Soft stick-on patches that stretch with the skin have been combined with off-the-shelf electronics to create sophisticated wireless health monitoring devices.
The patches incorporate a unique microfluidic construction, in which wires are folded like origami to allow the patch to bend and flex without being constrained by the rigid chip-based electronic components.
The patches stick to the skin like a temporary tattoo and could be used for everyday health tracking – wirelessly sending updates to a cellphone or computer – and could revolutionise clinical monitoring like electrocardiography (EKG) and electroencephalography (EEG) tests, used to monitor the heart and the brain respectively, by removing the need for bulky wires, pads and tape.
“We designed this device to monitor human health 24/7, but without interfering with a person’s daily activity,” said Professor Yonggang Huang, of Northwestern University in the USA, who co-led the work with professor John Rogers of the University of Illinois, USA.
“It is as soft as human skin and can move with your body, but at the same time it has many different monitoring functions. What is very important about this device is it is wirelessly powered and can send high-quality data about the human body to a computer, in real time.”
The researchers did a side-by-side comparison with traditional EKG and EEG monitors and found the wireless patch, described in a paper in journal Science today, performed equally to conventional sensors, while being significantly more comfortable for patients.
Such a distinction is crucial for long-term monitoring, situations such as stress tests or sleep studies when the outcome depends on the patient’s ability to move and behave naturally, or for patients with fragile skin such as premature new-borns.
Rogers’ group at Illinois previously demonstrated skin electronics made of very tiny, ultrathin, specially designed and printed components, but the ability to incorporate readily available chip-based components provides helps simplify the engineering design and greatly reduce costs.
“Our original epidermal devices exploited specialized device geometries – super thin, structured in certain ways,” Rogers said. “But chip-scale devices, batteries, capacitors and other components must be re-formulated 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-the-shelf parts for accelerated development, reduced costs and expanded options in device types.”
The patch is constructed of a thin elastic envelope filled with fluid and the relatively bulky chip components are suspended on tiny raised support points, bonding them to the underlying patch but allowing the patch to stretch and move.
The serpentine wires connecting the radios, power inductors, sensors and other electronic components are folded like origami, so that no matter which way the patch bends, twists or stretches, the wires can unfold in any direction to accommodate the motion. Since the wires stretch, the chips don’t have to.
“When you measure motion on a wristwatch type device, your body is not very accurately or reliably coupled to the device,” said Rogers. “Relative motion causes a lot of background noise.
“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.
“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.”
The researchers hope that their systems could not only monitor health but also could help identify problems before the patient may be aware, for example, using data analysis to detect motions associated with Parkinson’s disease at its very early onset.
“The application of stretchable electronics to medicine has a lot of potential,” Huang said. “If we can continuously monitor our health with a comfortable, small device that attaches to our skin, it could be possible to catch health conditions before experiencing pain, discomfort and illness.”