Nov 292010

A device prototype has been fabricated for implantation into human spinal column. It rests over the posterior and anterior (sensory and motor) spinal roots and allows recording from as well as selective stimulation of multiple spinal roots. The work is spearheaded by Prof. Nick Donaldson and Prof. Andreas Demosthenous at the University College London, UK. In collaboration with engineers from Freiburg University and the Tyndall Institute in Cork, they developed a device that includes a VLSI chip for processing the neural recordings and generating the electrical stimulation pulses. The VLSI chip is hermetically sealed into a can enclosure. Hermeticity of the enclosure is monitored using a humidity sensor. The chip feedthroughs are interconnected with the electrodes using wire bonds. The chip, wires, and electrodes are encapsulated into a soft shell, made presumably from silicone or epoxy. The electrodes are fabricated from platinum foil using laser etching and folded into a slot shape. There are four slots at the bottom of the implant, designed to bring the spinal roots (perhaps two anterior and two posterior ones) into close apposition with the electrodes. Such top placement of a neural interface is rather unusual as existing spinal root electrodes (e.g. Finetech-Brindley stimulators) have employed the cuff design. In order to be able to record neural activity and efficiently deliver the electrical current, the slots must be well-matched in size to the diameter of spinal roots. The initial application for the Active Book implant would be the control of bladder voiding in spinal cord injury. The effectiveness of the prosthetic bladder voiding will be similarly limited as in other sacral root stimulators, including the sensory perception of stimulation in people with residual below-injury sensation and concomitant activation of the bladder and urethral sphincter muscles, as well as other pelvic floor muscles. Other applications in paralyzed humans, such as the control of arm or leg muscles, are not unlikely to be successful with this implant as the applied surface stimulation would not be able to selectively activate a specific arm/leg muscle. Such lack of selectivity is inherent to the anatomy of the anterior spinal roots, which are comprised of mixed axonal bundles innervating different, sometimes antagonistic, muscles.

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