Advanced technologies for neural recording have enabled breakthrough discoveries of the connectivity and functionality of the brain. However, intracortical probes for electrical interrogation at the single-cell level still rely on rigid metal or silicon components, which poorly match the mechanical properties of soft brain tissue and can therefore cause extensive tissue damage.

Flexible electrodes have been shown to significantly reduce neural injury during chronic implantation and increase the quality and longevity of recordings. The need for stiffening agents to overcome the buckling force upon implantation, however, dramatically reduces the potential benefits of a small footprint and flexibility.

Here, we present a novel technology to precisely implant and actuate flexible microelectrodes without a stiffening support. Our technology uses fluid flow within a microfluidic device to drive electrodes into tissue. The hydraulic design of the microdrive combined with the on-chip valves together enable precise control of the electrode position with minimal injection of fluid into the tissue.

The microdrive is used to implant flexible carbon nanotube fiber (CNTf) electrodes in the small cnidarian Hydra and interrogate its neural circuits during spontaneous behavior. Using rodent brain slices, we also recorded spatially confined light-evoked neural activity in deep brain regions, demonstrating the precision of probe positioning provided by the microdrive. Finally, performing minor modifications to the device geometry and connection strategy allowed us to record single-unit activity in the cortex and subcortical regions of anesthetized rats, showing that this novel technology can also be used in vivo, with a potential impact on mitigating neuro-inflammation and improving chronic electrode stability.