Bionic nerves to battle wasting muscle

December 07, 1999

TINY implants that act as artificial neurons could herald a breakthrough in therapeutic treatments for stroke patients, claim researchers in Los Angeles. Their implants, dubbed BIONs, can be injected directly into muscles and stimulate them from within to prevent them wasting away.

The muscle wasting that afflicts many stroke patients can lead to serious complications such as thrombosis in bedridden patients. Unused muscles can also become so weak and flaccid that the arm dislocates from the shoulder.

To prevent these problems, researchers led by Gerald Loeb, a biomedical engineer at the University of Southern California, have developed electrodes that are not much bigger than a grain of rice. At just 2 millimetres in diameter they are small enough to be injected directly into a muscle using a 12-gauge needle. Once in place they are activated by a radio signal from a coil worn by the patient. This controls the frequency and intensity of the electrical stimuli produced by each implant.

Other approaches require surgery or leave wires sticking out from the skin-increasing the risk of infection. Electrodes can be placed on the skin, but this is a hit-or-miss affair, says Loeb, stimulating all underlying muscles indiscriminately. It can also cause unpleasant sensations and even burn the skin.

Loeb's team began trials last month. The first patient received BIONs in two muscles on one shoulder: the middle deltoid and supraspinatus. The implants stimulated these muscles, and the patient reported no ill effects-just a tickling sensation.

Jonathan Whiteson, a stroke specialist with the Howard Rusk Institute of Rehabilitation Medicine at New York University, is cautiously optimistic about the approach. But he wants to see long-term trials to ensure the BIONs don't cause any local tissue damage in years to come.

Loeb is confident that this won't be the case. At the maximum stimulus strength, he says, the electrodes are designed to deliver a pulse of 30 milliamps for about 0á5 milliseconds, well below the levels that damage tissues.

"Once the BION goes in you can evaluate what level of stimulation is required to get a contraction," says Loeb. Having determined the correct thresholds, doctors can then download a set of exercise programs into a portable controller for the patient to take home.

The ultimate aim, says Loeb, is to design more sophisticated BIONs that can stimulate useful movements-allowing someone with spinal cord injury or a debilitating stroke to grasp an object with their hand, for example. This will need implants that can sense movement as well as stimulating muscle contraction.

In the meantime, Loeb believes that a variety of patients could benefit from BIONs. For instance, they could help obese people with sleep apnoea, a potentially fatal condition in which people stop breathing when their tongues block the airway. "Large numbers of people are more or less suffocating every night," says Loeb. A BION implanted near the back of the tongue could stimulate its muscles to lift it out of the way.
Author: Duncan Graham-Rowe

New Scientist magazine issue 11 December 99


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