Artificial muscles will restore the ability to blink

The development of specialists from the Davis Medical Center at the University of California can restore the ability to blink to thousands of patients who have lost the ability to close their eyes as a result of injuries, stroke, nerve damage as a result of inflammation or surgery to remove a tumor. The device, consisting of the thinnest electrodes and an organosilicon polymer capable of contracting under the action of current (electroactive polymer artificial muscle, EPAM), is described in the current issue of the journal Archives of Facial Plastic Surgery (Force Requirements for Artificial Muscle to Create an Eyelid Blink With Eyelid Sling).

Blinking is very important for maintaining the normal functioning of the eyes, as the movements of the eyelids clean the surface of the eye and moisturize the cornea. With insufficient hydration, the eye is at risk of the rapid development of corneal ulcers, which is fraught with loss of vision.

Involuntary blinking movements are controlled by one of the cranial nerves - the facial one. Damage to this nerve is the main cause of irreversible eyelid paralysis in most patients. In many patients, due to individual anatomical features, there are no additional branches of the facial nerve that could be redirected to the paralyzed eyelid. Some patients, as a result of congenital Mobius syndrome, characterized by underdevelopment of facial nerves, also cannot blink or even smile.

Currently, medicine has two methods of treating eyelid paralysis. One of them consists in transplanting muscle flaps from the temporal, masticatory muscle or from the subcutaneous neck muscle with microvascular and nerve anastomosis – stitching the peripheral segment of the facial nerve with the central segment of another, specially crossed, motor cranial nerve. Such an operation takes from 6 to 10 hours and is associated with additional trauma, which is often undesirable for elderly and weakened patients.

The second method consists in implanting a small gold wire into the eyelid, acting as a weight, which helps to close the eyes under the influence of gravity. Although such an operation is successfully performed in more than 90% of patients, the eyelid eventually blinks slower than usual, and its movements cannot be synchronized with the second eye. Some patients also have difficulty closing their eyes during sleep.

As part of their research, plastic surgeon Travis Tollefson and his colleagues tested the latest alternative method for restoring eyelid function in irreversible facial nerve paralysis. To begin with, scientists imitated the process of blinking on corpses. To this end, they implanted strings of connective tissue or artificial biocompatible material – polytetrafluoroethylene into the eyelids of the deceased. With the help of tiny titanium screws, the strings were fixed to the bone at the inside of the eye. At the other end, the strings were connected to an artificial muscle powered by a battery. The artificial muscle, along with the battery, was placed in the natural recess of the temporal bone to hide their presence.

For the first time, artificial muscle was developed in the early 1990s by SRI International engineers from Palo Alto, California, and consists of three layers – two integumentary and internal, acrylic or organosilicon, coated with a layer of carbon lubricant. When tension is applied to the muscle, the force of electrostatic attraction causes the outer layers to converge and compress the elastic center, which causes stretching of the artificial muscle. When the current is turned off, the muscle takes its original shape, i.e. it contracts. The strength and nature of the movements of an artificial muscle are very similar to natural ones, and a source used in implantable hearing aids is sufficient to power such a muscle.

Tests of the implanted device have shown that the force required to close the eyelid with its help does not exceed the limits achievable with the help of an artificial muscle. This feature makes it possible to realistically recreate the natural blinking of the eyelid, as well as synchronize its movements with a normal, functional eyelid.

For patients whose second eyelid is not affected by paralysis, it is possible to lay a sensitive electrode to the healthy eyelid, which will record the impulses of natural blinking and contract the artificial muscle simultaneously with the healthy one. If the patient has lost control of both eyelids, an electronic pulse stimulator similar to those used to regulate the heart rate can be used.

Experiments with facial muscles mean only the first step in the development of artificial muscles to control other parts of the body. Facial muscles require significantly less effort than is necessary for finger movement or hand flexion. According to Dr. Tollefson, the number of ideas for applying their technology is infinitely large. For patients with other types of paralysis, the use of artificial muscles gives hope to restore the lost ability to smile or control the bladder.

Now researchers are improving their methodology on corpses and animal models. According to their estimates, this technology will become available to patients in the next five years.

Ruslan Kushnir
Portal "Eternal youth" http://vechnayamolodost.ru according to Science Daily: Artificial Muscles Restore Ability to Blink21.01.2010