Magnetic responsive Janus origami robot achieves diverse droplet manipulation

Diversified manipulation of droplets across scales has important application prospects in fields such as fine chemistry and biomedicine. From a practical perspective, effective droplet manipulation technology requires multifunctional integration and multi-scale applicability. In recent years, magnetic actuation has been widely used in the field of droplet manipulation due to its advantages such as remote controllability, good biosafety, and insensitivity to environmental transmittance and substrate charge. However, how to further expand the functionality of magnetically responsive droplet manipulation and extend the diverse droplet manipulation capabilities from the microliter scale to the nanoliter scale remains extremely challenging.

In view of this, the team of Professor Hu Yanlei and Professor Wu Dong from the Micro-Nano Engineering Laboratory of the University of Science and Technology of China used femtosecond laser micro-nano manufacturing methods to prepare a magnetically responsive Janus origami that can be used for cross-scale droplet manipulation, achieving effective integration of diverse droplet manipulation functions, including three-dimensional droplet transport, merging, splitting, sub-droplet distribution and on-demand release, stirring, and remote heating. At the same time, the high stability of this manipulation strategy gives it the ability to manipulate droplets across scales, and can achieve diversified manipulation of droplets in the volume range of ~ 3.2 nL to ~ 51.14 μL. The related results were published in the journal Nature Communations under the title "Magnec Janus igami robot for cs-scale droplet omni-manipulation".

The magnetically responsive Janus origami robot is a rectangular sheet-like structure. The upper and lower surfaces of the robot have different wetting properties. The upper surface is in a superhydrophobic low droplet adhesion state, while the lower surface is in a hydrophobic high droplet adhesion state. At the same time, two creases are designed on the upper surface of the robot so that when the robot contacts the droplet, it can spontaneously wrap the droplet along the crease under the action of capillary force. The processing and modification of the robot's overall contour, creases and surface micro-nano functional structures are all made by femtosecond laser scanning.

The magnetically responsive Janus origami robot can realize a variety of droplet manipulation functions. The robot actively approaches and wraps the water droplet by rolling, which can realize the controllable transportation of the water droplet (Figure 1b, 1). In addition, the robot can also separate sub-droplets from large droplets by directional rolling and folding (Figure 1c), and release the sub-droplets by folding, squeezing and controllable flipping (Figure 1d). The robot can also rotate under the action of a magnetic field to achieve controllable mixing of liquids, and combine its photothermal properties to achieve remote heating.

Figure 1 Magnetic responsive Janus origami robot and its multifunctional droplet manipulation application

Video 1: Magnetic responsive Janus origami robot wraps and transports droplets

As mentioned above, the magnetically responsive Janus origami robot can achieve stirring and heating functions similar to commercial magnetic stirrers. As shown in Figures 2a to 2c, the robot is suspended on top of the droplet and rotates rapidly under the drive of the magnetic field, which can efficiently mix the droplets. The fluorescence distribution diagram clearly shows the degree of mixing of the droplets during stirring (Video 2). The robot can also produce a photothermal effect by irradiating it with near-laser light, realizing remote heating of the droplets. The heating temperature can reach above 80°C. Combining photothermal properties and magnetically controlled rotation, the magnetically responsive Janus origami robot can effectively achieve rapid mixing of high-viscosity liquids (glycerol) (Figures 2d to 2f).

Figure 2 Droplet stirring, photothermal stirring and multifunctional droplet manipulation integration based on magnetic responsive Janus origami robot

Video 2 Magnetic responsive Janus origami robot for rapid droplet mixing

On the basis of realizing diversified droplet manipulation, the magnetically responsive Janus origami robot can effectively integrate multiple droplet manipulation functions to achieve the goal of continuous droplet manipulation. As shown in Figure 2g, the robot actively approaches the green droplet through tumbling motion and distributes a certain volume of sub-droplets, then transports the sub-droplets to the vicinity of the red droplet to achieve the merging of the two droplets, and finally completes the rapid mixing of the droplets through stirring (Video 3). This multifunctional droplet manipulation integration can be applied to the field of microchemical reactions to achieve accurate sampling of liquid samples, rapid reactions, and timely detection of reactants (Figure 2h). In addition, with stable liquid manipulation performance, the diversified droplet manipulation integration can also be effectively extended to nanoliter-scale droplets (Figure 2i).

Video 3: Integration of diverse droplet manipulation functions

Finally, as a proof of concept, the researchers successfully achieved the extraction and purification of nucleic acids by surface modification of the magnetically responsive Janus origami robot and combining it with its diverse droplet manipulation capabilities (Figure 3).

In summary, the magnetically responsive Janus origami robot can realize diverse cross-scale droplet manipulations, which is of great significance to a wide range of fields such as fine chemicals, medical diagnosis, and microfluidics that require precise acquisition and addition of reagents, microdroplet patterning, and rapid microdroplet reactions.

Figure 3. Application of nucleic acid extraction and purification based on magnetic responsive Janus origami robot

Dr. Jiang Shaojun from the School of Engineering Science is the first author of the paper. The corresponding authors are Professor Hu Yanlei and Professor Wu Dong from the University of Science and Technology of China and Professor Wang Liqiu from the Hong Kong Polytechnic University. Other co-authors of the paper include Professor Chu Jiaru and Associate Professor Li Jiawen from the University of Science and Technology of China, Researcher Zhu Ling from the Anhui Institute of Precision Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, and Professor Shen Zuojun from the First Affiliated Hospital of the University of Science and Technology of China. This research work was supported by the National Natural Science Foundation of China Excellent Young Scientist Fund, the Youth Innovation Promotion Association of the Chinese Academy of Sciences, the Ministry of Science and Technology National Key R&D Program and other funds.

This work is one of the recent advances in the team's research on magnetically responsive droplet manipulation. How to improve the flexibility of magnetically responsive droplet manipulation has always been the focus of current research. To this end, the team has developed a variety of magnetically responsive droplet manipulation strategies (vanced Marials, 2019, 31(15): 1807507; Nano Lette, 2020, 20(10): 7519-7529; S Applied Materials & Interfaces, 2020, 12(37), 42264–42273; Langmuir, 2023, 39(27), 9358-9366.), which has improved the speed of magnetically responsive droplet manipulation, expanded the spatial dimension of manipulation, and successfully expanded the magnetically responsive manipulation strategy from single-phase (liquid phase) to three-phase (liquid phase, solid phase and gas phase) controllable manipulation of materials (Advanced Functional Materials, 2022, 32(40): 2205831).

Review editor: Liu Qing