Hybrid Magnetic Micropillar Arrays for Programmable Actuation

Abstract

Stimuli‐responsive micro/nanostructures that can dynamically and reversibly adapt their configurations according to external stimuli have stimulated a wide scope of engineering applications, ranging from material surface engineering to micromanipulations. However, it remains a challenge to achieve a precise local control of the actuation to realize applications that require heterogeneous and on‐demand responses. Here, a new experimental technique is developed for large arrays of hybrid magnetic micropillars and achieve precise local control of actuation using a simple magnetic field. By manipulating the spatial distribution of magnetic nanoparticles within individual elastomer micropillars, a wide range of the magnetomechanical responses from less than 5% to ≈50% for the ratio of the bending deflection to the original length of the pillars is realized. It is demonstrated that the micropillars with different degrees of bending deformation can be configured in any spatial pattern using a photomask‐assisted template‐casting technique to achieve heterogeneous, site‐specific, and programmed bending actuations. This unprecedented local control of the micropillars offers exciting novel applications, as demonstrated here in encryptable surface printing and stamping, direction‐ and track‐programmable microparticle/droplet transport, and smart magnetic micro‐tweezers. The hybrid magnetic micropillars reported here provide a versatile prototype for heterogeneous and on‐demand actuation using programmable stimuli‐responsive micro/nanostructures.

Magneto‐Responsive Shutter for On‐Demand Droplet Manipulation

“…MRSS with various structured topographies including conical array, microcilia array, [ 1 , 2 , 7 , 23 , 24 ] micropillars, [ 25 , 26 , 27 , 28 , 29 , 30 , 31 ] and microplates have been designed for dynamical droplet manipulation under magnetic actuation. [ 6 , 21 , 32 , 33 ] For example, magneto‐responsive conical array was employed for static fog collection under windless regions.…”

Tailoring Flexible Arrays for Artificial Cilia Actuators

“…[27] For example, a heterogeneous cilia array was prepared via a photomaskguided template-casting approach. [73] In this case, poly(urethane acrylate) (PUA) was set as the matrix material and silica-coated iron oxide nanoparticles (Fe 3 O 4 @SiO 2 ) were the embedded magnetic particles. To fabricate this cilia array, PUA/Fe 3 O 4 @SiO 2 pre-solution was first filled into the cavities of a silicon template and then placed under a vertical magnetic field gradient Reproduced with permission.…”

“…Scale bars: 100 μm. Reproduced with permission [73]. Copyright 2020, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.…”

Fabrication and applications of stimuli‐responsive micro/nanopillar arrays

“…54 Copyright 2018, National Academy of Sciences actuators have been extensively investigated owing to the advantages of battery-free remote-control at room temperature with a fast response time. 161,162 Recently, various applications have been developed, such as droplet transportation, [163][164][165] modification of the optical property of the surface, 166 and cancer cell capture/release control for chemotherapy. 167 These applications were implemented by employing magnetically responsive nano/micropillars embedding ferromagnetic particles classified into two regimes: hard and soft magnets.…”