Scientists have created a smart prosthetic skin that’s stretchy and warm like real skin, and is jammed with tiny sensors that can pick up a variety of environmental cues such as heat, pressure and moisture. Although it’s early days yet, the dream is that with further development, it could transmit sensory information to the brains of amputees to give prosthetic limbs feeling.
Artificial limbs have come on in leaps and bounds recently. Scientists have 3D printed prosthetic arms, created artificial limbs that can be controlled by the user’s nerves or brain, and even designed prosthetic skin that is self-healing or 1,000 times more sensitive than human skin.
While these are all fantastic, the problem the devices tend to face is that they don’t enable the user to feel if something is dangerously hot, or whether the user is about to drop something because the grip is too soft. Furthermore, smart prosthetics that feature various sensors are often fairly rigid and easy to fracture, and therefore do not have the flexibility of actual limbs. These are all issues that scientists from the US and South Korea hoped to address, and they’ve managed to come up with a smart artificial skin that’s designed to mimic both the stretchability and high-resolution sensory capabilities of human skin.
Kim et al, via MIT Technology Review
As described in Nature Communications, the smart skin is composed of an elastic, transparent silicone material called polydimethylsiloxane (PDMS) that’s designed to coat prosthetic limbs. This material is jam packed with sensors—400 per square millimeter—made of silicone nanoribbons in a snake-like shape that allows the delicate sensors to withstand more strain. These sensors generate an electrical feedback signal when stretched or squashed, and can also detect whether surfaces are hot or cold. The skin also features tiny devices called capacitors that allow the material to detect humidity.
To test out how good the material is at picking up moisture levels, they first compared the humidity readings from the skin with those of commercial sensors and found they were pretty similar. Then, they went for the next logical step: poking diapers with varying degrees of wetness. Sure enough, the prosthetic hand coated in the skin could tell which ones were wet or dry.
To make it even more like skin, they fitted it with heating devices so that it matches the temperature of human skin. The team also filmed actual hand movements and used this information to guide the skin design. For example, in areas that don’t stretch much, such as fingertips, they added more sensors than in very mobile areas, such as the wrist, which need to focus on flexibility.
While this skin sounds great on paper, it’s only useful if the sensory information can be transmitted to the user’s brain, so the team hooked up the skin with nerve-stimulating electrodes and tested it out on rats. They found that data could be successfully transmitted, but they didn’t know to what extent the rat could feel stimuli such as heat and pressure. Furthermore, these kinds of electrodes are currently unsuitable for humans, which is why the researchers are intending on developing the device through larger animal studies.
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