Biomedicine

Clothes That Monitor Health

A new patch tracks electrolyte levels in sweat.

A new patch could one day monitor a person’s health using minuscule sweat samples. The patch is being developed by Biotex, a consortium of European research institutes and companies, including the Swiss Centre for Electronics and Microtechnology (CSEM).

Sweat collector: Researchers have designed a wearable sensor (shown above, in orange) that can continuously monitor electrolyte levels, such as sodium, in sweat.

Most clothing designed for health monitoring focuses on physiological measurements, such as body temperature and heart rate. This is one of the first attempts to continuously analyze biochemical signals using clothing. The team employed a novel approach for monitoring: a combination of hydrophilic and hydrophobic yarns woven together to channel the sweat to the sensors. By utilizing natural attraction and repulsion actions to move the sweat, the method also circumvents the need for additional power sources, which would add bulk to such a device and make it less convenient for everyday use.

Once the fabric has directed a few milliliters of sweat into the patch, the sensors determine the amount of potassium, chloride, or sodium present. Measuring these electrolytes can provide insight into a person’s metabolism. By comparing the electrolyte amounts to reference measurements, such a system could indicate if the user is overexerting herself or stressed, says Jean Luprano, project coordinator at the CSEM.

Once the tiny reservoirs are full of sweat, the user throws away the chemical part of the patch, which is about 5 to 10 square inches. The patch-embedded band or shirt can be washed, and the monitoring electronics reused.

“There are tons of people doing biomechanical and physical tests; most of them look at heart rate and body temperature,” says Jeffrey Chu, director of engineering at Simbex, a company that develops products on biomechanical feedback systems. But testing biochemical properties, he says, is “truly unique.”

“The idea of Biotex is to go beyond the normal measurement systems,” says Luprano. Aside from the electrolytes, sensors can also detect the commonly monitored pH, pulse, sweat conductivity, and oxygen saturation to monitor health.

Luprano and his colleagues plan to test the patch to see how well it works with two key groups: obese children and diabetics. Aside from the potentially helpful self-monitoring that the patch would allow, the system could also help researchers collect more data on these groups. Luprano says that during the next two weeks, the system will be tested on approximately 10 subjects. They will wear the sensor on their backs while riding a bike; meanwhile, physicians will read the output in real time.

Traditionally, diabetics use a glucometer for self-monitoring, which requires pricking a finger to get a blood sample. Biotex does not intend for its patch to replace this process, but Luprano says that the continuous monitoring provided by the patch could yield insight into individuals’ conditions.

For obese children, the patch could shed light on metabolic problems. Luprano says that the device is intended to be used for remote biochemical monitoring not only for research, but also to fill in the gaps between visits to the doctor.

Often referred to as smart clothes, such health-monitoring systems have been discussed for many years. Chu says that to be a commercial success, the system would have to be easy to put on, collect meaningful data, and convey the data in a useful way.

Currently, the wearable device is wired to a computer that the physician monitors. Eventually, the researchers will have to incorporate a display for the user as well, or take advantage of digital displays that he might already have, such as a cell phone. If the device detects heightening stress levels, it could send the user a text message, for example, telling him to relax.

Rehmi Post, a recent MIT Media Lab graduate who now develops electronic textiles for the companies Adozu and Asteism, is skeptical. “There’s so much that can go wrong,” he says, because chemical properties vary widely in a person and can depend on mood. “There are all sorts of factors [that are] difficult to control,” he says. “A lot of these initiatives are announced and don’t seem to make it to the market, because they tend to be expensive.” But Post says that he is glad that smart clothes are being studied for health-care applications and that the field is branching out from its roots in the military.

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