One of the most important challenges of tissue engineering is the reproduction of an "artificial" vascular system able to supply the growing cells with sufficient oxygen and nutrients, as well as to remove the waste matter generated by cells metabolism, are some of the most difficult issues.
Cell cultures developed on three-dimensional scaffolds under static conditions are specially sensitive to oxygen and nutrients depletion. Assuming that they are equally distributed across the volume of the scaffold at the beginning of the culture, cells should develop at a similar rate in the whole scaffold. However, those cells located at the inner areas of the scaffold transform all the available oxygen and nutrients into carbon dioxide and waste matter soon, since renovation rate by diffusion is too slow compared to cell metabolism. Then, it typically happens that scaffolds larger than 1 mm result in a shell of viable cells and matrix surrounding a necrotic core due to the absence of vascular supply.
Thus, the improvement of mass transport and nutrient exchange in three-dimensional in-vitro experiments is crucial to get viable cells populations, for which the imposition of certain flow rate across the scaffold (perfusion) has been experimentally shown very efficient, compared to static cultures.
Likewise, flow stimulation is also crucial for the appropriate development of certain kinds of tissue as, for instance, the vascular tissue. In this case, endothelial cells in the intimal layer are strongly influence by the effect of blood flow, which has been experimentally demonstrated to exert a strong influence of the behaviour of such cells and, in general, of the whole vessel. Thus, culturing of blood vessels under flow conditions is of vital importance, since no other conditions better reproduce conditions experienced by cells in-vivo.