Supplementary Material for: Complex Material Properties of Gel-Amin: A Transparent and Ionically Conductive Hydrogel for Neural Tissue Engineering

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, organic and inorganic 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. The inclusion of an ionic liquid increases conductivity while maintaining a high degree of optical transmission. 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.

组织工程领域已从天然与合成聚合物的蓬勃发展中获益匪浅。神经工程领域的大量研究已证实，导电材料可提升神经元自发放电活性，同时降低外源性电刺激所需的场域参数。此外，细胞命运与细胞培养基材的力学性能直接相关。提升水凝胶材料的导电率通常需要添加可促进电子迁移的有机与无机掺杂剂。然而，天然细胞信号传导过程中几乎不存在电子传递，且这类材料大多不透明，这严重限制了常用于评估细胞培养形态与功能的显微镜成像应用。为克服上述缺陷，将离子液体（ionic liquid）丙烯酸胆碱（Choline Acrylate）引入改性胶原蛋白聚合物的主链后，在1:1配比下可使材料的体积导电率提升5倍，同时保留可见光的透光性能。本研究探究了丙烯酸胆碱的引入对作为细胞培养基材的Gel-Amin水凝胶各项体积材料性能的影响，涵盖力学性能、溶胀性能与光学性能。所引入的离子液体可在提升导电率的同时，维持较高的可见光透光率。尽管相较于传统明胶甲基丙烯酸酯（GelMA）材料，该导电水凝胶的溶胀程度有所提升，但仍可支持完整背根神经节的包埋与轴突生长。本研究结果表明，我们开发的Gel-Amin体系具备神经工程应用潜力，且可降低外源性电刺激所需的电荷注入量。这是首次将离子液体-水凝胶体系用于体外原代神经元的培养与支撑。