Biopolymer-based inks and use thereof

A printable silk ink, comprising:

• an aqueous silk fibroin solution, substantially free of an organic solvent having
• a molecular weight of about 3.5 kD to about 350 kD;
• and
• a concentration of silk fibroin in a range of about 0.3 (wt/vol) % to at least about 10 (wt/vol) %;
• wherein when it is printed to a substrate, a droplet volume of about 0.1 pL to about 5 nL of the aqueous silk fibroin solution is characterized by
• a viscosity of about 1 centipoise to about 20 centipoise when viscosity is measured at room temperature;
• and
• a surface tension of about 15 dynes/cm and about 50 dynes/cm when measured at room temperature.