Over the years, scientists across the globe have been involved in the development of e-skin with wide-ranging applicability. They have been successful in improving the e-skin design by using varied materials and strategies. John Rogers and his team of researchers at Northwestern University in Evanston, Illinois, have successfully developed flexible and soft skin-like materials that can monitor health in real-time.
Globally, the ‘e-skin’ technology has been applied in clinics to monitor vital signs in premature infants and hydration in athletes. It also imparts a human-like touch to robots.
A new e-skin has been developed by Rogers and his team, which is wireless and is placed in the hollow at the base of the throat. The circuit of the device and the polymer patch are connected via Bluetooth. This device can be used for real-time monitoring of breathing, talking, heart rate, and other vital signs. It can be effectively used for individuals who have had a stroke and require speech therapy.
E-Skin Technology and COVID-19
Researchers at Northwestern have found that the device can detect the early symptoms of COVID-19. In this ongoing study, around 400 devices are been used to monitor the front-line health workers and patients in Chicago. A modification of the device has enabled the detection of the changes in the coughing rate among the individuals infected with SARS-CoV-2.
Development and Characteristic Features of E-Skin Devices:
Over the years, several researchers have improved the developmental strategies and the characteristic features of e-skin which have helped to enhance its applicability, manifold. Some of the strategies and characteristics are discussed below:
Flexible E-Skin:
The technology behind e-skin devices is similar to e-book readers and curved televisions. This technology depends heavily on carbon-based molecules or polymers that are flexible and can conduct electricity. According to George Malliaras, a bioelectronic researcher at the University of Cambridge, flexibility is the key feature of wearable electronics.
In 2004, Takao Someya, an electrical engineer at the University of Tokyo, and his team developed a flexible 8 cm × 8 cm robot skin patch. This skin patch was developed using several layers of pressure-sensing, high-performance polyimide plastic (organic semiconductor, known as pentacene), and layers of gold and copper electrodes. This skin patch, consisting of a 32 × 32 array of tiny pressure sensors, allowed a free flow of current even when it was wrapped around a 4 mm thick cylindrical bar. However, researchers believed that the skin needed to be more flexible. In 2005, Someya and his team converted the almost rigid polyimide polymer into a thin net-like structure by spinning. This net-like structure showed high flexibility and was able to sense pressure changes.
In 2006, Rogers and his team of researchers formulated a different method to develop an ultrathin structure from hard and inorganic materials. The researchers used submicrometric ribbons of single-crystal silicon and attached them to a sheet of rubbery polydimethylsiloxane (PDMS) under tension. After the tension was released, the silicon adopted a new undulating, flexible, and wavy structure.
According to Malliaras, wearable devices face different kinds of challenges such as maintaining a steady contact between an electrode and a person. This is because a moving person’s skin stretches, wrinkles, and bends. In 2004, Malliaras and his co-researchers developed a gel by combining ionic liquids (1-ethyl-3-methylimidazolium ethyl sulfate) with a conducting polymer. This gel could hold gold electrodes and the device retained electricity for three days. This device could resist sweat and block air exchange, making it irritating when worn. Further, owing to its fragility, it could not be used for a long period. Addressing these drawbacks, in 2017, Someya and his group created a porous, mesh-like sensor with greater flexibility. This mesh was produced by spinning polyvinyl alcohol (PVA) and deposition of gold circuitry. In 2020, they modified their design to measure the human heartbeat for ten hours.
E-Skin with high sensitivity:
Zhenan Bao, a professor of chemical engineering at Stanford University, is also involved with the development of e-skin. Her research is on the production of organic polymers and electronic components by employing a molecular approach. In 2010, Bao and her team of researchers developed an e-skin using elastic polymer PDMS. This e-skin could identify a small change in pressure, analogous to the sense of touch. The polymer patch contained capacitors pasted on an organic transistor, which could sense pressure changes. In 2019, her team of researchers designed a biodegradable, wireless sensor that could be wrapped around blood vessels. These sensors could, continuously, monitor blood flow post-surgery. It detected minor changes in capacitance when blood pulsed through the artery. An external coil was also attached near the patient’s skin such that it could convey a radio signal to a remote receiver.
In 2020, Bao’s team developed a prototype device, which can detect hormone changes in sweat, especially the levels of cortisol. This device can be used to determine anxiety as cortisol is a prominent indicator of stress. This technology can be used in developing organic electronics that are placed inside the body to mend damaged nerves.
E-Skin that can Sense Pain:
In 2020, Madhu Bhaskaran and her team at RMIT University in Melbourne, Australia, developed a device by combining a flexible gold-PDMS (pressure sensor) with vanadium oxide (temperature sensor) and strontium oxide (memristor) which can sense pain.
E-Skin in Use
In 2008, Rogers founded MC10 which is a company located in Lexington, Massachusetts. It has developed an e-skin called BioStamp that can assist clinical trials by collecting data on a huge number of vital signs from participants. This skin patch can be worn at home. In May 2018, this patch received approval from the US Food and Drug Administration. In 2019, another wireless sensor was developed by Rogers and his colleagues, that can be used to monitor premature babies in neonatal intensive care units. This e-skin patch can easily avoid the use of multiple devices to continuously monitor an infant’s vital signs. According to Rogers, about a thousand of these devices are in use in hospitals in Ghana, Zambia, and Kenya. This device is also used by Chicago’s Lurie Children’s Hospital and Prentice Women’s Hospital.
In 2015, Someya’s and his team established a Tokyo-based company called Xenoma that produces smart clothing. One of the applications of smart clothing is to monitor body temperature and connect it with an air-conditioning unit to adjust the room temperature.
