Viewing the video that shows a laser-assisted 3-D printing machine using metallic inks create delicate objects suspended in mid-air leaves you speechless.

This fantastic laser-assisted direct ink writing method prints microscopic metallic, free-standing 3-D structures in one step, without auxiliary support material. It was developed by researchers at Harvard University's Wyss Institute for Biologically Inspired Engineering and the John A. Paulson School of Engineering and Applied Sciences (SEAS).

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The research was led by Wyss core faculty member Jennifer Lewis, who is also the Hansjörg Wyss Professor of Biologically Inspired Engineering at SEAS.

Harvard said this fantastic technology could lead to customized electronic and biomedical devices. It said the increasing demand for flexible, wearable electronics, sensors, antennas and biomedical devices led a research team to innovate a jaw-dropping way of printing complex metallic architectures as though seemingly suspended in midair.

The laser-assisted direct ink writing method uses an ink composed of silver nanoparticles. The ink flows through a printing nozzle and is then annealed using a precisely programmed laser that applies just the right amount of energy to drive its solidification.

The printing nozzle moves along x, y, and z axes and is combined with a rotary print stage to enable freeform curvature. This method prints tiny hemispherical shapes, spiral motifs, even a butterfly made of silver wires narrower than a hair's width in free space within seconds. The printed wires also exhibit excellent electrical conductivity, almost matching that of bulk silver.

"I am truly excited by this latest advance from our lab, which allows one to 3-D print and anneal flexible metal electrodes and complex architectures 'on-the-fly,'" said Lewis.

Laser-assisted direct ink writing is superior to conventional 3-D printing because it allows the silver wires to be printed directly on low-cost plastic substrates.

It can produce sweeping curves and spirals and also sharp angular turns and directional changes written into thin air with silver inks. This technology opens-up nearly limitless potential applications in electronic and biomedical devices that rely on customized metallic architectures.

"The material is like toothpaste but made of silver. Toothpaste would be too floppy to hold its shape, but if you solidify it, you could hold it in midair," said Wyss Institute Postdoctoral Fellow Mark Skylar-Scott.

"We're no longer thinking about (3-D printing) as a layer by layer process. We still have gravity to fight, but now we can leave the substrate and go into free space."

Traditional 3-D printers slowly build objects by laying down successive layers of a material such as plastic and even food.

"This sophisticated use of laser technology to enhance 3-D printing capabilities not only inspires new kinds of products, it moves the frontier of solid free-form fabrication into an exciting new realm, demonstrating once again that previously accepted design limitations can be overcome by innovation," said Wyss Institute Director Donald Ingber, who is also the Judah Folkman Professor of Vascular Biology at Harvard Medical School and the Vascular Biology Program at Boston Children's Hospital, as well as professor of bioengineering at SEAS.

In addition to Lewis and Skylar-Scott, Suman Gunasekaran is a co-author on the study published in the Proceedings of the National Academy of Sciences. Gunasekaran is undergraduate researcher studying chemistry and physics at SEAS.

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