Fig. 7.

Unstirred layers in static and dynamic cell culture conditions. In static culture the medium is mixed through diffusion which can lead to a depletion in concentration close to the cell surface, a region termed the unstirred layer (UL). The application of convective mixing to the medium, such as with fluid flow, greatly increases the distribution of molecules within the medium and reduces the thickness of the unstirred layer, where diffusion is predominant. This in turn leads to greater levels of solute concentrations at the cell surface.