Hokkaido University researchers have found a soft and wet material that can memorize, retrieve, and forget information, much like the human brain. The human brain learns things, but tends to forget them when the information is no longer important. Recreating this dynamic memory process in manmade materials has been a challenge. Hokkaido University researchers now report a hydrogel that mimics the dynamic memory function of the brain: encoding information that fades with time depending on the memory intensity.
Hydrogels are flexible materials composed of a large percentage of water—in this case about 45%—along with other chemicals that provide a scaffold-like structure to contain the water.
In this study, the researchers placed a thin hydrogel between two plastic plates; the top plate had a shape or letters cut out, leaving only that area of the hydrogel exposed. For example, patterns included an airplane and the word "GEL." They initially placed the gel in a cold water bath to establish equilibrium. Then they moved the gel to a hot bath. The gel absorbed water into its structure causing a swell, but only in the exposed area. This imprinted the pattern, which is like a piece of information, onto the gel. When the gel was moved back to the cold water bath, the exposed area turned opaque, making the stored information visible, due to what they call "structure frustration." At the cold temperature, the hydrogel gradually shrank, releasing the water it had absorbed. The pattern slowly faded. The longer the gel was left in the hot water, the darker or more intense the imprint would be, and therefore the longer it took to fade or "forget" the information. The team also showed hotter temperatures intensified the memories.
More interestingly, the forgetting processes can be programmed by tuning the thermal learning time or temperature.
온도 및 노출 시간에 따라 fade out 되는 시간이 다르다는 것을 보여줌.
reference
Chengtao Yu et al. Hydrogels as dynamic memory with forgetting ability, Proceedings of the National Academy of Sciences (2020). DOI: 10.1073/pnas.2006842117