3D printing: Specialized antennas; recyclable ink; chip-based printer.
Researchers from the National University of Singapore developed a 3D printing technique that can be used to create three dimensional, self-healing electronic circuits.
Called tension-driven CHARM3D, the technique enables the 3D printing of free-standing metallic structures without requiring support materials and external pressure. It uses Field’s metal, a quick-solidifying eutectic alloy of indium, bismuth, and tin that has a low melting point of 62 degrees Celsius, a high electrical conductivity, and low toxicity. The CHARM3D technique exploits the tension between molten metal in a nozzle and the leading edge of the printed part, resulting in uniform, smooth microwire structures with adjustable widths of 100 to 300 microns.
The team used the method to print a 3D circuit for wearable battery-free temperature sensors, antennas for wireless vital sign monitoring, and metamaterials for electromagnetic wave manipulation. They suggest that arrays of 3D antennas or electromagnetic metamaterial sensors fabricated for specific applications could provide improved signal-to-noise ratios and higher bandwidths. [1]
Researchers from the University of California San Diego and Hanyang University created a recyclable 3D printable ink that cures in salt water and can be used to make easily recyclable electrical circuits.
The ink is a liquid polymer solution known as poly(N-isopropylacrylamide), or PNIPAM, which instantly solidifies when extruded through a needle into a calcium chloride salt solution. Salt ions draw water molecules out of the polymer solution, causing the hydrophobic polymer chains in the PNIPAM ink to densely aggregate and create a solid form. Dissolving the printed structure in fresh water returns the PNIPAM to its liquid form, which can be reused for further printing.
A structure created using a simple, eco-friendly 3D printing method developed by UC San Diego engineers. (Credit: Donghwan Ji / UC San Diego)
“This is all done under ambient conditions, with no need for additional steps, specialized equipment, toxic chemicals, heat or pressure,” said Jinhye Bae, a professor of chemical and nano engineering at the UC San Diego Jacobs School of Engineering, in a statement.
To demonstrate the method, the researchers printed structures from PNIPAM inks mixed with other materials. An electrical circuit capable of powering a light bulb was created by mixing the PNIPAM with carbon nanotubes. The circuit could be dissolved in fresh water. [2]
Researchers from MIT and the University of Texas at Austin built a chip-based 3D printer that consists of a single, millimeter-scale photonic chip that emits reconfigurable beams of light into a well of resin that cures when exposed to the beam’s wavelength of visible light.
The prototype consists of a single photonic chip containing an array of 160-nanometer-thick optical antennas. Liquid crystal modulators that can be tuned using an electric field are integrated onto the chip to control the amplitude and phase of light being routed to the antennas. A single waveguide on the chip holds the light from an off-chip laser, with tiny taps running along the waveguide to tap off a small amount of light to each of the antennas.
The chip sits below a clear slide, which contains a shallow indentation that holds the resin. When powered by an off-chip laser, the antennas emit a steerable beam of visible light into the well of resin. Electrical signals are used to nonmechanically steer the light beam, which causes the resin to solidify.
The prototype can be used to 3D print arbitrary two-dimensional shapes. They researchers plan to develop a chip that can emit a hologram of visible light to enable volumetric 3D printing. [3]
[1] Ling, S., Tian, X., Zeng, Q. et al. Tension-driven three-dimensional printing of free-standing Field’s metal structures. Nat Electron 7, 671–683 (2024). https://doi.org/10.1038/s41928-024-01207-y
[2] Ji, D., Liu, J., Zhao, J. et al. Sustainable 3D printing by reversible salting-out effects with aqueous salt solutions. Nat Commun 15, 3925 (2024). https://doi.org/10.1038/s41467-024-48121-7
[3] Corsetti, S., Notaros, M., Sneh, T. et al. Silicon-photonics-enabled chip-based 3D printer. Light Sci Appl 13, 132 (2024). https://doi.org/10.1038/s41377-024-01478-2
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