A team of scientists working at the Bristol Robotics Laboratory have created a prototype "robotic heart" which is capable of using human urine for fuel.

The device, fabricated with a 3D printer, is essentially a working robot in development which was printed using a rubber-like material called TangoPlus. In early tests, the device has managed to deliver a charge of up to 3.5 volts which it uses to create 33 pumping cycles and all on a scant 2 milliliters of human urine as fuel.

The goal of the project, to create EcoBots "powered by energy from waste collected from urinals at public lavatories," is as ambitious as it is novel.

In the work the team published in the trade journal Bioinspiration and Biomimetics, the team outlined their project in detail and it extended well beyond the heart project.

"The energy harvested could be used by the EcoBot to perform sensing tasks such as monitoring air quality and pollution levels, and a number of such EcoBots could form a distributed mobile sensor network within a future city environment."

Though a practical device is still a ways off (the current urine-driven robot heart produces an energy conversion efficiency of just 0.11 percent), they say the existing version of the "heart" is simply a "'proof-of-concept' prototype... and no effort has been made to investigate how it might be improved to give greater efficiency."

The heart, more accurately a pump made of "smart" materials which ape the movement of muscles, was inspired by the architecture of the human heart and built with flexible material, and the rigid parts of the body of the pump were fabricated using a 3D printer. The parts which required flexibility were cast in silicone using 3D printed molds.

The research team says, given a charging period of 12 hours, the device can provide enough energy to allow the pump to transfer 27 milliliters of fluid in total and recharge just over 2.5 hours.

Using what's known as microbial fuel cell technology, the device uses bacteria and other microorganisms stored in a battery of sorts which produces electrons as the organic materials digest and metabolize food.

The Bristol group has been pursuing other salvage materials for use as robotic fuel which include rotten fruit and vegetables, dead flies, waste water and sewage sludge.

The work at Bristol was partially funded by a $100,000 grant from the Bill & Melinda Gates Foundation.