Implantable LEDs Could Be Medical Sensors, or Sweet Glowing Tattoos | 80beats


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Flexible materials technology may just bring the next wave of trendy to the markets, in the form of glowing tattoos and T- shirts. Or the hot new tech could be used for its intended purpose: monitoring medical conditions.

This flexible light-emitting diode (LED) array uses many already existing materials and techniques to create a nano-sized, flexible patch of light. A team lead by [John Rogers][9] developed the array as a medical device; it could be implanted to serve as a readout for monitoring internal body conditions, like blood oxygenation or glucose levels, or it could turn on light-activated drugs.

“The applications we’re interested in mostly include interfaces with the human body,” says John Rogers…. For some biological applications, he adds, a conventional LED’s brightness, reliable operation and suitability for waterproof implementation make it a more attractive option than an organic LED. [[Scientific American][10]].

Each individual LED is a square that measures 2.5 micrometers thick (smaller than the diameter of your cells’ nucleus) and 100 micrometers on each side (the thickness of a coat of paint). Many of these LEDs can be printed together to form an array of light points connected by swirls of connective wire that give it additional flexibility. The substrate is flexible enough that it can be stretched and flexed up to 75 percent without losing function. The researchers described the technology in the journal [_Nature Materials_][11].

[The researchers] deposited LEDs on aluminum foil, the leaf of a tree, and a sheet of paper; they wrapped arrays around nylon thread and tied it in a knot; and they distended LED arrays by inflating the polymer substrate or stretching it over the tip of a pencil or the head of a cotton swab. “Eventually the students just got tired” of devising new tests for the light-emitting sheets, Rogers says. “There was nothing that we tried that we couldn’t do.” [[Scientific American][10]].

The arrays are made on a semiconductor called gallium arsenide and other materials that are traditionally very brittle, but when stamped onto a plastic array they become flexible. They are then coated in rubber, which makes them waterproof and ready to be implanted. No humans have glowing LED tattoos yet, but the researchers were able to implant the array into a latex glove, and also put one underneath an animal’s skin and in other materials including fabric, paper, and aluminum foil.

Brian Derby, a materials scientist at the University of Manchester, UK, agrees that the development is less a scientific breakthrough than a feat of engineering. However, he has spotted a drawback: the use of interconnecting wires to take the mechanical strain keeps the device density low. “The large spacing of the LEDs or photo-detectors will lead to a limited range of applications — no flexible displays, for example,” he says. [[Nature News][12]].

The researchers have anticipated that concern, and say the arrays can be layered on top of each other to create a denser patch of light.

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_All images: Nature Materials / [John Rogers][11]_

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