Arrayed rGO_SH/PMA_SH microcapsule platform integrating surface topography, chemical cues, and electrical stimulation for three-dimensional neuron-like cell growth and neurite sprouting

The biocompatible thiol-functionalized rGO_SH/PMA_SH microcapsules encapsulating nerve growth factor (NGF) are arrayed onto a transparent and conductive substrate, i.e., indium tin oxide (ITO), to integrate electrically stimulated cellular differentiation, electrically controlled NGF release, and topographically rough nano-surfaces into a 3-D platform for nerve regeneration. The rGO_SH/PMA_SH microcapsules with microscale topography function not only as an adhesive coating to promote the adhesion of PC12 cells but also as electroactive NGF-releasing electrodes that stimulate NGF release and accelerate the differentiation of PC12 cells during electrical stimulation. Once electrical treatment is applied, NGF release and electrically enhanced cellular differentiation lead to an obvious increase both in the percentage of cells with neurites and in the neurite length. This length can reach nearly 90 μm within 2 days of cell culture. The average neurite length is significantly increased (four-fold) after culture on the rGO _SH/PMA_SH microcapsule substrate for 2 days compared with culture on a substrate without an rGO_SH/PMA_SH coating. These multifunctional rGO_SH/PMA_SH microcapsules may be used as potential 3-D patterned substrates for neural regeneration and neural prosthetics in tissue engineering applications. The stimulus-responsive, well-ordered rGO_SH/PMA_SH microcapsules are arrayed into a 3-D ECM-mimic flexible substrate to accelerate the proliferation and differentiation of PC12 cells by controlling NGF release and manipulating rGO_SH/PMA_SH microcapsule interfaces. A combination of surface topography, chemical cues, and electrical stimulation not only has positive effects on cell viability but also strongly enhances the neurite outgrowth of PC12 cells.