It can maintain sensitivity even when stretched in all directions, and the bionic electronic skin is as flexible as crocodile skin.

Cover of the materials science academic journal "Small".
Image source: Pohang University of Science and Technology

Developing electronic skins with multiple senses is critical for many fields including rehabilitation, healthcare, prosthetics and robotics. One of the keys to this technology is a stretchable pressure sensor that detects various types of touch and pressure. Recently, a joint team from South Korea's Pohang University of Science and Technology and the University of Ulsan created an omnidirectional stretchable pressure sensor inspired by crocodile skin. The research results were published as a cover paper in a recent issue of Small magazine.

Crocodiles have extraordinary sensory abilities that allow them to detect small waves and the direction of prey, achieved through extremely complex and sensitive sensory organs in their skin. The organ consists of hemispherical sensory projections arranged in a repeating pattern with wrinkled hinges between them. When the crocodile moves its body, the hinge deforms, while the sensory part is not affected by mechanical deformation, allowing the crocodile to remain extremely sensitive to external stimuli when swimming or hunting underwater.

The research team drew inspiration from the unique sensory organs of crocodile skin to develop an omnidirectional stretchable pressure sensor with a micro-domed and wrinkled surface.

By inventing a hemispherical elastic polymer with fine wrinkles containing either long or short nanowires, the researchers created a device that outperforms current pressure sensors. Other sensors lose sensitivity when mechanically deformed, but the fine wrinkle structure on the surface of the new sensor expands when pressed, and can respond to pressure when stretched up to 100% in one direction and up to 50% in two different directions. Stay incredibly sensitive.

To evaluate its performance, the researchers mounted the sensor on a plastic alligator and submerged it in water. Interestingly, the installed sensors are also able to detect small water waves, successfully replicating the sensing capabilities of a crocodile's sensory organs. This new device is suitable for a wide range of wearable devices, such as pressure sensors for prosthetics, electronic skins for flexible robots, virtual reality, augmented reality, and human-machine interfaces.

When it comes to crocodiles, although most people have never touched them, they always subconsciously think that its skin should be quite rough. In fact, the spot-like ridges on the crocodile's skin are covered with nerve endings, which are very sensitive and can help the crocodile sense small changes in the water flow. You think your skin is just its armor, but in fact it is also its important and sensitive organ. Inspired by crocodile skin, researchers adopted a "wrinkles + ridges" structure to develop an all-around stretchable pressure sensor to simulate the capabilities of crocodile skin. It can sense subtle pressure changes from all directions and be embedded in electronic skin for wearable devices to improve the functionality of these products.