How a cell responds to localized stresses acting on it depends on the 'softness' of the cell itself, reports a study published online this week in Nature Materials. This suggests that small physical forces acting on cells might have far more important roles in early developments of soft embryos than previously thought.

Ning Wang and colleagues found that individual mouse embryonic stem cells, which are very soft, spread when a small oscillating local stress is applied to one side of the cell. In contrast, cells that are tenfold stiffer do not react to the same level of stress. However when the stiff cells are artificially softened, they react similarly to the soft stem cells.

It had already been shown that the rigidity of materials that the cell attaches to have a large influence on cell response. This study now shows that how much the cell's structure is deformed by a force is the primary factor that determines the extent of the cell's response.