The 'artificial heart' used to pump urine (Credit: Centre for Fine Print Research and the Bristol Robotics Laboratory)

'Artificial heart' could supply urine-powered robots

An ‘artificial heart’ has been designed that is capable of pumping human urine into the engine room of a self-sustaining robot.

The device, modelled on the human heart, incorporates smart materials called shape memory alloys and could be used to deliver human urine to future generations of EcoBot – a robot that can function completely on its own by collecting waste and converting it into electricity.

Researchers based at the Bristol Robotics Laboratory – a joint venture between the University of the West of England and University of Bristol – have created four generations of EcoBots in the past 10 years, but conventional motor pumps currently used to deliver liquid feedstock to the EcoBot’s fuel cells are prone to mechanical failure and blockages.

The new device works in a similar way to the human heart thanks to ‘artificial muscles’ made from shape memory alloys – a group of smart materials that are able to ‘remember’ their original shape – by compressing the body of the pump and forcing the liquid out.

“The artificial heartbeat is mechanically simpler than a conventional electric motor-driven pump by virtue of the fact that it employs artificial muscle fibres to create the pumping action, rather than an electric motor, which is by comparison a more complex mechanical assembly,” said lead author of the study Peter Walters, from the Centre for Fine Print Research, University of the West of England.

In research published in the journal Bioinspiration and Biomimetics today, the team demonstrated that when heated with an electric current, the artificial muscles compressed a soft region in the centre of the heart-pump, which has an internal volume of 24.5ml.

This caused the fluid to be ejected through an outlet and pumped to a height that would be sufficient to deliver fluid to an EcoBot’s fuel cells.

The artificial muscles then cooled and returned to their original shape when the electric current was removed, causing the heart-pump to relax and prompting fluid from a reservoir to be drawn in for the next cycle.

A stack of 24 microbial fuel cells fed on urine were able to generate enough electricity to charge a capacitor and the energy stored in the capacitor was then used to start another cycle of pumping from the artificial heart.

The EcoBots designed by the researchers are powered by electricity-generating microbial fuel cells that employ live microorganisms to digest waste organic matter such as rotten fruit and vegetables, dead flies, waste water, and human urine and generate low-level power.

Researchers from the two universities have previously collaborated to charge a Samsung phone using human urine.

In the future, it is believed that EcoBots could be deployed as monitors in areas where there may be dangerous levels of pollution, or indeed dangerous predators, so that little human maintenance is needed.

Walters said: “We speculate that in the future, urine-powered EcoBots could perform environmental monitoring tasks such as measuring temperature, humidity and air quality. A number of EcoBots could also function as a mobile, distributed sensor network.

“In the city environment, they could re-charge using urine from urinals in public lavatories. In rural environments, liquid waste effluent could be collected from farms.”

The group’s future research will focus on improving the efficiency of the device, and investigating how it might be incorporated into the next generation of microbial fuel cell-powered robots.

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