Holst Centre : From printed electronics to sm...
Holst Centre

From printed electronics to smart clothes that reduce stress

Stretchable and flexible printed electronics (Source: Holst Centre)
Stretchable and flexible printed electronics (Source: Holst Centre)

Smart clothing is more than the functionality and technology it brings. It also delivers the full experience of clothing: comfort, safety and intimacy. As an answer to the current societal needs, Holst Centre, Eindhoven/Netherlands, has developed a platform of thin, stretchable and washable printed electronic technologies for smart clothing and wearable medical devices such as health patches.

The Holst Centre platform allows a wide range of actuators and sensors – including ECG and bioimpedance electrodes, LEDs, solar cells and temperature, oxygen saturation, strain and motion sensors – to be combined and manufactured together.

Shared characteristics
Printed electronics form the basis for both smart clothing and wearable medical devices. Holst Centre has been developing solutions based on hybrid and thin-film electronics for over sixteen years. Charlotte Kjellander, wearable technology leader at TNO at Holst Centre, explains: “We use the same sensors and actuators for both smart clothing and health patches, as they share the same platform of characteristics such as flexibility, conformability, softness and unobtrusiveness. We unite material know-how, processing skills, electrical design, garment and patch design and engineering to reach the most suitable device configuration for both smart clothing and health patches.”

From a garment-fabrication point of view, the printed electronics can be thought of as a lining that is integrated into the garment using common heat-bonding processes. This offers complete design freedom and facilitates recycling through delamination. The smart clothing items have been developed and validated on electrical and mechanical performance, washability and wearability, both in partner applications and in-house platforms.

MYSA shirt
Holst Centre designed the MYSA shirt with a holistic approach, uniting technology, fashion and human interactions in one garment. Kjellander explains: “Breathing is the essence of life: it regenerates our minds and bodies and has proven to prevent disease. One of today’s largest societal challenges, stress, is a serious threat to human well-being. Prevention requires personalised solutions that discreetly integrate into everyday life. Clothing presents an invisible solution for on-body sensing and actuation, enabling direct connectivity between the body and digital networks.”

She continues: “For the MYSA shirt, we collaborate with fashiontech Pauline van Dongen. We selected a Lyocell fabric made from natural and sustainable raw materials (cellulose from wood pulp), which is known for its silky soft feel and beautiful drape, creating a ‘second skin’. The sleeveless shirt can be worn on its own or layered with other garments.”

Vibrating buttons are positioned along the spine and at the lower back, and are connected to printed conductive tracks that are seamlessly bonded to the fabric. The back panel of the garment consists of a second layer that can be tied around the body to increase contact between the buttons and the body, enhancing the tactile sensation. Charlotte Kjellander: “In short, the shirt makes you aware of your breathing and signals you to breath deeper, reducing stress.”

MYSA – smart garment with vibrotactile feedback for stress prevention (Source: Holst Centre)

Large volume manufacturing
The breathing rate and depth are continuously monitored by measuring bio-impedance. Recent developments in dry-electrode skin-contact biosensors enable large volume production methods of ultra-thin and stretchable printed electronics suitable for integration in smart fashion articles.

Charlotte Kjellander: “With a feedback loop between sensor input and haptic output, breathing exercises can be adapted to the actual breathing rate of the wearer to achieve a more personalised interaction. Unlike existing mobile apps and wrist-worn wearables that focus on visual and auditory breathing guidance, the MYSA shirt communicates haptically, offering a screen-free solution.”

Flight sensing shirt
Another example of smart clothing is the so-called Flight Sensing Shirt, developed within an AEOLUS innovation programme performed by TNO, Holst Centre and the Dutch Airforce (RNLAF/CML). In order to understand unexplained physiological events, there is a need for sensors that monitor the physiological status of a pilot and provide real-time feedback. Charlotte Kjellander explains: “It is not easy to introduce reliable sensors into the environment of pilots. Those sensors must be able to record physiological data in adverse conditions such as accelerations larger than 8G, combined with extreme temperature and pressure changes. Additionally, the sensors must comply with aviation regulations. To meet these needs, our research focuses on the design of smart shirts with integrated sensors for reliable and robust physiological monitoring during flights.”

Holst Centre explored the dry-electrode technology as the basis for the flight sensing shirt. Charlotte elaborates: “The electrodes are laminated on stretchable circuitry that is printed on thermoplastic polyurethane (TPU) foils. The TPU is seamlessly laminated on to fabrics for a slim and comfortable fit. This creates ultra-thin medical-grade skin-contact sensors for ECG and bio-impedance monitoring. The specific location of the sensors was a subject of extensive research. We identified unique body positions to ensure high-quality sensor signals with low disturbance and we had to exclude motion artifacts resulting from pilot movements in the cockpit.”

Challenges in smart clothing development and design
Smart clothing poses challenging demands on the electronics: clothes have to be washed and re-used, and fit all unique body shapes. Charlotte: “The advantages are clear: they are flexible, ultra-thin, stretchable and production is scalable. But of course, stretchability has its limits. The ultra-thin electronics can break when stretched too far and they have to be encapsulated to survive washing, not once, but multiple times.”

By understanding the fundamental material properties and the electrical performance, knowing how to design the garment and position the electronics, Holst Centre is able to offset these drawbacks. Charlotte Kjellander underlines: “We do not only develop stretchable printed electronics, we know exactly how to integrate these into garments and make production scalable. We fully understand the entire process of developing a smart, personalised piece of clothing.”

Smart clothing with the power of touch
Holst Centre is in the process of spinning off the MYSA smart clothing platform. Charlotte: “The spin-off company, Being-in-Touch, will be realised within a few weeks. The name describes the goal for our smart clothing: a haptic, comfortable garment that guides breathing and increases body awareness.”

Charlotte gives a glimpse of what the future holds: “To gain insight in the qualities of MYSA, the next step is to perform field tests to validate the long- and short-term effectiveness in breathing guidance. With this, we aim to deliver value to people in their daily work environment by following our mission to increase body awareness for a vital life through the power of touch.”

This article was published in OPE journal, No. 39, June 2022

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