Abstract
Objective. Neural electrophysiology is often conducted with traditional, rigid depth probes. The mechanical mismatch between these probes and soft brain tissue is unfavorable for tissue interfacing. Making probes compliant can improve biocompatibility, but as a consequence, they become more difficult to insert into the brain. Therefore, new methods for inserting compliant neural probes must be developed. Approach. Here, we present a new bioresorbable shuttle based on the hydrolytically degradable poly(vinyl alcohol) (PVA) and poly(lactic-co-glycolic acid) (PLGA). We show how to fabricate the PVA/PLGA shuttles on flexible and thin parylene probes. The method consists of PDMS molding used to fabricate a PVA shuttle aligned with the probe and to also impart a sharp tip necessary for piercing brain tissue. The PVA shuttle is then dip-coated with PLGA to create a bi-layered shuttle. Main results. While single layered PVA shuttles are able to penetrate agarose brain models, only limited depths were achieved and repositioning was not possible due to the fast degradation. We demonstrate that a bilayered approach incorporating a slower dissolving PLGA layer prolongs degradation and enables facile insertion for at least several millimeters depth. Impedances of electrodes before and after shuttle preparation were characterized and showed that careful deposition of PLGA is required to maintain low impedance. Facilitated by the shuttles, compliant parylene probes were also successfully implanted into anaesthetized mice and enabled the recording of high quality local field potentials. Significance. This work thereby presents a solution towards addressing a key challenge of implanting compliant neural probes using a two polymer system. PVA and PLGA are polymers with properties ideal for translation: commercially available, biocompatible with FDA-approved uses and bioresorbable. By presenting new ways to implant compliant neural probes, we can begin to fully evaluate their chronic biocompatibility and performance compared to traditional, rigid electronics.
Highlights
Neural depth probes are neural interfaces designed to record neural activities and are used to help researchers understand the complex electrochemical mechanisms inside the brain
A zero insertion force (ZIF) cable was first attached to the parylene probe as temperatures above the melting temperatures of the polymers are applied during attachment of the cable
We demonstrated that very high quality local field potential (LFP) recordings were achieved by using a bioresorbable polymer shuttle to insert flexible probes into the brain
Summary
Neural depth probes are neural interfaces designed to record neural activities and are used to help researchers understand the complex electrochemical mechanisms inside the brain. Many researchers require long-term, stable recordings, yet irreversible brain damage and complete loss of recording function are unpreventable consequences when using traditional depth probes [1, 2]. These traditional depth probes are made of silicon or metal, which are rigid materials that have elastic moduli above 100 GPa [1, 2]. At the end the flexible probe is left behind while the mechanically stiff shuttle diminishes on its own, which is a very promising solution to improve the long-term function of neural interfaces
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