This work fabricates mechanically exfoliated graphite paper with layered microstructures, which not only ensures the high flexibility of the resulting electrochemical capacitor, but substantially boosts its electrochemical properties.

Polydimethylsiloxane (PDMS) is a commonly used insulation/packaging material for implantable neural electrodes. Nevertheless, the PDMS-initiated tissue response would lead to the deterioration of the electrode performances post-implantation, owing to its intrinsic hydrophobic and cell-repellent surface. The conventional physical coatings by hydrophilic hydrogels or bioactive molecules are unable to maintain during the long-term implantation due to their low stability by physical adhesion. In this work, we first anchor both hydrophilic polyethylene glycol (PEG) and bioactive molecule poly-L-lysine (PLL) on the PDMS surface by chemical coupling to change the PDMS surface from hydrophobic and cell-repellent to hydrophilic and cell-adhesive. XPS tests indicate the chemically coupled modification layers are stable on the PDMS surface after experiencing a harsh rinse process. Contact angle measurements show that the use of PEG 600 with the moderate molecular weight results in the highest hydrophilicity for the resulting PDMS-PEG-PLL. PC12 cell evaluation results exhibit that the PDMS-PEG-PLL with PEG 600 leads to significantly larger cell adhesion area, more neurite number, and longer neurite length than the PDMS. The PDMS-PEG-PLL with PEG 600 featuring stable modification layers, high hydrophilicity, and superior cell affinity has great potential in stabilizing the neural electrode-tissue interface for the long-term implantation.

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