(A) Schematic and (B) setup of multi-channel perfusion bioreactor capable of providing cyclic, circumferential stretch to tubular collagen gel constructs for 3-D dynamic culture. It consists of a cylindrical culture chamber (a), with centrally placed silicone tubing, around which the collagen gel constructs compacted. The silicone tubing was in turn connected to metallic bellows (b), forming a closed, airtight conduit into which a constant volume of water was maintained. The bioreactor worked on the principle that when the bellows contract and expand, the resultant displacement of water within the closed loop will proportionally expand or contract the silicone tube, and in turn the cell-seeded collagen gel construct around it. The contraction and expansion of the bellows were controlled by a stepper DC motor (d) and its controller (e), programmed to deliver the required 2.5 % strain at 1.5 Hz frequency via a piston (c).