New sensors from MIT detect small and fast pressure changes at the fingertip. When placed on a silk glove, the stud-like components help to create a valuable picture for doctors.
The inventors of the highly attuned sensors, which pick up slight vibrations across the skin, provide specific pressure maps that could someday support patients with a range of assistance, from simple pulse monitoring to the complex restoration of motor functions.
The Cambridge, MA-based team envisions integrating the pressure sensors not only into tactile gloves but also into flexible adhesives to track heartbeat, blood pressure, and other vital signs.
“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, in a recent news release.
How to Make a Pressure Map
The MIT researchers lined the inside of a glove with the small, kernel-sized detectors designed to map subtle changes in pressure. The glove generated specific pressure layouts, or maps, depending on the held object.
The sensor-glove registered pressure differences between a grasped balloon and a beaker, for example. Holding a balloon produced a relatively even pressure signal across the entire palm, while grasping a beaker created stronger pressure at the fingertips.
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. The tactile aids could someday help patients with motor dysfunction to calibrate and strengthen their hand dexterity and grip, according to Prof. Fang.
“Some fine motor skills require not only knowing how to handle objects, but also how much force should be exerted,” Prof. 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."
Fang and his colleagues detail their results in a study from Nature Communications. The study’s co-authors include Huifeng Du and Liu Wang at MIT, along with professor Chuanfei Guo’s group at the Southern University of Science and Technology (SUSTech) in China.
Sensing the Small Stuff
The tactile sensors swap out the conventional dielectric layer for a surprising, natural ingredient: human sweat. Sweat contains sodium and chloride ions, which accumulate and have the power to change the capacitance between two thin, flat electrodes placed on the skin.
The MIT team increased the sensing electrode’s sensitivity by adding a bunch of tiny, bendy, conductive hairs. The thin, kernel-sized sensing electrodes, in fact, are lined with thousands of these gold microscopic filaments, or “micropillars.”
In their study, Fang and the inventors demonstrated that the sensors could accurately measure the degree to which groups of micropillars bent in response to various forces and pressures.
When pressure is applied to, say, a corner of the electrode, the hairs in that specific region bend in response, and accumulate ions from the skin; the degree and location of the ions can then be precisely measured and mapped.
The sensors were able to pick up subtle phases in the person’s pulse, such as different peaks in the same cycle.
“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.
In a short Q&A with Tech Briefs below, Fang explains more about the possibilities of a pressure map, beyond just pulse.
Tech Briefs: What is the most exciting application or application area that you envision for this technology? Why is this glove so important, do you think?
Prof. Nicholas Fang: We envision that integration of high-fidelity haptic feedback into fabrics and textiles will open up novel medical and healthcare device applications, such as recovering the sensory capability in patients with tactile dysfunction, and it may also enable VR/AR gaming and training.
Tech Briefs: Why is taking a pressure map so important? What can you do with a pressure map once you have it?
Prof. Nicholas Fang: I think the high-resolution pressure map measured by a smart glove, which is insensitive to motion artifact, can provide more accurate assessment of the motor skills of the hands and fingers for point-of0care applications. Our glove opens up the opportunity for constant monitoring of hand and finger dexterity [during activities], such as assembling puzzles, sorting beads, folding cards, playing board games, or tying shoelaces.
Tech Briefs: What inspired you to sense with sweat? What are the pros and cons of using sweat?
Prof. Nicholas Fang: Just to clarify, only a minimal amount of sweat on naturally hydrated skin is needed for our glove to work, and this is satisfied by our skin under physiological condition.
On our sensor design, we were inspired by two ideas.
One is the long hair sensors found on insects, such as wandering spiders which have an amazing sense of touch and ground vibration.
Another is on the electrodes-on-skin setup widely applied in healthcare, and our innovation here is to harness the prescribed deformation of carbon cloth, electrostatically flocked PET [polyethylene terephthalate] pillars that are in conformal contact with hydrated skin, and these flocked PET micropillars acts as pressure sensing devices with outstanding sensitivity to subtle change of applied force.
Tech Briefs: What will you be working on next with this glove?
Prof. Nicholas Fang: Next, we'll evaluate the perception of texture of different material on the smart glove so they can further augment human sense of touch that are important for grasping and manipulation of small objects.
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