By Deirdre Tynan • 09 August 2021 • 16:38
The glove design could help restore motor function after stroke and enhance virtual gaming experiences.
When someone picks up a balloon, the pressure to keep hold of it is different from what they would exert to grasp a jar. Now engineers at MIT and elsewhere have a way to precisely measure and map such subtleties of tactile dexterity.
The team has designed a new touch-sensing glove that can “feel” pressure and other tactile stimuli. The inside of the glove is threaded with a system of sensors that detects, measures, and maps small changes in pressure across the glove. The individual sensors are highly attuned and can pick up very weak vibrations across the skin, such as from a person’s pulse.
When subjects wore the glove while picking up a balloon versus a beaker, the sensors generated pressure maps specific to each task. Holding a balloon produced a relatively even pressure signal across the entire palm, while grasping a beaker created stronger pressure at the fingertips.
The MIT researchers said the tactile glove could help to retrain motor function and coordination in people who have suffered a stroke or other fine motor condition. The glove might also be adapted to augment virtual reality and gaming experiences. The team envisions integrating the pressure sensors not only into tactile gloves but also into flexible adhesives to track pulse, blood pressure, and other vital signs more accurately than smart watches and other wearable monitors.
“The simplicity and reliability of our sensing structure holds great promise for a diversity of health care applications, such as pulse detection and recovering the sensory capability in patients with tactile dysfunction,” said Nicholas Fang, professor of mechanical engineering at MIT.
Fang and his collaborators detail their results in a study appearing in Nature Communications.
Sensing with sweat
The glove’s pressure sensors are similar in principle to sensors that measure humidity. These sensors, found in HVAC systems, refrigerators, and weather stations, are designed as small capacitors, with two electrodes, or metal plates, sandwiching a rubbery “dielectric” material that shuttles electric charges between the two electrodes.
In humid conditions, the dielectric layer acts as a sponge to soak up charged ions from surrounding moisture. This addition of ions changes the capacitance, or amount of charge between the electrodes, in a way that can be quantified and converted to a measurement of humidity.
In recent years, researchers have adapted this capacitive sandwich structure for the design of thin, flexible pressure sensors. The idea is similar: When a sensor is squeezed, the balance of charges in its dielectric layer shifts, in a way that can be measured and converted to pressure. But the dielectric layer in most pressure sensors is relatively bulky, limiting their sensitivity.
For their new tactile sensors, the MIT and SUSTech team did away with the conventional dielectric layer in favour of a surprising ingredient: human sweat.
They found they could boost the sensing electrode’s sensitivity by covering its underside with a forest of tiny, bendy, conductive hairs. Each hair would serve as a microscopic extension of the main electrode, such that, if pressure were applied to, say, a corner of the electrode, the hairs in that specific region would bend in response, and accumulate ions from the skin, the degree and location of which could be precisely measured and mapped.
In their new study, the team fabricated thin, kernel-sized sensing electrodes lined with thousands of gold microscopic filaments, or “micropillars.” They demonstrated that they could accurately measure the degree to which groups of micropillars bent in response to various forces and pressures. When they placed a sensing electrode and a control electrode onto a volunteer’s fingertip, they found the structure was highly sensitive. The sensors were able to pick up subtle phases in the person’s pulse, such as different peaks in the same cycle. They could also keep up accurate pulse readings, even as the person wearing the sensors waved their hands as they walked across a room.
“Pulse is a mechanical vibration that can also cause deformation of the skin, which we can’t feel, but the pillars can pick up,” Fang said.
Several volunteers took turns wearing the tactile glove and performing various tasks, including holding a balloon and gripping a glass beaker. The team collected readings from each sensor to create a pressure map across the glove during each task. The maps revealed distinct and detailed patterns of pressure generated during each task.
The team plans to use the glove to identify pressure patterns for other tasks, such as writing with a pen and handling other household objects. Ultimately, they envision such tactile aids could help patients with motor dysfunction to calibrate and strengthen their hand dexterity and grip.
“Some fine motor skills require not only knowing how to handle objects, but also how much force should be exerted,” Fang said. “This glove could provide us more accurate measurements of gripping force for control groups versus patients recovering from stroke or other neurological conditions. This could increase our understanding, and enable control.”
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Deirdre Tynan is an award-winning journalist who enjoys bringing the best in news reporting to Spain’s largest English-language newspaper, Euro Weekly News. She has previously worked at The Mirror, Ireland on Sunday and for news agencies, media outlets and international organisations in America, Europe and Asia. A huge fan of British politics and newspapers, Deirdre is equally fascinated by the political scene in Madrid and Sevilla. She moved to Spain in 2018 and is based in Jaen.
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