Preparation of Graphene Oxide-Doped Polypyrrole Composite Films with Stable Conductivity and Their Effect on the Elongation and Alignment of Neurite.

Conductive composite films (CCFs) of polypyrrole (PPy) doped with sodium dodecyl benzenesulfonate (DBS) and graphene oxide (GO) were prepared via electrochemical deposition of PPy nanoparticles on the aligned PLLA fibers. The doping amount of GO in CCF sheaths reached to ∼3.8%, leading to ∼32 S cm of the mean conductivity of DBS-GO-doped CCF. The electrical potential image of DBS-GO-doped CCFs showed that the charges were mainly distributed on the tops of GO sheets protruded from the PPy surface. The immersion results indicated that the more stable conductivity of DBS-GO-doped CCF resulted from the reservation of GO sheets in the PPy film because of the van der Waals's force between GO and the pyrrole rings in CCF sheath. The results of PC12 cell test showed that, the rougher surface of DBS-GO-doped CCF could positively affect the neurite elongation due to the slight protrusion of GO sheets from the CCF surface. The electrical stimulation (ES) of 50 mV cm through DBS-GO-doped CCF could significantly promote neurite elongation and alignment, as well ∼149 μm of the mean neurite length and 70% of alignment on DBS-GO-doped CCF were significantly higher than those without ES, respectively. These results indicated that the more stable conductivity of DBS-GO-doped CCF could enhance the ES efficiency on the elongation and alignment of neurites, due to the more charges accumulation on the tops of the protruded GO sheets in the CCF surface. A mechanism was proposed to explain the positive effect of the GO-nanosheets protrusion, rougher PPy surface and stable conductivity on the elongation and alignment of neurites. These results suggested the possibilities for the long-term peripheral nerve repair in vivo via ES through DBS-GO-doped CCF.