Effectiveness of Concentrated Electrical Stimulation and Fabrication of Hybrid Directional Electrode

Abstract

The effectiveness of invasive and non-invasive stimulation was compared using rats: the iES group stimulated with fully implantable device, the tES group stimulated with TENS, and the injury group with no stimulation. The iES and tES groups received stimulation for 6 weeks. Sciatic functional index values and histomorphometric evaluation showed same tendency; faster and superior recovery was observed in the iES group than in the tES group. To assess the cause of the difference in efficiency, a 3D rat anatomical model was used to simulate the induced electric fields. A significantly higher concentration and intensity around the sciatic nerve was observed in the iES group than in the tES group. The results indicated that even though rats in the tES group showed better recovery than those in the injury group, it cannot replace direct stimulation yet. This was likely attributable to the greater concentration and parallel distribution of electric field with respect to target nerve. With the need of electrode for concentrated electrical stimulation, this paper presents an easy way to fabricate a 3-dimensional hybrid directional electrode with a complex pattern for deep brain stimulation (DBS) using MEMS. The fabrication process consists of two parts: fabricating a flexible thin film then wrapping it around a core to make it 3-D. The impedance of the fabricated electrode was around 92 kΩ (@ 1 kHz), and the fabricated electrode was about 1/3 to 1/5 times as stiff as conventional wire electrode. In vivo experiment showed that urination is inhibited during subthalamic nucleus and pedunculopontine tegmental nucleus stimulation, showing that the hybrid directional electrode could function as a DBS electrode. This method allows the electrode pattern to be as complicated as 2-D MEMS technique allows, and will therefore enable minute electric field modulation.