Recent Progress on the Development of Magnetically‐Responsive Micropillars: Actuation, Fabrication, and Applications

Abstract

Stimuli-responsive micro-pillared structures can perform complex and precise tasks at the microscale through dynamic and reversible deformation of the pillars in response to external triggers. Magnetic field is one of the most common actuation strategies due to its incomparable advantages such as instantaneous response, remote and nondestructive control, and superior biocompatibility. Over the past decade, many researches are attempted to design and optimize magnetically-responsive micropillars for a wide range of applications and great progresses are accomplished. In this review, the most important aspects of recent progress of magnetically-responsive micropillars are covered to give a comprehensive and systematical introduction to this new field, from the actuation mechanisms, fabrication methods, and deformation patterns to the practical applications. The increasingly maturing fabrication techniques can provide low-cost and large-scale magnetic micropillars with homogeneous responses. Some advanced techniques are developed to fabricate micropillars with programmable and reprogrammable responses for site-specific and reconfigurable actuations. On the other hand, practical applications for particle/droplet/light manipulation, flow generation, miniature swimming/climbing/carrying microrobots, tunable adhesion, cellular probe, fog collector, and anti-ice surfaces are also summarized. Finally, current challenges that limit the industrial implementation are discussed and the authors' perspectives on the future directions of magnetically-responsive micropillars are stated.

Dynamics Behavior of Droplet Impact on a Controllable Curved Micropillar Array Surface Induced by a Magnetic Field

“…Inspired by this, many biomimetic asymmetric structures have been created. In the method of surface preparation, a magnetic response surface has been widely examined by scholars because of its advantages, such as remote and accurate operation and lack of contact. Research on the behavior of droplets under a magnetic field was also carried out, for example, the dynamic behavior of droplets under the surface of inclined microcone arrays, , inclined microcolumns, blade arrays, etc. These methods can not only realize the directional fast transportation of the droplet but also induce the droplet to detach quickly from the surface …”

“…v hz p p b ln( / ) v2 0 2 (11) The expression of the viscous dissipation between the droplet and the wall could be obtained: The viscous force between the droplet and the base surface could be expressed as 39…”

Magnetic Responsive On‐Site Switching of the Directional Droplet Self‐Transport in Shape Memory Slippery Tube

“…By leveraging the synergistic effects of active and passive strategies and combining the variation in the tube's macroscale shape with dynamic control of the inner surface microstructure, smart onsite switching can be achieved during the self-transport process. To the best of our knowledge, magnetic-responsive microstructures have been extensively utilized in droplet manipulation, including droplet transport, [57,58] droplet bouncing, [59] and droplet directional sliding, [60] owing to their instantaneous responsivity and remote control through magnetic fields. However, in situ controlled moving/ceasing transition in tubes during the selftransport process has yet to be explored.…”

Magnetic field induced the assembling of Photothermal evaporator for efficient solar‐driven desalination

“…To simplify the structure construction, external field effects are introduced to induce the controllable assembly of nanoparticles to form the proposed structure. [20][21][22][23][24] In particular, magnetic field is considered an ideal tool for applications in structure management, [25][26][27] especially in the construction of functional structures with reconfigurable, recoverable, and dynamically adjustable. [28][29][30] In Jeong's work, Fe 3 O 4 nanoparticles were sprayed onto a Si substrate with patterned nickel islands, and attracted by the external magnetic field to form magnetic micropillars.…”