Facile photopatterning of polyfluorene for patterned neuronal networks

In this paper, we demonstrated a facile photopatterning method that uses photocrosslinkable polyfluorene to fabricate micro-sized photopatterns on transparent indium tin oxide substrate for neuronal patterning. The modified poly(ethyleneimine) (m-PEI) with trimethoxysilane moiety was chemically attached to the hydroxyl group-terminated ITO surface and then the photopatternable polyfluorene derivative was spin coated as a cell-repellent layer onto the m-PEI-coated surface. The well-defined micropatterns were easily created over an entire surface by photocrosslinking of bromoalkyl-substituted polyfluorene (Br-PF) via the radical coupling reaction of a C-Br bond under UV irradiation without an initiator. UV-Vis absorbance, photoluminescence, ATR-FTIR and X-ray photoelectron spectroscopy were used to confirm the photocrosslinking process and the surface composition before and after the photocrosslinking of polyfluorene. The pairing of adhesive m-PEI and repulsive Br-PF effectively guided the neurite outgrowth and controlled neurite extension from individual neurons to the pre-patterned direction with excellent pattern fidelity. Guided neuronal cells were maintained for at least 25 days in vitro without any detachment of neuronal cells during cell culture. A photopatternable polyfluorene derivative in combination with cell-adhesive m-PEI is proved to be an effective way to modify the electrode surface to achieve single cell level neuronal networks.