What is the difference between culturing cells in Biosilk compared to a hydrogel?
There are big differences in the spreading and expansion of cells within Biosilk compared to when encapsulating cells in a hydrogel. Biosilk provides a more tissue-like environment that promotes the formation of focal adhesion points that trigger the organization of the cytoskeleton. In a scientific publication from 2019, the authors compared Biosilk to an Alginate hydrogel coupled with the cell-binding motif RGD (0.01-0.04 μmole/mg). Mammalian cells cultured in Biosilk and alginate showed markedly different growth curves. A clear expansion phase was seen for cells integrated into Biosilk, while cells encapsulated in alginate remained at an almost steady metabolic state, an observation is in line with previous reports of the limited proliferation of cells encapsulated in alginate hydrogels. Cells cultured in Biosilk had a more elongated shape (a sign of attachment) and increasingly spread out within the silk scaffold with a clear directional alignment in the fibers. Contrary, cells encapsulated within the hydrogel exhibited a rounded morphology and no spreading was observed (static encapsulation in the hydrogel). In the Biosilk cultures, punctate vinculin-rich focal adhesions sequestered to the tips of cell protrusions were observed, confirming integrin-involved binding of cells to the Biosilk. In the hydrogel, the coupled RGD-motif is available for integrin binding, but the very thin alginate chains (one saccharide unit thick) do not physically allow the gathering of several integrins to the same spot. That prohibits the formation of focal adhesion points which explains the rounded morphology of cells within the alginate gels.