SEM–EDS study of ionically cross-linked alginate and alginic acid bead formation

Alginate is a natural polysaccharide that is widely used in industrial applications. Here, beads of alginic acid, calcium, and copper alginate were prepared by the addition of soluble sodium alginate to a solution of hydrochloric acid or the corresponding cation. The progress of gelation inside the beads was followed by the degree of opacity at different times, which corresponded well to an apparent morphology change observed in freeze-dried bead cross sections analyzed by scanning electron microscopy. Furthermore, diffusion of Cu2+ ions across the beads was followed by energy dispersive X-ray spectroscopy, which revealed colocalization of the cross-linking cation and the morphologically distinct bead regions.