MIT develops optical textiles for comms and biomedical apps

10 Aug 2018

Novel technique incorporates fiber and opto-diodes into wearable material creating washable "smart" fabrics.

Researchers at MIT have embedded optoelectronic semiconductor devices, including LEDs and photodetectors, within fibers that are then woven into soft, washable fabrics (at Inman Mills, SC, US) and then made into novel types of communications systems.

The MIT development team says this combination “achieves a long-sought goal of creating smart fabrics incorporating semiconductors, which enable sophisticated functionality”.

The work is described in Nature in a paper by former MIT graduate student Michael Rein; his research advisor Yoel Fink, MIT professor of materials science and electrical engineering and CEO of AFFOA (Advanced Functional Fabrics of America); along with a team from MIT, AFFOA, Inman Mills, EPFL in Lausanne, Switzerland, and Lincoln Laboratory.

Rein commented, “our development could unleash a new Moore’s Law for fibers — in other words, a rapid progression in which the capabilities of fibers would grow rapidly and exponentially over time, just as the capabilities of microchips have grown.”

The key breakthrough for producing the new fibers was to add to the preform light-emitting semiconductor diodes the size of a grain of sand, and a pair of copper wires a fraction of a hair’s width. When heated in a furnace during the fiber-drawing process, the polymer preform partially liquified, forming a long fiber with the diodes lined up along its center and connected by the copper wires.

In this case, the solid components were two types of electrical diodes made using standard microchip technology: LEDs and photosensing diodes. “Both the devices and the wires maintain their dimensions while everything shrinks around them in the drawing process,”said Rein. “The resulting fibers were then woven into fabrics, which were laundered 10 times to demonstrate their practicality as possible material for clothing.”

He added, “This approach adds a new insight into the process of making fibers. Instead of drawing the material all together in a liquid state, we mixed in devices in particulate form, together with thin metal wires.”

Waterproof

One of the advantages of incorporating functionality into the fiber material itself is that the resulting fiber is inherently waterproof. To demonstrate this, the team placed some of the photodetecting fibers inside a fish tank.

A lamp outside the aquarium transmitted music (appropriately, Handel’s “Water Music”) through the water to the fibers in the form of rapid optical signals. The fibers in the tank converted the light pulses into electrical signals, which were then converted into music. The fibers survived in the water for weeks.

Staff at the Advanced Functional Fabric of America Institute, led by Jason Cox and Chia-Chun Chung, developed the pathways to increasing yield, throughput, and overall reliability, making these fibers ready for transitioning to industry. At the same time, Marty Ellis from Inman Mills developed techniques for weaving these fibers into fabrics using a conventional industrial manufacturing-scale loom.

The Nature paper describes a scalable path for incorporating semiconductor devices into fibers. Fink commented, “We are anticipating the emergence of a Moore’s Law analog for fibers. It is already allowing us to expand the fundamental capabilities of fabrics to encompass communications, lighting, physiological monitoring, and more. In the years ahead fabrics will deliver value-added services and will no longer just be selected for aesthetics and comfort.”

Fink believes that the first commercial products incorporating this technology will reach the marketplace as early as 2019: “Such rapid lab-to-market development was a key part of the reason for creating an academic-industry-government collaborative such as AFFOA in the first place,” he said.

Initial applications are expected to be specialized products involving communications and safety. “It's going to be the first fabric communication system. We are right now in the process of transitioning the technology to domestic manufacturers and industry at an unprecendented speed and scale,” said Fink.

Defensive applications

He added that the US Department of Defense — one of AFFOA’s major supporters — “is exploring applications of these ideas to our women and men in uniform.”

Beyond communications, the fibers could potentially have significant applications in the biomedical field, the researchers say. For example, devices using such fibers might be used to make a wristband that could measure pulse or blood oxygen levels, or be woven into a bandage to continuously monitor the healing process.

The research was supported in part by the MIT Materials Research Science and Engineering Center (MRSEC) through the MRSEC Program of the National Science Foundation, by the U.S. Army Research Laboratory and the U.S. Army Research Office through the Institute for Soldier Nanotechnologies. This work was also supported by the Assistant Secretary of Defense for Research and Engineering.