Natural materials like skin are incredibly dynamic and can maintain control in a wide range of environments through self-regulation. By contrast, synthetic materials cannot easily replicate homeostasis. Even the "smartest" materialslike eyeglasses that darken in sunlight, or a piezoelectric sensor that converts the vibrations of an acoustic guitar into a digital audio signaltypically only react to one specific environmental stimulus and do not self-regulate.
"By building dynamic feedback loops into SMARTS from the bottom up, we were able to integrate the desired regulatory features into the material itself," says co-lead author Ximin He, a postdoctoral fellow in the Aizenberg lab. "Whether it is the pH level, temperature, wetness, pressure, or something else, SMARTS can be designed to directly sense and modulate the desired stimulus using no external power or complex machinery, giving us a conceptually new robust platform that is customizable, reversible, and remarkably precise."
To demonstrate SMARTS, He, Aizenberg, and the team chose temperature as the stimulus and embedded an array of tiny nanofibers, akin to little hairs, in a layer of hydrogel. The hydrogel, similar to a muscle, can either swell or contract in response to changes in the temperature. (See movie.)
When the temperature drops, the gel swells, and the hairs stand upright and make contact with the 'nutrient' layer; when it warms up, the gel contracts, and the hairs lie down. The key aspect is that molecular catalysts placed on the tips of the nanofibers can trigger heat-generating chemical reactions in the 'nutrient' layer.
"The bilayer system effectively creates a self-regulated on-and-off switch controlled by the motion of the hairs, turning the reaction on and generating heat when it is cold. Once the temperature has achieved a pre-determined level, the hyd
|Contact: Michael Patrick Rutter|