Implants Bring Hope To The Toughest Medical Handicaps

Imagine implants that detect cancer and deliver the appropriate drugs. Or read the brain's electrical signals and control motor functions affected by diseases like epilepsy and multiple sclerosis. Or restore sight to the blind. Actually, you don't have to imagine. These devices, if they're not here yet, are in advanced stages of testing. And they're taking advantage of improvements in MEMS sensors and wireless communications.

Hope For Heart Patients
Less than a year ago, the Food and Drug Administration gave Abiomed Inc. a Humanitarian Device Exemption for the AbioCor implantable replacement heart (Fig. 1). One of the most sophisticated medical implantable devices ever developed, the AbioCor can extend the lives of patients who would otherwise die of heart failure. The self-contained unit is the world's only artificial heart that operates by remote control, without the need for external wires or tubes, via an internal miniaturized electronics package and an external battery pack.

The two-pound thoracic unit (replacement heart) includes two artificial ventricles with their corresponding valves and a motor-driven hydraulic pumping system. The implantable electronics package monitors and controls the pumping speed of the heart based on the physiologic needs of the patient. The AbioCor operates on both internal and external lithium batteries.

The internally implanted battery is continually recharged from an external console or from a basic patient-carried external battery pack. This is achieved via transcutaneous energy transmission (TET). The TET system consists of internal and external coils that transmit power across the skin. External battery packs can power the AbioCor for approximately four hours.

Morbidly ill heart patients who need an immediate transplant can benefit from the CardioWest temporary total artificial heart (TAH-t) from SynCardia Systems (Fig. 2). A modern version of the Jarvik 7 artificical heart first implanted in 1982, it temporarily replaces the diseased heart until a donor is found. The TAH-t pumps more blood (up to 9.5 liters/minute) than any ventricular-assisted device, helping patients regain their strength.

The Eyes And Ears Have It
Researchers have been attempting to see if visual perception could be triggered by electrical stimulation of the retina. Germany-based Intelligent Medical Implants came up with a system for patients suffering from retinitis pigmentosa (RP). The Learning Retinal Implant consists of a retinal stimulator, a pair of spectacles with an integrated camera and transmitter for wireless transmission of signals and energy, and a photoprocessor worn at the patient's waist (Fig. 3). This device is still in clinical trials.

Second Sight Medical Products and the Doheny Eye Institute of the University of Southern California are developing the Argus II retinal prosthesis for RP patients. It consists of a camera and a microprocessor mounted in eyeglasses, a receiver implanted behind the ear, and an electrodestudded array that's attached to the retina.

The microprocessor sends images from the camera to the receiver. Using a tiny cable, the receiver transmits a signal to the array, which then emits pulses that travel along the optic nerve to the brain. The brain perceives patterns of light and darkness corresponding to the stimulated electrodes.

Last year, the National Eye Institute of the U.S. National Institutes of Health (NIH) awarded a $6.5M grant to a host of organizations to develop the National Center for the Design of Biometric Nanoconductors, located at the University of Illinois in Urbana-Champaign.

The center will design, model, synthesize, and fabricate medical devices based on natural and synthetic ion transporters—proteins that control ion motion across the membranes of living cells. The first task is the development of a nanobattery to power an implantable artificial retina (Fig. 4). Sandia National Laboratories is taking the lead in the project's theoretical and computational tasks.

The University of California at Berkeley and Lawrence Berkeley National Laboratory (LBNL) are working together to create light-sensitive switches that can be flipped on and off as easily as a television's remote control in the body's cells. The optical switches work by triggering a chemical reaction, initiating a muscle contraction, and activating a drug or stimulating a nerve cell—all at a flash of light (Fig. 5).

A major goal of the UC Berkeley-LBNL Nanomedicine Development Center is to equip cells of the retina with photoswitches. This would ideally enable blind nerve cells to see, restoring light sensitivity in people with diseases like macular degeneration.