Wearable Tech Goes Green

The full promise of wearable and sticker-like flexible electronics has not yet been realized due to a number of technological challenges. But given the speed of innovation we have grown accustomed to in recent decades, it should be safe to say that these issues will be largely resolved in the near future. When that happens, a world of new applications ranging from health monitoring and IoT to smart packaging will be enabled.

Wearable electronics, once perfected, will revolutionize healthcare. Imagine a world where you can monitor your vital signs continuously, effortlessly, and with high precision, thanks to a comfortable and unobtrusive electronic patch on your skin. This could enable early detection of health issues, allowing for prompt intervention and improved patient outcomes. Doctors could remotely monitor patients, and individuals could take greater control of their health, all while going about their daily lives.

And that will be just the tip of the iceberg. In augmented reality and virtual reality, wearables will transport users into immersive digital worlds, redefining gaming, education, and training experiences. Additionally, wearables will have a pivotal role in workplace safety, especially in hazardous environments, by continuously monitoring environmental conditions and the health of workers.

And as that list of use cases continues to grow, so will the number of devices — many of which will be disposable. It is easy to envision the number of wearable devices being produced dwarfing the number of smartphones. That will mean piles and piles of e-waste, and the environmental threats and loss of valuable resources that come with it.

A team of engineers at Carnegie Mellon University and the University of Coimbra believe that the time to start planning for this future is now, before it arrives. Towards that end, they have developed an eco-friendly conductive ink, a crucial component in the flexible, thin-film circuitry needed to produce wearable electronics. The ink has excellent electrical and mechanical properties, and is very easy, and environmentally-friendly, to recycle.

Printing and processing of traditional conductive inks for flexible circuits relies on toxic organic solvents that can impact human health and threaten natural ecosystems. Moreover, they tend to require refrigeration for long-term storage, further exacerbating issues with energy consumption and pollution.

In contrast, the researchers’ approach leverages a combination of silver flakes, waterborne polyurethane dispersion, and a liquid metal alloy. The materials are free of organic solvents, and can be produced and stored at room temperature. The inks are printable and require no thermal sintering or other high-energy steps to produce a circuit. The properties of the ink make it suitable for attaching traces to surface-mounted chips and other devices. Additionally, the ink is highly electrically conductive and tolerant to mechanical strain.

Recycling the material is as simple as placing it in alcohol and letting it dissolve. The silver, and any electronic components, can be recovered, and no harmful or toxic e-waste remains behind. The simplicity of the recycling procedure makes even single-use devices much more environmentally-friendly.

To demonstrate their innovation, the team produced a printed smart sticker that includes a temperature sensor. This smart sticker was attached to a package of meat to monitor its temperature during transportation and storage. If the temperature rose above a critical threshold at any point, an LED would be illuminated to indicate that the product may be spoiled. The LED would remain illuminated even if the temperature dropped back down to a safe level.

Similar devices were developed to monitor both body temperature and muscle movements, but it is important to note that these systems were all supported by traditional, rigid electronics like microcontroller development boards and batteries.

There are still a number of problems to be worked out to make devices like this practical, but the focus of this research team was on developing a performant, environmentally-friendly conductive ink. Until other technologies catch up with these prototypes, we will have to continue to wait for the future of wearable devices.