‘Green’ wearable sensors can detect early signs of hypothermia
Hypothermia onset can be detected by monitoring changes in skin temperature, slowing heart rate and body movements which can become less coordinated as body temperature drops to dangerous levels. But such sensors for remote monitoring and early warning alerts need to be lightweight, flexible and able to be worn next to the skin. An innovative wearable pressure sensor system based on natural and biodegradable materials has been developed from scratch by the WEARSENSNANO project. Unlike most rigid sensors, these are porous, can be compressed to accommodate body movements and are very lightweight. “These sensors can sit on a flower petal without any problem,” says Fevzihan Basarir, senior researcher at the Department of Chemistry and Materials Science, Aalto University, Finland. He developed the wearable sensors from scratch with the support of the Marie Skłodowska-Curie Actions programme.
Biodegradable sensor
The sensors are made of biodegradable materials, he notes, pointing to the huge problem of electronic waste around the world and the need for greener technologies. The project originally proposed a pressure sensor based on silver nanowires, but the synthesis ended with a low yield. “It means you waste a lot of silver and it is not biodegradable, so I shifted to biomass-based carbon paste,” Basarir explains. The ‘green’ sensor’s carbon electrodes are made from carbon cryogel particles mixed with natural wax and vegetable oil – producing a low-resistivity carbon paste. Porous dielectric material was prepared from pectin xerogels obtained by freezing and solvent exchange. “The response time of our sensor is 118 milliseconds, producing a repeatable and consistent result even with 10 000 cycles, so performance is really good,” he notes. The sensor was successfully applied in human motion detection such as walking, running, the wrist, movements of the index finger joint and knee bending, as well as smiling and eye blinking.
‘Do-it-yourself’ sensor
In addition, cost-effective capacitive pressure sensors were fabricated using readily available commercial components. To showcase their application, a sensor grid was fabricated on cotton fabric and integrated with an Arduino processor – a microcontroller integrated with open-source software that converts the sensor signals into data – to produce a wearable ‘keyboard’. The materials and components are all readily available on the market. Basarir described it as a “do-it-yourself sensor that anyone can make.” “The advantage is that it costs just EUR 0.073 including the cost of all the materials, so it is very cheap,” he says.
Use with the elderly
The system has been tested on healthy people with good results. Hypothermia requires measurements from both pressure sensors and temperature sensors but testing the system on people with hypothermia is not easy, Basarir explains. “If they have hypothermia they would normally be sent directly to hospital, so it is difficult to find people with hypothermia. The system has only been used to monitor healthy people so far.” He adds: “The next phase will be utilising the sensors with elderly people in their own homes.” He notes that the elderly are an important target group, as a fifth of the population in Europe is over 65, and this will rise to 30 % of the population within 25 years. The work also chimes with research into other wearable technologies such as the European Research Council funded ModelCom project on adapting smart soft materials into textiles that react to the environment, and other smart wearables such as the Smart2Go project.
Keywords
WEARSENSNANO, hypothermia, sensors, nanowires, biodegradable, pressure sensors, wearable sensors, elderly
