Advancing the interfacing performances of chronically implantable neural probes in the era of CMOS neuroelectronics

Abstract

Tissue penetrating microelectrode neural probes can record electrophysiological brain signals at resolutions down to single neurons, making them invaluable tools for neuroscience research and Brain-Computer-Interfaces (BCIs). The known gradual decrease of their electrical interfacing performances in chronic settings, however, remains a major challenge. A key factor leading to such decay is Foreign Body Reaction (FBR), which is the cascade of biological responses that occurs in the brain in the presence of a tissue damaging artificial device. Interestingly, the recent adoption of Complementary Metal Oxide Semiconductor (CMOS) technology to realize implantable neural probes capable of monitoring hundreds to thousands of neurons simultaneously, may open new opportunities to face the FBR challenge. Indeed, this shift from passive Micro Electro-Mechanical Systems (MEMS) to active CMOS neural probe technologies creates important, yet unexplored, opportunities to tune probe features such as the mechanical properties of the probe, its layout, size, and surface physicochemical properties, to minimize tissue damage and consequently FBR. Here, we will first review relevant literature on FBR to provide a better understanding of the processes and sources underlying this tissue response. Methods to assess FBR will be described, including conventional approaches based on the imaging of biomarkers, and more recent transcriptomics technologies. Then, we will consider emerging opportunities offered by the features of CMOS probes. Finally, we will describe a prototypical neural probe that may meet the needs for advancing clinical BCIs, and we propose axial insertion force as a potential metric to assess the influence of probe features on acute tissue damage and to control the implantation procedure to minimize iatrogenic injury and subsequent FBR.

Recycling and Degradation of Polyamides

“…The incineration of polyamides only produces 30.2 MJ kg −1 of energy [77]. However, the production of polyamides is energy-intensive, and it takes 163 MJ Kg −1 of polymer to produce PA-66 [78]. It can be seen that the efficiency of incineration of polyamides is very low.…”

“…The general steps of mechanical recycling are shown in Figure 13. After grinding polyamide waste, additives are added to blend or directly mold [78].…”

“…The general steps of mechanical recycling are shown in Figure 13. After grinding polyamide waste, additives are added to blend or directly mold [78]. Early research on mechanical recycling was about ABS, PA, PC, and PMMA [81].…”

“…Through mechanical recycling of carbon fiber reinforced with a mass fraction of 30% PA-66, it was found that mechanical recycling can only degrade original samples to a limited extent, and aging causes significant performance loss [83]. Table 1 shows the literature related to mechanical recycling with polymer types, reinforcing materials, and processing methods [78]. Early research on mechanical recycling was about ABS, PA, PC, and PMMA [81].…”

“…The currently reported chemical recycling methods for PA include alkaline hydrolysis, hydrothermal reaction, microwave-assisted hydrolysis, acidic hydrolysis, ammonolysis, alcoholysis, hydrogenolysis polymerization, depolymerization reaction in ionic liquids, etc. [78].…”