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Stick-On Health Tracker Twists, Stretches, and Bends

May 1, 2014


A thin, stretchy stick-on patch loaded with electronic components could some day replace health and fitness monitors worn as wristbands or clipped to your belt. The new patches could also monitor health conditions and alert doctors if something goes awry.

Developed by engineers at the Univ. of Illinois at Urbana-Champaign (UIUC) and Northwestern Univ., the health patch incorporates off-theshelf, rigid electronics, including integrated circuits, sensors, and power sources, into a patch that molds to the skin. Borrowing concepts from microfluidics and other fields of study, the researchers decoupled the rigid mechanics of the electronic components from the soft, elastic mechanics of the patch.

"We designed this device to monitor human health 24/7, but without interfering with a person's daily activity," says Yonggang Huang, a professor of mechanical engineering at Northwestern Univ. "It is as soft as human skin and can move with your body, but at the same time it has many different monitoring functions," Huang says. "What is very important about this device is that it is wirelessly powered and can send highquality data about the human body to a computer, in real time."

Flexible electronics with skinlike mechanical properties have been made in the past. For example, UIUC researchers led by John Rogers, a professor of materials science and engineering who was also involved in the development of this new health patch, developed a way to make electronic patches to measure heart, brain, and muscle activity that bend, wrinkle, and stretch like human skin (CEP, Sept. 2011, pp. 12-13). To achieve the skin-like properties, Rogers' group used thin slices, or nanoribbons, of silicon printed in a mesh-like pattem onto a flexible substrate. While this and other approaches offer electronic components for health monitoring in a thin, flexible format, the new development offers a way to incorporate any available chipbased components into these monitoring patches.

"Our original epidermal devices exploited specialized device geometries - super thin, structured in certain ways," Rogers says. "But chip-scale devices, batteries, capacitors, and other components must be reformulated for these platforms. ... There's a lot of value in complementing this specialized strategy with our new concepts in microfluidics and origami interconnects to enable compatibility with commercial off-theshelf parts for accelerated development, reduced costs, and expanded options in device types."

The new patch incorporates several design features that embody it with skin-like properties. One such feature is the snake-like design of the wires connecting the electronic components (CEP, Apr. 2013, pp. 14-15). The interconnect forms an S shape and then within this larger S are smaller S shapes. When the patch is stretched, the outer, larger S unfolds, leaving a wire of smaller squiggles behind. Upon further stretching, the smaller Ss unfold. The electronic components are suspended in fluid-filled envelopes to mechanically isolate the rigid materials from the compliant, elastomeric enclosures. Each component is bonded to tiny raised support points molded onto the elastomer substrate.

The team made patches capable of collecting data for measuring electrocardiograms (ECGs), electromyograms (EMGs), electrooculograms (EOGs), and electroencephalograms (EEGs). These patches include modules for wireless power supply through resonant inductive energy transfer, low-noise amplification and filtering of electrophysiological (EP) signals, and frequency-modulated radiofrequency transmission of measured data. Another patch was made with a triaxial accelerometer and a thermal sensor - capabilities important for applications in sports training, sleep apnea studies, monitoring in neonatal care, and assessing cognitive state and awareness.

Skin-mounted patches offer several advantages over conventional health-monitoring devices. "When you measure motion on a wristwatch type device, your body is not very accurately or reliably coupled to the device," Rogers says. "Relative motion causes a lot of background noise," he notes. "If you have these skin-mounted devices and an ability to locate them on multiple parts of the body, you can get a much deeper and richer set of information than would be possible with devices that are not well coupled with the skin," he explains. "And that's just the beginning of the rich range of accurate measurements relevant to physiological health that are possible when you are softly and intimately integrated onto the skin."

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Source: Chemical Engineering Progress

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