Novel Neural Microprobe with Adjustable Stiffness

To successfully insert a microprobe into the brain and record/stimulate the target neural tissue, it must meet two opposing requirements. Firstly, it must be stiff enough to tolerate the penetration force during insertion. Secondly, it must be compliant enough to withstand brain micromotion during operation, since a mechanical mismatch between the stiff microprobe and soft surrounding neural tissue leads to neural tissue damage and, ultimately, the failure of the microprobe within a few weeks/months of implantation. The design proposed in this study enables the creation of a neural microprobe whose elastic modulus varies from 4.2 GPa during insertion to 149 kPa during operation, as a function of the applied motion. The proposed mechanism for changing the stiffness works independently of the microprobe fabrication material and the surrounding environment's conditions. The microprobe and surrounding neural tissue are simulated to calculate the elastic modulus of the microprobe based on the finite element method and investigate the induced strain on the tissue by the brain longitudinal and lateral micromotions, simultaneously. The obtained results show that the maximum strain on the tissue surrounding the proposed microprobe is ~59 % less than that of the classic cylindrical microprobe with the same material, diameter, and length. The microprobe is fabricated based on two-photon polymerization technology.