Effect of Ca²⁺, Ba²⁺, and Sr²⁺ on Alginate Microbeads

TLDR

Microcapsules of alginate cross‑linked with divalent ions are the most common system for cell immobilization. In this study, we aimed to characterize how different alginates and cross‑linking ions affect key microcapsule properties. Binding studies showed that Ca²⁺ binds to G‑ and MG‑blocks, Ba²⁺ to G‑ and M‑blocks, and Sr²⁺ only to G‑blocks, indicating ion‑dependent block interactions. Replacing Ca²⁺ with Ba²⁺ increased dimensional stability and gel strength of high‑G alginate beads, reduced bead size and IgG permeability, while Sr²⁺ produced intermediate effects; conversely, high‑M alginate beads became larger, more swollen, and more permeable when cross‑linked with Ba²⁺ or Sr²⁺.

Abstract

Microcapsules of alginate cross-linked with divalent ions are the most common system for cell immobilization. In this study, we wanted to characterize the effect of different alginates and cross-linking ions on important microcapsule properties. The dimensional stability and gel strength increased for high-G alginate gels when exchanging the traditional Ca2+ ions with Ba2+. The use of Ba2+ decreased the size of alginate beads and reduced the permeability to immunoglobulin G. Strontium gave gels with characteristics lying between calcium and barium. Interestingly, high-M alginate showed an opposite behavior in combination with barium and strontium as these beads were larger than beads of calcium−alginate and tended to swell more, also resulting in increased permeability. Binding studies revealed that different block structures in the alginate bind the ions to a different extent. More specifically, Ca2+ was found to bind to G- and MG-blocks, Ba2+ to G- and M-blocks, and Sr2+ to G-blocks solely.