Progress in Mechanical Modeling of Implantable Flexible Neural Probes

Implanted neural probes can detect weak discharges of neurons in the brain by piercing soft brain tissue, thus as important tools for brain science research, as well as diagnosis and treatment of brain diseases. However, the rigid neural probes, such as Utah arrays, Michigan probes, and metal microfilament electrodes, are mechanically unmatched with brain tissue and are prone to rejection and glial scarring after implantation, which leads to a significant degradation in the signal quality with the implantation time. In recent years, flexible neural electrodes are rapidly developed with less damage to biological tissues, excellent biocompatibility, and mechanical compliance to alleviate scarring. Among them, the mechanical modeling is important for the optimization of the structure and the implantation process. In this review, the theoretical calculation of the flexible neural probes is firstly summarized with the processes of buckling, insertion, and relative interaction with soft brain tissue for flexible probes from outside to inside. Then, the corresponding mechanical simulation methods are organized considering multiple impact factors to realize minimally invasive implantation. Finally, the technical difficulties and future trends of mechanical modeling are discussed for the next-generation flexible neural probes, which is critical to realize low-invasiveness and long-term coexistence in vivo.