Bio-interfacing and biodegradable flexible hybrid electronics (FHE) devices can help tackle some of the world’s great challenges including environmental degradation and food scarcity.

Body-interfacing electronics has existed for decades. Developed in the 1970s, the wireless heart rate monitor is a good example. While continuous heart monitoring with a compact, inexpensive wearable device is widely accessible technology, other bodily parameters, such as hydration levels or stress biomarkers, have not usually been captured with wearable devices. However, establishing a baseline health state, and its deviations from this baseline, is a much more comprehensive approach.

That’s where bio-interfacing comes in. Bio-interfacing devices can continuously measure and analyze complex biogenic substances such as sweat, breath, blood, and urine. A smart patch for continuous sweat monitoring, for example, would overcome several challenges in biological testing. Data collection by a wearable patch combines sample collection and transport, readout electronics, and data processing within a single device and reduces the amount of infrastructure around sample handling, contamination avoidance, and sample disposal.

While FHE in principle delivers the right building blocks and is an ideal form factor for a wearable sweat analytics patch, flexible circuits are not yet ready for out-of-the box interaction with biological matrices. However, our mission at VTT Technical Research Centre of Finland, Ltd. (Espoo, Finland), is to anticipate and develop the upscaling of process know-how required for FHE devices that either interface with biological systems — or that must themselves biodegrade.

We’re also focusing on biodegradable electronics. Environmentally conscious end-users and manufacturing companies want biodegradable versions of energy-autonomous, label- or sticker-like Internet of Things (IoT) sensors. Typically used for packaging, logistics, and environmental monitoring as well as medical diagnostics applications, these sensors — which have a lifetime of a few days, weeks, or months, but used in large quantities — have become very popular. Unless they are biodegradable, however, they just add to landfill.

In our Business Finland-funded “ECO-tronics ” ecosystem project, we are working with research and industrial partners to create recyclable and compostable electronics and optics that use renewable resources. For example, devices developed using substrate materials like paper, cardboard, or VTT’s in-house-developed nanocellulose films and biopolymer films for environmental monitoring or skin patches, can be easily recycled or even biodegrade naturally. Where possible, we use roll-to-roll printing to generate the device circuitry with efficiency of energy and material, and on a component level, we have optimized our assembly process towards bare-die component bonding to reduce the overall footprint of non-biodegradable waste per device.

Refining the Environmental Impact of Single-Use Tests

Figure 2. A prominent example of a single-use test that generates a large amount of waste is the digital pregnancy test. (Photo credit: hartphotography/Shutterstock)

A prominent example of a single-use test that generates a large amount of waste is the digital pregnancy test. When breaking it down into components, you will find a rigid circuit board with a microprocessor, a couple of coin cell batteries, a liquid crystal display, an LED light source and photodiode, and a large chunk of plastic packaging around it. The materials and battery capacity of such a device would be sufficient to run hundreds of pregnancy tests — actually technical overkill. By using printed circuits on biodegradable substrates, bare-die assembled components such as ASICs, LED light sources, photo diodes, and thin film batteries as power sources and also device packaging composed of biodegradable plastics, the environmental footprint of single-use tests can be completely redefined. We are currently developing a toolbox to transform existing conventional tests into ECOtronic form factors.

Sweat Sensor

Another exciting use case is a sweat sensor that we developed collaboratively with Ali Javey, Ph.D., professor of Electrical Engineering and Computer Sciences, UC Berkeley, and the co-director of Berkeley Sensor and Actuator Center (BSAC). Together with his team, we created a wearable electrochemical sensor for continuous sweat analysis during exercise. With the UC Berkeley group providing the chemistry to monitor N+, K+ ion and hydration levels in sweat over the duration of several hours, VTT delivered the underlying sensor platform, featuring the printed sensor electrodes and sweat harvesting microfluidic channels for fluid management and transport. It’s exciting to see what we can achieve by combining techniques from different disciplines, in this case electrochemistry, printing, packaging, and microelectronics.

Scalability

As many FHE devices target large-volume markets, scalability of manufacturing is key: How can I get from a working prototype to a handful of devices (a feasibility study); to thousands (pilot manufacturing); to a million (mass manufacturing); without compromising the quality of the system’s performance and reliability?

Figure 3. VTT has developed a roll to roll process for manufacturing sensor arrays. (Image credit: VTT Ltd.)

Infrastructure is essential for the development of novel FHE devices and methods, but infrastructure is expensive. That’s where our establishment of a roll-to-roll pilot printing line to bridge the gap between laboratory R&D and mass manufacturing has proved invaluable. We can provide a unique worldwide upscaling infrastructure for advanced FHE devices, with a strong focus on large-area roll-to-roll processes and hybrid assembly. This service removes our customers’ burden of high infrastructure investment in the early development stages and it allows us to guide customers along their development path, from prototype to mass production.

The success of FHE devices depends on several factors: It requires a high degree of automation, well-optimized processes, reliable supply chains, and perhaps most importantly, clear standards and rules for designers to guarantee flawless interoperability of all the different elements on a flexible and hybrid circuit.

The latest technologies and innovations in microelectronics, MEMS, printing, materials, and biosensors provide us a toolbox for true innovation in the FHE space. Now we need cross-disciplinary thinking and daring steps to combine different manufacturing methods and skillsets. The ideal cross-disciplinary team might include:

  • The printing engineer who knows how to design contact pads for a bare-die IC assembly.

  • The biologist who knows about the thermal and mechanical stress in a printing environment to design processes for bio-functionalization of surfaces.

  • The electronics engineer who knows how to optimize a circuit powered with an enzymatic biofuel cell.

Eyes on the Future

The number of sensors deployed on (or inside) our body, in our drinking water, in our cars, on our fields, in our pets, and everyday products will surely grow. Let us make sure they leave the smallest environmental footprint possible.

This article was written by Dr. Antti Vasara, President & CEO of VTT Ltd. , Espoo, Finland. For more information, visit here .


Sensor Technology Magazine

This article first appeared in the June, 2020 issue of Sensor Technology Magazine.

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