A new material inspired by living systems changes its electrical behavior based on previous experience. Developed by researchers at Aalto University, it has effectively achieved a basic form of adaptive memory.
Adaptive materials such as this could play a key role in the development of next-gen medical and environmental sensors, as well as in soft robots and active surfaces.
Responsive Materials in Living Systems
Responsive materials can be found across a wide range of applications, such as glasses that darken in sunlight. However, existing materials always react the same way, and their response to a change is independent of their history. This means they do not adapt based on their past experiences.
On the other hand, living systems adapt their behavior based on previous conditions.
Bo Peng is an Academy Research Fellow at Aalto University and one of the senior authors of the research.
“One of the next big challenges in material science is to develop truly smart materials inspired by living organisms,” Peng says. “We wanted to develop a material that would adjust its behavior based on its history.”
Achieving Adaptive Memory in Materials
The team first synthesized micrometer-sized magnetic beads before stimulating them with a magnetic field. The beads stacked up to form pillars whenever the magnet was turned on, and the strength of the magnetic field impacted the shape of the pillars. These shapes affect how well the pillars conduct electricity.
‘With this system, we coupled the magnetic field stimulus and the electrical response. Interestingly, we found that the electrical conductivity depends on whether we varied the magnetic field rapidly or slowly,” Peng explains. “That means that the electrical response depends on the history of the magnetic field. The electrical behavior was also different if the magnetic field was increasing or decreasing. The response showed bistability, which is an elementary form of memory. The material behaves as though it has a memory of the magnetic field.”
The system’s memory enables it to behave in a way similar to rudimentary learning. During the learning process in living organisms, the basic element in animals is a change in the response of connections between neurons. This is referred to as synapses, and depending on how frequently they are stimulated, the synapses in neurons become either harder or easier to activate. The change is called short-term synaptic plasticity, and it makes the connection between a pair of neurons stronger or weaker depending on their history.
The team of researchers achieved a similar system with the magnetic beads, but the mechanism is different. When the beads are exposed to a quickly pulsing magnetic field, the material can better conduct electricity. But if they are exposed to slower pulsing, they conduct poorly.
Olli Ikkala is a Distinguished Professor at Aalto.
“Our material functions a bit like a synapse,” Ikkala says. “What we’ve demonstrated paves the way for the next generation of life-inspired materials, which will draw on biological processes of adaptation, memory and learning.”
“In the future, there could be even more materials that are algorithmically inspired by life-like properties, though they won't involve the full complexity of biological systems. Such materials will be central to the next generation of soft robots and for medical and environmental monitoring,” Ikkala concludes.