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.

Effects of Micro-Milling and Laser Engraving on Processing Quality and Implantation Mechanics of PEG-Dexamethasone Coated Neural Probe

Compared with stiff silicon-based probes,flexible neural probes can alleviate biological inflammation and tissue rejection.A polyethylene glycol(PEG)coating can facilitate the insertion of flexible probes,and the fabrication methods have a significant impact on the dimensional accuracy and structural strength of the coating.In this study,a novel melting injection moulding method is used to process a PEG-dexamethasone(PEG-DEX)coating with high structural strength for a type of mesh-shaped photosensitive polyimide(PSPI)based neural probe.Combined with the digital image correlation(DIC)method,an in vitro test system with high accuracy is developed to evaluate the effects of the elastic modulus of the PEG component and two fabrication methods,i.e.,computer-numerical-control(CNC)micro-milling and laser engraving,on the processing quality and implantation mechanics of a PEG-DEX coated probe.The results show that compared with laser engraving,CNC micro-milling can ensure high dimensional accuracy and sharpness for the composite coating,thus leading to small damage from implantation,whereas the elastic modulus of the composite coating has a limited effect on the implantation mechanics of the PEG-DEX coated probe.