Biomedical device for health monitoring is powered by sweat

Materials World magazine
3 Jun 2020

An electronic skin powered by sweat offers a new mode for tracking health at molecular levels. Idha Valeur reports. 

Instead of relying on solar power, batteries or human movement, continuous wireless sensing of your health may be possible through sweat alone. The self-powered electronic skin, or e-skin, developed at the California Institute of Technology (Caltech), USA, can now track health at molecular levels, researchers say. 

The e-skin is made from an ultra-soft polyimide (PI) substrate and metallic electrodes that are patterned onto the substrate through thin film evaporation. 

Wei Gao, Assistant Professor at the Andrew and Peggy Cherng Department of Medical Engineering at Caltech, says, ‘Our biofuel cell consists of two electrodes – a bioanode, immobilised with an enzyme lactate oxidase that can catalyse the oxidation of lactic acid, and a cathode, immobilised with metallic catalysts. The biofuel cells can efficiently convert the lactic acid in human sweat to electricity.’

This means the biosensors can analyse metabolic biomarkers such as glucose, urea and pH, and this information is then sent wirelessly to a 
user interface. 

Gao adds, ‘The soft e-skin complies with the skin’s modulus of elasticity and conformally laminates on different body parts for accurate sensing. We further modified our biofuel cell electrodes with various carbon nanomaterials, such as carbon nanotubes and graphene, to increase their power output and stability.’ 

By using human sweat, the e-skin overcomes a common problem that other wearable health trackers face – the issue of power. Widely available trackers rely on either batteries, solar power or human movement to be powered. Another benefit, according to Gao, is how the new e-skin can track more than just vital signs and activity levels because of its ability to monitor health at molecular levels.

‘The development of a fully self-powered e-skin opens the door to numerous robotic and wearable healthcare possibilities. Wearable sensor arrays could be used for health monitoring, early disease diagnosis and potentially nutritional intervention. In addition, self-powered e-skin could be used to design and optimise next-generation prosthetics,’ Gao says. 

Currently, the team is testing the system in further human studies to ‘investigate the use of sweat biomarkers for non-invasive metabolic and nutritional management’. Gao adds that improvements to stability and packaging are necessary for commercialisation. ‘Most importantly, we will need to work closely with clinical experts to validate the system towards major medical applications,’ he concludes.