Tunable Hydrogel Viscoelasticity Modulates Human Neural Maturation

Human induced pluripotent stem cells (hiPSCs) have emerged as a promising in vitro model system for studying neurodevelopment. However, current models remain limited in their ability to incorporate tunable biochemical and biomechanical signaling cues imparted by the neural extracellular matrix (ECM). The native brain ECM is viscoelastic and stress-relaxing, exhibiting a time-dependent response to an applied force. To recapitulate the remodelability of the neural ECM, we developed a family of protein-engineered hydrogels crosslinked with either static or dynamic covalent bonds that exhibit tunable stress relaxation rates. hiPSC-derived neural progenitor cells (NPCs) encapsulated within these gels underwent relaxation rate-dependent maturation. Specifically, NPCs within hydrogels with faster stress relaxation rates extended longer, more complex neuritic projections, exhibited decreased metabolic activity, and expressed higher levels of genes associated with neural maturation. By inhibiting actin polymerization, we observed decreased neuritic projections and a concomitant decrease in the expression of neural maturation genes. Taken together, these results suggest that microenvironmental viscoelasticity is sufficient to bias human NPC maturation. To explore the effects of matrix viscoelasticity on hiPSC differentiation and maturation, we encapsulated hiPSC-derived NPCs in protein engineered matrices with three distinct stress relaxation profiles and collected cells at cells after seven days.