Pt/PEDOT:PSS modification and SF-doped PEG transient coating of helical neural electrodes for deep-brain implantation and long-term stable recording

Flexible neural electrodes can reduce mechanical mismatch, but their chronic use remains limited by high interfacial impedance, coating instability, and difficult deep-brain insertion. Here, we report a polyimide-based 3D helical neural electrode integrating Pt/PEDOT:PSS interface modification and a low-dose silk-fibroin (SF)-doped polyethylene glycol (PEG) transient support coating. Sequential Pt/PEDOT:PSS deposition reduced the 1 kHz impedance from 1.93 MΩ to 24 kΩ (98.7%) and increased the charge-storage capacity by 23.5-fold. After 2000 cyclic-voltammetry cycles, the composite-modified electrodes showed a 22.6% impedance increase, compared with 129.4% for PEDOT:PSS-only electrodes. Helical devices retained stable impedance and phase responses after 2000 cycles of 10% tensile strain. Among all tested formulations, PEG/SF (50:1) achieved a 60.8% increase in critical buckling force and maintained a force above 0.8 N after 20 s of immersion in phosphate-buffered saline (PBS), with no detectable in vitro cytotoxicity observed. Pure-PEG-coated probes were implanted in M1 and PEG:SF-coated probes in CA1; because coating formulation and brain target were varied together, these experiments are presented as separate feasibility demonstrations rather than a direct coating comparison. Whisker stimulation elicited region-specific LFP responses. Over 120 days of chronic implantation, the electrodes retained stable impedance, steady signal-to-noise ratio (SNR) of 5.5–6.5 dB, and intact single-unit waveforms. These findings validate the effectiveness of our integrated strategy for electrochemical stabilization, structural compliance improvement, and transient insertion assistance.