Tiny implants that act as artificial nerves could help reduce potentially dangerous muscle wastage in stroke patients, researchers say.

The implants, called BIONs, can be injected directly into muscle tissue and stimulate them from within to prevent them wasting away through lack of use.

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.

New Scientist magazine reports that a team of researchers from the University of Southern California have developed two millimetre (mm) electrodes that can be directly injected into the muscle.

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.

Doctors can then download a set of exercise programs into a portable controller for the patient to take home.

The muscles can be stimulated in other ways, but these require surgery or leave wires sticking out from the skin, increasing the risk of infection.

Attaching electrodes to the skin can work, but makes targeting of specific muscle groups difficult, and can burn the skin.

Trials begin

Trials of the BIONs began 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.

Lead researcher Dr Gerald Loeb said the BIONs were designed to emit a pulse that while strong enough to stimulate the muscles, would not damage the surrounding tissues.

Dr Loeb said the ultimate aim was to design more sophisticated BIONs that can stimulate useful movement.

This could, for example, enable a patient with a spinal cord injury or a debilitating stroke to grasp an object with their hand.

However, this would require implants that can sense movement as well as stimulating muscle contraction.

Dr Loeb believes the existing technology could help patients who suffer from sleep apnoea, a potentially fatal condition in which the tongue blocks the airway while the patient is asleep.

A BION implanted near the back of the tongue could stimulate its muscles to lift it out of the way.