Development of neural probes using thermal drawing

Abstract

The treatment of neurodegenerative and neurological conditions relies on better understanding the system that they afflict. However, the tools currently available to probe neural circuits are often limited to use in short-term studies primarily due to poor of biocompatibility. To address this challenge, flexible, minimally invasive neural probes were fabricated using a thermal drawing process, with polymers serving as their main structural constituent. Through the use of different polymers, probes containing arrays of tin electrodes as small as 5 [mu]m were fabricated, as were probes combining capabilities for electrical recording, optical stimulation, and drug delivery. A technique was developed to combine functionalities of these devices into a single probe to study the effect of optical stimulation with different waveforms on the brain activity. To break the longitudinal symmetry inherent to probes fabricated using the thermal drawing process, and to allow the incorporation of functionalities along the probe length, a method to combine thermal drawing with a method commonly used to fabricate neural probes, photolithography, was developed, along with the selection of the polymer that would allow consecutive processing using these two techniques. All of the fabricated probes were characterized and tested in vivo by implantation into mice and assessing their functionality. High signal-to-noise ratio (13±6) recordings were obtained using multielectrode arrays. Recordings of neural activity during simultaneous optical stimulation and drug delivery were performed with multifunctional probes. Hybrid probes combining metal electrodes with a polymer waveguide were used to study the response of large groups of neurons to different forms of optical stimuli. Most importantly, the biocompatibility of these probes was assessed over a 3 month period and compared favorably to that of steel microwires of similar size.