Artificial muscles will help to rehabilitate a paralyzed leg

Flexible exoskeleton allows to return mobility of the paralyzed limb

Kirill Stasevich, CompulentaWhen we hear about prosthetic legs, what do we imagine?

Some pirates, John Silver, leg-shaped pieces of wood (at best) and other images from the dark past. There is no doubt that for most of those who have lost a leg and at the same time live in not too prosperous countries, such prostheses are the only alternative to a wheelchair and crutches. At the same time, in a variety of science fiction books and films, you can see artificial limbs that are almost no different from the real ones. And modern science, I must say, is trying its best to bring this fiction to life.

Not so long ago we wrote about an artificial leg, for which it was possible to improve the control, achieving more precise movements, so that a person could even climb the stairs, alternating legs – which is impossible to do with conventional mechanical prostheses. Something similar has been achieved by a group of researchers from Carnegie Mellon University, Harvard and the Massachusetts Institute of Technology (all USA). However, in this case we are not talking about a complete prosthesis replacing the missing leg, but about some kind of device that helps to cope with certain disorders of the musculoskeletal system. (In addition, clinical trials with the new device have not yet been conducted, apparently, limiting themselves to demonstrating a constructive idea.)

A human leg and its analogue based on a flexible exoskeleton (drawing by the authors of the work).

This orthopedic device consists of soft, elastic plastic, pneumatic muscles and stretch-sensitive sensors, and all this is designed to restore the normal mobility of the ankle joint. There are several diseases (like the so-called hanging foot) when the foot loses mobility and some movements (for example, bending the foot to the left or right) become impossible. The cause of the disease may be some kind of neuromuscular defect, paralysis, etc., which, in turn, may occur due to multiple sclerosis, trauma or, say, stroke.

An orthopedic device made of a soft exoskeleton and pneumatic muscles simulates the very structure of the leg, with its own muscles and ligaments. Four "pneumomuscles" correspond to the muscles of the lower leg and perform all the work on the movement of the foot for them. The angle of movement is controlled by sensors, which are a thin elastic film with microchannels inside. These microchannels are filled with a special liquid conductor, the conductivity of which varies depending on what form they take, that is, on whether they are stretched or compressed. Sensors are located on the ankle, stretching and compression occurs when the foot moves.

Mobility is provided thanks to a flexible exoskeleton, but this same flexibility presents a certain problem, since such a device is much more difficult to control than an exoskeleton made of conventional, rigid materials. Therefore, the sensors here must be sensitive, and the methods of control are more skillful than usual.

Researchers will need to work a lot more to make the device more convenient for everyday use; however, they have no doubt that the very principle of creating such orthopedic devices will find the widest application. After all, with its help, in principle, it is possible to restore almost natural mobility not only to the ankle joint alone, but also to the entire leg or arm.

The results of the study are published in Bioinspiration & Biomimetics: Park et al., Design and control of a bio-inspired soft wearable robotic device for ankle–foot rehabilitation.

Prepared based on the materials of Carnegie Mellon University:
Bio-Inspired Robotic Device Could Aid Ankle-Foot Rehabilitation, CMU Researcher Says.

Portal "Eternal youth" http://vechnayamolodost.ru22.01.2014