Researchers have developed a new material that mimics the dynamic properties of skin as it tenses - and that changes colors in the process. Skin protects the body in a number of ways, including by rapidly stiffening in order to prevent injury. In some organisms, such as chameleons, skin can even change color when the animal goes from a relaxed to an excited state. However, combining these two abilities -- stiffening and color change -- into a single manmade material has remained challenging. Here, Mohammad Vatankhah-Varnosfaderani and colleagues sought to build a polymer-based material that mimics the proteins in skin that are responsible for stiffness: collagen and elastin. In skin, a scaffold of stiff collagen fibers resists deformation, while an interwoven network of elastin ensures the skin can recoil to its original form. To create a synthetic version of this, the researchers developed a type of "bottlebrush" polymer that exhibits a linear backbone with side chains. While the backbone of the polymer forms a soft matrix, the flexible linear chains become rigid when pushed together. This combination results in a rigid-while-flexible and soft-while-stiff material, the authors report. Furthermore, the changes in the distance between polymer sidechains affect how light is reflected off the material, meaning the material shifts towards a blue color when elongated and shifts towards a red color when more condense.
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Science