Smart textiles monitor health on a large scale

Materials World magazine
26 Jun 2020

By measuring deformations in fabric across large surfaces, smart textiles could feed back health and safety-related data. Idha Valeur finds out more.  

Researchers from École Polytechnique Fédérale de Lausanne, Switzerland, have created a smart textile with a soft one-dimensional sensor, marrying the concepts of electrical reflectometry, soft electronics and wearables. 

‘Practically, this means that we have created thin and deformable multi-material fibres that can be sensitive to, and localise, a variety of mechanical deformations applied simultaneously to the fibre,’ says Professor Fabien Sorin, at the University’s Laboratory of Photonic Materials and Fibre Devices. 

The transmission lines are made up of a gallium, indium and tin liquid metal conductor, as well as a thermoplastic elastomer block copolymer styrene-ethylene/butylene-styrene dielectric. The materials have been selected based on their mechanical and electrical properties as well as their processing attributes. The liquid metal offers a combination of deformability and conductivity, while the thermoplastic elastomer is an insulator as well as being soft and elastic.

The researchers believe this technology could be used in hospital sheets to monitor vital signs. Andreas Leber, Doctoral Assistant at the laboratory, explains how the soft transmission lines are able to differentiate between several types of movements, such as between stretching and bending. This allows it to overcome the hurdles of monitoring convoluted movements and working across large surfaces, currently facing smart textiles. ‘It consists physically of long and thin fibres, which can be intuitively integrated into textiles using existing techniques such as embroidery. Thus, we can capture the entire collection of fine and complex deformations that the textile is exposed to by integrating a single functional fibre.’ 

Sorin adds, ‘For example, when integrated into a textile, the fibre can evaluate and localise several pressure points applied on the 2D surface, while at the same time measuring any stretching of the fabric. The additional beauty of our approach is that we can do all of this with only two electrical contacts on one fibre end.’

The researchers foresee several applications for the smart textile such as in safety engineering where it is integrated into car seats to capture its pressure profile, determining if the passenger is an adult or child and if the airbag should be activated or not. Another area is healthcare – the textile can be integrated into bed sheets and chairs to eliminate cables attached to a patient. 

However, this poses the issue of hygiene. Leber outlines that the fibres are robust and, because they are soft and stretchable, they endure extreme strains. ‘In related studies we found that they bear humid environments and are even machine washable. Our approach would be to design a robust connector between the electronic textile and the peripheral electronics. The textile can thus be disconnected, treated in whichever way necessary, and then reconnected to the electronics. Alternatively, the electronic textile could quite simply be placed underneath a waterproof intermediate layer.’

Although currently at a proof-of-concept stage, the team has a three-step plan to develop it further. ‘First, we seek to scale down the peripheral electronics, which are needed to interrogate our soft transmission lines, both in terms of footprint and cost. Second, we will employ professional textile techniques to integrate the lines into textiles in a repeatable and scalable fashion,’ Leber states. 

‘Finally, we wish to validate our prototypes in real-world applications. This includes fashioning an electronic textile employable in hospital beds to capture the various mechanical loads and thus reconstruct valuable health signals, such as respiration and other important body movements.’

Sorin adds that for the long-term research, his team at the laboratory are starting to investigate several areas, including creating fibres that can sense and also actuate, plus tackling the issue of a power source by developing an integrated self-powering device.