Materials

"Memorizing and forgetting" gel mimics the human brain

"Memorizing and forgetting" ge...
A memorized airplane image is forgotten by the gel, after being placed in cold water
A memorized airplane image is forgotten by the gel, after being placed in cold water
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A memorized airplane image is forgotten by the gel, after being placed in cold water
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A memorized airplane image is forgotten by the gel, after being placed in cold water

Our brains not only memorize things, they also forget them. While that may seem like a limitation, it's a quality that's been copied in a new hydrogel – and it may actually have some practical applications.

Developed by scientists at Japan's Hokkaido University, the material consists largely of water, along with temperature-sensitive polymers known as polyampholytes. The latter provide the gel's supporting structure, containing the water within it.

To demonstrate its brain-like capabilities, the researchers started by placing a sheet of the hydrogel between two plastic plates, the top one of which had shapes or letters cut out of it – the gel was left open and exposed in these areas. That setup was then immersed in a cold-water bath, causing the gel to shrink and expel much of its water content, essentially making it a transparent blank slate.

Next, the rig was transferred into a hot-water bath. The exposed parts of the hydrogel responded by absorbing water and swelling, while the rest of the gel remained unaffected. When the setup was subsequently placed back in the cold-water bath, those swollen areas turned opaque and highly visible, thanks to a phenomenon called "structure frustration."

Over several hours, however, as the entire sheet of water-cooled gel shrank and released its absorbed water, the opaque image faded away and disappeared. That said, the longer that the gel had spent in the hot water – or the hotter that the water had been – the longer the image took to vanish in the cold water. This is not unlike the manner in which our brains work, insofar as the things that we spend the longest time memorizing (or that we memorize under the most intense circumstances) are generally the ones that we remember the longest.

Additionally, it was found that if the gel was removed from the cold water right after the image became opaque, that image wasn't affected by stretching, or by fluctuations in the ambient air temperature.

"The hydrogel’s brain-like memory system could be explored for some applications, such as disappearing messages for security," says Asst. Prof. Kunpeng Cui, who led the study along with Prof. Jian Ping Gong.

A paper on the research was recently published in the journal PNAS. In the time-lapse video below, you can see the word "gel" sequentially disappearing one letter at a time, due to the fact that each letter cut-out had been exposed to the hot water for an increasingly longer time period.

Source: Hokkaido University

"GEL" hydrogel sequential disappearance

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