Protein conformational transition microenvironment in silk fibroin hydrogels: Proliferation and chondrogenesis of encapsulated stem cells

Abstract Chemically crosslinked silk fibroin (SF) hydrogels exhibit excellent extracellular matrix-mimicking features and tunable mechanical characteristics, making them highly promising for three-dimensional (3D) cell culture and tissue engineering. However, the protein segments within SF hydrogels can spontaneously undergo a conformational transition from random coil to β-sheet, inducing dynamic changes in the material’s mechanical properties and pore structures. Such dynamical material cues could probably have significant effects on cell behaviors, thus inducing a kind of unknown influence which cannot be ignored when applying these hydrogels in 3D cell culture and tissue repair. Based on this, the current research seeks to clearly reveal the impacts of the protein conformational transition microenvironment within SF hydrogels on the proliferation and chondrogenic differentiation of encapsulated stem cells. To this end, this study successfully constructed a series of SF hydrogels with highly similar initial properties but different conformational transition rates, which was enabled by modulating the uniformity of the chemical crosslinking points while fixing the similar crosslinking density. Results showed that the SF hydrogel with lower uniformity of crosslinking points exhibited faster conformational transition rates, and vice versa. Encapsulated mesenchymal stem cells’ responses further clearly illustrated that the protein conformational transition microenvironment in SF hydrogels could obviously regulate cell proliferation and chondrogenesis. Specifically, a relatively slower conformational transition rate was more favorable for encapsulated cell proliferation, whereas a moderate transition rate was more beneficial for encapsulated cell chondrogenesis. Related research is expected to expand the knowledge and understanding of the impacts of dynamical protein conformational transition microenvironment on cell behavior within hydrogels, and provide valuable insights for the development of efficient SF-based cell culture matrices and cartilage scaffolds.