Vibration response in prostheses

A new way to improve the control of bionic limbs

Ivan Sychev, Geektimes

Prostheses throughout their history have become more and more complex: bionic hands perform various grips, knees bend and unbend with effort on their own, simplifying walking up stairs. But until now, one of the most important problems remains the lack of feedback. Amputees have to focus mainly on vision, so using a prosthesis in the dark or to search for objects in a backpack is not the most effective activity.

A group of scientists from the Cleveland Clinic has presented a new way to receive feedback from prostheses based on vibration in the muscles of the prosthetic limb. Within a few minutes, according to the researchers, three amputees began to use prosthetic hands more effectively. 

Researchers led by Paul D. Marasco have developed a neuro-machine interface that transmits vibrations to muscles to improve control of prosthetic limbs. The system simulates kinesthesia – a sense of body position and limb movement, effort, force and gravity. Scientists consider this approach to be the most effective strategy for increasing the effectiveness of the use of prostheses and improving the quality of life of patients. 

The average healthy person is able to perform various movements, control their actions in the dark or with their eyes closed. Thanks to proprioreceptors in our muscles, ligaments, joints, we know where our arm or leg is at a particular moment, we are able to predict movement to the end point and change any parameters to achieve it - for example, to increase strength. In the case of a prosthesis, a person focuses only on vision, which reduces the effectiveness of the device. 

"Due to the lack of feedback, it is impossible to operate with objects in the dark. I need to see the item to take it. When he is not visible, it is impossible to understand where he is. In principle, you can feel the weight. Therefore, there is hope for artificial skin and other developments in the field of feedback," Konstantin Deblikov, owner of bionic prostheses BeBeonic and MyoFacil, told Geektimes in an interview.

The study, conducted by Paul Marasco, involved people with amputated hands using invasive prosthetic hands – devices connected directly to the nerves of the limb, allow them to be controlled intuitively using signals from the brain. During the experiment, the scientists installed vibrating devices on the stumps: the vibrations created the illusion of kinesthesia. The device allowed not only to "feel" how the grip is compressed or unclenched, but also helped to intuitively control the prosthesis without having to constantly look at it. Efficiency increased when vision was added to this process. 

According to the head of the group, Paul Marasco, scientists have known about the ability of vibrations in muscles to create the illusion of kinesthesia since the 1970s. But his team is amazed at how much this technique affects patients. 

In addition to improving limb control, feedback plays another important role: it is designed to eliminate the feeling of foreignness. "If you lose a limb, you not only lose a physical part of yourself, you also lose a part of the spiritual component," says Jacob George, author of another study conducted in 2017. Then the thought-controlled prosthesis helped to restore 100 realistic tactile sensations.

Sensors installed in the prosthesis send information to the brain through two implanted devices. The brain converts them into feelings of pressure, vibration and movement. This allows you to trick the brain and make it think that the limb really belongs to this body.

In the photo below, one of the participants in the experiment holds and feels his wife's hand with the help of an experimental bionic prosthesis.

The scientific work was published in the journal Science Translational Medicine in May 2018 (Marasco et al., Illusive movement perception improves motor control for prosthetic hands).

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