In Vivo Chronic Brain Cortex Signal Recording Based on a Soft Conductive Hydrogel Biointerface

Abstract

In neuroscience, the acquisition of neural signals from the brain cortex is crucial to analyze brain processes, detect neurological disorders, and offer therapeutic brain−computer interfaces. The design of neural interfaces conformable to the brain tissue is one of today's major challenges since the insufficient biocompatibility of those systems provokes a fibrotic encapsulation response, leading to an inaccurate signal recording and tissue damage precluding long-term/permanent implants. The design and production of a novel soft neural biointerface made of polyacrylamide hydrogels loaded with plasmonic silver nanocubes are reported herein. Hydrogels are surrounded by a silicon-based template as a supporting element for guaranteeing an intimate neural-hydrogel contact while making possible stable recordings from specific sites in the brain cortex. The nanostructured hydrogels show superior electroconductivity while mimicking the mechanical characteristics of the brain tissue. Furthermore, in vitro biological tests performed by culturing neural progenitor cells demonstrate the biocompatibility of hydrogels along with neuronal differentiation. In vivo chronic neuroinflammation tests on a mouse model show no adverse immune response toward the nanostructured hydrogel-based neural interface. Additionally, electrocorticography acquisitions indicate that the proposed platform permits long-term efficient recordings of neural signals, revealing the suitability of the system as a chronic neural biointerface.

A simple route of providing a soft interface for PEDOT:PSS film metallic electrodes without loss of their electrical interface parameters

“…The hydrogel precursor solution was a composition of 97.2 mg N-isopropylacrylamide, used as the main monomer (NIPAAm), 2.8 mg N,N′-methylenebisacrylamide (BIS-AAm) as a cross-linker in the proportion 35:1, dissolved in deionized water (90% wt.). The selected monomer and cross-linking agent lead to the formation of a biocompatible hydrogel, which has recently been used in many applications, including bioelectrodes 23,24 . In the end, 5 mg of photoinitiator 2-hydroxy-4′-(2-hydroxyethoxy)-2methylpropiophenone was added to the solution to trigger the hydrogel polymerization reaction upon UV irradiation.…”

Conducting polymer‐based nanostructured materials for brain–machine interfaces

“…The final system was placed on the mouse skull with stereotactically drilled holes through which hydrogel could reach the brain cortex and permit a specific ECoG signal acquisition. Reprinted with permission from Rinoldi et al (2022). Copyright 2022, American Chemical Society.…”

“…Due to their high water content, ionic transfer through hydrogel allows for fast ionic conduction. Rinoldi et al developed a soft and flexible neural interface from polyacrylamide (PA) loaded with silver nanocubes (Figure 2h; Rinoldi et al, 2022). The mechanical parameters of the hydrogel-nanoparticle composite were chosen to minimize the mismatch between the nerve tissue and the biomaterial (Young's modulus <10 kPa).…”

Conducting Polymer-Hydrogel Interpenetrating Networks for Improving the Electrode–Neural Interface

“…Among these, interpenetrating hydrogel networks have emerged as a compelling solution due to their enhanced mechanical stability and the capacity to integrate polymers with favorable properties into a cohesive and robust structure . Moreover, by integrating electro-conductive materials with hydrogels, a promising and innovative avenue has been opened for the advancement and customization of bioelectronic devices. − Despite recent progress, further efforts are required to fabricate more integrated conductive polymer-hydrogel-based materials that can minimize tissue damage and inflammatory responses, achieve high-quality recording signals, and maintain long-term in vivo stability.…”