Electronic skin

    Today, around the world, the development of humanoid robots, bionic prostheses, and artificial organs is underway. Perhaps, at the moment, scientists and designers are the most advanced in prosthetics. Unfortunately, the appearance of these masterpieces of bioengineering still leaves much to be desired in terms of indistinguishability from living flesh. In addition, for the successful use of such prostheses, visual control is necessary, since the artificial limb is devoid of tactile sensations. And to solve all these problems, scientists are developing artificial electronic skin. What successes have they already achieved?

    Artificial tactile sensitivity in people and cars so far remains the lot of science fiction films and books. But there is every reason to believe that the first real engineering models of existing systems will appear soon. Moreover, in addition to prosthetics and equipping robots, artificial leather technology promises to find application in the field of wearable gadgets.

    Robots themselves have not surprised anyone for a long time, except for old women from the outback. And the more mechanical "beings" penetrate our daily lives - and this, apparently, is inevitable - the more important it will become to enable them to "feel the skin." This will be necessary at least for the safety of their own functioning: in addition to the shape of the objects, it is necessary to determine the slippery, texture and surface temperature, otherwise the robot may drop the object or fall by itself. Feeling the properties of the object, the robot will be able to accurately calculate the necessary and sufficient holding force.

    This benefit of a distributed sensor network that accurately measures small changes in pressure attracts the attention of manufacturers and enthusiasts of wearable gadgets and smart clothes. Artificial electronic skin (E-skin) can also be useful in the creation of wearable sensors for monitoring physical condition, and even find application in minimal invasive surgery.

    Softness, flexibility and elasticity

    As already mentioned, flexible artificial leather is especially in demand in the field of prosthetics. Modern high-tech prostheses using myoelectric interfaces receive signals directly from the human muscle tissue and use complex algorithms to transform them into the movement of servomotors. But, despite the efforts of designers to give artificial prostheses the most natural look, their artificiality will be very noticeable. And the hardness of the outer shell of the prosthesis plays a crucial role in this perception. She does not bend and stretch, like real skin, and even about the touch and say no.

    A real breakthrough in the field of artificial skin will occur when it manages to give the mechanical properties of human skin. This will allow you to interact with objects very accurately and save people with prostheses from the lion's share of discomfort and inconvenience.

    However, this is one of the main difficulties. After all, in order for the skin to accurately follow the contours of objects, the electronics contained in it must also be flexible. Unfortunately, almost the entire modern microelement base cannot boast of such a property. Although a lot of efforts on the part of developers are aimed at solving this problem. For example, the first attempts to create artificial leather were printed on a flexible substrate conductive circuits with standard microelectronic components and sensors soldered to them. Such decisions were extremely awkward, because the finished products represented a kind of surface, under which solid "islands" of electronic components, connected to each other by traditional metal soldering, were distinctly probed.

    Nevertheless, a similar approach formed the basis of the ROBOSKIN project. The outer cover was a semi-rigid material with embedded sensors and electronics. Of course, this was far from the concept of “skin,” but such a coating provided minimal tactile capabilities and was well suited for use on large surfaces of complex shape. This prototype faux leather has even been tested on various robots, including the iCub .

    Another interesting approach to creating e-skin was the use of organic thin-film semiconductor transistors. This technology was developed by scientists from Tokyo and Stanford Universities. Due to the peculiarities of its molecular structure, organic semiconductors initially have flexibility, which is their most important advantage. On the other hand, the speed and stability of organic components are low due to low electrical conductivity.

    But to create effective artificial skin, a response speed of not more than one millisecond is necessary so that the robot can respond quickly enough. And according to this indicator, highly mobile materials, for example, single-crystal silicon, are best suited.

    However, the use of silicon brings us back to the problem of flexibility. One approach allows you to solve it using thermal transfer printing.. For this, a silicon nanowire is applied under heating to a flexible plastic substrate. It is an elastic material called polymide. Such a substrate coated with conductive circuits made of silicon nanowires is then equipped with thin-film transistors and sensors. This technology is now being actively developed at the University of Glasgow (note, these are still Scottish scientists!).

    Another promising material has also recently been developed at the Israel Institute of Technology. Sensors are applied to the polyethylene terephthalate substrate, which are single-layer sections of gold particles with a diameter of 5-8 nanometers. They are, like petals, surrounded by ligandsacting as connectors-conductors. These sensors are capable of measuring pressure in the range from tens of milligrams to tens of grams.

    Now the main efforts are aimed precisely at achieving sufficient flexibility and strength of the cover, but, besides this, the issue of tactile "naturalness" is acute. In addition, artificial leather, in fact, is an electric device, a gadget. And the efficiency of its energy consumption will also require the attention of developers. Of course, these are not smartphones with their low battery life, but still you need to think about recharging your skin as little as possible.

    In general, the current state of affairs with the creation of artificial leather allows us to hope that in the coming years it will reach the level of a commercial product. And who knows, maybe after 20 years you shaking someone's hand, then you will be surprised to hear that it turns out to be a prosthesis.

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