Reviewed by Emily Henderson, B.Sc.Nov 16 2022
Having gained inspiration from the living systems, scientists at Aalto University have come up with a new material that has the potential to change its electrical behavior depending on earlier experience. This helps in efficiently providing it with a fundamental form of adaptive memory.
The shape and conductivity of the pillars formed by magnetic beads in a magnetic field depend on the fields' strength and history. Image Cap: microzoomer.
Such adaptive materials could play a crucial role in the next generation of environmental and medical sensors, as well as in active surfaces or soft robots.
Responsive materials have turned out to be highly common in a range of applications, right from glasses that tend to get darkened in sunlight to drug delivery systems. However, present materials always react similarly—and their response to a change does not rely on their history, nor do they adapt based on their past.
This is different from living systems, which dynamically adapt their behavior depending on earlier conditions.
One of the next big challenges in material science is to develop truly smart materials inspired by living organisms. We wanted to develop a material that would adjust its behavior based on its history.
Bo Peng, Study Senior Author and Academy Research Fellow, Aalto University
The scientists synthesized micrometer-sized magnetic beads, further stimulated by a magnetic field. When the magnet was on, the beads piled up to develop into pillars. The power of the magnetic field impacts the shape of the pillars, which in turn impacts how well they 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.
Bo Peng, Study Senior Author and Academy Research Fellow, Aalto University
Peng added, “That means that the electrical response depends on the history of the magnetic field. The electrical behavior was also different if the magnetic field increased or decreased. The response showed bistability, which is an elementary form of memory. The material behaves as though it has a memory of the magnetic field.”
Basic Learning
Furthermore, the system’s memory enables it to act in a way that matches rudimentary learning. Even though learning in living organisms seems to be hugely complicated, the majority of the basic element in animals is a variation in the response of connections between neurons called synapses. Based on how frequently they have been stimulated, synapses in a neuron will turn out to be tougher or simpler to trigger.
This change, called short-term synaptic plasticity, makes the connection between a pair of neurons stronger or weaker based on their recent history.
Researchers could achieve something that is with their magnetic beads, even though the mechanism seems to be completely different. When they were exposed to the beads to a rapidly pulsing magnetic field, the material turned out to be better at conducting electricity, whereas slower pulsing made it conduct poorly.
This is reminiscent of short term-synaptic plasticity. Our material functions a bit like a synapse. What we’ve demonstrated paves the way for the next generation of life-inspired materials, which will draw on biological process of adaptation, memory and learning.
Olli Ikkala, Distinguished Professor, Aalto University
Ikkala added, “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.”