The squid’s ability to change its skin color in response to complex environmental information has fascinated scientists for decades. Now, Chinese researchers have taken inspiration from squids to create a new artificial skin that can not only withstand extreme cold but can also kill bacteria and fungi, opening the door to a range of potential uses.
Like other cephalopods, tropical fish, and chameleons, squids possess periodic photonic nanostructures, enabling them to change skin color in response to external environmental stimuli and for camouflage, communication, and courtship.
Squids have many thousands of cells called chromatophores just below the surface of their skin, connected to their nervous system. At the center of the chromatophore is an elastic sac full of pigment. Muscle contractions control the size of the chromatophores, varying the squid’s skin color and enabling them to change their patterning to match nearby rocks or coral. Reflectin proteins found in certain squid varieties refract light and are responsible for the animal’s dynamic pigmentation and iridescence.
In the past, researchers have adapted this process to create heat-retaining skin, develop devices that monitor sun exposure, and turn human cells transparent. Now, inspired by the innate abilities present in the squid's skin, researchers at the Dalian University of Technology, China, have created a new, flexible artificial skin that can withstand extreme temperatures and bacteria.
“Biological skin transforms environmental information into bioelectrical signals and transmits it to the nervous system for perceiving external strain, tactile sensation, vibration, temperature, et cetera,” Wenbin Niu, the study’s corresponding author, told Tech Xplore. “In addition to bioelectrical signals, particularly, cephalopod skin can further actively perceive the complex environment through color change.”
The researchers mimicked the arrangement of reflectin in squid skin to create the novel photonic-ionic skin they call PIskin. When PIskin is exposed to external stimuli, such as a surface, its photonic (light-manipulating) nanostructure causes a rapid color change. At the same time, ionic transport in the skin changes, enabling mechanical and temperature stimuli to be transduced into electrical signals.
“Inspired by color-changing squid skin, we have introduced photonic nanostructures into e-skin, greatly enriching its sensory capabilities,” Niu said. “In addition to providing quantitative feedback, recording, and analyzing stimulus changes through electrical signal, more complex information such as the location, shape, and distribution of stimulus can also be visually identified through its colors.”
Wanting to push the skin’s properties further, the researchers added glycerol monolaurate (GML), a compound with potent antimicrobial properties, and polyethylene glycol 200 (PEG-200), an industrial-grade surfactant, emulsifier and detergent. GML enables the PIskin to kill almost all bacteria and fungi, whereas PEG-200’s low freezing point means the skin can withstand low temperatures without freezing and is less likely to dry out.
Researchers found that the skin performed well under harsh conditions and accurately measured strain, pressure and temperature.
The creation of PIskin has opened the door to future applications in the areas of wearable medical devices, soft robotics, prosthetics, and human-computer interfaces. It’s also encouraged the researchers to look at other color-changing animals.
“There any many intriguing animal species with such color-changing capability,” Niu said. “In our next works, we will further explore the biological structure of species other than squid and develop the corresponding biomimetic skin. Ultimately, these skins could be used in wearable devices, interactive sensing, and other real-world applications.”
Source: Tech Xplore
