A research team from UCLA has been able to 3D print a small robot in (almost) a single print job.
piezoelectricity
3D Printed Microbots Are Powered By Vibration
3D printed microbots are now possible due to the invention of a method to power two photon polymerized prints using external vibrations.
How To 3D Print Electricity
Researchers have developed highly useful new approaches for 3D printing piezoelectric materials.