Theoretical and experimental investigation of alginate microtube extrusion for cell culture applications

Abstract

A novel cell culture technology, consisting of hollow alginate tubes, OD ~550μm, ID ~450μm containing a cell suspension, provides stress-free conditions. Cells reach confluency in approximately ten days with cell densities of 0.5−1 billion cells per mL. Tubes are manufactured in a tri-axial needle extruder with three concentric flows. The cell suspension flows in the inner needle (N1), the alginate solution flows in the annulus between N1 and the second needle (N2) and a CaCl2 solution is the sheath fluid between the second and third needle (N3). Beyond the tip of N2, the sheath solution is in contact with the alginate and Ca2+ diffuses into the alginate solution and crosslinks it to form an alginate microtube around the core fluid. The cross-linked layer moves radially inwards like a front, starting at the sheath/annulus interface and ends at the annulus/core interface. A mathematical model is used to find the minimum length zC of direct contact between the CaCl2 solution and the alginate solution to complete the cross-linking. Experimental results support the theoretical findings that stable tubes can only be manufactured if the contact length exceeds zC. Experiments also show that the extruder configuration N3 > N2 is best for alginate tube manufacture.