The surroundings of cells have various mechanical properties. The brain, for example, is a very soft environment, whereas bone structures are very stiff. Cells are not only able to sense such mechanical differences of their environment but can also respond to them. This process of detection and biochemical reaction to mechanical stimuli is called mechanotransduction and is of great importance for all materials that are in touch with biological systems. For example, for the design and development of coatings for biomedical applications it is relevant to know how cell behavior is influenced by the mechanical properties of the coating itself. However, cells are known to be capable of sensing a stiffer substrate underneath a soft structure. Mesenchymal stem cells, for example, show decreased spreading on thin, soft hydrogels (thickness 10-20 µm) compared to the same hydrogels with a more rigid underlying substrate.
We here report results on cell adhesion as a function of hydrogel thickness and elasticity. We produce polyacrylamide layers with thicknesses ranging from less than 100 µm to semi-infinite bulk samples (ca. 0.5 mm). Glass slides are fixed below the hydrogels to enable a suitable reference substrate. Furthermore, we use two cross-linker densities to investigate if the cellular substrate sensing is influenced by the elastic modulus of the samples.
Our results show a strong correlation between spreading area as well as circularity and the thickness of the polyacrylamide samples.