Accurate and efficient particle and droplet manipulation is crucial for disease diagnosis, targeted drug delivery, and sample purification. Particle and droplet manipulation based on specific microstructures has been widely used in biological detection. However, current technologies are mainly based on fixed microstructures, making it challenging to dynamically modulate the manipulation effect by adjusting the microstructure morphology and excitation conditions.
Recently, a research team reported a method for particle capture and droplet manipulation using a morphologically reconfigurable magnetic micropillar array combined with acoustic streaming. This approach achieves efficient particle capture, cargo transportation, and droplet manipulation. The related results were published in the journal Sensors and Actuators: B. Chemical under the titled “Morphologically reconfigurable magnetic micropillar arrays using acoustic streaming for particle capture and droplet manipulation.”
The team designed four orthogonally arranged interdigital electrodes to induce the acoustic streaming effect, and placed a permanent magnet under the device. This setup caused NdFeB magnetic powder to assemble into a reconfigurable magnetic micropillar array with a porous surface morphology. Figure 1 shows a schematic diagram of the acoustic streaming capture device based on reconfigurable magnetic micropillars. The magnetic micropillars can capture particles driven by the acoustic streaming effect through the porous microstructure on their surface. Due to the customizability of the external magnetic field, the morphology of the magnetic micropillar array is reconfigurable, as shown in Figure 2. This method allows for customized assembly into magnetic micropillar arrays of various complex shapes. To demonstrate the reconfigurability of the magnetic micropillar array, the team successfully achieved the controllable assembly and acoustic streaming loading of magnetic micropillar arrays in the shapes of the letters “Z,” “J,” and “U.”
Fig.1 Schematic diagram of the acoustic flow capture and manipulation device based on reconfigurable magnetic micropillars
Fig.2 Characterization of acoustic streaming capture performance of morphologically reconfigurable magnetic micropillar array
After acoustic flow loading, the magnetic micropillar array does not need to be confined in the chamber, but can be taken out to perform more complex functions, including complex maze navigation, cargo transportation, droplet fixation, etc. Figure 3 demonstrates that the magnetic micropillar can navigate through a maze of narrow channels, changing its shape to adapt to winding flow channels while moving. Since the magnetic micropillars are assembled from 5-micron diameter magnetic powder, they exhibit excellent morphological reconstruction capabilities and can traverse complex environments, such as slits and irregularly shaped obstacles. In addition, due to the spike structure and reconfigurable characteristics of the magnetic micropillars, they can capture and transport target cargo and fix droplets, as shown in Figure 4. Beyond acoustic flow loading, navigation, cargo transportation and droplet fixation, the magnetic micropillars can use their structural characteristics combined with the acoustic flow effect to accelerate the mixing of different components and efficiently manipulate droplets. To demonstrate the orderly cooperation of magnetic micropillars and acoustic flow effects in droplet transport and reaction acceleration, the manipulation of sodium bicarbonate and phenolphthalein droplets to accelerate the color reaction is used as an example, as shown in Figure 5. This study provides a new solution for achieving efficient, multi-scenario controllable particle loading and droplet manipulation by introducing a magnetic micropillar array combined with the acoustic streaming effect.
Fig.3 The precise movement capability of magnetic micropillars in complex terrain after acoustic streaming
Fig. 4 Performance characterization of magnetic micropillar arrays for cargo transport and droplet immobilization
Fig.5 Magnetic micropillar array achieves efficient droplet manipulation and acoustic flow-accelerated mixing of multiphase droplets
This work represents one of the latest advances in the team’s recent research on multi-directional coherent surface acoustic wave reconfigurable control technology. In recent years, the team has focused on surface acoustic wave programmable control technology and sound-assisted photocuring of heterogeneous functional materials for applications in the preparation of smart composite materials. Previously, the team proposed a programmable manipulation technology for particles and cells based on multidirectional coherent surface acoustic waves (Lab Chip 2022, 22, 1149-1161; Lab Chip 2023, 23, 215-228; Sep. Purif. Technol. 2023, 311, 123215; J. Colloid Interface Sci. 2023, 643, 115-123). They also explored the acoustic-assisted photocuring process in the preparation of heterogeneous smart composite materials (Addit. Manuf. 2022, 60, 103247; J. Manuf. Process 2024, 112, 179-186; J. Manuf. Process 2024, 121, 374-381) to promote the practical application of high-precision acoustic fluidic technology in clinical medicine and intelligent manufacturing.
Reference:
Hemin Pan et al. “Morphologically reconfigurable magnetic micropillar arrays using acoustic streaming for particle capture and droplet manipulation.” Sensors and Actuators B: Chemical vol. 412 (2024). doi: 10.1016/j.snb.2024.135776
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