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Electronic Skin - Robots That Can Feel Touch
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From a cold hard technical point of view, skin is our interface with the world around us. It protects our bodies and connects them to the environment at the same time, and one might say it would be impossible to replicate.

Electronic Skin,Diagnosis,Robots That Can Feel Touch,Sci & Tech,Technology,Medicine,nanowire transistors

But nothing is impossible with the new advancements in nanotechnology: researchers and manufacturers are on their way to delivering a fully-functional replacement for it. Electronic skin, also called e-skin, is a thin electronic material that aims to mimic certain features of human skin, creating an entirely new form of human-machine interface when the natural one is lost. More specifically, electronic skin aims to develop the flexibility, ability to recognize touch, pressure, strain, humidity, light and temperature, and the power to heal itself that our natural skin already has.

This innovation opens up the door to a vast array of creative uses, not only in the field of robotics, but also in diagnosis, healing and prosthetics. Electronic skin has a relatively short history, but a promising future. In 2010, a research team from the University of California, Berkeley made the first steps towards e-skin, hoping to one day restore the sense of touch to patients with artificial limbs. They developed a method to attach nanowire transistors to a sticky substrate, more specifically a plastic film, creating an extremely conductive material that was later imbedded in a thin pressure sensitive rubber. This result was a product able to sense various types of pressure and more importantly, had an incredible flexibility, capable of withstanding bending 2000 times. Another project, led by Zhenan Bao, associate professor of chemical engineering at Stanford University, focused on stretching an electricity-conducting-rubber membrane between two electrodes. Their innovation lies in the unique structure of this rubber, allowing it to regain its shape after being applied pressure. Equipped with 25 million sensors per square centimeter, this material was so sensitive that it could even detect a fly sitting on it. Molding the rubber in different shapes allows sensors to respond to different ranges of pressure, much in the way that human skin has different ranges of sensitivity. For example, the fingertips are far more sensitive than the skin covering the elbow.

Electronic Skin,Diagnosis,Robots That Can Feel Touch,Sci & Tech,Technology,Medicine,nanowire transistors

A year later, Bao’s team from Stanford came up with a bendable solar cell, finding a new way to power the e-skin they have developed. They also added bio-chemical sensors to the material to enhance its sensitivity. New possibilities already arise: the team imagined their product could one day be used for robots’ hands, allowing them to detect diseases or intoxication through touch. It could even improve automobile safety: as the tired or drunk driver’s grip of the steering wheel will loosen, pressure sensors sensing that no hands are holding the wheel could trigger some form of automatic safety device and sound an alarm or make the car slow the car down. The same year, an international team developed what they then called ”electric skin”, an electronic patch for monitoring vital signs in patients. The patch consists of sensors embedded into a thin film, then placed onto a polyester backing, much like the one used for temporary tattoos. Tests were promising, showing that the device was able to stay in place for 24 hours without any kind of adhesive, and was flexible enough to move along with the natural movements of the skin it was applied on. The team suggested that their invention could be used for monitoring brain waves, detecting speech from vibrations of the larynx, emitting heat to help healing, or even serve as artificial skin once it is developed enough to sense touch.

In 2012, the same team from Stanford University developed a new type of flexible, pressure-sensitive electronic skin, now capable of healing itself. Unlike self-healing polymers already available, the team’s material based on plastic and nickel did not depend on high temperature or UV lights to activate its self-healing process. The molecules within the plastic are not very difficult to break apart, but the bonds are capable to restore themselves easily, and experiments showed the process could be repeated up to 50 times. This new e-skin could detect downward pressure as well as pressure from bending, so in theory it had the power to detect both the pressure and angle of the common human handshake. The researchers suggested their e-skin could largely benefit prosthetics and self-healing components for electronic devices. In 2013, new research team from Berkeley joined the adventure and launched a new type of electronic skin that lights up when touched. The device was equipped with blue, green, red and yellow LEDs sandwiched between synthetic rubber and plastic layers. Pressure triggers these LEDs to light up, and the light gets brighter as the stimulus increases. This new technique allows spatial mapping of the applied pressure and instantaneous response. Made up of hundreds of circuits containing a pressure sensor, a transistor and an extremely small LED, was thinner than a piece of paper. The scientists proposed it could be used for the manufacturing of ”sensitive” artificial limbs, as a health monitoring device that can be applied directly on patients’ skin and in robotics, but could find even more outlandish uses, like smart wallpapers, smartphone displays, interactive interfaces for all sorts of electronic devices, car dashboards or even smart watches.

As anyone who’s ever been in a hospital knows, current diagnosis machines are connected to patients through wires, cables and other sorts of invasive contraptions, which can be very distressing for people already in a frail condition. New developments in electronic skin could change it all to the better. Dae-Hyeong Kim, chemical and biological engineering professor at Seoul National University and his collaborators at the University of Texas at Austin have made a new wearable device, taking e-skin to a whole new level. As thin as a temporary tattoo, this patch is capable to store and transmit data about a person’s movements by monitoring muscle movements and then decide to release drugs into skin based on the data patterns it collects. With its sensors, memory, and drug delivery components, all made of nanomaterial’s, embedded onto a soft and flexible polymer substrate, this is the first device of its kind that can not only store information, but also deliver medicine – a priceless aid in the monitoring and treatment of patients with movement disorders such as Parkinson’s disease or epilepsy. “The novelty is really in the integration of the memory device,” says Stéphanie Lacour, an engineer at the Swiss Federal Institute of Technology in Lausanne, who also highlights that no other device can store patient data locally. Current efforts focus on developing similar flexible, stretchable electronics that could be plastered on the heart or brain. The Massachusetts-based company MC10 created another similar device called Biostamp, which attaches flexible electronic circuits to the wearer's skin using a rubber stamp, aiming to help doctors monitor their patients’ health remotely, free from large machinery.

Modern prosthetic limbs are incredibly dexterous, being able to mimic actions fairly well and allow their wearers to comfortably perform common tasks like tying their own shoelaces, picking up an object or even playing cards. The i-limb created by Touch Bionics can even sense signals from the wearer’s muscles and change positions. But as much as they can receive input from the wearer’s body, what they still lack is the ability to feel, or to give any kind of feedback from the surrounding environment. There is hope though, as a team from the Israel Institute of Technology is developing a new type of electronic skin specifically for this purpose. Their e-skin contains gold nano-particles and molecules called ligands. Scientists discovered that bending influences how this e-skin conducts electricity - as particles move closer or farther from each other they enable it to detect as little as tens of milligrams of pressure. Research leader Dr. Hossam Haick claims that the material "is at least 10 times more sensitive in touch than the currently existing touch-based e-skin systems." Since the material is extremely dense, the range of pressure it can detect is highly improved, offering scientists the hope that they can one day make it detect textures. The new developments could also have a great use in robotics.

Electronic Skin,Diagnosis,Robots That Can Feel Touch,Sci & Tech,Technology,Medicine,nanowire transistors

Robots are great tools, able to perfectly grip objects like hard metal parts in factories. However, they cannot interact physically with humans. How can we one day use them for household chores or caring for the elderly if they lack tactile sensation and, for example, the ability to sense if an object is breakable or not? The ever more developed types of e-skin could one day change this. The Israeli team's material could also be used to detect stresses or tiny cracks that would otherwise go unnoticed on bridges or machines. Another team of European scientists has created the ”Roboskin”, consisting of stiff sensing components mounted onto bendable circuit boards. This semi-rigid, tactile skin has already found a wearer - the humanoid robot named iCub.

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