The influence of solution viscosities and surface tension on calcium-alginate microbead formation using dripping technique

Abstract

Currently, there is a growing interest for encapsulation of bioactive ingredients using calcium alginate microspheres or beads. Diffusion of the Ca in the alginate droplets provokes an ionic gelation and their conversion to hydrogel beads. The main objective of this study is to investigate the influence of physical properties of alginate and CaCl2 solutions on alginate droplet formation and penetration into gelling bath, in size and shape of Ca-alginate beads. The droplet formation and penetration in the calcium bath was investigated using a high-speed video recording. Viscosity of alginate solution was modified by changing the alginate concentration (from 10 to 30 g/L) and the viscosity of the bath was modified by using different water/glycerol mixes (0–90% of glycerol) to prepare the CaCl2 solution. Surface tension of CaCl2 solution is reduced by adding different concentrations of surfactants (Tween 20) in a range of 0.01–1 g/L. Droplets detach from the tip with a tear shape. In all conditions tested, the droplets reach a spherical shape in less than 15 ms after detachment and less than 25 mm from the tip. Spherical beads are obtained when the kinetic energy is high enough to break the surface resistance of the calcium bath and droplet viscosity high enough to avoid deformations. Penetration depth of alginate droplets were mainly affected by viscosity and surface tension of CaCl2 solution. When viscosity and surface tension of CaCl2 solution increases, sphericity decrease and shape deformations are observed. The surfactant addition enhanced penetration and prevented shape deformations of Ca-alginate beads.