Active Book: A novel electrode book for multi-functional restoration after spinal cord injury

This is a technology development project to produce an "active electrode book" that may be directly implanted in the human spinal canal for multi-functional restoration after spinal cord injury. In addition, we are developing new minimal integrated circuit sealing methods for use in small implanted devices, and a new micro-fabrication method to cut the platinum electrodes out of foil with a laser and join them to the stimulator chip.

Background and summary:

It has been shown that electrical stimulation of the lumbar and sacral anterior and posterior nerve roots in the spinal canal can restore many functions to people with serious spinal cord injury, to improve their health and quality of life. This requires the use of many stimulating electrodes. However, a major concern in implanted nerve root stimulators for chronic use with patients is safety. Electrodes that are meant for
stimulation could, under fault conditions, corrode or electrolyse water in the tissue causing nerve damage. This danger is usually diminished and made acceptable by placing a large "blocking" capacitor (in the uF range) in series with each stimulating electrode. These capacitors determine the physical size of the stimulator which is too large to fit in the spinal canal. Thus, existing implanted devices have a subcutaneous stimulator connected with cables to the intra-thecal nerve root electrodes. Surgeons
consider that it is an unacceptable surgical risk to increase the number of cables which pass through the dura, and this limits the number of functions that can be obtained. This is a serious disadvantage given the number of valuable functions that have been shown to be possible. One way to overcome this limitation is to generate the stimulation currents close to the electrodes, inside the dura, but that means that the size of the electronic package must be very small and yet it must still be safe. We have invented a method which allows us to use blocking capacitors as small as 50pF, so that the complete stimulator can be integrated on a single silicon chip, and still be fail-safe.

This EPSRC-funded project is a collaboration with the Analogue Electronics Research Group (UCL), the Tyndall National Institute in Cork, Ireland and the Institute of Microsystems Technology (IMTEK) of the University of Freiburg, Germany. 

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