A new spray device can turn them into wearable sensors

Purdue University scientists have developed a new spray device and a flexible and conductive polymer that can be sprayed onto any clothing to turn it into a wearable sensor that can be used to monitor human movement during physical therapy. The relevant paper was published in the latest issue of ACS Nano.

The newly developed spraying device contains two chambers, each filled with a different compound. These compounds are mixed only during the spraying process and chemically react to form polymers. The solid, elastic and conductive polymer formed in this reaction then hits the fabric and becomes the most important component of the strain sensor. The researchers say they can place the polymer in any way with sub-millimeter precision.

When they stretch the fabric, the polymer pattern, such as wavy lines or spirals, stretches with it, changing its electrical resistance. The researchers spray-coat a pattern on a glove or kneepad and then detect movement of a hand or leg joint by running a small current through the polymer and monitoring changes in its electrical resistance.

The study found that the approach worked well on common fabrics such as cotton, wool and lycra. Furthermore, after adding a commercial fabric sealant to the polymer, the garments continued to function as sensors even after 30 washes.

The researchers say the spray-on method could be used in physical therapy or other medical settings, where adding sensors to a patient's clothing is more practical than using bulkier devices with hard parts and wires. They hope to design more polymers with slightly different chemical compositions that can sense not only strain, but also properties such as pressure, temperature or the chemicals present in sweat.