Stretchable Microwrinkled Soft Neural Probe with Minimized Insertion Shuttle for Low Invasion

Compared with traditional silicon neural probes, softer materials are more suitable as the substrate to decrease the mechanical mismatch, reduce tissue inflammation, and prolong the service time. However, most soft neural probes made of silicone face the main challenges of poor micro/nanopatterning, insufficient air/water proofness, prone to buckling, and severe trauma of tissue. Here, we present a soft neural probe on oil-extracted silicone substrate with stretchability and microwrinkles, as well as a minimized shuttle that enables minimally invasive insertion. The polydimethylsiloxane (PDMS)-Ecoflex silicone substrate (Young's modulus of 160 kPa) can greatly reduce the tissue damage caused by brain micromotion. The microwrinkles are originated by depositing Parylene-C film (3μm thick) on the silicone substrate. The Parylene-C film is patterned as the serpentine layout to ensure the stretchability of 17% along with the deformation of soft substrate. As a whole, the soft probe with ∼100μm in thickness and 7 mm in shank length and eight microelectrode sites with a diameter of 20μm and pitch of 500μm, which is suitable for rodents. To insert this probe into soft tissue without buckling, the insertion shuttle is optimized as the combination of a stainless needle (20μm thick) and a spin-coating layer of molten polyethylene glycol (PEG) (20μm thick), causing invasion as low as possible. The soft probe causes little stress concentration with the micromotion (100μm) compared with the rigid silicon probe in simulation. Besides, the microwrinkles facilitate the stability of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) coating as a superior method to improve the electrochemical properties.