Cellular stress can arise from mechanical forces acting on the cells, with excessive forces causing rupture of the cell membrane and ultimately cell death. However, below this upper limit, mechanical stress is an important environmental stimulus, defined by physical forces that have a magnitude and most importantly a direction, so called vectors. The most basic forms are compression, tension, bending and torsion. More complex forms include hydrostatic pressure and shear stress.
Mechanical forces are an essential component of the cellular microenvironment, which in vivo is gradually changing its physicochemical properties. This dynamic nature is closely related to tissue/organ development, regeneration, wound healing, and disease progression. Mechanical stress can guide the cells during differentiation or proliferation and trigger secretion of different extracellular matrix (ECM) molecules. Forces also help cells to organize spatially, to align like we see in muscle and tendon or build layered structures e.g. in skin. Therefore, in vitro platforms that mirror dynamic in vivo signalling may improve the understanding of essential biological processes and help to advance tissue engineering and regenerative medicine. Therefore, unlike in static culture conditions, the use of bioreactors for dynamic culture provides the physical cues and an improved nutrient supply which bears the potential to achieve a more organ- or tissue-specific environment for the cells.