The flow of engineering thought

Daniil Kuznetsov, N+1 

A group of British engineers from the University of the West of England (Bristol) has created the first wearable microbial fuel cells in the form of leg warmers. As the main resource for the production of electricity, they use human urine, and its circulation inside the device occurs due to mechanical pressure during walking. The work was published in the journal Bioinspiration and Biomimetics (Taghavi et al., Self sufficient wireless transmitter powered by foot-pumped urine operating wearable MFC).

Scientists were inspired to create a fuel cell circulation system by the device of the circulatory system of fish. Its artificial analogue consists of many plastic tubes through which urine circulates. From below (under the heel), each tube is attached to a mechanical pump. By pressing on it while walking, a person forces urine to rise up the ascending tubes to the fuel cells fixed near the knee on a special splint. Further, after passing through the fuel cell, the urine under the influence of gravity and the pressure formed in the pump flows down the descending tube – again under the heel. All tubes are equipped with special valves – opening under the pressure of urine from below (or above) and closing with reverse outflow. All together, this allows the urine to constantly circulate inside the device, allowing twelve elements (one on each ascending and descending tubes) to generate electricity.

The microbial fuel cell itself consists of three parts: an anaerobic anode chamber, an ion-selective membrane and an aerobic cathode chamber. Bacteria in the anode chamber break down urea, releasing carbon dioxide and releasing protons and electrons. Free electrons are transferred to the anode. From there, they move to the cathode via the external office. In parallel, positively charged hydrogen protons pass through the ion-selective membrane towards the cathode. In the cathode chamber, they combine with oxygen and form water. An electric current is generated.

Schematic image and photo of a newly created wearable microbial fuel cell. 

Image: Ioannis Ieropoulos et als. / Bioinspiration and Biomimetics

All 12 fuel cells could create no more than 110 microwatts of electricity at peak power, but this was enough to power a wireless transmitter that sends a text message every two minutes. 

Earlier, the same group of researchers managed to charge a mobile phone with the help of microbial fuel cells running on uranium. At the moment, scientists are aiming to create equally effective portable MTE that could become part of wearable emergency supplies (survival kits) and be used to transmit accurate coordinates, for example, tourists lost in the forest or shipwrecked people drifting in lifeboats. The use of urine generators for this kind would allow them to be used in any kind of extreme conditions, when any other source or resource for the production of electricity is simply unavailable. 

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14.12.2015