MakerBots can churn out plastic Yoda heads all day long, but even relatively simple electromechanical constructions are still far beyond the capabilities of even the most advanced 3-D printers.

It turns out the challenge isn’t so much the machines, but rather what’s put into them. Professor Jennifer Lewis is the head of the Lewis Lab at Harvard and has spent the last couple decades working on a series of smart “inks” that allow designers to create bespoke batteries and electrical contacts using entry-level 3-D printers. “