Photoexcited wireless electrical stimulation elevates nerve cell growth

Electrical stimulation was restrained by an external power supply and wires, despite its ability to promote nerve cell growth. Bismuth sulfide (Bi₂S₃) offered a novel prospect for achieving wireless electrical stimulation due to its photoelectric effect. Herein, silver nanoparticles (Ag NPs) were in-situ grown on Bi₂S₃ surface (Ag/Bi₂S₃) and then mixed with poly-L-lactic acid (PLLA) powders to fabricate PLLA-Ag/Bi₂S₃ conduits. On the one hand, Bi₂S₃ would generate photocurrent under light excitation, forming a wireless electrical stimulation. On the other hand, Ag NPs would form localized electrical fields under light excitation to inhibit rapid electron-hole recombination of Bi₂S₃. Moreover, Ag NPs would act as electron mediators to accelerate electron transfer, further elevating photocurrent. Electrochemical tests and FDTD simulations revealed the localized electrical fields generated by Ag NPs acted on Bi₂S₃, resulting in a boosted electron-hole separation evidenced by a reduction in photoluminescence intensity. EIS measurements demonstrated a faster electron transfer occurred on Ag/Bi₂S₃. As a result, the photocurrent of PLLA-Ag/Bi₂S₃ increased from 0.26 to 1.03 μA as compared with PLLA-Bi₂S₃. The enhanced photocurrent effectively promoted cell differentiation by up-regulating Ca²⁺ influx and nerve growth-related protein SYN1 expression. This work suggested a promising countermeasure in the design of photocurrent stimulation conduits for nerve repair.