Memory-retentive materials: Researchers have found unique properties in various substances.

Some materials have the ability to retain past events, much like a crumpled sheet of paper keeps its creases. A group of physicists from Pennsylvania State University recently discovered that under certain conditions, some materials can remember not only that they were deformed but also the exact sequence of those deformations. This finding could lead to new methods of storing information in mechanical systems, such as combination locks or even performing calculations without electricity, reports Penn State.

Materials often retain memories through a process known as point memory, where variable forces leave an imprint that can be read or erased. This concept is similar to a combination lock, where turning the dial in a specific way determines whether it will open. Nathan Keim, an associate professor at Penn State and author of the study published in the journal Science Advances, explained that this mathematical principle is applicable to many systems, from computer hard drives to rock formations.

However, it was previously thought that point memory required forces to be applied in both directions—pulling and pushing. Keim's team discovered an exception: some materials can retain the sequence of actions even when force is applied in only one direction, much like a bridge that sags under the weight of traffic but does not rise when vehicles exit. To investigate this, the researchers conducted computer simulations to examine how different forces affect memory retention.

They focused on basic elements known as hysterons, which can remain in a past state even when conditions change. Hysterons either cooperate, encouraging each other to change, or frustrate one another by resisting those very changes. The team found that frustrated hysterons, similar to segments of a bendable straw that open sequentially, allow the material to encode the sequence of past deformations even when force is applied in only one direction.

This discovery could have practical applications in creating artificial systems with memory, particularly mechanical systems that do not rely on electricity. Keim noted that such materials could confirm the sequence of past events, aiding in forensic analysis or diagnostics. For instance, a material that tracks its largest and most recent deformation could be used to detect structural stress in buildings or machines.

In medicine, this breakthrough could lead to the development of self-monitoring materials that assess stress or deformation in implants and prosthetics, potentially enhancing patient safety. Additionally, artificial joints or bone implants could utilize such memory to track usage patterns and alert doctors to early signs of wear or failure.

Such technology could help design advanced wound dressings that remember pressure levels and adjust accordingly to improve healing.