Preparation and characterization of hydrogel. Stock solution (10% w/w) of collagen furan was prepared in deionized water and stored at 4 ºC. Hydrogels were prepared by mixing collagen furan stock solution and 8-arm PEG maleimide (10 kDa) in PBS using a syringe mixing system as described previously. The final concentration of collagen furan in the hydrogel was maintained at 2% (w/w). Four different formulations were prepared by changing the concentration of PEG maleimide in hydrogel to obtain a furan to maleimide ratio of 1:1, 1:2, 1:3, and 1:4 (r1, r2, r3, r4).