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In the field of medical prosthetics, things are changing quickly. Learn about mind-controlled limbs, and research that suggests that we may be able to go high-tech with low-cost materials.

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Hosted by: Michael Aranda
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Mind-Controlled Arm/Fingers

Synthetic Skin

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Michael: We’ve talked before about things like human enhancement and wearable technologies, but in the field of medical prosthetics, things are changing … fast! There’s a lot of work being done to make prosthetic limbs exactly like the ones that they replace. And this month, scientists reported that -- for the first time -- a patient was able to control individual robotic fingers with his mind with barely any training.

Let’s first talk about the robotic arm those fingers were attached to. Engineers at Johns Hopkins’ Applied Physics Laboratory have been developing a device called a Modular Prosthetic Limb, or MPL, which is an incredibly functional robotic arm. It’s got a huge range of motion, with joints in the shoulder, elbow, wrist, and hands. But most importantly, it can be controlled by your mind -- just like a natural limb.

Well... not your mind. Not unless you’ve had some very specific neural surgery. Before someone can control this arm, they need to have a neural implant inserted, or undergo a surgery called targeted muscle reinnervation. In this procedure, a neurosurgeon re-routes the nerves that control the arm muscles to another muscle group. That way when a patient thinks about moving their arm, a different set of muscles’ contracts -- say, in the chest. This motion can be easily detected by a sensor, which then signals the prosthetic limb. In 2014, this surgery allowed a patient, who lost both arms as a teenager, to wear and control two MPLs and perform basic tasks by just thinking about them.

As cool as that is, though, these tasks were limited to simple actions. The patient could move his fingers all at once to grip or ungrip something, like a ball or a cup -- but he couldn’t control individual fingers. But the latest study, released this month, went a step beyond that. A man with epilepsy was in the hospital, undergoing surgery so doctors could find out where in his brain the seizures were originating. A neurosurgeon implanted electrode sensors in the sensorimotor regions of the patient’s brain. So, even though the patient didn’t need a prosthetic arm, researchers working on the MPL were able to use the information from his sensors to program their device. They had him curl his index finger, for example, and taught the MPL to recognize that signal as the mental instruction for “curl your index finger.” Then, when he thought about moving a finger, the same finger on the robotic arm moved too -- thanks to the very precise electrodes in his brain.

So, soon, amputees might be able to point, play piano, or pick their noses with robotic fingers. But motion isn’t the only important part of prostheses. What about the sensation of touch? Well, thankfully, scientists are also working on synthetic human skin! Engineers have been working on synthetic skin for a while, creating flexible materials that can detect things like temperature, humidity, and pressure. But this skin usually uses materials like carbon nanotubes, which act as really good touch receptors, but they don’t come cheap. Think: thousands of dollars. But, last week, a team of scientists and engineers said they had made fully functional synthetic skin from “ridiculously common fabrication tools” -- their words, not mine.

They used things like aluminum foil, sticky notes, scissors, and sponges to prove that they, or anyone, could make cheap artificial skin. With the aluminum foil they made a temperature sensor. When the aluminum heats up, its atoms space themselves farther apart, and the foil won’t conduct electric current as well -- which is something that can be measured by sensors. To sense humidity, they used a post-it note. Paper is made of porous fibers of cellulose, which happen to be really good at adsorbing moisture -- or making water molecules adhere to the surface. More humidity means more water molecules, which means a greater ability to store an electrical charge, which also can be detected by sensors. And for pressure, they sandwiched a sponge between two ‘plates’ of aluminum foil, along with a small air-gap. As the thickness of this contraption changes, it also creates a change in electric charge, which can then be measured by sensors. The researchers stacked up these layers, plus a few more, into a tidy little square. And ta-da, they had functional paper skin that performs almost as well as the way-more-expensive counterparts. I mean, it’s not the most sophisticated technology, but it shows that pretty much anyone can experiment with cheaper, recycled electronics and come up with something that may someday make people’s lives better.

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