The fictional human-powered machines that appear in the The Matrix trilogy are still far from reality — but maybe not that far. Last month, scientists at the Bristol Robotics Laboratory in the UK announced they had successful create a prototype robotic "heart" that runs on human urine, fabricated with a 3D printer. A full working robot is still under development. For now, researchers built only the heart itself out of a rubber-like 3D printed material known as TangoPlus, and demonstrated its ability to charge up to 3.5 volts and perform 33 pumps using just 2 milliliters of "fresh" human urine. But they have ambitious ideas for a future fleet of ecologically-friendly robots, or EcoBots, "powered by energy from waste collected from urinals at public lavatories."

"powered by energy from waste collected from urinals at public lavatories."

As the scientists wrote in their paper on the demo heart, published in the December issue of the journal Bioinspiration and Biomimetics: "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." But the researchers are still a ways out from that reality. As they readily admit in their paper, their urine-powered robot heart achieved an energy conversion efficiency of only 0.11 percent, which "appears very low." However, as they also add, the heart is just a "'proof-of-concept' prototype of its kind, and as yet no effort has been made to investigate how it might be improved to give greater efficiency." The researchers also say they have some ideas on how to squeeze more energy out.

The demo heart uses microbial fuel cell technology, in which bacteria and other microorganisms are stored in a battery-like device and produce electrons as they digest and metabolize their own food. The Bristol group has been pursuing other throwaway materials as robotic fuel sources in the past, including "rotten fruit and vegetables, dead flies, waste water" and "sewage sludge." So far, they've build three other models of EcoBots powered by various waste products, and the urine-powered EcoBot IV is currently under development. The group has also been pursuing other urine powered electronics for years, even demonstrating a urine-powered cell phone last summer. Their work is funded in part by a $100,000 grant from the Bill & Melinda Gates Foundation, and it's not even the wildest project the philanthropic group is backing: see research into more pleasurable and effective male condoms.