Smart Sweatshirt Monitors Your Health

The underlying technologies may still be in the early stages of development, but even still, wearable sensors are already transforming the way we monitor and evaluate health and athletic performance. They have shown themselves to be capable of enabling the collection of vital signs, biomarkers, and other physiological signals in a minimally invasive and convenient manner. These devices have proven to be immensely valuable in providing real-time feedback, allowing individuals to make informed decisions about their well-being and optimize their performance.

The utility of wearable sensors lies in their ability to continuously track and analyze a wide range of physiological parameters. For instance, heart rate monitors, worn as wristbands or chest straps, offer insights into cardiovascular health and provide valuable data during exercise or daily activities. Similarly, on-skin patches can collect and analyze sweat samples to measure parameters such as glucose levels, body temperature, and oxygen saturation.

Despite their numerous benefits, it has become clear that wearable sensors can cause stress on the subject due to their potential for discomfort and intrusiveness. The physical presence of these devices on the body can lead to pain, skin irritation, allergic reactions, or restrictions in movement. Moreover, some individuals may find the constant monitoring and feedback overwhelming, leading to heightened stress levels or anxiety.

Moving those wearable sensors away from direct skin contact, and instead transparently embedding them in the clothing that we normally wear, might enable monitoring without these drawbacks of traditional methods. That is the belief of a team of researchers at the Tokyo University of Science, anyway. They have developed a simple fabrication method that allows sensors to be printed onto articles of clothing for the non-invasive monitoring of biomarkers.

The team applied their methods to the problem of detecting chloride ions in sweat. Chloride is the most prevalent electrolyte in human sweat, so it serves as an important indicator of the body’s overall electrolyte balance. It is also useful in diagnosing and preventing certain medical conditions, like heat stroke. Since this biomarker is typically monitored with on-skin patches that can cause irritation, a clothing-based sensor would be desirable.

The sensor was fabricated using a heat-transfer printing process in which layers of overcoat ink, carbon ink, Ag/AgCl ink, resist ink, and adhesive are first printed onto a substrate that has been treated with a release agent. The functional design of the sensor is laid out in the conductive inks. The entire device is then transferred to an article of clothing by applying heat, which causes the adhesive to activate and the substrate to be released.

As the sensor was transferred to the outside of a shirt, it does not come into direct contact with the skin. This makes the chance of irritation very small. Moreover, the fabric serves an important role via a wicking effect that allows sweat to spread evenly between the sensor’s electrodes. As a result, the device is able to establish, and maintain, a good electrical contact.

A series of experiments were conducted to assess the performance of the sensor. In one such test, a volunteer exercised on a static bicycle for 30 minutes. During this time, measurements were taken from the wearable sensor, and also from blood and saliva samples. Based on these experiments, it was observed that the new textile-based device was capable of accurately measuring the concentration of chloride ions in sweat.

For practical, real-time monitoring applications, the researchers demonstrated how the sensor could be paired with a wireless transmitter to instantly forward measurements to a smartphone app. It is their hope that this new technology will advance the fields of personalized medicine and athletic training management by enabling the collection of vital information where it was not previously practical.