Strain-sensing polymer skin gives robots clever touch

Researchers at Saudi Arabia’s King Abdullah University of Science and Technology (KAUST) have created an artificial skin for robots that combines strain-sensing with conductivity.

(Reproduced with permission from reference 1 © 2018 Wiley-VCH)

The material, which also has potential applications in wearable electronics, could provide robots with sensory feedback to assist them with navigation and handling tasks. Its key innovation is embedding both electrical conductivity and strain-sensing into a single stretchy polymer, using meshed silver nanowires for both purposes. Up until now, researchers have used different materials for the sensing and conductive wiring components.

Each individual nanowire is conductive, but high resistance at the junctions between them limits overall conductivity through the material. Resistance increases significantly when the material is flexed and the nanowires are pulled apart such that the nanowire network acts as a strain sensor. Applying a DC voltage made the nanowire network very hot at the points of high resistance, where the nanowires meet. This localised heating acts to weld neighbouring nanowires together, forming a highly conductive firmly bonded network that the researchers claim is impervious to stretching and flexing. The work is described in the journal Advanced Electronic Materials.

Electrical welding forms strong welded joints between the mesh of nanowires (Reproduced with permission from reference 1 © 2018 Wiley-VCH)

“Electrical welding joins thousands of junctions in the network within 30 seconds,” explained Ragesh Chellattoan, a KAUST PhD student working in the lab of Gilles Lubineau, who led the research.

To demonstrate their material, the KAUST team created a stretchy skin for a toy action figure. They coated one of the figure’s legs with the artificial skin and then applied DC voltage to the limb’s left side before flexing the leg at the knee and observing the results. On the right side, the nanowire network acted as a strain sensor that could detect leg position as the figure’s knee was bent and straightened. The left side showed high conductivity regardless of leg position.

According to Chellattoan, the next step is to gain greater control over where the nanowire welds form, giving the researchers the ability to draw precise conductive patterns into the artificial skin.