POLYIMIDE-BASED MODULAR PROBE PLATFORM FOR MINIMALLY INVASIVE ACCESS TO DEEP NEURAL STRUCTURES

Intracortical recordings are key for understanding brain function, but conventional rigid probes suffer from poor long-term stability due to mechanical mismatch with soft brain tissue, leading to inflammation, glial scarring, and signal loss. Flexible polymer-based devices offer a more biocompatible alternative for long-term neural interfacing. Here, we validate a novel modular polymer-metal stereoelectroencephalography probe with an extended shank, designed to access deep brain regions while minimizing tissue damage.
Probes were microfabricated using polyimide, iridium oxide, and gold bonding junctures. Components were assembled via flip-chip thermocompression bonding. Devices were temporarily stiffened using a tungsten shuttle or polyethylene glycol (PEG) before implantation. Performance was evaluated in anesthetized rats (acute/chronic) and one cat (acute). Validation included electrochemical impedance spectroscopy (EIS), electrophysiology, and histology. Wideband signals were recorded from the cortex, hippocampus, and thalamus. Data analysis utilized KiloSort, Phy, and SpikeInterface for single-unit isolation.
EIS confirmed functional sites with ~200kΩ magnitude. Tungsten shuttles enabled reliable insertions up to 8 mm, while PEG reduced artifacts. High-quality LFP and MUA were recorded in both species, revealing physiological patterns like hippocampal gamma oscillations or cortical/thalamic slow waves. Single units were isolated in all the aforementioned brain areas, and thalamic neurons showed sensory-evoked responses (somatosensory in rats, visual in cat). Histology confirmed accurate targeting. Chronic recordings showed single-unit stability for several weeks.
Our modular, ultra-long flexible probe was successfully validated in vivo, yielding high-quality recordings across deep structures. This design overcomes limitations of rigid probes and enables minimally invasive implantation in rodents or even in larger animal models.