Magnetically Actuated Surface Microstructures for Efficient Transport and Tunable Separation of Droplets and Solids

Abstract

Efficient transportation of droplets (≈101–102 μL) and small solid objects (≈101–102 mm3) have important applications in many fields, such as microfluidics, lab‐on‐a‐chip devices, drug delivery, etc. A novel multifunctional surface consisting of a periodic array of micro‐lamellae from a soft magnetoactive elastomer on a plastic substrate is reported for these purposes. The physical origin of the propulsion is the bending of soft magnetic lamellae in nonuniform magnetic fields, which is also observed in uniform magnetic fields. The magnetoactive surface is fabricated using a facile and rapid method of laser ablation. The propulsion of items is realized using a four‐pole rotating magnet. This results in a cyclic lamellar fringe motion over the microstructured surface and brings an advantage of easy reciprocation of transport by rotation reversal. Two modes of object transportation are identified: “pushing” mode for precise control of droplet and solid positioning and “bouncing” mode for heavier solid objects transportation. A water droplet of 5 μL or a glass sphere with a 2.1 mm diameter can be moved at a maximum speed of 60 mm s−1. The multifunctionality of the proposed mechatronic platform is demonstrated on the examples of selective solid–liquid separation and droplet merging.

Surface Modification of Magnetoactive Elastomers by Laser Micromachining

“…In 2022, a new method of MAE surface patterning with laser micromachining was introduced by Kravanja et al [51]. This technique was employed to manufacture magnetically controllable lamellar structures in a surface area of 1 cm 2 [52,53]. Investigations of the dynamic response of lamellae to the variable magnetic field were carried out, and a simple magneto-mechanical model of the observed phenomena was proposed [52].…”

“…Investigations of the dynamic response of lamellae to the variable magnetic field were carried out, and a simple magneto-mechanical model of the observed phenomena was proposed [52]. Such lamellae can be employed for the transportation of liquid droplets and solid objects [53,54]. Lamellar surfaces also provide control of the droplet impact [55] and switchable wettability [47,52].…”

Magnetically-responsive microwall arrays with path-guide for directional transportation of droplets

“…For example, Cui et al [22] proposed biologically sized magnetic artificial cilia, demonstrating selfcleaning functions in microfluidic systems, and suggested potential applications for lab-on-a-chip and organ-on-a-chip devices. Since the droplet manipulation method with magnetically responsive micro patterned surface was first proposed by Drotlef et al [23], various applications have been explored to extend the range of applicable objects and improve manipulation mechanisms [24][25][26]. For example, Song et al [26] created a high-aspect ratio magnetically responsive microcolumn array (HAR-MRMA) that enables directional lossless transportation of droplets, indicating its use for microfluidics, chemical micro reaction, and intelligent droplet control systems.…”