Love in prosthetics

Lizards can regenerate after losing their tails, and crabs can regenerate after losing their feet, but compared with these seemingly "primitive" animals, humans have lost a lot of the ability to regenerate during the course of evolution. The ability to regenerate limbs in adults is almost nil, with the exception of babies who may regenerate when they lose their fingertips. As a result, the quality of life of those who lose limbs due to accident or disease can be greatly affected, and finding biological replacement has been an important option for doctors to improve the lives of amputees.

As far back as ancient Egypt, there have been records of artificial limbs. In Conan Doyle's "The Sign of the Four," there is also a description of a murderer using prosthetic limbs to kill people.

Such prosthetics, however, provide simple support but are unlikely to significantly improve an amputee's life experience. Good prosthetics should be able to send signals in both directions: on the one hand, the patient can control the prosthetics autonomously; On the other hand, a prosthetic limb would need to be able to send sensations to the sensory cortex of the patient's brain, just like a natural limb with nerves, giving them a sense of touch.

Previous studies have focused on decoding brain codes to allow subjects (monkeys and humans) to control robotic arms with their minds. But it's also important to give the prosthetic a sense. A seemingly simple process like grasping involves complex feedback, as we subconsciously adjust the force of our fingers according to how our hands feel, so that we don't slip things off or pinch them too hard. Previously, patients with prosthetic hands had to rely on their eyes to determine the strength of objects. It takes a lot of attention and energy to do things that we can do on the fly, but even then they often break things.

In 2011, Duke University conducted a series of experiments on monkeys. They had monkeys use their minds to manipulate virtual robotic arms to grasp objects of different materials. The virtual arm sent different signals to the monkey's brain when it encountered different materials. After training, the monkeys were able to correctly pick out a particular material and receive a food reward. Not only is this a preliminary demonstration of the possibility of giving prosthetics a sense of touch, but it also suggests that monkeys can integrate the tactile signals sent by the prosthesis brain with the motor control signals sent by the brain to the prosthesis, providing a full range of feedback from touch to sensation to control arm selection based on sensation.

The experiment, while good, was purely neurobiological and did not involve an actual prosthetic limb. And to do that, you have to combine neurobiology and electrical engineering. In January and February of this year, two universities in Switzerland and the United States published papers independently using the same method to attach sensory prosthetics to experimental patients.

In February, scientists at the Ecole Polytechnique in Lausanne, Switzerland, and other institutions, reported their research in a paper published in Science Translational Medicine. They gave a 36-year-old subject, Dennis Aabo S? Rensen, with 20 sensory sites in the robotic hand that produce different sensations.

The whole process is complicated. First, doctors at Rome's Gimili Hospital implanted electrodes in Sorensen's two arm nerves, the median and ulnar nerves. The ulnar nerve controls the little finger, while the median nerve controls the index finger and thumb. After the electrodes were implanted, doctors artificially stimulated Sorensen's median and ulnar nerves, giving him something he hadn't felt in a long time: he felt his missing hand moving. Which means there's nothing wrong with Sorensen's nervous system.

Scientists at the Ecol Polytechnique in Lausanne then attached sensors to the robotic hand that could send electrical signals based on conditions such as pressure. Finally, the researchers connected the robotic arm to Sorensen's severed arm. Sensors in the robotic hand take the place of sensory neurons in the human hand, and electrodes inserted into the nerves replace the nerves that can transmit electrical signals in the lost arm.

After setting up and debugging the equipment, the researchers conducted a series of tests. To prevent other distractions, they blindfolded Sorensen, covered his ears and let him touch only with the robotic hand. They found that Sorensen could not only judge the hardness and shape of the objects he touched, but also distinguish between different materials, such as wooden objects and cloth. What's more, the manipulator and Sorensen's brain are well coordinated and responsive. So he can quickly adjust his strength when he picks something up and keep it steady. "It surprised me because SUDDENLY I could feel something THAT I hadn't felt for the last nine years," Sorensen said in a video provided by the Ecole Polytechnique in Lausanne. "When I moved my arm, I could feel what I was doing instead of watching what I was doing."

A similar study was done at Case Western Reserve University in the United States. Their subject was Igor Spetic, 48, of Madison, Ohio. He lost his right hand when a hammer fell on him while making aluminum parts for jet engines.

The technique used by the Case Western Reserve University researchers is roughly the same as the technique used at ECOLE Polytechnique in Lausanne, with one important difference. The electrodes used at the Ecole Polytechnique in Lausanne pierced the neurons in Sorensen's arm into the axon; The electrodes at Case Western Reserve University don't penetrate the neuron, but instead surround its surface. The former may produce more precise signals, giving patients more complex and nuanced feelings.

But doing so has potential risks for both the electrodes and the neurons. Some scientists worry that the invasive electrodes could cause chronic side effects on the neurons, and that the electrodes would be less durable. However, researchers at both institutions are confident they can overcome the weaknesses of their approach. The Spiderdick also produces a fairly precise sense of separation from sandpaper, cotton balls, and hair. The researchers at the Ecole Polytechnique in Lausanne, however, said they were confident of the durability and stability of their invasive electrode, which lasted between nine and 12 months in rats.

Still, it's too early to put this research on the market. In addition to durability and safety, the convenience of sensory prosthetics is still far from enough. Sorenson and Specdick stayed in the lab while the prosthetics were being fitted. Their hands, with lots of wires and gadgets, look nothing like the bionic limbs of science fiction. Silvestro Micera, a professor at the Ecole Polytechnique in Lausanne who worked on the study, said it would be several years before the first sensory prosthetics, which look just like normal ones, could leave the laboratory.

"I'm excited to see what they're doing. I hope it helps others. I know science takes a long time. If I can't use it now, but the next person can, that's great."

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Post time: Aug-14-2021