People left paralysed by a stroke could soon get some movement back thanks to artificial neurons that stimulate muscle in a coordinated way.
Dubbed BIONs, the injectable devices the size of rice grains are already used to stimulate muscles to stop them wasting away. Now their developer, Gerald Loeb of the University of Southern California, Los Angeles, is developing a system that will coordinate a network of BIONs to allow someone whose arms have been paralysed by a stroke, cerebral palsy or spinal-cord injury to lift a glass of water or turn the pages of a book.
Battery-powered implants are already used to help paralysed people walk or grasp objects, but these require surgery when they are implanted and have to be replaced when the batteries run out. BIONs, by contrast, pick up power via an induction coil from an armband that the user wears.
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The system will pick up weak residual signals from the brain generated when the person decides to make a movement. These are transmitted wirelessly to a wearable control unit, which instructs each implant to apply a current of the appropriate strength and duration to its muscle area.
The system will also monitor the trajectory of the limbs and adjust their movements, based on information from sensors that pinpoint their position relative to three magnetic coils in the wearer’s wheelchair. To detect finer movements such as rotation of the hand, each BION will send out radio signals and monitor signals from its neighbours. Any change will indicate that a BION has moved slightly closer or further away. This information, combined with readings from accelerometers, will be sent to the control unit, which will analyse it and send out fresh commands.
The entire process takes just 80 milliseconds – matching the speed with which the brain communicates with muscles in a healthy person, says system designer Nuria Rodriguez. The implants will ignore commands that would cause a sudden jump in current strength, to prevent violent movements that could cause injury.
The team will unveil a blueprint of the system at the Body Sensor Networks workshop in Aachen, Germany, on 28 March. They plan to integrate sensors into the BIONs this year, and hope to implant them in patients within a year.
