Magnetic field–driven particle assembly and jamming for bistable memory and response plasticity

Abstract

Unlike classic synthetic stimulus-responsive and shape-memory materials, which remain limited to fixed responses, the responses of living systems dynamically adapt based on the repetition, intensity, and history of stimuli. Such plasticity is ubiquitous in biology, which is profoundly linked to memory and learning. Concepts thereof are searched for rudimentary forms of “intelligent materials.” Here, we show plasticity of electroconductivity in soft ferromagnetic nickel colloidal supraparticles with spiny surfaces, assembling/disassembling to granular conducting micropillars between two electrodes driven by magnetic field B . Colloidal jamming leads to conduction hysteresis and bistable memory upon increasing and subsequently decreasing B . Abrupt B changes induce larger conduction changes than gradual B -changes. Periodic B pulsing drives to frequency-dependent facilitation or suppression of conductivity compared to exposing the same constant field. The concepts allow remotely controlled switching plasticity, illustrated by a rudimentary device. More generally, we foresee adaptive functional materials inspired by response plasticity and learning.

pH-feedback systems to program autonomous self-assembly and material lifecycles

“…In the interest of a more complete coverage of applications, we point to the transient gels with front propagation established by Taylor, Pojman and co-workers, 83 as well as the removal of memories in ''learning material'' by Ikkala and co-workers, 84 as well as the transient regulation of catalysis by Ward and co-workers, 85 and the transient operation of molecular switches and machines by Di Stefano and coworkers. 76,77,79,81 These studies clearly show the flexibility with which pH-FS can be applied for augmenting the behavior of classical materials towards autonomous, active and adaptive systems.…”

Micro/Nanorobotic Swarms: From Fundamentals to Functionalities

“…Microrobotic swarms have also been demonstrated to be capable of controlling electric current flow in microcircuits. 321,327 When the orientation of electrically conductive microswarms was changed, the on-demand switching of LED arrays was achieved (Figure 8G). Chemical reactions at micro/nanolevels can be regulated by using micro/nanorobotic swarms.…”

“…Through the tuning of magnetic field strengths, magnetic particles can form a tunable aperture (Figure F), which blocks the light flow to desired levels. Microrobotic swarms have also been demonstrated to be capable of controlling electric current flow in microcircuits. , When the orientation of electrically conductive microswarms was changed, the on-demand switching of LED arrays was achieved (Figure G).…”

Trainable bioinspired magnetic sensitivity adaptation using ferromagnetic colloidal assemblies

“…Still, some of them have already inspired new simplistic functional materials using classical conditioning, response plasticity, and spiking. 20 , 21 , 22 The simplest form of triggerable memory is bistability (i.e., difference between increase and decrease of the applied stimulus, so far amply described in neuromorphic devices in current-voltage base). 23 …”