Electroactive MnO2-poly(3,4-ethylenedioxythiophene) composite nanocoatings enhance osteoblastic electrical stimulation

Highlights: • MnO₂-PEDOT nanocoatings were prepared via a facile two-step redox method. • PEDOT improved the electroactivity and stability of the composite nanocoatings. • MnO₂-P2 nanocoating showed the greatest promotion in osteoblastic functions. • MnO₂-P2 nanocoating under ES induced the highest cell proliferation rate. • ES-induced cation-FN interactions contributed to the enhanced cell proliferation. Electroactive biointerfaces on metallic implants can transduce electrical into ionic signals under exogenous electrical stimulation (ES), which have been proposed to compensate the mislaid bioelectricity signals in bone defects. However, unsatisfied electrical properties and long-term stability are the major issues that hinder their clinical applications. Herein, based on the merits of birnessite-type MnO₂ (the large capacitance and effective surface area) and poly(3,4-ethylenedioxythiophene) (PEDOT, the high conductivity and physicochemical stability), MnO₂-PEDOT composite nanocoatings (MnO₂-P1 and MnO₂-P2) were prepared by coating trace amounts of PEDOT onto the MnO₂ nanocoating surfaces via an in-situ polymerization method. The composite nanocoatings exhibited decreased charge transfer resistance and concurrently enhanced charge storage capacity. More importantly, the MnO₂-P2 nanocoating with thicker PEDOT layer withstood higher voltages with minor loss of mass and charge injection capacity, thus enhancing mechanical and electrochemical stability. The composite nanocoatings were further applied to MC3T3-E1 osteoblastic cells to enhance their adhesion, proliferation and differentiation with the MnO₂-P2 showing the greatest enhancement. Enhanced cellular proliferation on the MnO₂-P2 nanocoating under ES could be ascribed to the combination of the ES-induced Ca²⁺-fibronectin interactions and the limited Mn²⁺ release prevented by PEDOT protective layer.