# Multimodal Layer‐Crossing Interrogation of Brain Circuits Enabled by Microfluidic Axialtrodes

## TL;DR

A new flexible device called the microfluidic axialtrode allows simultaneous stimulation, recording, and drug delivery in multiple brain layers, improving neural research and therapy.

## Contribution

The axialtrode introduces a novel multimodal neural interface with axial redistribution of electrodes and microfluidic channels via angled cleaving.

## Key findings

- Axialtrodes enable spatially distributed optogenetics and multisite electrophysiological recording in vivo.
- The device allows targeted drug delivery along the fiber axis while reducing inflammation compared to conventional fibers.
- Integration with a 3D-printed scaffold ensures mechanical stability and compatibility with standard hardware.

## Abstract

Modulating and recording neuronal activity are essential for probing brain function and developing therapies for neurological disorders. However, conventional flat‐end optical fibers—widely used for deep brain access—interact with neural tissue only at their distal tip, limiting spatial resolution across brain layers. To address this challenge, we introduce the microfluidic axialtrode, a flexible neural interface that exploits controlled angled cleaving of a thermally drawn multimaterial fiber to achieve axial redistribution of integrated electrodes and microfluidic channels. We demonstrate in vivo that this design enables spatially distributed optogenetics, multisite electrophysiological recording, and targeted drug delivery along the fiber's axis, allowing simultaneous interaction with multiple neuronal layers. The axial configuration increases the functional interface with brain tissue, while the soft polymer construction and reduced footprint significantly suppress the inflammatory response compared to conventional silica fibers. Integration with a 3D‐printed scaffold, fabricated from FDA‐approved biocompatible resin, provides mechanical stability and compatibility with standard experimental hardware. The monolithic integration of these features positions the axialtrode as a scalable and versatile platform for next‐generation neural interfacing.

The study introduces a flexible microfluidic axialtrode that integrates optical, electrical, and chemical modalities within a single polymer fiber. By redistributing electrodes and fluidic channels along the fiber axis via angled cleaving, it enables simultaneous optogenetic stimulation, electrophysiological recording, and drug delivery across brain layers, offering a minimally invasive platform for advanced neural interrogation.