It's strange to wrap one's mind around the idea of human pee powered robots, but that's exactly what a group of UK researchers are attempting to create. Mimicking the human heart, their latest innovation is a heart pump with artificial muscles that aims to deliver human urine to their latest generation of Ecobots – a self-sustaining robot that runs on all manner of waste matter collected from its environment.

Previous generations of ecobots, created over a period of almost 12 years, consumed everything from dead flies to shells, waste water, vegetables and rotten fruits, to power themselves. The Ecobot IV, from the Bristol Robotics Laboratory, a collaboration between the University of Bristol and the University of the West of England (UWE), is the latest in the line and uses conventional motors to pump liquid feedstock to its fuel cells. This however, rendered it vulnerable to blockages and mechanical failures causing the team to look around for other types of waste matter they could tap into.

"An advantage of using urine is that it is easier to pump than a viscous fluid like, say, sewage sludge, which wouldn’t be suitable for our pump," Dr. Peter Walters, Research Fellow at UWE, tells Gizmag. "Also urine is a currently an untapped resource which is in plentiful supply – at present it is simply flushed down the drain when it could provide a source of energy."

Improving its fuel source was only one part of the problem; the researchers also needed a more efficient pump and energy management system to operate the robot. Getting artificial muscle fibers to imitate a heart's pumping action, they found, was simpler than having an electric motor-driven pump do the job.

Created using shape memory alloys, a type of smart material, the 24.5 ml volume heart pump expands and contracts just like a human heart to deliver waste matter to an array of 24 microbial fuel cells (MFCs). The MFCs act as energy converters allowing the live microbes living inside it, to break down organic matter, in this case urine, to generate electricity.

"Urine works extremely well as a fuel for the electroactive microbes inside the MFCs, since it balances the pH and improves the conductivity, as well as serve as a carbon-energy source for the microbes’ growth and maintenance," says Dr Ioannis Ieropoulos, Senior Research Fellow at UWE. "Compared to other fuels used in our work, such as, wastewater and sludge, urine is at least 3 times better."

The urine fed MFC's are capable of generating enough electricity to charge a capacitor and the stored energy is used to start one pumping cycle of the artificial heart. It takes the fuel cells 2-3 hours to recharge the capacitors running the pump. Matching the energy consumption of the heart with the energy production from the cells was one of the challenges the team had to solve. The fuel cells can currently produce around 2-3 mw of power at a voltage of 3 V continuously.

"This is sufficient to charge a mobile phone over 24 hours, and provide functionality for about 20 minutes, including making and receiving voice calls," Ieropoulos explains. "This may sound like very little for everyday life, but for an emergency in a remote location, it could prove to be extremely useful."

Aside of mobile phones the team has also been able to power conventional bench-top pumps, LEDs, digital wristwatches, electric fans and toy cars. The goal is to get the robots to operate in remote areas or ones that are undesirable for humans to go to and to be entirely self-sufficient in the process. Ecobots could re-charge themselves from urine collected from public toilets in the cities, the researchers state, or load up on wastes collected from farms in the outlying areas.

The team plans to incorporate the new pump on board the Ecobot IV and when they do, the robot will be the first to have an artificial muscle-driven pump powered by MFCs feeding on human urine. When fitted with sensors, the Ecobots could take on environmental monitoring without needing maintenance or an external battery recharge, surviving solely on waste products like urine.

"The sensing will be based on living organisms, which will naturally respond to changes in their environment," Ieropoulos tells us, "This is of course a future projection in our opinion, and there is a lot of work to be done before we get there."

Check out a video below of urine fed MFCs powering a mobile phone.