Customizing MRI‐Compatible Multifunctional Neural Interfaces through Fiber Drawing

Abstract

Fiber drawing enables scalable fabrication of multifunctional flexible fibers that integrate electrical, optical, and microfluidic modalities to record and modulate neural activity. Constraints on thermomechanical properties of materials, however, have prevented integrated drawing of metal electrodes with low‐loss polymer waveguides for concurrent electrical recording and optical neuromodulation. Here, two fabrication approaches are introduced: 1) an iterative thermal drawing with a soft, low melting temperature (Tm) metal indium, and 2) a metal convergence drawing with traditionally non‐drawable high Tm metal tungsten. Both approaches deliver multifunctional flexible neural interfaces with low‐impedance metallic electrodes and low‐loss waveguides, capable of recording optically‐evoked and spontaneous neural activity in mice over several weeks. These fibers are coupled with a light‐weight mechanical microdrive (1 g) that enables depth‐specific interrogation of neural circuits in mice following chronic implantation. Finally, the compatibility of these fibers with magnetic resonance imaging is demonstrated and they are applied to visualize the delivery of chemical payloads through the integrated channels in real time. Together, these advances expand the domains of application of the fiber‐based neural probes in neuroscience and neuroengineering.

Opsin-free optical neuromodulation and electrophysiology enabled by a soft monolithic infrared multifunctional neural interface

“…This specific metal was selected for the integrated electrodes due to its relatively low melting point (∼155 °C) and low Young’s modulus compared to other metals. Moreover, indium has been recently reported to be a suitable material for EE electrodes [21]. The choice of high-performance polymers with high melting points (>200 °C) as starting materials was critical in achieving the desired outcome, since it allowed the use of any metal with a melting point lower than the fibre’s materials as electrodes.…”

Modular Integration of Hydrogel Neural Interfaces

“…We then characterized the electrical, optical, and fluid delivery properties of these hydrogel-integrated probes (Figure S2–S4). The recording electrodes, 25 μm W wires, had impedance of 80 kOhm at 1 kHz which is well within the range suitable for extracellular recordings of neuronal potentials . We chose W over nickel chromium (NiCr) used in tetrodes to avoid gold-plating, which is necessary to achieve sub-MOhm impedance, as that step would expose our hydrogel to an organic solvent .…”

“…The fiber drawing process enables the fabrication of flexible neural probes that can simultaneously interrogate neuronal circuits via electrical, optical, and chemical modalities. During fiber drawing, a macroscopic model (the preform) of the desired probe is fabricated and drawn into hundreds of meters of fibers with microscale features. , To date, these probes have enabled one-step optogenetics, in vivo photopharmacology, and in situ electrochemical synthesis of gaseous molecules for neuromodulation . Despite these advancements, this approach has several limitations.…”

Biocompatible and Biodegradable Polymer Optical Fiber for Biomedical Application: A Review

“…Historically, electrode materials have been limited to carbon-based polymer composites and drawable metals, such as tin [ 54 ], which have low conductivity and, thus, require a larger fiber probe. Recently, a group of researchers introduced two approaches based on thermal drawing to resolve this dilemma: iterative thermal drawing with low T m indium and metal convergence drawing with previously undrawable high T m tungsten [ 134 ]. The multifunctional fiber probes were capable of recording neural circuits in real-time in mice for several weeks.…”