Chronic neural recording with probes of subcellular cross-section using 0.06 mm² dissolving microneedles as insertion device

Abstract

Ultra-flexible electrode arrays with a cross-sectional area of only a few μm² show great promise for long-term, high resolution neural interfacing without detrimental scar tissue formation. However, due to their low stiffness, insertion is a challenge. In this work, we investigate microneedles consisting of quickly biodegradable, short-chained, acid terminated PLGA (50:50 lactide:glycolide ratio) as insertion device for a polyimide-based neural electrode array of 1 μm thickness. An upscalable, wafer-level fabrication process is presented. Both separate PLGA microneedles as well as complete, assembled neural probes were tested in vivo for up to 4 months. The arrays allowed to record spontaneous spike activity and evoked local field potentials in the somatosensory cortex of rats on all measured timepoints. Very limited lesion formation, measuring about 20% of the cross sectional area of the original microneedle, was observed. Neurons can be seen to infiltrate the area originally taken up by the dissolving PLGA microneedle. The results indicate that the presented electrode arrays and insertion method are well suitable for application in long-term, high resolution neural recording.