Stretchable Micro-wrinkled 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/nano patterning, 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 micro-wrinkles, as well as a minimized shuttle that enables minimally invasive insertion. The PDMS-Ecoflex silicone substrate (Young's modulus of 160 kPa) can greatly reduce the tissue damage caused by brain micromotion. The micro-wrinkles are originated by depositing Parylene-C film (3 mu m 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 similar to 100 mu m in thickness, 7 mm in shank length, 8 microelectrode sites with diameter of 20 mu m and pitch of 500 mu m, 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 (20 mu m thick) and a spin-coating layer of molten PEG (20 mu m thick), causing invasion as low as possible. The soft probe causes little stress concentration with the micromotion (100 mu m) compared with the rigid silicon probe in simulation. Besides, the micro-wrinkles facilitate the stability of PEDOT: PSS coating as a superior method to improve the electrochemical properties.