An Intracortical Polyimide Microprobe With Piezoelectric-Based Stiffness Control

Abstract

Abstract Insertion of a microprobe into the brain is challenging because it needs to have a minimum stiffness to be successfully implanted and a maximum softness to exhibit compliance with surrounding neural tissue during operation. A microprobe’s critical buckling force not only dictates the microprobe resistance to buckling during insertion but also reveals the corresponding compliance during operation. The methods that are currently used to insert flexible microprobes into the brain are far from perfect because they may adversely affect the microprobe intrinsic softness. In this article, a piezoelectric-based mechanism is presented, theoretically modeled, and simulated to precisely adjust the critical buckling force of a polyimide microprobe during insertion into the brain. Two parallel piezoelectric layers are extended along the length of a polyimide microprobe and connected to a voltage source. Based on analytical modeling and simulation results, placing the piezoelectric layers closer to the neutral axis of the structure leads to a microprobe with higher buckling capacity and greater compliance during insertion and operation, respectively. Depending on the applied voltage and the configurations of the microprobe and piezoelectric layers, the critical buckling force of the modified polyimide microprobe can be adjusted from less than 0.02 mN to higher than the minimum brain penetration force of 0.5 mN, compared to a fixed critical buckling force of a polyimide microprobe without the piezoelectric layer.