Researchers in Australia have designed an electronic skin that displays human-like reactions to pressure, temperature and pain. Madhu Bhaskaran and colleagues at RMIT University developed the material by combining artificial sensors for these three stimuli into a single, biocompatible film. Their design represents a significant advance in our ability to mimic human skin, and could lead to important developments in both healthcare and robotics.
As our largest sensory organ, the skin contains an abundance of sensory neurons that continually monitor the levels of certain stimuli in our surrounding environments. These sophisticated receptors transmit the information they gather to the brain, which makes real-time decisions about how we should react to them. If the levels of any stimuli rise above certain dangerous thresholds, the brain can then trigger reactions that take us out of harm’s way.
Three types of receptor are particularly important for our survival: the Pacinian corpuscle, which monitors pressure; the thermoreceptor for temperature; and the nociceptor for pain. As researchers attempt to mimic the function of our skin in artificial materials, it is crucial for them to recreate the behaviours of these neurons. However, the sheer complexity of their reaction-triggering mechanisms has so far proven extremely challenging to imitate.
Bhaskaran’s team overcame these issues using a device named a “memristor”, which can regulate the current in electrical circuits, while remembering how much charge has previously flowed through it. Just as the brain uses its long-term memory to decide how to react to stimuli, memristors can evaluate when to switch between different memory states, based on stimuli detected by sub-nanometre conductive filaments.
To develop an artificial skin, the researchers combined a strontium titanate-based memristor with a stretchable, gold-on-silicone (polydimethylsiloxane) pressure sensor, allowing them to mimic the behaviour of the Pacinian corpuscle. In addition, Bhaskaran and colleagues incorporated the memristor into a vanadium oxide temperature trigger, which could be tuned to transition between a metal and an insulator at a defined temperature. This enabled them to imitate the thermoreceptor, as well as four critical functions of the nociceptor.
As well as being transparent, durable and biocompatible, the resulting film exhibited responses to multiple different stimuli that accurately reproduced those of the human nervous system. When applied levels of pressure, temperature and pain rose above human-tolerable thresholds, the sensors became triggered almost instantaneously.
Since the electrical skin is both affordable and easy to manufacture, it opens up new opportunities for advances in healthcare – including the ability to replace damaged receptors with non-invasive skin grafts, and even to augment human experiences of certain stimuli for applications including defence and sports. Elsewhere, it could lead to new advances towards human-like robots, as well as smarter feedback mechanisms for interfaces between humans and machines.
The researchers report their findings in Advanced Intelligent Systems.
Herein, three critical skin receptors created by realizing integrated electronic systems that mimic the feedback response of somatosensors are experimentally demonstrated. Fully functional Pacinian corpuscles, thermoreceptors, and nociceptors are realized using a combination of stretchable pressure sensors, phase‐change oxide thin films, and threshold‐based resistive switching (memristor) memory elements. The ability to detect and respond to pressure, temperature, and pain stimuli above a threshold with real‐life performance characteristics is demonstrated with explanation of underlying mechanisms.
The ability to design and realize artificial skin receptors enables replacement of affected human skin regions, augment skin sensitivity for agile applications in defense and sports, and drive advancements in intelligent robotics.