The field of tissue engineering has benefited greatly from the broad development of natural and synthetic polymers. Extensive work in neural engineering has demonstrated the value of conductive materials to improve spontaneous neuron activity as well as lowering the necessary field parameters for exogenous electrical stimulation. Further, cell fate is directly coupled to the mechanical properties of the cell culture substrate. Increasing the conductivity of hydrogel materials often necessitates the addition of dopant materials that facilitate electron mobility. However, very little electron transfer is observed in native cell signaling and most of these materials are opaque, severely limiting microscopy applications commonly employed to assess cell culture morphology and function. To overcome these shortcomings, the inclusion of an ionic liquid, choline acrylate, into the backbone of a modified collagen polymer increases the bulk conductivity 5-fold at a 1:1 ratio while maintaining optical transmission of visible light. Here, we explore how the inclusion of choline acrylate influences bulk material properties including the mechanical, swelling, and optical properties of our hydrogels, referred to as Gel-Amin hydrogels, as a material for tissue culture. Despite an increase in swelling over traditional GelMA materials, the conductive hydrogels support whole dorsal root ganglia encapsulation and outgrowth. Our results indicate that our Gel-Amin system holds potential for neural engineering applications and lowering the required charge injection for the application of exogenous electrical stimulation. This is this first time an ionic liquid-hydrogel system has been used to culture and support primary neurons in vitro.
Keywords: Hydrogels; Ionic liquid; Mechanical properties; Neural engineering; Viscoelasticity.
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