Today’s 3-D printers can generally only build things out of one type of material—usually a plastic or, in certain expensive industrial versions of the machines, a metal. They can’t build objects with electronic, optical, or any kind of functions that require the integration of multiple materials. But recent advances in the research lab—including a 3-D printed battery and a bionic ear—suggest that this might soon change.

Last month, researchers unveiled what they say is the world’s first 3-D printed battery, made from two different electrode “inks.” Led by Jennifer Lewis, a professor of biologically inspired engineering at Harvard, the group used tiny nozzles to precisely deposit the anode and cathode inks, which contain nanoparticles of lithium titanium oxide and lithium iron phosphate, respectively.