Implants and Prosthetic Devices: Helping the Body Reach its Full Potential

Medical technology is currently capable of treating such physical hardships as loss of limb, eyelid paralysis, and chronic osteoarthritis – but researchers are continually finding ways to improve upon the effectiveness of these and other implanted and prosthetic device technologies. What follows is a sample of new technologies and research efforts that hold promise for a future in which human beings are able not just to survive, but thrive in the face of any conceivable physical difficulty.

Sling Mechanism for Eyelid Paralysis

Humans blink about 15 times a minute – more than 14,000 times in a typical 16-hour day. Because this activity is crucial for cleaning and lubricating the eyes, patients suffering from eyelid paralysis need treatment. Most of these patients injured the cranial nerve that controls involuntary eye blinking, whereas others may have been born with Moebius syndrome, a rare neurological disorder that affects the facial nerves. One current treatment for eyelid paralysis requires the transfer of a muscle from the leg into the face in a 6- to 10-hour surgery, and is not always a suitable option for elderly patients. An alternate treatment involves suturing a small gold weight into the eyelid. The weight closes the eyelid using gravity, but it cannot synchronize the eyes to create a natural blinking pattern.

Now, Craig Senders and Travis Tollefson of the University of California-Davis Department of Otolaryngology, Head, and Neck Surgery, are developing a more attractive third option: an artificial muscle used in conjunction with a sling mechanism to help facial paralysis patients restore the ability to blink more naturally. Illustration of left eyelid sling that is attached to the electroactive polymer artificial muscle device (EPAM) after passing through an interpolation unit that is implanted in the lateral orbital wall (note screw fixation). (UC Davis Health System photo)

The mechanism uses an artificial muscle – invented by SRI International of Menlo Park, CA – to drive eyelid movement. The muscle includes a piece of soft acrylic or silicon layered with carbon grease. When a current is applied, electrostatic attractions cause the outer layers to pull together and squash the soft center. This motion expands the artificial muscle, which is powered by an implanted battery source similar to what is used in cochlear implants. Once the charge is removed, the muscle contracts and flattens the shape of the sling, blinking the eye. When the charge is reactivated, the muscle relaxes and the soft center reverts back to its original shape.

Operating experimentally on cadavers, the researchers 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 surgeons disguised the entire device in a natural hollow located at the temple. For patients with one functioning eyelid, a sensor wire threaded over the normal eyelid could detect the natural blink impulse and program the artificial muscle to blink at the same time. Patients with two paralyzed eyelids could use an electronic pacemaker to blink their eyes at a steady rate.

Researchers are still refining the mechanism on cadavers and animal modes, but it is estimated to be available for human patients within the next five years.

Smaller Heart Monitor Implants

Someday, wearable or implanted devices driven by microchip technology could conveniently detect and diagnose heart problems, monitor patients with Parkinson’s disease, or predict seizures in epileptic patients. Researchers at MIT’s Microsystems Technology Laboratory (MTL) have built a prototype device that incorporates a low-power chip to measure and record electrocar-diograms (ECGs). Patients could wear the monitor at home to give doctors a more detailed picture of their everyday heart health. The ECG device currently prescribed to monitor recent heart attack victims is not able to store much data, and runs on a bulky battery that is inconvenient to wear.

The new MIT monitor prototype is an L-shaped device, about 4” long on each side, that sticks to the chest and can be worn without any external wires protruding. It is capable of storing up to two weeks of data in Flash memory, and runs on just two milliwatts of power. In the future, researchers hope to engineer chips that can be powered by energy from the body of the person wearing the device.

ECG data from the chip can be downloaded for analysis, allowing doctors to spot future problems. Down the line, the researchers envision working the algorithm into the chip so that data can be analyzed more immediately. They also plan to incorporate an alarm that will alert the patient and/or doctor if a heart attack appears imminent. The researchers plan to start testing the device on healthy subjects this spring, followed by trials involving patients with cardiovascular disease.