An experimental neuroprosthesis: assembly and encapsulation

An increasing number of disabilities are being treated by neuroprostheses: permanent electronic implants which interact with the body. Recently, the first few British patients with neck-level spinal cord injury have received an implant which was developed in Cleveland, Ohio, to restore grasp. We have been investigating the use of implants for the restoration of leg function. In the 1980s we implanted devices which stimulated peripheral nerves, close to the muscles. These were disappointing unreliable and required very extensive surgery. Since then, an improved design of stimulator implant has been developed with many new electronic features; this has received approval from the Medical Devices Agency for use in a clinical trial which is now underway. The new device stimulates the nerves differently - on the nerve roots where the nerves emerge from the spinal cord which has the advantage that all the motor nerves are accessible to electrodes at one surgical site. This paper reviews the materials considerations in the design and discusses a hermeticity problem which occurred in a prototype.