Bring convenience to wearable electronics with TPU's hybrid 3D printing technology
HC Plastics News: A common cause of malfunctions in wearable electronic devices is the mismatch between rigid electrical components and soft, flexible materials that conform to human motion. This mismatch is concentrated at the stresses of the connection of the hard and soft materials. Today, researchers have created a new soft-electronic additive manufacturing technology called hybrid 3D printing that integrates flexible conductive inks and thermoplastic polyurethane (TPU) with rigid electronic components into a single stretchable device. Researchers believe this is the first step in making customizable, wearable electronics, at a lower cost than current equipment, and with good mechanical stability.
The device consisting of 12 light-emitting diodes (LEDs) on a flat thermoplastic polyurethane sheet produced by hybrid 3D printing is repeatedly bent into a cylindrical shape, however, the light intensity of the LED does not decrease and the device does not experience mechanical failure. Image courtesy of Harvard University Alex Valentine, LoriK. Sanders and Jennifer Lewis.
This major breakthrough was discovered by the Jennifer Lewis lab at Harvard's Wesley Institute for Bioinspired Engineering and Dr. Daniel Berrigan and Dr. Michael Durstock at the Harvard John Paulson School of Engineering and Applied Sciences (SEAS) and J. US Air Force Research Laboratory. of. The study is described in detail in the press release on the WyssInstitute website reproduced below, and a paper on this research is published in Advanced Materials magazine.
The stretchable conductive ink is made of a TPU mixed with a sheet. Pure TPU and silver-TPU inks were printed to create the underlying soft substrate and conductive electrodes of the device, respectively. "As the substrate and the electrodes contain TPU, they are strongly bonded to each other before drying," After the solvent evaporates, both inks solidify, creating an integrated system that is both soft and stretchable."
The printing process causes the silver flakes in the conductive ink to self-align in the printing direction, so that their flat slab sides are stacked on top of each other, such as overlapping blades on forest land. This structural alignment increases the ability to conduct electrical energy along the printed electrodes. Dr. WillBoley said, “Because inks and substrates are 3D printed, we have full control over the position of the conductive features and can design circuits to create soft electronic devices of almost every size and shape,†said Boley, Lewis Laboratory of SEAS. Postdoctoral researcher and co-author of this article.
Researchers combine the changes in conductivity exhibited by soft sensors composed of conductive materials (ie, how they detect movement) with programmable microcontroller chips to process experimental data and communicate data in a form that humans can understand. To achieve this, the researchers combined the printed soft sensor with a digital pick and place process that applied a moderate vacuum through an empty print nozzle to pick up the electronic components and place them on the substrate surface in a specific programmable manner. on.
Because these surface mount electrical components are inherently rigid and rigid, the team utilized the adhesion properties of the TPU before applying it to the underlying soft TPU substrate, applying a little TPU ink under each component. Once dry, the TPU points anchor these rigid components and distribute stress throughout the matrix, allowing the device to be stretched to 30% while maintaining performance. The device consisting of 12 light-emitting diodes (LEDs) on a flat TPU sheet manufactured using this method can be repeatedly bent into a cylindrical shape without causing a decrease in the light intensity of the LED or a mechanical failure of the device.
As a simple proof of concept, the team created two soft electronics to demonstrate the full capabilities of this additive manufacturing technology. Strain sensors are fabricated by printing TPU and silver-TPU-ink electrodes onto a textile substrate and applying the microcontroller chip and readout LEDs by pick and place methods. The resulting wearable sleeve-like device represents the degree of bending of the traverser's arm through the continuous illumination of the LED. A second device, a human left footprint shaped pressure sensor, is formed by printing alternating layers of conductive silver-TPU electrodes and insulating TPU to form a capacitor on the flexible TPU substrate. The morphing pattern is processed by a manual electrical reading system to create a visual image of the foot as the person steps on the sensor.
Hybrid 3D printing has been widely used to manufacture countless electronic devices as teams continue to optimize materials and methods. Lewis said: "We have expanded the palette of printable electronic materials and expanded the programmable multi-material printing platform to enable digital selection of electronic components."
Dr. Don Ingber, Ph.D., founding director of Wyss and professor of vascular biology at Harvard Medical School and Boston Children's Hospital, and professor of bioengineering at Harvard SEAS, said, "This new approach distinguishes the Wyss Institute from many other laboratories. A good example of interdisciplinary collaborative work, we are building the future by combining the physical precision of 3D printing with the digital programmability of electronic components."
The study was supported by the Air Force Research Laboratory Materials and Manufacturing Bureau and UES, the VannevarBush Professor Scholarship Program at the Naval Research Office, GETTYLAB, and Harvard University's Wyss College. 
Editor in charge: Wang Ning 12
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