Printed sensors are flexible, adaptable and compact. That's why they increasingly find their way into medical applications that remain beyond the grasp of earlier sensors. Wearable sensor technology is an example of this - adhered directly to the patient's skin or embedded in clothing.
Printed sensor next to a running shoe.
Large quantities of printed sensors can be produced inexpensively and with moderate effort because the process is similar to printed products on paper. There are basically two production methods to create them: one is inkjet printing, the other is roll-to-roll processing (R2R). In the former case, a solution of conductive polymers is printed on a substrate, similar to how it works with a home or office inkjet printer. However, instead of being printed on paper, sensors for medical applications are printed on carrier foils, from which they can be peeled off and adhered to the patient's skin.
Once the aqueous components of the printed solution have evaporated, a solid structure is left behind. It is frequently very thin, yet elastic and conductive to where it renders measurements on patients possible. "Neurophysiologists tell us that this type of technology opens the door to new applications, especially when it comes to ECG recordings. Key examples of this are applications for recording brain waves or facial electromyography (fEMG)," says Professor Francesco Greco in a COMPAMED-tradefair.com interview. Along with his team, he develops inkjet-printed sensors at the Institute of Solid State Physics at the Graz University of Technology.
In R2R processing, the desired structure is printed directly from one roll that features a mirror image of the structure onto a foil or other flexible substrate that runs over said roll. The substrate is gradually rolled off at one side of the printing machine and rolled up at the other end after the printer solution has dried. "During the first step of the sensor production, we print the graphene electrode structures onto a foil. In a second step, we coat the electrodes in the same unit and also with a protein layer during the same cycle, which ensures improved cell adhesion," says Dr. Thomas Velten, Head of the Biomedical Microsystems Department at the Fraunhofer Institute for Biomedical Engineering (IBMT).
The inkjet printing and R2R processing methods make a fast and low-cost serial production of sensors possible. Printed sensors - or more commonly printed electronics – have an edge over conventional electronics, which is manufactured using expensive and sophisticated processes, such as etching for example. Having said that, one drawback of printed sensors is their reduced durability. Since the conductive layer is printed on a flexible substrate, it is more prone to damage. One example of this is sensors worn on areas of skin that are more stressed and in frequent motion. Both aspects make printed sensors destined for one-time use. However, unlike earlier approaches, they are less complex, save costs and conserve resources. Meanwhile, Francesco Greco and his team are already working on sensors that exhibit longer durability by comparison. "We have tested the electrodes for up to five days in some new experiments and they still worked quite well."
Printed sensors at COMPAMED 2018
The COMPAMED HIGH-TECH FORUM by IVAM will highlight printed sensor technology with a session on Monday, November 12, during the COMPAMED 2018 trade fair. R2R sensor technology manufacturing will be the primary focus. An application scenario for a wearable sensor is also on the agenda: Eero Kaikkonen from the Finnish company Movesole Oy introduces the MoveSole StepLab. These sensor-equipped shoe insoles enable gait measuring along with an app and thus promote the healing process of diabetic foot ulcers. It also enables gait analysis outside of biomechanical laboratories, hospital or rehabilitation facilities.
This illustrates one of the biggest advantages of printed sensors that is not related to their production but pertains to the benefit for patients: since the sensors can be discreetly worn on the body and do not cause any discomfort or concerns, it might make it easier to monitor chronic diseases and conditions and make things more comfortable for patients in the future.
Lectures during COMPAMED 2018
Learn more about printed sensors in these lectures at COMPAMED 2018: