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Second skin. Paper-thin patch (right) monitors tremors in Parkinson's patients and releases medication automatically. The fluid-filled patch (left) allows readily available rigid electronics to be used in a flexible device.

Second skin. Paper-thin patch (right) monitors tremors in Parkinson's patients and releases medication automatically. The fluid-filled patch (left) allows readily available rigid electronics to be used in a flexible devi

(Left) Image courtesy of the University of Illinois; (Right) Donghee Son and Jongha Lee

Forget Smart Watches, 'Smart Skin' May Be the Next Big Thing in Wearable Computers

Parkinson’s patients could one day ditch their pills for a stretchy skin patch with a mind of its own. Using specialized sensors, the patch would monitor the wearer's vital signs, beam the information to a doctor, and administer medication as needed. While such devices still face substantial obstacles before wide-scale implementation, two teams of researchers have announced innovations combining standard electronics with flexible materials that may bring the futuristic concept closer to reality.

Conventional electronics, such as those found in computers and smartphones, are built on stiff slabs of silicon. While durable, the design makes for bulky and uncomfortable wearable devices. Flexible electronics instead print circuits onto limber strips of silicone or plastic. The bendable base layers make devices twist and stretch when attached to the skin, but they are limited by a lack of key components such as batteries and processors that currently do not exist in flexible form.

Researchers from Seoul National University led by bioengineer Dae-Hyeong Kim have now developed a patch that automatically delivers medication to Parkinson’s patients. Parkinson's disease is a neurological disorder that causes movement impairments such as hand tremors that require regular medication to suppress. Typically, patients take pills every few hours, leading to a spike in medication levels followed by a gradual decline that causes the tremors to return. The team’s skin patch instead supplies a series of smaller measured doses as needed by using a tremor-detecting sensor. Because the device needs to track the tremors over time, they utilized a newly invented memory format called resistive random-access memory to create the first flexible data storage for wearable devices. The new format can be used in a thin, low-power form, making it ideal for inclusion in wearable electronics.

Kim’s team combined the thin data storage with a novel drug delivery system. The patch’s bottom layer is coated with porous silica nanoparticles loaded with drugs. Unlike a nicotine patch, the team’s device releases medication only when needed. A small heater in the patch automatically warms the nanoparticles, causing them to release their drug payloads into the skin, the team reported on Sunday in Nature Nanotechnology. A temperature sensor prevents the device from overheating and causing burns. Because flexible batteries and processors don’t yet exist for skin-based electronics, the device utilizes an external power source and processor. The patch covers an area comparable to a medium-sized adhesive bandage, and the researchers say the entire patch is thinner than a dime. “This could be a big deal for Parkinson’s disease patients,” Kim says. “The patient can attach the patch and forget about it without worrying about side effects or remembering to take pills.”

Despite their benefits for wearable devices, flexible electronics including Kim’s remain cumbersome to manufacture and are currently built by hand one by one in university labs. A team of researchers led by John Rogers, a materials scientist at the University of Illinois, Urbana-Champaign, has developed a way to incorporate widely available rigid electronic components into a structure that would still be flexible like Kim’s device. Rogers likens the prototype patch to a jelly doughnut: A transparent outer shell of flexible silicone rubber holds a small amount of silicone fluid similar in consistency to pancake syrup. Rigid components, purchased from suppliers and shaved down to a smaller size, float in the fluid, anchored at points to the outer shell. When the patch stretches with the skin, snakelike wires connecting the components unfurl like origami, allowing the rigid components to glide freely. As the patch contracts, the connectors return to their original positions, the team reports online today in Science. While the team’s research simplifies the manufacturing and lowers the cost of wearable electronics, the design is bulkier and less durable than those that use entirely flexible components such as Kim’s Parkinson’s patch.

“This is certainly a bridge to a time when we can get all flexible parts,” Rogers says. “We can use components that are already commercially available to implement these ideas today. This lowers the cost of getting these devices into the world.”

Although these recent innovations solve some of the problems facing wearable electronics, both Kim and Rogers admit that many major challenges remain before wide-scale adoption. Zhenan Bao, a chemical engineer developing similar wearable health sensors at Stanford University in California, says that some key components such as batteries and processors do not yet have a flexible form suitable for skin patches. “These two research projects show the field is steadily moving forward with new components made into stretchable form,” she says. “But more components are needed for these devices to be fully wearable and run on their own.”

Kim proposes that smartphones and smart watches could provide remote power and processing to the wearable patches. He is now working on a method of using the wireless antennas in smartphones to transmit power over short distances with the potential to recharge or even replace batteries in wearable electronics. Outsourcing data crunching and transmission to an external device could also reduce the patches' power consumption and reduce production costs.