26 August 2016

Almost perfect prosthetic arm

A woman who lost her arm received one of the most advanced bionic prostheses in the world

marks, Geektimes

Melissa Loomis, who lives in Canton (Ohio, USA), lost her arm in 2015. She was bitten by a raccoon, and although the damage was not too severe, the infection that got into the wound led to a strong infection. The source of infection was in the forearm, which had to be amputated, since the patient's very life was at risk. 

Now Melissa has received a new limb. She feels her palm and four of her five fingers. In addition, she can move her right hand and make rotational movements with her wrist and fingers. But still, the differences between the new and old hands are very great. The fact is that her new hand is artificial. 

The American woman became a voluntary participant in the trials of a new type of bionic prosthetic arm almost immediately after losing her own limb. In order for the prosthesis to be controlled, the doctors had to perform a 16-hour operation, during which the shoulder muscles were reinnervated and sensitivity was restored. Thanks to this, the patient was able to control her prosthesis with the help of thought. 

The head of the project Ajay Seth believed that the first results could be seen 4-8 months after the operation. But everything happened much faster. Loomis began to feel her missing hand after only six weeks. When Dr. Seth asked her to imagine that she was moving her wrist, the doctors saw that the shoulder muscles were tensing and working in the same way as it happens when a person's wrist moves. 

After that, the doctor drew a continuation of Loomis' hand, showing where the fingers could be at the moment. And when he touched the painted finger, Loomis felt that touch. In general, doctors have been aware of such a phenomenon as a "phantom limb" for a very long time. Many people who have had their arm or leg cut off sometimes feel their limbs many months or even years after surgery. A number of patients complain of "phantom pains" when it hurts unbearably, for example, a missing palm or a foot that was cut off years ago itches badly. All this torments patients, and doctors in such cases perform operations on the nerve endings of the remainder of the limb in order to rid a person of false sensations. 

In Loomis' case, feeling her missing limb was vital. Without this, she would never have been able to control the bionic prosthesis created as part of the Modular Prosthetic Limb project sponsored by DARPA. The prosthesis was created by Johns Hopkins University specialists. 

The prosthesis itself consists of two parts. This is a transceiver attached to the nerve endings of a woman's shoulder and the prosthesis itself with a signal receiver. As soon as Loomis decides to move his limb, the receiver picks up signals in the nerve endings, decodes them and transmits them to the prosthesis. The bionic prosthesis reacts accordingly, activating one or another servo drive of the system. The result is that the artificial arm is moving. Plus, Loomis feels 4 out of 5 fingers of his artificial hand and the "palm" itself, as already mentioned above. 

Creating a bionic prosthesis of this type is not an easy and expensive task. Dr. Seth had to conduct a series of negotiations with representatives of various organizations before DARPA agreed to start working with him. 

This month Loomis tried out her prosthetic for the first time, and she managed to achieve impressive success in managing this system.

About 100 different contacts are installed in her shoulder, connecting nerve endings with a transceiver and several temperature sensors. Unfortunately, this prosthesis is not ideal, because it is still far from creating a full-fledged human–machine communication interface - this is a very difficult task. But the specialists managed to solve a huge number of issues related to the connection of an electronic-mechanical system to the human body and create a number of new design solutions.

According to the information posted on the developer's website, such a prosthesis is capable of performing almost all movements of a person's hand. 

MPL (Modular Prosthetic Limb) is a very complex system. Now, in addition to Loomis, six more similar systems are being tested, and four are in development. 

Features of the prosthesis:

  • Anthropomorphic design and working principle;
  • Characteristics similar to a human hand (mass, developed force, etc.);
  • High accuracy of work – positioning, coverage of objects;
  • Neurointerface for system management;
  • The ability to feel the structure of the object that the prosthesis touches and the temperature of this object.
  • Sensors at the tips of the "fingers" are able to assess the force when the object is wrapped around.


Colour Sensor/Sensor Type Quantity
aqua Positional sensor 21
aqua Touch sensor 10
aqua Rotation sensor 14
aqua Temperature sensor 17
aqua 3-axis accelerometer 3
aqua 3-axis load sensor 3
aqua Additional sensors

The main requirements for the prosthesis are as follows: 

  • Anthropomorphic design;
  • Reliability of fastening the system to the human body;
  • The possibility of producing copies of the prosthesis;
  • Optimal weight comparable to the weight of the corresponding limb or part of it;
  • High energy efficiency;
  • Maintainability;
  • Sensor support;
  • The ability to transmit information about the structure of the surface that the prosthesis touches, the sensation of vibration (if there is one), surface temperature.

There are two variants of the working brush of the prosthesis – fully functional, but very different from the appearance of an ordinary human brush (such a prosthesis is cheaper). And the same functional prosthesis that copies the appearance of the brush, including color. 

Modular Prosthetic Limb is one of the most advanced systems of this type. The fact is that scientists have managed to use every nerve of the shoulder responsible for touch. These nerve endings were connected to the interface of the prosthesis. MPL fingers are equipped with touch sensors and temperature sensors. The connection of the prosthesis with the hand is two–sided - that is, when touching the prosthesis to an object, a woman can feel the touch, feel the structure of the surface, plus feel heat or cold.

"We are close to Loomis becoming the owner of the most technically advanced prosthesis in the country, and soon – all over the world," says Seth. And it looks like it really is.

Portal "Eternal youth" http://vechnayamolodost.ru  26.08.2016

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