Polydopamine-doped PEDOT interfaces improve cell-electrode interactions and neural signal transmission.

Here, we report an innovative conductive polymer composite, polydopamine (PDA)-doped poly(3,4-ethylenedioxythiophene) (PEDOT-PDA), deposited onto titanium nitride (TiN) electrodes. TiN films (~ 150 nm thick) were prepared via physical vapor deposition, followed by rapid galvanostatic electrochemical co-polymerization to form pure PEDOT and PEDOT-PDA layers. Field-emission scanning electron microscopy revealed that PEDOT-PDA films exhibit a compact, tightly packed architecture, enhancing structural cohesion, mechanical stability, and charge transport efficiency. Atomic force microscopy demonstrated increased surface roughness of the PEDOT-based coatings compared to the bare TiN substrate, promoting better cell interfacing. Notably, PDA incorporation rendered the PEDOT-PDA surface superhydrophilic, with a contact angle of 7°, representing a substantial improvement over the 65° measured for pure PEDOT films. Electrochemical analyses showed that PEDOT-PDA interfaces achieved a remarkably low impedance of 0.27 Ω, over 94% lower than that of commercial gold electrodes (4.7 Ω), facilitating efficient ion-electron mixed charge transfer via electrochemical (de)doping mechanisms. All fabricated samples exhibited high biocompatibility (> 85% cell viability), with PEDOT-PDA films particularly promoting enhanced cell adhesion and spreading, as evidenced by extensive filopodia penetration into the interface layer. Computational simulations further revealed that PDA doping improved the binding energy of PEDOT-based films to cellular membranes by up to 685%, increased lateral molecular diffusion at the interface by nearly 1000%, and boosted the average number of molecular contacts (~ 3010 at 310 K over 5 ns) by 16–47%. Together, experimental and computational results demonstrate that PEDOT-PDA composites significantly enhance both biological and electrochemical interactions at the cell-electrode interface.