Wearable Sensors in Fabric May Help Monitor Disease Progression

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by Steve Bryson, PhD |

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A woman wearing workout clothes walks holding small weights in each hand.

Scientists have created wearable, flexible sensors — which can be integrated into fabrics, and detect touch pressure as well as measure body movements — that may be used to gauge motor disease progression in people with Parkinson’s, a study reported.

Placing the sensors in the soles of patients’ shoes or on their knee or foot joints using cotton cloth could aid in monitoring walking problems in patients in real-time, the scientists said.

The team currently is evaluating the sensors in people with the neurodegenerative disease at a Parkinson’s rehabilitation center in the Netherlands.

“They are being used to monitor the deterioration of [patients’] gait over time,” Ajay Kottapalli, PhD, assistant professor at the University of Groningen and the study’s senior author, said in a press release.

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Kottapalli said the sensors also show promise as a way to prevent falls.

“Some patients already use a system that gives them instructions on walking speed and step length through earphones. We know that just before a fall, patients take shorter steps,” Kottapalli said. “Our sensor system could alert them to this.”

The study, “Electrospun bundled carbon nanofibers for skin-inspired tactile sensing, proprioception and gesture tracking applications,” was published in the journal Nature Flexible Electronics.

People with Parkinson’s experience motor symptoms such as tremors, slow movements, and muscle rigidity. Many also have difficulties maintaining balance and walking, and experience uncontrolled, involuntary movements that can affect the head, arms, legs, or the whole body.

Wearable electronic sensor technology to measure human motion in real-time may provide valuable information regarding disease progression, according to scientists. Indeed, accurate monitoring of breathing patterns, as well as posture, muscle tremors, gait, and joint and limb movements, can help in obtaining an early diagnosis, in following changes in motor symptoms, and in supporting patient-specific treatment plans.

Now, scientists at the University of Groningen, in the Netherlands, have created wearable, stitchable, and sensitive sensors from bundles of carbon nanofibers (CNFs), which can respond to pressure and measure body movements and position.

Although there are shirts with electrodes that measure muscle activity — many used by professional athletes — they have limited flexibility and low resolution to monitor a wide range of human body movements accurately.

“Our sensors would add body movement to this, which is an entirely different approach,” Kottapalli said.

“Apart from joint movement, we could also register breathing movements,” he added.

The carbon nanofibers were generated by a process called electrospinning, which created piezoresistive fibers — in which electrical conductivity changes when stretched. The fibers were then embedded in a rubber-like material in a crossing pattern that created a “pixel” to measure movement where two fibers cross.

“Electrospinning is similar to the way in which fabric is made, and the material can be stitched, whereby it is possible to use conductive yarn that can act as an electrode,” Kottapalli said.

The team showed that the sensor could be stretched to at least 50% of the original length and was sensitive to various degrees of pressure, even with prolonged use.

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To demonstrate the sensor’s applicability to monitoring human movements, gait experiments were conducted, focusing on wrist movements, breathing motions, walking, and jogging.

For wrist movement experiments, the sensor was attached to a patient’s left-hand wrist, and the individual was asked to bend the wrist either forward or side to side. Large wrist movements generated more intense signals compared with smaller movements, and the sensor could distinguish between leftward and rightward movements.

“The consistent mismatch of signal intensities while flicking the wrist left and right directly corresponds to the person’s maximum achievable bending angle towards each direction,” the team wrote.

When sensors were secured on the diaphragm region at the base of the chest, they showed different signal responses between normal and deep breathing exercises.

“Clear differentiation between various breathing patterns could be achieved by observing the signal intensity and frequency,” they wrote.

A strain sensor was then placed on an individual’s heel to measure responses to walking and jogging on the spot. During walking, the sensor demonstrated smaller signals compared with very sharp, intense signal peaks when jogging, “signifying the capability of the sensor to distinguish between different movement patterns encountered daily,” the researchers wrote.

The sensors also were integrated into a glove to allow measurements such as touch pressure, finger movements, gestures, and the perception of movements. These results showed the glove was able to sense various movements of different fingers. Here, one potential application is a hand prosthesis, in which signals can be fed into a patient’s nervous system, the researchers said.

“The glove can tell you the hardness of an object, like a normal hand can,” Kottapalli said.

“This is a unique combination,” he said, adding, “Our sensors have a skin-like function.”

A sports kneecap made of cotton cloth was developed and tested to demonstrate the feasibility of including the sensors in wearable fabric-like materials. The signals between the straight and bent knee were clearly different, but also the signal width varied depending on the speed of knee bending, “which can be useful for precisely tracking knee movements,” they wrote.

The team also demonstrated that the sensors could detect and measure touch pressure at multiple points. In a glove, they could sense hand shape and vibrations that mimic many of the nervous system functions of the human hand.

“In conclusion, this work demonstrates the applicability of electrospun CNF bundles as sensitive, flexible, and linear yet inexpensive piezoresistive sensing element in developing apparel integrable sensors for wearable human motion monitoring and tactile sensing applications,” the team wrote.