A graphene-containing sponge, developed by scientists in South Korea, could pave the way towards artificial skin that can detect pressure and vibrations.

The graphene-infused polyurethane sponge could act as a tactile sensor in artificial skin

In the pursuit for new robotic materials, investigations have focused on flexible force sensors that simulate skin. The intricacies of human skin mean that any potential sensor for this application must detect a vast range of pressures and vibrations with the utmost precision.

Replicating the performance of the mechanoreceptors responsible for sensing vibrations has proved challenging, particularly when incorporating technology into softer, flexible materials. ‘Until now, an accelerometer has been introduced as a sensor element to detect vibrations,’ explains Wanjun Park from Hanyang University, one of the researchers involved in this study. ‘Unfortunately, extending this approach to artificial skin is limited because of the rigid nature of accelerometers.’

To solve this problem, Park’s team synthesised an elastic polyurethane sponge embedded with fine flakes of piezoresistive graphene, using a simple dip coating method. Adjusting the number of dipping steps, or the concentration of the graphene dispersion, modified the conductivity of the sponge.

Filling pores in a polyurethane sponge (left) with graphene flakes (right) creates a piezoresistive network

The sensor responds to miniscule forces that deform the sponge and the network of graphene flakes within it. Altering the connectivity between these flakes gives a resistance change, which the team could measure. Ridges and grooves on the sponge, designed to mimic a human fingerprint, can then pick up vibrations when moved across a rough surface.

‘The key point here is the simplicity of the [manufacturing] process – they’re using a sponge, basically,’ comments graphene technology expert Felice Torrisi, from the University of Cambridge, UK. ‘It isn’t completely new technology, although it’s very easy, so ideally, if this were to go into mass production, every company could make it.’