Neural Implants without Electronics - Challenges and Limitations of Capacitive and Transcutaneous Coupling for Restoring Sensory Feedback

This dissertation investigates the challenges and limitations of multi-channel transcutaneous and capacitive energy and signal supplies for neural interfaces. For this purpose, requirements for the provision of somatosensory feedback for patients with upper limp prostheses following shoulder disarticulation and targeted muscle reinnervation surgery were addressed.

A fundamental understanding of the electrical transmission path through explanted human skin was obtained using various coupling electrodes and approaches. The focus was on miniaturization while achieving sufficient coupling performance and low crosstalk. The insights were transferred on a fully implantable system with transcutaneous energy and signal supply, which was capable of exciting action potentials in the sciatic nerve of rodents. Based on these in vivo studies, the feasibility and limitations of this approach for a human application were demonstrated. Furthermore, special requirements for the subcutaneous implant and its manufacturing processes were derived utilizing a risk analysis. Accordingly, engineering concepts and design proposals have been developed and evaluated to make silicone-based electrode arrays more robust and long-term stable by eliminating potential stress riser points at material interfaces. This was achieved by reducing the bending stiffness of the electrode spots through design modifications while preventing their delamination by introducing a suitable adhesion-promoting layer. The stretchability of the electrode arrays was improved by embedding conductive silicone tracks in a printing process.

These novel technologies contribute to increasing the safety and longevity of silicone-based neural interfaces that are subjected to severe mechanical loading at their implantation site.