Researchers have made an electronic skin patch that can monitor muscle movement, store the data it collects and use stored data patterns to decide when to deliver medicine through the skin. The patch could be useful for monitoring and treating Parkinson’s disease and epilepsy, its creators say.

Wearable devices that continuously monitor physiological cues can help doctors understand and treat diseases such as epilepsy, heart failure and Parkinson’s. A few research groups have been trying to develop discreet health monitoring devices based on flexible, stretchable electronics that can be plastered on the skin, heart or brain.

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But the new system is the first that can store data and deliver drugs, says Dae-Hyeong Kim, a chemical and biological engineering professor at Seoul National University and one of the device’s creators. In the "closed-loop feedback system," says Kim, the stored data is used for statistical pattern analysis, which helps to track symptoms and drug response. "For more quantitative tracking of progression of symptoms and responses to medications, wearable healthcare devices that monitor important cues, store recorded data, and deliver feedback therapeutic agents via the human skin in a controlled way are highly required," he says.

Kim and his collaborators at the University of Texas at Austin and wearable health-monitoring device-maker MC10 integrated the sensors, memory and drug-delivery components, all made of nanomaterials, onto a stretchable polymer substrate that is soft and flexible like human skin. They reported their design in the journal Nature Nanotechnology.

On the topside of the skin-like polymer patch, the research team printed three things: silicon nanomembrane strain sensor arrays; serpentine chromium-and-gold nanowires that act as both heaters and temperature sensors; and drug-loaded porous silica nanoparticles. The strain sensors detect motion such as Parkinson’s tremors. The heater controls the temperature of the polymer, which in turn controls the diffusion of the drugs into the skin (heat degrades the physical bonding between the nanoparticles and the drugs). The temperature sensors monitor skin temperature during drug delivery to prevent burns.

What’s most unique about the new electronic patch is the stretchable memory. Researchers have previously made resistive random access memory, an up-and-coming class of nonvolatile memory, using metal oxide nanomembranes. Those devices were stiff and brittle. Here, the researchers have made stretchable memory devices by sandwiching three layers of gold nanoparticles between ultra-thin titanium oxide nanomembranes printed on aluminum electrodes.

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The memory device can be bent and twisted, it works when stretched to 125 percent of its original length, and works well even after 1000 stretching cycles.

As a simple demonstration, the researchers placed the wearable patch on the wrist. The motion sensors measured frequency of simulated tremors by sensing tension and compression of the muscle. The frequency was recorded and fed through a control circuit that recognizes characteristic patterns of Parkinson’s disease. This, in turn, triggered drug release.

Right now, the memory element requires a power supply and a data transmitter. The researchers say that they will need batteries or wireless power transmission and wireless communication in stretchable formats to make a truly wearable and wireless patch.

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