A recent article published in PubMed describes an internal pneumatic shuttering method designed to improve aerosol printing (AP) for the fabrication of three-dimensional (3D) microstructures. The approach enables layer-by-layer construction using dot modulation with diameters ranging from 20 to 144 µm.
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Background
Traditional microfabrication techniques, such as lithography, vacuum deposition, fused deposition modeling, selective laser melting, and chemical etching, can produce microscale 3D structures with high precision. However, these methods often require specialized equipment, complex procedures, and trained personnel.
Additive manufacturing techniques offer alternatives by enabling direct deposition of structures. Aerosol printing, in particular, is a non-contact technique that supports a range of materials and substrates, including those that are fragile or non-planar.
However, AP has mainly been used for line-based patterns, which require minimal on-off control of the material stream. In contrast, dot-based printing is more suitable for constructing detailed 3D microstructures but has been difficult to achieve reliably using conventional AP systems.
Methods
The study introduced an AP system incorporating an atomizer, a shuttering unit, a virtual impactor, and a focusing unit. Mass flow controllers (MFCs) regulated the flow of atomizer and sheath gases, and a three-port external air pilot solenoid valve, along with a vent MFC, comprised the pneumatic shuttering system.
Nitrogen-based pneumatic atomization generated aerosol droplets, which were refined in the virtual impactor and then collimated by a sheath gas before being focused through a nozzle to form a high-speed jet. Two cameras monitored the printing process, one for pattern inspection and one for jetting status. Control was managed via custom LabVIEW software.
Silver nanoparticle ink was used in AP and inkjet printing to compare results. Surface morphology was assessed using optical microscopy, coherence scanning interferometry, and field emission scanning electron microscopy (FESEM).
Results and Discussion
The pneumatic shuttering system allowed for improved control of the aerosol jet by minimizing pressure fluctuations, which reduced delays between printing and non-printing states. The dot-based aerosol printing (AP) technique produced ink dots with diameters ranging from 20 to 144 µm and thicknesses between 1 and 6.25 µm, depending on the deposition time (Td), which was varied from 15 to 120 ms.
The 3D surface morphology of dot arrays produced via AP differed from those created by inkjet printing. In inkjet printing, increasing the number of droplets primarily increased the dot diameter, while the height remained limited (0.15 to 0.4 µm) and was affected by the coffee-ring effect. In contrast, AP achieved greater dot heights (3 to 5.4 µm) under similar conditions.
The shuttering method was further evaluated by printing vertical and angled (40° to 140° relative to the substrate) 3D pillars. These structures were produced with adjustable diameters and without requiring support materials.
Additionally, the method was used to fabricate 3D interconnects and bridge structures with limited overspray. As a demonstration, 3D electrical lines were printed to connect a bottom glass substrate with two light-emitting diodes (LEDs) and two resistors on an upper substrate. The LEDs functioned when voltage was applied, indicating that the printed interconnects were electrically conductive.
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Conclusion
This study presents a pneumatic shuttering mechanism that enhances control over aerosol jetting, enabling both line and dot-based printing. The system supports dot modulation for the fabrication of 3D microstructures, such as angled conductive pillars, without support structures.
Grayscale bitmap printing was also demonstrated by mapping image intensity to deposition time, offering additional flexibility for patterning. These developments may expand the applicability of aerosol printing in electronics and materials research.
Journal Reference
Mosa, M. A., Jo, J. Y., Park, S.-H., Kwon, K.-S. (2025). Aerosol Printing of 3D Conductive Microstructures via Precision Dot Modulation. PubMed, e2504037. DOI: 10.1002/smll.202504037, https://onlinelibrary.wiley.com/doi/10.1002/smll.202504037
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