Microactuated Neural Probes to Compensate for Brain Micromotion

One of the dominant failure modes of chronic neural implants is micromotion of the surrounding brain tissue relative to the implant leading to neuronal drift and shear injury. In this study, we have (a). Assessed the micromotion in the somatosensory cortex and (b). Designed, developed and tested a microactuated neural probe that can compensate for brain micromotion. We used a differential variable reluctance (DVRT) transducer in adult rats (n=8) to monitor micromotion in the somatosensory cortex. Electrostatic microactuators were fabricated using the SUMMIT (Sandia's Ultraplanar Multilevel MEMS Technology) process, a 5-layer polysilicon micro machining technology of the Sandia National labs, NM. In anesthetized rats, surface micromotion was observed to be in the order of 2-25 μm due to pressure changes during respiration and 1-3 μm due to vascular pulsatility. In addition there were long-term drifts in the order of 80 μm due to changes in the anesthetic level. The microactuated neural probe was capable of moving in steps of 1 μm with an aggregate translational capability in the order of several millimeters. In conclusion, there is significant micromotion in the surface of the somatosensory cortex that could lead to failure of chronic neural implants. Microactuated neural probes are capable of compensating for this micromotion.