Electric field gradients and bipolar electrochemistry effects on neural growth: A finite element study on immersed electroactive conducting electrode materials

Implantable electrodes act with direct electrical contact although recent work has shown that electrostimulation is also possible through non-contact wireless settings, through the generation of dipoles at the borders of the material by bipolar electrochemistry. The experimental observations with neural cell cultures demonstrate a clear difference between insulator and conducting materials, but also between conducting and mixed conducting intercalation materials used as substrates of neural growth. Known bipolar electrochemistry effects may explain voltage profiles induced on conducting materials. Finite element studies shown here with the same configuration that the experimental processes described, evidence voltage profiles in qualitative agreement with known bipolar effects, although with a clear difference between intercalation materials and metals. Calculations also show a clear mapping of charge gradients at the material surface influencing growing neurons cells. While insulating materials only distort the electric field space distribution, the dipole generated at the borders of an implanted conducting material, inverted with respect to the insulating case, extends along the material interface, being relevant that is much smoother in intercalation materials. Mapping of the gradients as the distance is increased from the conducting material is also discussed. These observations may explain the differences in neural cell growth observed for various substrate materials.