2.3.2 Fabrication of the enzymatically-crosslinked silk fibroin hydrogel microfluidic chip
Hydrogels were prepared by mixing the concentrated SF solution with PBS 1x at appropriate volumes to make the final desired concentrations: 6 wt%, 12 wt% and 14 wt% eSF solutions. To promote gelation, 1 mL of SF solution was mixed with Horseradish Peroxidase (HRP) (100 µL) and hydrogen peroxide (H2O2) (65 µL) solutions at 37°C, as reported previously (19). HRP solution (0.84 mg mL−1) and H2O2 (0.36 wt%) were both prepared in PBS 1x. The mixture was then poured on the PDMS mold, degassed carefully in a vacuum chamber for air bubble removal and left to crosslink at 37ºC. The devices were easily detached from the mold due to their elasticity. Bonding to a 12% thin partially crosslinked SF hydrogel flat layer was done to seal the chip. All the steps were performed in sterile conditions.