Researchers at Hokkaido University have found a soft and moist material that can remember, retrieve, and forget information like the human brain. They described the details of their development in an article for the journal Proceedings of the National Academy of Sciences.

The human brain learns things but tends to forget them when information ceases to be important and relevant. Recreating this dynamic memory process in artificial materials has been challenging. Hokkaido University researchers are now reporting a hydrogel that mimics the brain’s dynamic memory function: coding information that disappears over time based on memory intensity.

HYdromel memory effect

Hydrogels are flexible materials made up of a large percentage of water – in this case about 45% – along with other chemicals that provide a scaffold-like structure for holding water. Professor Jiang Ping Gong, Assistant Professor Kunpeng Cui, and their students and colleagues at the Institute of Chemical Reaction Engineering and Discovery at Hokkaido University (WPI-ICReDD) are striving to develop hydrogels that can serve biological functions.

Hydrogels are excellent candidates for mimicking biological functions because they are soft and moist like human tissue. Scientists have found a way to demonstrate how hydrogels can mimic some of the memory functions in brain tissue.

In this study, scientists placed a thin hydrogel between two plastic plates; the top plate was shaped or cut out letters, leaving only the hydrogel area open. For example, the patterns included an airplane and the word “gel”. First, they put the gel in a cold water bath. Then they transferred the gel to a hot bath. The gel absorbed water into its structure causing swelling, but only in the open area. This captured the information-like drawing onto the gel.

When the gel was returned to the cold water bath, the exposed area became opaque, making the stored information visible. At low temperatures, the hydrogel gradually shrank, releasing the water it had absorbed earlier. The painting slowly faded away.

The longer the gel stays in hot water, the darker or more intense the print will be and, therefore, the longer it will fade or “forget” information. The team also showed how high temperatures heightened memories.

It looks like people. The longer you learn something, or the stronger the emotional stimulus, the longer you forget it.

Professor Jiang Ping Gong

Hydrogel technology

The team has shown that the memory embedded in the hydrogel is resistant to temperature fluctuations and extreme physical stretching. More interestingly, forgetting processes can be programmed by adjusting the time or temperature of the heat learning.

The team used materials containing hydrogels – polyampholytes or PA-gels. The memory-forgetting behavior is achieved through the rapid absorption of water and the slow release of water, which is provided by dynamic bonds in hydrogels. This approach should work for a variety of physically bound hydrogels, scientists say. A memory system similar to the hydrogel brain can be used for some applications, such as fading messages for security purposes.