The device can track the amount of bending of fingers, knuckles and wrist, and distinguish the differing extent of movement occurring simultaneously in all the three joints of the hand, says Chandramouli Subramaniam (left) and Mihir Kumar Jha.

The device can simultaneously measure the amount of motion taking place in all the three joints during any activity or gesturing.

A thin, light, wearable gesture-tracking device that behaves like a second skin and is able to precisely detect mechanical movements such as bending and stretching of the joints of the hand — fingers, knuckles and wrist — has been developed by researchers at the Indian Institute of Technology (IIT) Bombay.  The results of the research were published in the journal ACS Omega.

The device can find applications in physiotherapeutic recuperation of stroke patients, personalized point-of-care health monitoring systems, and robotics.

While commercially available activity trackers can estimate parameters such as number of steps taken and calories burnt, this device can accurately measure the amount of motion taking place in all the three joints during any activity or gesturing. The device is capable of instantaneously detecting movements and is quite sensitive — can detect variations of about 2 mm during stretching and about 5 degrees during bending in all the three joints.

It is inexpensive to make the device and be used repeatedly for over several hundred times.

What makes the device particularly unique is its ability to track the amount of bending of individual joints and distinguish the differing extent of movement occurring simultaneously in all the three joints of the hand.

At 140 degrees, the fingers bend the most among the three joints of the hand; the knuckles and wrist bend up to 90 and 80 degrees respectively. Since the device can track the amount of bending of say the fingers, it can distinguish between holding a bottle (30 degrees), using a forceps (90 degrees) and a clenched fist (140 degrees).

We made the electrodes by coating a cotton thread with carbon nanotubes, says Priya Rathi.

“The device can be directly put on skin, on gloves or any artificial surface,” says Prof. Chandramouli Subramaniam from the Department of Chemistry at IIT Bombay. Unlike currently available gesture tracking devices, the performance and sensitivity of the device is not compromised by humidity or temperature.

“Though we tested the device on the three joints of the hand, it can be used for tracking the movement of any joint in the body,” says Prof. Subramaniam who is the corresponding author of the paper.

Making of the device

The researchers used a polymeric film as a matrix in which carbon nanotubes are uniformly distributed resulting in a continuous, electrically conductive network. Thus when the matrix is stretched or bent the way the carbon nanotubes are connected changes and that produces changes in the electrical pathway across the device. This results in resistance change when the device is bent, stretched or twisted.

The amount of change in resistance is a reflection of the location and extent of movement. “Each joint bends to different extent (angle) and bends either sharply like in the case of a finger or makes a broad sweep (curvature) as in the case of the wrist,” he says. “The device measures the curvature and extent of bending to find which joint is being bent and by how much.”

Unlike other devices which use metallic electrodes, the one developed by the IIT Bombay team uses the same carbon nanotubes for electrodes. “Metal electrodes are more prone to failure and fatigue and are uncomfortable when used directly on skin. So we made the electrodes by coating a cotton thread with carbon nanotubes,” says Priya Rathi, the first author of the paper. By not using any metallic component, the researchers have overcome important shortcomings on the way to making wearable components.

“Early-stage detection of arthritis and muscular disorders require extensive database-creation and validation. Efforts are on to do these,” says Prof. Subramaniam. “Studies will be carried out on healthy individuals and those with arthritis to understand the difference in movement of joints. Later, those with early-stage arthritis will be enrolled and a longer-duration study will be conducted.”

This work and its presentation by Priya Rathi was one among the five selected all over the world by the McDonnells Academy for presentation at the 6th International Symposium addressing global challenges held in Brisbane, Australia between September 22 and 25, 2016.

Published in The Hindu on August 8, 2017