Production of Small, Monodispersed Alginate Beads for Cell Immobilization

Abstract

Gel entrapment retains suspension cells in a bioreactor for high-density operations without the difficulties of cell separation. To achieve and sustain high cell densities in animal cell culture, beads under 1 mm in diameter are desirable to minimize diffusional limitations. The challenge is to develop a controllable, scaleable process to produce small, monodispersed beads for cell immobilization. In this work, alginate bead populations were produced in the 0.5–1 mm size range with less than 10% standard deviation by destabilizing a viscous jet with a controlled disturbance. Systematic study of the drop formation with this “vibration” method demonstrated that Weber's theory for the instability of viscous jets qualitatively applies to the alginate system and provides a predictive tool for selecting the wavelength of disturbance for controlled bead formation. Nonlinear theory also provided guidance in establishing proper operating conditions to avoid satellite drop formation which decreases bead uniformity. A viscosity range 150–500 cp was found to be optimum for bead formation and served to rapidly establish the appropriate alginate concentration for the wide variety of commercial alginates. Through an understanding of the interaction of viscosity, linear velocity, nozzle diameter, and frequency of disturbance used to destabilize the jet, the predictable formation of small, uniform alginate beads was demonstrated with this method. As an example of scaleup, a 10-nozzle manifold can process 3–50 L of alginate/h, depending on the desired bead size.