Synthetic muscle brings back eye blink
UC DAVIS—Researchers have developed artificial muscles that may help patients with facial paralysis regain the ability to blink.
The technique, which uses a combination of electrode leads and silicon polymers, could benefit the thousands of people each year who no longer are able to close their eyelids due to combat-related injuries, stroke, nerve injury, or facial surgery. Researchers say the approach could be used to develop synthetic muscles to control other parts of the body.
“This is the first-wave use of artificial muscle in any biological system,” says Travis Tollefson, a facial plastic surgeon at the University of California, Davis. “But there are many ideas and concepts where this technology may play a role.”
The new procedure is described in an article in the January-February issue of the Archives of Facial Plastic Surgery.
Tollefson and his colleagues were seeking to develop the protocol and device design for human implantation of electroactive polymer artificial muscle (EPAM) to create a long-lasting eyelid blink that will protect the eye and improve facial appearance.
EPAM is an emerging technology that has the potential for use in rehabilitating facial movement in patients with paralysis. Electroactive polymers act like human muscles by expanding and contracting, based on variable voltage input levels.
For people with other types of paralysis, the use of artificial muscles could someday mean regaining the ability to smile or control the bladder.
Otolaryngologist Craig Senders says reanimating faces is a natural first step in developing synthetic muscles to control other parts of the body.
“Facial muscles require relatively low forces, much less than required to move the fingers or flex an arm,” he explains.
Blinking is an essential part of maintaining a healthy eye. The lid wipes the surface of the eye clean and spreads tears across the cornea. Without this lubrication, the eye is soon at risk of developing corneal ulcers that eventually can cause blindness.
Involuntary eye blinking is controlled by a cranial nerve. In most patients with permanent eyelid paralysis, this nerve has been injured due to an accident, stroke, or surgery to remove a facial tumor.
Many patients have no other functioning nerves nearby that can be rerouted to close the eyelid. Others were born with Mobius syndrome, characterized by underdeveloped facial nerves. These patients are expressionless and can neither blink nor smile.
Eyelid paralysis currently is treated by one of two approaches. One is to transfer a muscle from the leg into the face. This option, however, requires hours of surgery, creates a second wound, and is not always suitable for elderly or medically fragile patients.
The other treatment involves suturing a small gold weight inside the eyelid. The weight closes the eye with the help of gravity. Though successful in more than 90 percent of the estimated 3,000 to 5,000 patients who undergo this surgery every year in the United States, the resulting eye blink is slower than normal and cannot be synchronized with the opposite eye. Some patients also have difficulty keeping the weighted lid closed when lying down to sleep.
For the study, Senders and Tollefson used an eyelid sling mechanism to create an eyelid blink when actuated by an artificial muscle. Using cadavers, the surgeons inserted a sling made of muscle fascia or implantable fabric around the eye. Small titanium screws secured the eyelid sling to the small bones of the eye. The sling was attached to a battery-operated artificial muscle.
They found that the force and stroke required to close the eyelid with the sling were well within the attainable range of the artificial muscle. This capability may allow the creation of a realistic and functional eyelid blink that is symmetric and synchronous with the normal, functioning blink. A similar system also could give children born with facial paralysis a smile.
“The amount of force and movement the artificial muscle generates is very similar to natural muscle,” Tollefson says. An implanted battery source similar to those used in cochlear implants would power the artificial muscle.
For patients who have one functioning eyelid, a sensor wire threaded over the normal eyelid could detect the natural blink impulse and fire the artificial muscle at the same time.
Among patients lacking control of either eyelid, an electronic pacemaker similar to those used to regulate heartbeats could blink the eye at a steady rate, and be deactivated by a magnetic switch.
The researchers are now refining the technique on cadavers and animal modes. They estimate the technology will be available for patients within the next five years.
The study was funded by a grant from the American Academy of Facial Plastic and Reconstructive Surgery.
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