A novel tube forming process for preparing engineered blood vessels is described. The process involves charging a vertical cylindrical tube with a matrix fluid. A slightly buoyant sphere, introduced at the bottom of the tube, is propelled vertically upwards by the injection of a second fluid into the base of the cylinder. Tubes are created by the passage of the sphere, which deposits matrix fluid on the interior of the cylinder. By introducing a fixing agent into the second fluid, stable tubes can be produced which is vital for the intended bioreactor design and application. A lubrication analysis predicts that, in the limit of a thin gap (delta(0)/a -> 0), the tube wall thickness tends to 0.66 delta(0), where delta(0) is the gap between the sphere and cylinder wall and a is the cylinder radius. When the alginate tubes do not set, the tube thickness varies from 0.52 to 0.55 delta(0), whereas for setting algiante tube, the thickness is 0.66 delta(0). The use of flow tracking CFD also yielded similar predictions of the ratios and gave further insight into the flow trajectories of the system. (C) 2012 Elsevier Ltd. All rights reserved.