Wireless stick-on sensors promise unobtrusive health monitoring

Engineers have demonstrated a thin, stick-on wireless health monitoring system that stretches and moves with the skin whilst incorporating commercial, off-the-shelf chip-based electronics.

The patches, developed at the University of Illinois at Urbana-Champaign and Northwestern University, are said to stick to the skin like a temporary tattoo and incorporate a microfluidic construction with folded wires to allow the patch to bend and flex without being constrained by rigid electronics components.

The patches could be used for routine health monitoring – wirelessly sending updates to a mobile phone or computer – and could prove beneficial when monitoring EKG and EEG readings, as the system doesn’t require wires, pads or tape.

‘We designed this device to monitor human health 24/7, but without interfering with a person’s daily activity,’ said Yonggang Huang, the Northwestern University professor who co-led the work with Illinois professor John A. Rogers. ‘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.’

According to a statement, the researchers did a side-by-side comparison with traditional electrocardiogram (EKG) and Electroencephalogram (EEG) monitors and found the wireless patch performed equally to conventional sensors, while being 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 prematurely new born children.

Rogers’ group at Illinois previously demonstrated skin electronics made of small, ultrathin, specially designed and printed components. While those also offer high-performance monitoring, the ability to incorporate readily available chip-based components provides new capabilities in engineering design at low cost.

‘Our original epidermal devices exploited specialised 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 specialised 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 multi-university team turned to soft microfluidic designs to address the challenge of integrating relatively big, bulky chips with the soft, elastic base of the patch. The patch is constructed of a thin elastic envelope filled with fluid. The chip components are suspended on raised support points, bonding them to the underlying patch but allowing the patch to stretch and move.

One of the biggest engineering feats of the patch is the design of the wires connecting the electronics components such as radios, power inductors, and sensors. The serpentine-shaped wires are folded, so that no matter which way the patch bends, twists or stretches, the wires can unfold in any direction to accommodate the motion.

The team has published its design in Science.