Think goose bumps. We’ve all experienced that tingling sensation when the air gets colder and the hairs on one’s arm stand up, creating an insulating layer. The tiny muscles at the base of those hairs contract when the air gets warmer.
This is the principle behind SMARTS, or the Self-regulating, Mechano-chemical Adaptively Reconfigured Tunable System. Engineers at Harvard and the University of Pittsburgh have spent the past two years modeling a strategy for producing thermoregulating nanomaterials whose purpose is to create products that can respond more flexibly to their environments.
Right now, there aren’t any synthetic materials that self-regulate or –monitor themselves, explains Ximin He of Harvard’s Wyss Institute of Biologically Inspired Engineering. So the research team applied the concept of homeostasis to the design of an autonomous material by adding nanofibers (i.e., the hairs) that adhere to a layer of hydrogel (i.e., the muscle). The team published its findings in the July 12 issue of Nature magazine.
When the temperature gets colder, the gel swells and the nanofibers “stand up.” The reverse occurs when the temperature warms. “We apply this design to trigger organic, inorganic, and biochemical reactions that undergo reversible, repeatable cycles synchronized with the motion of the microstructures and the driving external chemical stimulus,” the team wrote in its paper. These dynamic feedback loops, organized hierarchically, are what would allow a SMARTS-enhanced material to self-regulate, depending on different conditions.
The process, with research funded by the DOE, is “highly customizable” and theoretically could be fabricated into any kind of structure that has the capacity to expand or contract, He says. A recent article about SMARTS published by Harvard suggests that the technique could be incorporated into materials for medical implants to stabilize bodily functions. According to He, there may be many opportunities for medical applications, including hand-held diagnostics that could track pH and other factors.
The research team also sees potential for making construction materials more adaptable to regulate a building’s energy usage. He points specifically to products such as silicone and polymers that could be improved by this system. Even glass windows could be made more energy efficient with a surface layer of hydrogel and nanofibers.
He also envisions SMARTS being incorporated into heat-generating products like large computers to better control their temperatures and to reduce a building’s need for air conditioning.
Building SMARTS into synthetic materials should be “relatively easy,” says He, who anticipates that her team is probably two years away from coming up with something marketable.
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