The structure of the ultrathin mesh-type polymer PTC thermistors used in wearable medical devices. (Credit: Chihiro Okutani/Shinshu University)

On-skin medical sensors and wearable health devices must be flexible and ultrathin so they can move with the human body. Researchers demonstrated how an important component of the sensors — a thermistor — can be constructed using an ultrathin fiber-mesh. Thermistors are a type of resistor whose resistance significantly varies with temperature.

Researchers used electrospinning to create the ultrathin mesh-type polymer PTC thermistor. The newly designed thermistor was then tested to ensure that it achieved similar performance capabilities of existing technology. Like typical film-type thermistors, the mesh-type polymer PTC thermistor showed an increase in resistance of three orders of magnitude, an important characteristic for preventing overheating and burns.

By using a mesh structure, the thermistor also achieved transparency, which can help the sensors blend into the skin, and gas-permeability. Gas-permeability is necessary because it prevents irritation and discomfort.

Even with this fiber layer, which serves to give the mesh structure and additional heat sensing, the thermistor remained very thin. This is important because any wearable medical device must be able to withstand bending and when the device is thinner, there is less strain.