Injectable Shear Thinning Hydrogels from Functionalized Silk Proteins for 3D Mammalian Cell Culture.

Silk fibroin hydrogels are a promising platform for tissue engineering due to their biocompatibility and tunability, yet efficient cell recovery from gels remains a challenge. This work synthesizes reversible hydrogels by electrostatically-crosslinking carboxylated silk with linear and branched polyamine. Solvent choice (water, saline, or medium) and protein concentration impacted gel stiffness, mesh size, degradability, and function as an in vitro culture substrate. Hydrogels flowed as a liquid and recovered their viscoelastic properties when cycled under shear. Unlike enzymatically-crosslinked silk hydrogels, β-sheet content did not significantly increase during culture. Encapsulated mesenchymal stem cells proliferated, and live cells were recovered with high efficiency (>90%) by disrupting gels with shear. Lower protein concentrations resulted in hydrogels with lower stiffness, larger mesh size, and increased cell recovery. Electrostatic crosslinking of carboxylated fibroin is a viable route to silk hydrogels that permit encapsulation and subsequent retrieval of live stem cells for regenerative engineering applications.