Editorial Feature

Electronic Polymer Fibers: The Future of Clothing as a Means of Detection

The widespread adoption of wearable technology over the past decade has significantly transformed the way we receive, share and process data. Researchers at MIT have developed 'smart' digital fiber capable of sensing, storing, and processing data while incorporated into traditional fabrics. This advancement could dramatically expand the capabilities of wearable technology in the near future.

POLYMER, fiber, wearable sensor

MIT researchers have created the first fabric-fiber to have digital capabilities, ready to collect, store and analyze data using a neural network. Image Credit: Anna Gitelson-Kahn. Photo by Roni Cnaani / MIT

Wearable technology is currently one of the fastest-advancing sectors, outpacing the development of smartphones. Wearables such as smartwatches and smart glasses have transformed the way we receive, use, and share data, particularly in health monitoring, motion sensing, and human-machine interaction.

Such wearable devices, capable of detecting and monitoring individual health parameters in real-time (such as body temperature, heart and respiratory rates), or identifying biomarkers present in sweat and breath, have been commercialized in various forms such as wrist bands, lenses, and headbands.

Wearable Technology and Electronic Textiles for Health Monitoring

However, most of the available wearable systems adhere to a relatively small number of specific form factors. These typically comprise an inflexible device placed over a relatively small part of the human body, limiting the contact area between the device and the skin. This, in turn, may restrict the type of parameters these devices can detect and the way we can interact with the devices. There is also a potential inconvenience for the prospective users associated with carrying the actual device.

Fabrics and clothing are, on the other hand, ubiquitous in human life. Being in close contact with the human body, they are ideal platforms for non-invasive detection of vital signs and monitoring of physiological processes through the skin.

Several approaches have been explored to integrate electronic devices into textile fabrics, such as metal-coated yarns and conductive ink printing on fabrics to serve as temperature, humidity, or gas sensors. However, most of these smart textiles cannot be scaled up for large-area (full-body) sensing and cannot provide stretchability and unrestricted mobility.

Integrated Circuit in a Flexible Polymer Fiber

A novel digital fiber strand created by a research group from the Massachusetts Institute of Technology in the US, led by Prof. Yoel Fink from the Department of Materials Science and Engineering, might prove to be the solution to some of the abovementioned issues.

The innovative fiber integrates hundreds of microscale electronic components that can perform multiple distinctly addressable digital functions. At the same time, the flexible polymer strand can be seamlessly woven into electronic textiles.

Prof. Fink's team employed a thermal drawing process, widely used in optical fiber manufacturing, to fabricate the composite fibers together with precisely embedded and connected microchips within. First, a macroscopic preform was created with all the fiber components arranged in a specifically designed pattern.  The preform is a sandwich of polycarbonate (PC) and poly(methyl methacrylate) (PMMA) polymer layers into which microscopic pockets were machined to hold the microchips. These pockets were machined at a specific angle of 26.56°. The preform contained three different types of square-shaped microchips (temperature sensors 0.84 mm in size, low-capacity memory devices 0.5 mm in size, and slightly larger high-capacity memory devices) with precisely machined contact pads in the four corners.

Four tungsten wires (with a diameter of 25 μm) were laid on top of the microchips in the preform, while a fifth tungsten wire (50 μm in diameter) was used as a backing wire on the opposite side of the preform.

The whole assembly was then heated and stretched out to form a fiber. The process stretched the preform (together with all the components) lengthwise and simultaneously contracted it crosswise while preserving the relative positions of the components. The specific orientation of the microchips ensures the accurate connection of the four coplanar tungsten wires to each of the four individual contact pads on the chips. The final result was a flexible fiber with a diameter of around 300 μm and an inter-device spacing of approximately 5 cm to 20 cm depending on the draw ratio.

Fabrics with Memory and Processing Power

Most notably, the resulting electronic fiber is so thin and flexible that it can be threaded through a needle or sewn into fabrics. The composite polymer core provides outstanding mechanical properties - the fiber can be bent with a radius of curvature of 3 mm before it fails and can be washed at least 10 times without breaking down.

To communicate with the microchips connected along the fiber, the researchers employed a standard digital addressing protocol (I2C) which allows access and control to each of the microchips individually.

When incorporated into the fabric of a shirt, the electronic polymer fiber collected and stored 270 minutes of surface body temperature data over several days and allowed the researchers to monitor the wearer's physical activity in real-time. The fiber's onboard memory and processing power were sufficient to store and play a 767 kb (kilobit) full-color short movie and a 0.48 MBytes music file.

Wearable Artificial Intelligence

The best demonstration of the electronic polymer fiber capabilities was the implementation of a neural network with 1650 neuronal connections within the fiber memory.

By using machine learning algorithms, the researchers trained the neural network to recognize temperature-time-activity correlation patterns in the data stored in the same fiber. When presented with an unknown temperature-time data set, the fiber's neural network recognized the type of physical activity with 96% accuracy.

This effectively transformed the digital fiber into a distributed intelligent sensor network that can map multiple physical activity physiological parameters across different regions of the body.

With such analytical power, the electronic fibers can be used in personalized healthcare to detect and analyze respiratory changes or irregular heartbeat in real-time, and alert users well in advance for health-related problems.

References and Further Reading

G. Loke, et al. (2021) Digital electronics in fibres enable fabric-based machine-learning inference. Nat Commun. 12, 3317. https://doi.org/10.1038/s41467-021-23628-5

B. Ham (2021) Engineers create a programmable fiber. [Online] www.news.mit.edu Available at: https://news.mit.edu/2021/programmable-fiber-0603 (Accessed on 25 June 2021)

I. Wicaksono, et al. (2020) A tailored, electronic textile conformable suit for large-scale spatiotemporal physiological sensing in vivo. npj Flex Electron 4, 5. https://doi.org/10.1038/s41528-020-0068-y

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Cvetelin Vasilev

Written by

Cvetelin Vasilev

Cvetelin Vasilev has a degree and a doctorate in Physics and is pursuing a career as a biophysicist at the University of Sheffield. With more than 20 years of experience as a research scientist, he is an expert in the application of advanced microscopy and spectroscopy techniques to better understand the organization of “soft” complex systems. Cvetelin has more than 40 publications in peer-reviewed journals (h-index of 17) in the field of polymer science, biophysics, nanofabrication and nanobiophotonics.

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