Nervous tissues have minimal capacity to repair damage due to trauma or from disease. Delivery of therapeutic, multipotent cells is a promising strategy to repair these tissues. Progress in this goal requires development of therapeutically viable cell sources, optimization of chemical factors that promote regeneration, and advances in delivery vehicles, which provide an ideal microenvironment for delivered cells, reduce inflammatory host responses, and participate in the healing process. In our group, we have focused on developing materials that balance maximizing the therapeutic potential of delivered cells, along with minimizing some of the drawbacks associated with material-assisted cell delivery. We utilized annealing of gelatin-based microgels, hydrogels with diameter in the micrometer scale, for the encapsulation of neural progenitor cells (NPCs). Encapsulated in the interstitial space between microgels, NPCs are encased in an environment that promotes cell attachment, elongation, and cell-cell connections, which are known to be important for mature synapse formation. In addition, we describe a facile enzymatic chemistry for the conjugation of bioactive proteins to the surface of gelatin microgels, and demonstrate how this conjugation can be used to influence cell attachment and organization, using laminin. Encapsulation in the microgel assembly with immobilized laminin substantially improved NPC viability compared to the nonporous hydrogel with the same chemical composition and resulted in enhanced neural differentiation (both neuronal and glial) with physiologically relevant morphological changes and cell-cell connections evidenced by immunofluorescence imaging. The firing of functional neurons when stimulated by glutamate was confirmed by calcium flux imaging after 4 weeks of differentiation. These results describe a simple method to conjugate the surface of gelatin microgels, and show the potential usage of these microgels as an injectable formulation for NPC delivery for neural tissue regeneration.
