Hybrid 3D printing: The next level of flexible wearables manufacturing

It’s 5pm, and it’s time to call it a day. You turn your computer off, but remember that you still need to send a couple of emails. You fold your new laptop a few times, much like you’d fold a piece of paper, and put in your bag. As you do, you don’t even notice the flexible, clear patch on your hand that locks and unlocks office doors and ensures that the lights are off when you’re not there. And it takes care that the AC is off, saving you the trouble of remembering these trifles.

But this can’t really be called ‘the future’, as these things will be commonplace much sooner than you might think. It’s all thanks to a torrent of tech breakthroughs emerging daily.

Flexible 3D-printed wearables

The electronic industry is evolving so fast that we can barely keep up with all the breakthroughs. It’s not that long ago that we we’re using computers with processing power far weaker than the average smartphone sports now. Then came laptops, tablets, and all the ‘smart’ gadgets that enable our mobile, digital lives. Most recently, we’ve seen a new generation of smart sensors that are unparalleled in their versatility: they’re used in the healthcare sector (think of ‘patches’ that measure your temperature and blood pressure), in the automotive industry (car proximity sensors that help you park your car), and in agriculture (drones equipped with sensors that ensure better yields by providing accurate data about soil quality, humidity, pest infestation, and so on). But they’re about to get a substantial upgrade through the application of stretchable electronics.

The next generation of sensors will be pliable and ‘bendy’. Thanks to their flexibility, they can be attached to any surface. Just imagine sensors that are comfortable to wear against your skin while they’re collecting data about your health, or in sports where a player won’t be distracted by the sensors that measure muscle strain, hydration, and heart rate, preventing unnecessary injuries. These go anywhere sensors promise to leverage smart tech in new and exciting ways.

And according to the latest Research and Markets’ report, the market for this emerging field will hit $ 360 billion by 2021, at a compound annual growth rate of 106.18 per cent. Stretchable electronic devices demonstrate immense potential for a number of applications. But the quest for finding the best way to manufacture ‘stretchable electronics’ is a bit of a challenge as electrical components in general tend to be rigid.

To enable this new tech, researchers at Missouri University of Science and Technology are using 3D printing, also known as additive manufacturing, which allows printing “highly conductive materials onto an elastomer surface layer by layer”. In plain English, 3D printing allows them to print circuitry in flexible plastics. Their project, dubbed ‘direct aerosol printing’, “involves spraying then integrating a conductive material with a stretchable substrate”.

Heng Pan, an assistant professor of mechanical and aerospace engineering at the Missouri University of Science and Technology, outlined for R&D Magazine the advantages of 3D printing in manufacturing ‘stretchable devices’. “Additive manufacturing has the benefit that it can easily change from one material to the other and integrate all the different materials together in one print. You can pretty much print any material in 3D geometry. We believe the additive technique has a very strong advantage in the creation of electronics,” said Pan. However, the team acknowledges other issues that require more work, such as “improved longevity and the development of stretchable batteries.” “We are intensely working on the battery”, he shared.

But scientists at Harvard University have managed to find a way to manufacture “flexible, durable wearable devices that move with the body and offer increased programmability”, and this is going to be a real game changer for the world of stretchable electronics.

Hybrid 3D printing

A collaboration between the Wyss Institute at Harvard University, Harvard’s John A. Paulson School of Engineering and Applied Sciences, and the Air Force Research Laboratory, has resulted in developing a method “that integrates soft, electrically conductive inks and matrix materials with rigid electronic components into a single, stretchable device”. They’re using thermoplastic polyurethane (TPU), both pure and with silver flakes, to make the circuits and the flexible layers.

And simplicity is the key here. As Alex Valentine, who was a staff engineer at the Wyss Institute when the study was completed, explained, “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.  After the solvent evaporates, both of the inks solidify, forming an integrated system that is both flexible and stretchable.” As a proof-of-concept, the team created two devices – “a wearable sleeve-like device that indicates how much the wearer’s arm is bending through successive lighting-up of the LEDs” and “a pressure sensor in the shape of a person’s left foot”.

But the possibilities for their methods are nearly endless. Jennifer Lewis, of the School of Engineering and Applied Sciences (SEAS) and the Wyss Institute for Biologically Inspired Engineering at Harvard University said that “We believe that this is an important first step toward making customizable, wearable electronics that are lower-cost and mechanically robust.”

There’s no doubt that stretchable electronics industry may have a bright future and we’re excited to see developments in this area in years to come.

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