Effect of Insertion Parameters on Insertion Force and Tissue Damage During Rigid Neural Probe Implantation

The implantation of neural probes is critical for precise recording and stimulation of target neurons. However, the implantation of rigid neural probes, involves risks such as tissue damage and foreign body reactions, which can lead to probe failure and irreversible brain injury. Previous studies have employed force response and crack formation during probe insertion to understand the mechanical dynamics of implantation. While many researchers have explored the impact of different probe parameters on the implantation and long-term biological responses, the study of mechanical parameters during insertion remains incomplete. In particular, there are ongoing debates surrounding the quantitative impact of insertion speed on potential tissue damage. This study investigates the interaction effects of insertion speed, insertion depth, and probe geometry parameters on insertion force and insertion-induced damage during probe implantation. Tungsten and boron-doped diamond (BDD) probes were used as representative examples in this research. Peak insertion force and crack size were quantitatively evaluated in both agarose hydrogels and brain tissues, taking insertion direction and relatively wide speed range into account. Our results revealed a previously unreported fourth-order relationship between insertion speed and peak force within a certain insertion depth range, which can be understood as a Taylor-series approximation of the underlying rate- and state-dependent friction behavior within the experimental velocity regime. Meanwhile, crack analysis further showed an inverse relationship between crack size and insertion speed. These findings offer valuable insights into the mechanics of probe implantation with the goal of further improving the safety and reliability of neural implants.