A bioreactor is generally defined as a system capable of providing the cells the intake of nutrients and removal of waste products of cell metabolism. Normally bioreactors are used in industry for the cultivation of bacteria, yeasts, fungi, algae, plant cells and animal cells on a large scale, thanks to the advantage of being able to optimize the control of vital parameters with respect to culture performed on the plate. The environment in which they grow the cells is tightly controlled from the point of view of the chemical-physical parameters: thanks to the presence of special sensors can monitor specific parameters of the crop, such as the temperature, the concentration of gases dissolved in the culture medium, the pH, concentration of inorganic ions and carbohydrates. In case be detected alterations of these components, control systems ensure their appropriate correction via the administration of liquid or gas.
The cells can grow in suspension or adherent to a substrate; the homogeneous distribution of the cell suspension through the substrate is ensured by a perfusion system that uses a flow of liquid through the substrate. Even the flow of culture medium within the bioreactor can increase the viability and cellular activity. The use of the bioreactors was thus proposed for the construction of artificial tissues in a three-dimensional system, where also the mechanical stress influence the development and tissue remodeling. In this regard, the bioreactor can be used to generate specific physical stimuli, for example compression and tension, which can stimulate the growth and maturation of the tissues during their development in vitro . Numerous studies have been made for the building of tissues in the bioreactor such as cartilage, tendon and blood vessels, as well, although still at the theoretical level, for the generation of organs such as liver, pancreas and kidney.
