 °C	Overnight	—	β-sheet	2 wt.%
15	Increasing SF concentration or temperature, decreasing pH, addition of ions, or polyethylene glycol	＜1 day	~200–6000 (C)	β-sheet	4–20 wt.%
17	Freezing the SF solution with organic solvents at −20 °C	> 6 hours	~3–50 (C)	β-sheet	6 wt.%
37 a	Sonication treatment on SF solution	>0.5 hour	369–1712 (C)	β-sheet	4–12 wt.%
45	Vortex treatment on SF solution	~35 minutes	0.1–70 (S)	β-sheet	1.3–5.2 wt.%
27	Electrical (direct current) treatment on SF solution	~3 minutes	~1 (S)	Amorphous	8.4 wt.%
46	Addition of ethylene glycol diglycidyl ether in SF solution at 50 °C	Within 2 hours	0.01–100 (S)	β-sheet	4.2 wt.%
47	Addition of sodium dodecyl sulfate in SF solution	~15 minutes	—	β-sheet	4% (wt/vol)
48	Addition of methylcellulose in SF solution at 50 °C	~40 hours	—	β-sheet	2 wt.%
49	Freezing the SF solution, and then immersion them in ethanol	Overnight	—	β-sheet	5 wt.%
39 b	HRP mediated crosslinking of SF solution	1 hour	0.2–10 (S)	Random coil	1–6 wt.%

Ref.: reference; (C): compressive modulus; (S): storage modulus tested in rheometer.

^aAqueous SF solution was mixed with cells (final concentration: 0.5 million/mL). The mixture would gel in 0.5–2 hours. The compression modulus was tested without cells.

^bThe hydrogels was allowed to cure for 1 hour at 37 °C for cell seeding, while the shortest gelling time was not mentioned.