Crocodile-inspired e-skin could improve prosthetics

The development of flexible electronic skin could greatly help innovation in the fields of rehabilitation, healthcare, prosthetic limbs and robotics.

The team at Pohang University of Science and Technology (Postech) and the University of Ulsan in South Korea, was inspired by the qualities of crocodile skin to develop a new type of stretchable pressure sensors, which can detect various types of touch and pressure.

Crocodiles possess a remarkable ability to sense small waves and detect the direction of their prey.

This ability is made possible by an incredibly sophisticated and sensitive sensory organ located on their skin. The organ is composed of hemispheric sensory bumps that are arranged in a repeated pattern with wrinkled hinges between them.

When the crocodile moves its body, the hinges deform while the sensory part remains unaffected by mechanical deformations, enabling the crocodile to maintain an exceptional level of sensitivity to external stimuli while swimming or hunting underwater.

Inspired by these characteristics, the research team used pressure sensors with microdomes and wrinkled surfaces, to develop an omnidirectionally stretchable pressure sensor.

This crocodile-inspired sensor has outperformed currently available pressure sensors. Rather than losing sensitivity when subjected to mechanical deformations, this new sensor maintains its sensitivity even when stretched in one or two different directions.

In order to achieve this, the sensor uses a hemispheric elastomeric polymer with delicate wrinkles containing either long or short nanowires.  

When an external mechanical force is applied, the wrinkled structure unfolds, reducing stress on the hemispheric sensing area that is responsible for detecting applied pressure. This stress reduction enables the sensor to preserve its pressure sensitivity even under deformations.

As a result, the new sensor exhibits exceptional sensitivity to pressure, even when stretched up to 100 per cent in one direction and 50 per cent in two different directions.

To evaluate its performance, the researchers mounted the sensor onto a plastic crocodile and submerged it in water. Interestingly, the mounted sensor was able to detect small water waves, successfully replicating the sensing capabilities of a crocodile’s sensory organ.

“This is a wearable pressure sensor that effectively detects pressure even when under tensile strain,” explained Professor Kilwon Cho, who led the team. He added, “It could be used for diverse applications such as pressure sensors of prosthetics, electronic skin of soft robotics, VR, AR, and human-machine interfaces.”

The team's findings have been published in the journal Small.