Basic design and construction of the Vienna FES implants: existing solutions and prospects for new generations of implants

We can distinguish 3 generations of FES implants for activation of neural s tructures: I. RF-powered implants with antenna displacement dependent stimu lation amplitude; 2. RE-powered implants with stabilised stimulation amplit ude; and 3. battery powered implants. In Vienna an 8-channel version of the second generation type has been applied clinically to mobilisation of para plegics and phrenic pacing. A 20-channel implant of the second generation t ype for mobilisation of paraplegics and an 8-channel implant of the third g eneration type for cardiac assist have been tested in animal studies. A dev ice of completely new design for direct stimulation of denervated muscles i s being tested in animal studies. There is a limited choice of technologically suitable biocompatible and bio resistant materials for implants. The physical design has to be anatomicall y shaped without corners or edges. Electrical conductors carrying direct cu rrent (D.C.) have to be placed inside a hermetic metal case. The establishe d sealing materials, silicone rubber and epoxy resin, do not provide hermet icity and should only embed DC-free components. For electrical connections outside the hermetic metal case welding is preferable to soldering; conduct ive adhesives should be avoided. it is advisable to use a hydrophobic oxide ceramic core for telemetry antenna coils embedded in sealing polymer. Clea ning of all components before sealing in resin is of the utmost importance as well as avoidance of rapid temperature changes during the curing process . (C) 2001 IPEM. Published by Elsevier Science Ltd. All rights reserved.