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 encaps ulator, together with techniques for the continuous production of beads fro m 250 mu m to 1 mm in diameter, with a size distribution below 5%, at a flo w rate of 1-15 mL/min, is described. A modification of the device, to incor porate an electrostatic potential between the alginate droplets and an inte rnal 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 Pha ffia rhodozyma, it is possible to generate 700 mu m 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 mu m beads. The alginate be ads have been characterized with respect to mechanical resistance and size distribution immediately after production and as a function of storage cond itions. The beads remain stable in the presence of acetic acid, hydrochlori c acid, water, basic water, and sodium ions. The latter stability applies w hen the ratio of sodium: calcium ions is less than 1/5. Complexing agents s uch as sodium citrate result in the rapid solubilization of the beads due t o calcium removal. The presence of cells does not affect the mechanical res istance of the beads. Finally, the mechanical resistance of alginate beads can be doubled by treatment with 5-10 kDa chitosan, resulting in reduced le aching of cells. (C) 2000 John Wiley & Sons, Inc.