Artificial muscle could help facial paralysis sufferers blink again

A life changing fix

Even a partial loss can damage vision and allow infection to take hold of the eye. For those with permanent and irreversible facial paralysis, the consequences can be even more dramatic, including impaired eye closure, leading to permanent vision loss, more severe infections, and, in extreme cases, even death.

While short-term paralysis can often be treated with interventions as simple as lubricating drops, chronic paralysis can require more intensive procedures, including weights to facilitate the complete closing of the eye or, in some cases, a procedure known as “tarsorraphy,” which sees the upper and lower eyelids being sewn together to protect the eye’s surface.

Other surgical solutions include grafting nerves and transferring muscles to the affected regions of the face to achieve dynamic facial reanimation. However, these interventions require long waiting times and surgeries on the face and the regions of the body from which nerves and muscles are harvested, with all the risks that accompany such procedures.

This research introduces a soft artificial muscle that can be placed under the skin of a patient suffering from facial paralysis. This implant facilitates facial reanimation without those drawbacks.

“Artificial muscles function through actuators that produce motion of contraction and expansion, similar to the ones of natural biological muscles,” the authors wrote in the study. “A significant advantage of this method over traditional therapies is that it eliminates the need for nerve grafts or muscle flaps, thereby avoiding the lengthy waiting periods between surgical procedures and eliminating the need for surgical intervention on other parts of the body.”

Artificial muscle mirrors healthy blinking motion

Several artificial muscle technologies are currently being researched and applied in robotics and prosthetics science, including pneumatic artificial muscles, alloys capable of retaining shape-memory, and ElectroActive Polymers, which are polymers capable of changing size and shape when introduced to an electric field.

The team focused on an example of the latter material called a dielectric elastomer actuator. These excel as soft actuators due to their ability to move in multiple directions while operating silently, coping with large strains, and possessing the ability to store a great deal of energy relative to their size.

In the team’s prosthetic, the dielectric elastomer actuators are coupled with a mechanical system placed on the eyelid. The actuator is attached to the center of a beam and placed on the forehead of the facial paralysis sufferer. A realistic and anatomically precise eyelid is then fabricated and introduced to the system.

“To mimic natural eyelid movements, the artificial muscle will be placed on the paralyzed side of the face and be synchronized with the activity of the healthy side,” the authors wrote. “This method mirrors traditional surgical dynamic treatments that utilize cross neuronal transfer, drawing signals from the healthy side to the paralyzed side to achieve symmetric movements.”

By enabling real-time control of the artificial muscle from the healthy hemisphere of the patient’s face, the researchers’ prosthesis allows a patient to blink symmetrically.

Testing their implant, the researchers measured the stroke, force, and frequency, including the opening and closing time of the eyelid, with a natural blinking movement achieved and a resulting displacement of the artificial eyelid of 2.5 millimeters.

This showed the use of a dielectric elastomer actuator with a mechanical system is a promising approach to the restoration of blinking and the treatment of facial paralysis. Of course, the next step for this research will be to test this platform with actual sufferers of facial paralysis.

“In future work, the control as well as the implementation and testing of the prosthesis [in the living body] should be addressed,” the authors conclude.