Abstract: A bioreactor for the formation of mature blood cells from haematopoietic stem cells is disclosed. The bioreactor comprises a first zone and a second zone. The first zone and the second zone are separated by a first membrane. The first membrane allows the preferential passage of red blood cells relative to the haematopoietic stem cells and their 5 other progeny excluding red blood cells. The first membrane is formed by at least a separating layer and a porous layer, where the porous layer is in contact with the first zone, such that the haematopoietic stem cells can be grown in the porous layer. The bioreactor comprises a third zone. The first zone and the third zone are separated by a second membrane, and the second membrane allows the passage of nutrients from the 10 third zone to the first zone and the passage of metabolites of the cells from the first zone to the third zone, while substantially preventing the passage of growth factors from the first zone to the third zone.