Photo of Soft Sensors
Safe, soft sensors on the top and tip of the index finger detect the movements, strain and force of the finger while performing different activities, such as flexing and extending the finger and picking up weights and boxes. (Credit: Siyi Xu, Daniel M. Vogt, and Andreas W. Rousing/Harvard SEAS)

Researchers have developed a soft, non-toxic wearable sensor that unobtrusively attaches to the hand and measures the force of a grasp and the motion of the hand and fingers. It could help children born prematurely who often develop neuromotor and cognitive developmental disabilities.

The best way to reduce the impacts of those disabilities is to catch them early through a series of cognitive and motor tests. But accurately measuring and recording the motor functions of small children is tricky. As any parent will tell you, toddlers tend to dislike wearing bulky devices on their hands and have a predilection for ingesting things they shouldn’t.

The sensing solution is made from potassium iodide, which is a common dietary supplement, and glycerol, which is a common food additive. After a short mixing period, the glycerol breaks the crystal structure of potassium iodide and forms potassium cations (K+) and iodide ions (I-), making the liquid conductive. Because glycerol has a lower evaporation rate than water, and the potassium iodide is highly soluble, the liquid is both stable across a range of temperatures and humidity levels and highly conductive.

The design of the sensors also takes the need of children into account. Rather than a bulky glove, the silicon-rubber sensor sits on top of the finger and on the finger pad. This research only tested the device on adult hands. Next, the researchers plan to scale down the device and test it on the hands of children.