Technologically and inexpensively

More than five million people in the world have undergone upper limb amputation and need prosthetics. Prostheses have come a long way from traditional mannequin–like ones that perform only a cosmetic function, to neuroprostheses - bionic limbs capable of perceiving the residual muscle signals of the carrier and performing the desired movements. But there is a price to pay for this high-tech dexterity. Neuroprosthetics can cost tens of thousands of dollars and is built on metal frames with electric drives, which can be heavy and tight.

Engineers at the Massachusetts Institute of Technology and Shanghai Jiao Tong University have developed a soft, lightweight and potentially inexpensive neuroprosthesis of the hand. Volunteers who tested the prosthesis performed everyday actions (zipped the suitcase, poured juice from the box into a glass, stroked cats) just as successfully, and in some cases better than with a more complex and severe neuroprosthesis.

The photo is provided by the developers of the prosthesis.

The researchers found that the prosthesis, developed using a tactile feedback system, restored some simple sensations in the volunteers' residual limb. The new design is surprisingly durable and in tests quickly recovered after being hit by a hammer or hit by a car.

The new prosthesis is soft and elastic, it weighs about 200 grams, and its components cost about $ 500 in total – a small part of the weight and material costs associated with existing neuroprostheses.

Developed by Professor Xuanhe Zhao and his colleagues, the artificial hand is made of a soft elastic material – ecoFLEX elastomer – and has five fingers with segments similar to the phalanges of real fingers. They are attached to the "palm" created on a 3D printer.

Instead of separate electric motors controlling each finger, as is the case in most neuroprostheses, the researchers used a simple pneumatic system to precisely inflate the fingers and bend them in certain positions. The system includes a small pump and valves that can be worn on the belt, significantly reducing the weight of the prosthesis itself.

A specially developed computer model helped to correlate the desired position of the fingers with the pressure that the pump must create to achieve this position. Using this model, the group has developed a chip that controls a pneumatic system to "inflate" the fingers in positions that mimic five common combinations, including bringing two and three fingers together, clenching into a fist and cupping the palm.

The pneumatic system receives signals from electromyographic sensors that read the activity of motor neurons that control muscles. Sensors are installed on the upper part of the prosthesis, where it contacts the limb, and pick up signals from the stump, for example, when the patient imagines a fist.

With the help of a special algorithm, the signals of motor neurons in the control chip are converted into combinations of movements created by the pneumatic pump. For example, when a person imagines holding a glass of wine, sensors pick up residual muscle signals, which the chip then translates into the appropriate pressure. The pump creates this pressure to inflate each finger and hold the real glass.

Another advantage of the new prosthesis is tactile feedback, which is absent in most commercial neuroprostheses. To create it, the developers attached a pressure sensor to each finger, which, when touched or pressed, generates an electrical signal proportional to the pressure felt. Each sensor interacts with a specific area of skin on the residual limb, so the user can "feel" when, for example, the thumb of the prosthesis comes into contact with the index finger.

To test the new prosthesis, the researchers recruited two volunteers, each of whom had their upper limbs amputated. They learned to use it by repeatedly contracting the arm muscles and simultaneously imagining five specific movements.

After completing such a 15-minute workout, the volunteers were asked to perform a series of tests to demonstrate strength and sleight of hand. These tasks included turning book pages, writing with a pen, lifting heavy balls and light objects such as strawberries and bread. They repeated the same tests using a tougher, commercially available bionic arm, and reported that the inflatable prosthesis was just as comfortable or even better at most tasks compared to its counterpart.

One volunteer was also able to intuitively use a soft prosthesis in everyday activities: take and bring crackers, cakes and apples to his mouth, handle various objects and tools – a laptop, bottles, a hammer and pliers. This participant also learned more gentle movements, such as shaking someone's hand, touching a flower, or petting a cat.

The wonders of his agility are shown at the beginning, and the slow and difficult training process is shown at the end of the YouTube video.

In one of the exercises, the researchers blindfolded a volunteer and found that he could distinguish which prosthetic finger they were touching. He was also able to "feel" bottles of different sizes that were placed in the prosthetic arm and picked them up. The authors consider these tests as a promising sign that people with amputated limbs can restore tactile sensations using an inflatable prosthesis.

The group has applied for a patent and is working to improve the sensitivity and accuracy of movements.

Article G.Gu et al. A soft neuroprosthetic hand providing simultaneous myoelectric control and tactile feedback is published in the journal Nature Biomedical Engineering.

Amina Ibragimova, portal "Eternal Youth" http://vechnayamolodost.ru based on MIT materials: Inflatable robotic hand gives amputees real-time tactile control.