Characterization of an encapsulation device for the production of monodisperse alginate beads for cell immobilization

An encapsulation device, designed on the basis of the laminar jet break-up technique, is characterized for cell immobilization with different types of alginate. The principle of operation of the completely sterilizable encapsulator, together with techniques for the continuous production of beads from 250 microm to 1 mm in diameter, with a size distribution below 5%, at a flow rate of 1-15 mL/min, is described. A modification of the device, to incorporate an electrostatic potential between the alginate droplets and an internal electrode, results in enhanced monodispersity with no adverse effects on cell viability. The maximum cell loading capacity of the beads strongly depends on the nozzle diameter as well as the cells used. For the yeast Phaffia rhodozyma, it is possible to generate 700 microm alginate beads with an initial cell concentration of 1 x 10(8) cells/mL of alginate whereas only 1 x 10(6) cells/ml could be entrapped within 400 microm beads. The alginate beads have been characterized with respect to mechanical resistance and size distribution immediately after production and as a function of storage conditions. The beads remain stable in the presence of acetic acid, hydrochloric acid, water, basic water, and sodium ions. The latter stability applies when the ratio of sodium: calcium ions is less than 1/5. Complexing agents such as sodium citrate result in the rapid solubilization of the beads due to calcium removal. The presence of cells does not affect the mechanical resistance of the beads. Finally, the mechanical resistance of alginate beads can be doubled by treatment with 5-10 kDa chitosan, resulting in reduced leaching of cells.