Magnetic-actuated “capillary container” for versatile three-dimensional fluid interface manipulation

Abstract

Fluid interfaces are omnipresent in nature. Engineering the fluid interface is essential to study interfacial processes for basic research and industrial applications. However, it remains challenging to precisely control the fluid interface because of its fluidity and instability. Here, we proposed a magnetic-actuated “capillary container” to realize three-dimensional (3D) fluid interface creation and programmable dynamic manipulation. By wettability modification, 3D fluid interfaces with predesigned sizes and geometries can be constructed in air, water, and oils. Multiple motion modes were realized by adjusting the container’s structure and magnetic field. Besides, we demonstrated its feasibility in various fluids by performing selective fluid collection and chemical reaction manipulations. The container can also be encapsulated with an interfacial gelation reaction. Using this process, diverse free-standing 3D membranes were produced, and the dynamic release of riboflavin (vitamin B2) was studied. This versatile capillary container will provide a promising platform for open microfluidics, interfacial chemistry, and biomedical engineering.

A review on control of droplet motion based on wettability modulation: principles, design strategies, recent progress, and applications

“…In Figure 6(b–f) , a magnetic force is converted to droplet driving force. Strategies such as deforming a magnetic substrate by rendering it superhydrophobic and moving droplets by gravity ( Figure 6(b) ) [ 88 ], using magnetic fluid in LIS to deform the film by Rosensweig instability spiking phenomenon ( Figure 6(c) ) [ 89–92 ], liquid marbling with magnetic particles ( Figure 6(d) ) [ 93 , 94 ], manipulating magnetic water solutions on a superhydrophobic surface ( Figure 6(e) ) [ 95–97 ], and transporting magnetic hydrophilic beads by attaching magnetic hydrophilic beads to droplets ( Figure 6(f) ) [ 90 , 98 ] have been reported. The advantage of magnetic transport is that the droplet position can be adjusted in situ depending on the position of the magnet.…”

Switchable capillary and drainage containers for programmable three-dimensional liquid manipulation

“…When the frames are slowly lifted out of the liquid, the capillary force can overcome gravity, allowing the frames to capture the liquid. These frames are named "capillary containers" in our previous study 22 . Interesting phenomena emerge when the frames are connected in different ways (Supplementary Video 1).…”

“…The working principle of capillary containers is easy to understand. When capillary containers are lifted from the liquid, the liquid-philic frames provide the capillary force to capture the liquid, while the single rod between the frames only acts as a mechanical connection without affecting the independent liquid-trapping behavior of each frame 22 . In this section, we mainly focus on the working mechanism of drainage containers.…”

“…manipulation, some recent studies have developed 3D capillary architectures to control liquid behavior. Notable examples include flexible 3D fluid interface manipulation by the magneticactuated printed frame 22 , 3D fluidic transport control with unit-cell-based structure 23 , liquid directional steering using the 3D capillary ratchet 11,24 , and periodic liquid array creation in 3D micropillar scaffolds 25 . However, despite these encouraging developments, the existing capillary structures still suffer from great challenges in flexible 3D liquid manipulation.…”

Directional and Adaptive Oil Self‐Transport on a Multi‐Bioinspired Grooved Conical Spine

“…Spontaneous and directional transport of specific fluids using bio‐inspired interfaces is of great importance to optimize the current technologies in the fields of microfluidics, [ 1 ] interface catalysis, [ 2 ] oil‐water separation, [ 3 ] biomedical applications, etc. [ 1a,4 ] The designed interface possessing the structural asymmetry and wettability gradient can effectively generate the directional propulsion and drive the droplet motion without any energy input.…”