Cells in multicellular organisms are exposed to a range of forces that would kill unicellular lifeforms. To cope, these cells have evolved a mechanically-sensitive signaling pathway called mechanotransduction. Mechanotransduction can direct lineage differentiation by detecting changes in environmental viscoelasticity. It has been shown that stiffness differs within and between tissues, resulting in a range of mechanical signals sensed by cells. [1][2] Researchers have developed a wide array of techniques to study cellular mechanotransduction by dynamically tune cell scaffolds [3], including integrating photoswitchable molecules, incorporated superparamagnetic molecules or materials whose stiffness changes with temperature. One simple, alternative novel, to the above techniques, means of dynamically tuning both the viscosity and stiffness of a polymer hydrogel by incubating it in crowding agents.

For this purpose, alginate, with pore sizes of about 5 nm was used as a hydrogel, and poly(ethylene glycol) (PEG) as a crowding agent, which can easily penetrate the polymer matrices, taking up network space without other kinds of interactions. Here, we have demonstrated that the hydrogel viscoelasticity can be dynamically increased/decreased with increasing/decreasing PEG’s concentration by incubating the hydrogel in PEG’s solution. By dynamically changing hydrogel’s viscoelasticity, results on 2D substrates have shown that such changes affect both cell adhesion and the cytoskeleton (Figure 1), without any negative effect on cell vitality or proliferation. This technique can serve as an effective tool for studying the effects of external and internal mechanical forces and their interactions with molecular signaling pathways.