The development of electronic skin with multiple senses is essential in various fields, including rehabilitation, healthcare, prosthetics, and robotics. A key component of this technology are stretchable pressure sensors, which can detect different types of touch and pressure. Recently, a joint team of researchers from POSTECH and Ulsan University in Korea recently made a breakthrough by creating omnidirectional stretchable pressure sensors inspired by crocodile skin.
The team responsible for the research was led by Prof. Kellun Cho, Dr. Jewon Lee, and Dr. Jonghyun Sun from the Department of Chemical Engineering at POSTECH, along with a team led by Professor Seung Goo Lee from the Department of Chemistry at the University of Ulsan. They took inspiration from the unique sensory organ of crocodile skin and developed pressure sensors with microdome and wrinkled surfaces. The result is a pressure sensor that can be stretched in all directions.
Crocodiles, which are massive predators that spend most of their time submerged under water, have a remarkable ability to sense small waves and detect the direction of their prey. This ability is made possible by an incredibly developed and sensitive sensory organ located on their skin. The organ consists of hemispherical sensory protuberances arranged in a repeating pattern with wrinkled hinges between them. When a crocodile moves its body, the hinges deform while the sensory part remains unaffected by the mechanical deformations, which enables the crocodile to maintain an exceptional level of sensitivity to external stimuli while swimming or hunting underwater.
The research team succeeded in simulating the structure and function of a crocodile’s sensory organ to develop a stretchable pressure sensor. By inventing a hemispherical flexible polymer with fine wrinkles containing either long or short nanowires, they have created a device that is superior to the currently available pressure sensors. While other sensors lose sensitivity when subjected to mechanical deformations, this new sensor maintains its sensitivity even when stretched in one or two different directions.
Thanks to the fine wrinkled structure on its surface, the sensor can maintain high pressure sensitivity even when subjected to significant deformation. When an external mechanical force is applied, the wrinkled structure unfolds, reducing pressure on the hemispheric sensing region responsible for detecting applied pressure. This pressure reduction enables the sensor to maintain its pressure sensitivity even under distortions. As a result, the new sensor exhibits exceptional sensitivity to pressure, even when tensioned up to 100% in one direction and 50% in two different directions.
The research team has developed a stretchable pressure sensor that is suitable for a wide range of wearable devices with diverse applications. To evaluate its performance, the researchers attached the sensor to a plastic crocodile and immersed it in water. Interestingly, the composite sensor was able to detect small water waves, successfully replicating the sensing capabilities of the crocodile’s sensory organ.
“This is a wearable pressure sensor that effectively detects pressure even under tensile stress,” explained Professor Zhou, who led the team. He added, “It can be used in applications as diverse as pressure sensors for prostheses, electronic skin for soft robots, virtual reality, augmented reality, and human-machine interfaces.”
The study was conducted with the support of the Korea National Research Foundation of the Ministry of Science and ICT and key research institutes of the Universities Program of the Ministry of Education. The paper outlining the search results appeared on the cover small.