Packaging Design for Implantable Microstimulator

Implantable biomicrosystems for restoring neuromuscular functions have gained more attention for studying the characteristics of various types of neural interfaces. In our previous study, we have developed a microprocessor-based microstimulation system by using the surface mount device (SMD) components on printed circuit board (PCB) and stimulating electrodes, prepared for implantation into animal on neuromodulation studies. The aim of this study is to investigate the feasibility of packaging design of an implantable microstimulator. In current study, Micro Electro Mechanical System (MEMS) fabrication process for microassembly and interconnection on flexible polyimide substrates was employed to integrate microstimulator circuitry and nerve cuff electrodes as an implantable biomicrosystem for peripheral nerve applications to achieve a module package. The flexible mechanical structure design of microstimulator is more suitable for module design and implantation purposes. Dam-and-fill process was applied to seal the module, which was later encapsulated with medical grade silicone rubber for biocompatible package. The implantable microstimulator measured at 4 cm in diameter and 8 mm in height with cuff electrode interconnected to it. Finally, in-vitro experiment in the normal saline has confirmed that it is feasible to employ dam-and-fill encapsulation and medical-grade silicone rubber to package the biomicrosystem for a period of 30 days. The microstimulator is undergoing in vivo tests through the implantation of implantable microstimulator for stimulating rabbit's sciatic nerve.