Sep 6, 2017 | By Benedict

The Wyss Institute at Harvard University and the US Air Force Research Laboratory have collaborated on a new “hybrid 3D printing” technique for soft electronics. The technique can be used to make wearable electronic devices.

Big-brand wearable electronics like the Apple Watch aren’t everyone’s cup of tea, but there’s no doubting that soft electronics have a major role to play in future tech innovations, especially in areas like sport and human performance analysis.

A new collaboration between the Wyss Institute at Harvard University and the US Air Force Research Laboratory could be about to take wearable electronics to the next level, with the two institutions creating an additive manufacturing technique for soft electronics called “hybrid 3D printing.”

The potential of the new process could be massive. According to the researchers involved, hybrid 3D printing integrates soft, electrically conductive inks and matrix materials with rigid electronic components into a single, stretchable device.

Electronic sensors can be 3D printed directly onto the soft material, while the process can also digitally pick-and-place electronic components and print the conductive interconnects that complete the electronic circuitry required to read sensor data.

Importantly, the technique could significantly reduce manufacturing time and cost, and could result in more robust devices.

“With this technique, we can print the electronic sensor directly onto the material, digitally pick-and-place electronic components, and print the conductive interconnects that complete the electronic circuitry required to ‘read’ the sensor’s data signal in one fell swoop,” says first author Alex Valentine, who was a Staff Engineer at the Wyss Institute.

During the new 3D printing process, a stretchable conductive ink made of thermoplastic polyurethane (TPU) mixed with silver flakes is 3D printed onto a TPU substrate, “providing complete control over where the conductive features are patterned” and enabling the construction of soft electronic circuits “of nearly every size and shape.”

The process causes the silver flakes in the conductive ink to align themselves along the printing direction so that their flat, plate-like sides layer on top of one another.

“Because both the substrate and the electrodes contain TPU, when they are co-printed layer-by-layer they strongly adhere to one another prior to drying,” explains Valentine. “After the solvent evaporates, both of the inks solidify, forming an integrated system that is both flexible and stretchable.”

A programmable microcontroller chip and readout device (for interpreting the sensor's data in a manner that humans can understand) are integrated into the soft sensor using the digital “pick-and-place process” that applies a modest vacuum through an empty printing nozzle.

This vacuum printing nozzle—through which ink is usually dispensed—can be programmed to place electronic components onto the substrate surface in a precise manner.

But the researchers found a clever way to ensure that these rigid electronic components remain compatible with the stretchable device: a dot of TPU ink is placed beneath each component prior to attaching it to the underlying soft TPU substrate. These TPU dots, when dried, anchor the rigid components and distribute stress throughout the entire matrix. This means the devices can be stretched up to 30 per cent while still maintaining function.

Of course, readers will be most interested in seeing exactly what hybrid 3D printing can make, and the research team has obliged with two impressive demonstration products.

One involves a strain sensor, made by printing silver-TPU-ink electrodes onto a textile base and applying a microcontroller chip and readout LEDs with the pick-and-place tech. The result is a wearable sleeve-like device that can precisely measure how much a wearer’s arm is bending, indicating the results through an LED display. This wearable device could be used to analyze an athlete’s throwing technique, for example.

The other device, a pressure sensor in the shape of a person’s left foot, was made by “printing alternating layers of conductive silver-TPU electrodes and insulating TPU to form electrical capacitors on a soft TPU substrate.” Deformation patterns in the device are then visualized in a “heat map” of the foot when the user steps on the sensor.

The researchers—Alexander D. Valentine, Travis A. Busbee, John William Boley, Jordan R. Raney, Alex Chortos, Arda Kotikian, John Daniel Berrigan, Michael F. Durstock, and Jennifer A. Lewis—have published their findings in the journal Advanced Materials, in a paper titled “Hybrid 3D Printing of Soft Electronics.” It can be read here.

Lewis, one of the researchers involved in the project, is the brains behind the Voxel8 Developer’s Kit 3D printer. She says the new hybrid 3D printing process is incredibly exciting: “We believe that this is an important first step toward making customizable, wearable electronics that are lower-cost and mechanically robust.”



Posted in 3D Printing Technology



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