The Impact of S-220–Loaded Silk Hydrogels on In Vitro Neurite Outgrowth in 2 and 3 Dimensions

Abstract

Silk hydrogels have attracted increasing interest as biocompatible substrates for neural cell culture and regenerative research. Recent research has shown that activation of exchange protein directly activated by cAMP 2 (Epac2) promotes neurite outgrowth in several neuronal models. Here, we investigated the effects of Bombyx mori silk hydrogel, alone or in combination with S-220, a non-hydrolysable cAMP analogue that selectively activates Epac2, on neurite outgrowth. Epac2 activation significantly and dose-dependently enhanced both the total and longest neurite length. Neurons cultured on silk hydrogel alone exhibited neurite outgrowth comparable to control neurons, indicating good biocompatibility of the hydrogel. Addition of S-220 to the culture medium with silk hydrogel modestly improved neurite morphology; however, incorporation of S-220 directly into the hydrogel did not enhance neurite outgrowth but instead reduced neurite length. A subsequently established three-dimensional cortical neuron culture model using silk hydrogel supported neurite extension and increased branching complexity beyond that observed with two-dimensional cultures, despite a shorter overall neurite length. Collectively, these findings support silk hydrogel as a permissive biomaterial substrate for in vitro cortical neuron culture. The system provides a useful platform for investigating neurite outgrowth, neuron-biomaterial interactions and the delivery of bioactive compounds in two- and three-dimensional neural cultures.