Image of a piece of electronics with physical properties, i.e. stiffness, bending rigidity, thickness and mass density, matched to the epidermis.
Credit: John A. Rogers
These ‘epidermal’ electronic systems seamlessly integrate and conform to the surface of the skin in a way that is mechanically invisible to the user. The devices have the potential to provide a range of healthcare and non-healthcare related functions.
Credit: John A. Rogers
Credit: John A. Rogers
The circuit level is also constructed in innovative serpentine shapes that allow it to be drastically stretched and bent without any negative effects.
Credit: John A. Rogers
LONDON: Temporary, stick-on tattoos hold the key to new, wireless and self-powering electronic devices to treat patients with heart disease and other physical ailments.
The stretchable, electronic 'skin' is an ultra-thin electronic device affixed to the epidermis like a temporary tattoo. The device is stretchy, bendable and adhesive, and no thicker than a human hair, and it contains miniature sensors, light-emitting diodes and tiny transmitters and receivers.
Complicated wiring and bulky monitors are currently needed to track patients needing cardiac, brain wave or muscular monitoring. The gel-coated adhesive pads currently used to monitor patients (requiring things like electrocardiograms) are often worn for up to 30 days. Their continued use often causes skin rashes, and can be inconvenient and distressing to patients.
The epidermal electronic skin (EES) has been dubbed a 'super Band-Aid' by John Rogers, co-author of the paper published in Science today. "We envision devices that are not only monitoring but also stimulating and interacting with the tissue at a deep level - so they become a functioning, co-equal part of the tissue that could have benefits for a variety of health problems," he said. "We're blurring the distinction between biotic and non-biotic systems."
Stretchable electronic 'skin'
Scientists and engineers have been working for nearly 80 years to build electronic circuits that bend and stretch. Despite their accuracy, external monitoring device design is dated and limited to clinical settings.
The paper's lead author Dae-Hyeong Kim from the University of Illinois and colleagues in America, China and Singapore sought a solution that was practical for both doctors and patients, both inside and outside labs and hospitals. The venture was backed by MC10, the company also working with Reebok to create 'smart', sensor-driven sportswear.
In 2006, Rogers developed a method that allowed his team to 'stretch' the rigid silicon without breaking it. The breakthrough occurred by reducing the width of the silicon: at 100 nanometres thick (one nanometre is a thousand-millionth of a metre). The device became bendy. Speaking with The Economist in early 2011, Rogers said, "Any material is flexible if it is thin enough. You can crumple a piece of paper, but not a plank of wood."
Help from geckos
Attaching electronic skin to natural skin presents significant challenges. For optimal adhesion, Rogers and his team were inspired by another unlikely source: geckos.
An interaction between atoms, molecules and surfaces known as the Van der Waals force enables geckos to climb vertical glass surfaces. A replication of this interaction between the natural and electronic 'skins' created a bond so close it conjoins at a molecular level.
The EES itself is made of rubbery polyester with carefully mechanised, skin-like properties. The circuit layer is sandwiched between two polarised, protective layers that work together to eliminate stress on the circuit. The circuit level is also constructed in innovative serpentine shapes that allow it to be drastically stretched and bent without any negative effects.
Transform premature baby care
Currently, the EES has an end-life of 24 hours, and can only be applied to arms, legs, forehead, cheek, chin and the scalp. Despite its superior flexibility, EES mounted on challenging areas like elbows detached before the 24-hour period was up. However, because the existing temporary-transfer mechanisms are already in place, the practical use of EES is projected to be both viable and low-cost.
Timothy Rowe, department head at B.C. Women's Hospital in Vancouver, Canada commented, "This potentially could transform the care of neonates, especially premature babies."
Rogers notes that, "This work is really just beginning. Our focus is on wireless communication and improved solutions for power." He also stresses that active work is being done to improve the scope of clinical applications: sleep apnea, neonatal care, burns and wound-treatment acceleration and touch-sense for patients with prosthetic devices is now more of a reality than ever before. Long-term use, however, will rely on the development of materials that can withstand the shedding of dead skin cells and sweat.
