Graphene turns rubber bands into stretchy body sensors

Researchers have found a way to turn rubber bands into cheap, flexible body monitoring sensors by infusing them with graphene.

A team from Surrey University and Trinity College Dublin said their method could be used to create low-cost strain sensors that work by measuring the changing flow of electricity through them as they move and stretch.

This could allow them to accurately monitor bodily movements, breathing and heart rate, either as a stand-alone device or by being worn into clothes. They could even be used to measure changes in buildings, particular where rubber is already used as a construction material, for example in some bridge cables.

‘You can easily produce similar types of devices but the advantage of this system is it’s extraordinarily easy to make,’ said Dr Alan Dalton, who led the Surrey team.

‘We’re using shop-bought rubber bands and such a small amount of graphene that the cost is in pennies, but it performs as well as any commercial sensor.’

The researchers created the sensors by infusing conventional rubber bands with molecules of graphene (the single atomic layer form of carbon), enabling them to conduct electricity. When the bands are stretched, the conductive pathways between the infused graphene molecules change, reducing the flow of electricity.

Measuring this change can be used to work out how much the band has stretched and, if the band is worn on the body, this can indicate how the user is moving in real-time.

’We can stretch it to 800 per cent of its original length and still see measurable and quantifiable changes in conductivity,’ said Dalton. ‘Because the response is so good we can do it very quickly, we can see how fast we’re straining it, so for applications such as measuring pulse or breathing it can give you a very accurate measurement.’

To create the sensors, the researchers used a process developed by Prof Jonathan Coleman from Trinity College in which a solvent dissolves a sample of graphite into single-layer molecules of graphene.

The rubber is then swollen with toluene to create pores between its polymer threads. Another solvent made from water and NMP (N-methyl-pyrrolidone) was then used to disperse the graphene molecules into the pores – thereby solving the problem that rubber molecules naturally dislike being mixed with carbon.

The researchers are now looking for a way to scale up the process in order to be able to manufacture large amounts of graphene-infused rubber.