Nanomaterial Duplicates Self-Regulation of Living Organisms

First time an artificial material actively self-regulates itself to a variety of environmental stimuli

2 min read
Nanomaterial Duplicates Self-Regulation of Living Organisms

Bio-inspired nanomaterials seem to be the rage this week, at least on this blog.  Adding to the furor, researchers at Harvard University have developed a nanomaterial that can actively self-regulate depending on environmental changes. 

While living organisms have developed sophisticated systems for responding to the external environment, the Harvard team believe this to be the first instance in which artificial materials have been able to self-regulate themselves in response to external factors, such as temperature or pH.

The research, which was published in the July 12th issue of Nature, aimed initially at making the material regulate itself based on temperature. But the researchers believe in principle that the material can be made to regulate itself according to pH, pressure or some other parameter. This ability to self-regulate itself according to a variety of external factors is one of the features that distinguish it from something like photochromic eyeglasses, which can only react to a single stimulus and cannot self-regulate.

The material itself is fairly simple. Dubbed SMARTS (Self-regulated Mechano-chemical Adaptively Reconfigurable Tunable System), it consists of nanofibers that have been embedded into a hydrogel. When set up for temperature regulation, the hydrogel swells in the presence of colder temperatures causing the nanofibers to stand upright; and it contracts in warmer temperatures causing the nanofibers to lie down.

“Think about how goosebumps form on your skin,” explains lead author Joanna Aizenberg, and Professor of Materials Science at the Harvard School of Engineering and Applied Sciences (SEAS) in the university press release covering the research. “When it is cold out, tiny muscles at the base of each hair on your arm cause the hairs to stand up in an insulating layer. As your skin warms up, the muscles contract and the hairs lie back down to keep you from overheating. SMARTS works in a similar way.”

This is clearly early stage research, but the researchers have suggested applications in medical implants and buildings that could react to the outside temperatures. Added to these fairly specific applications are the broad fields of robotics, computing and healthcare.

“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,” co-lead author Ximin He noted.

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How the First Transistor Worked

Even its inventors didn’t fully understand the point-contact transistor

12 min read
A phot of an outstretched hand with several transistors in the palm of it.

A 1955 AT&T publicity photo shows [in palm, from left] a phototransistor, a junction transistor, and a point-contact transistor.

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The vacuum-tube triode wasn’t quite 20 years old when physicists began trying to create its successor, and the stakes were huge. Not only had the triode made long-distance telephony and movie sound possible, it was driving the entire enterprise of commercial radio, an industry worth more than a billion dollars in 1929. But vacuum tubes were power-hungry and fragile. If a more rugged, reliable, and efficient alternative to the triode could be found, the rewards would be immense.

The goal was a three-terminal device made out of semiconductors that would accept a low-current signal into an input terminal and use it to control the flow of a larger current flowing between two other terminals, thereby amplifying the original signal. The underlying principle of such a device would be something called the field effect—the ability of electric fields to modulate the electrical conductivity of semiconductor materials. The field effect was already well known in those days, thanks to diodes and related research on semiconductors.

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