Photothermally Reconfigurable Shape Memory Magnetic Cilia

Abstract

Stimulus-responsive polymers are attractive for microactuators because they can be easily miniaturized and remotely actuated, enabling untethered operation. In this work, magnetic Fe microparticles are dispersed in a thermoplastic polyurethane shape memory polymer matrix and formed into artificial, magnetic cilia by solvent casting within the vertical magnetic field in the gap between two permanent magnets. Interactions of the magnetic moments of the microparticles, aligned by the applied magnetic field, drive self-assembly of magnetic cilia along the field direction. The resulting magnetic cilia are reconfigurable using light and magnet fields as remote stimuli. Temporary shapes obtained through combined magnetic actuation and photothermal heating can be locked by switching off the light and magnetic field. Subsequently turning on the light without the magnetic field drives recovery of the permanent shape. The permanent shape can also be reprogrammed after preparing the cilia by applying mechanical constraints and annealing at high temperature. Spatially controlled actuation is demonstrated by applying a mask for optical pattern transfer into the array of magnetic cilia. A theoretical model is developed for predicting the response of shape memory magnetic cilia and elucidates physical mechanisms behind observed phenomena, enabling the design and optimization of ciliary systems for specific applications.

Microfluidic Applications of Artificial Cilia: Recent Progress, Demonstration, and Future Perspectives

“…Similarly, another artificial cilia array was reported [ 118 ], fabricated using the PDMS and CrO 2 nanoparticles. The study has discussed the multi-responsive technique [ 119 ], where apart from actuating artificial cilia through the magnetic field, the shape can be further reconfigured through photo-thermal heating.…”

Noncontact All‐In‐Situ Reversible Reconfiguration of Femtosecond Laser‐Induced Shape Memory Magnetic Microcones for Multifunctional Liquid Droplet Manipulation and Information Encryption

“…Recently, Liu et al. [ 29 ] reported that the micropillar can be easily obtained by the self‐assembly method, but the structure is hard to keep consistent. To the best of our knowledge, the noncontact, all‐in‐situ reversible configuration of magnetic particles doped SMP microscale structures to achieve the manipulation of liquid droplets with microscale size has rarely been reported (Figure S1, Supporting Information).…”

Smart Refreshable Braille Display Device Based on Magneto‐Resistive Composite with Triple Shape Memory

“…These can be deformed and molded into a temporary shape, and then recovered at different temperatures, lighting conditions, and salt concentrations in solution. [ 16–26 ] The heat‐triggered SMP possesses a shape memory effect similar to that of SMA. It can be programmed into a temporary shape when the temperature is higher than the melting point of the temperature‐controlling component, then fixed through cooling, and finally reverted to its original shape through reheating.…”

“…Owing to the good mechanical properties of non‐magnetic matrices and the unique magneto‐induced capability of ferromagnetic particles, magnetorheological elastomers (MREs) have promising applications, such as untethered actuation, [ 26,44–49 ] vibration control, [ 50–53 ] and non‐contact sensing. [ 31,36,54–58 ] Under an external magnetic field, the magnetic interactions of the particles actuate the matrix, and the gaps between the conductive fillers and magnetic particles are varied, resulting in changing conductivity.…”

“…The introduction of ferromagnetic particles, such as iron and nickel, into LMEEs can significantly enhance the sensing performance of LMEEs. [ 26,28 ] These particles not only establish additional percolation pathways among LM droplets and improve the response performance, but also assemble along the external magnetic field and allow untethered actuation in the devices. Therefore, combining the shape memory effect of SMP, high electrical and thermal conductivity of LM, and good resilience and magnetic field‐dependent property of MRE can be a new approach for developing a smart refreshable Braille display device (SRBDD) with stable deformation capability, good tactile perception, and multiple sensitivity.…”