The role of the CaCl2–guluronic acid interaction on alginate encapsulated βTC3 cells

Previously we demonstrated that alginate composition has a significant effect on the growth of encapsulated betaTC3 cells and consequently on the overall metabolic and secretory activities of the encapsulated cultures. Based on these results we postulated that the mechanical properties of alginate were not responsible for the observed effects but rather, changes in the strength of the alginate gel network caused by changes in the number of alginate strands held together in the "egg-box" model are responsible for the observed effects. In this study we address this hypothesis with a series of experiments in which the strength of this interaction is manipulated by varying the calcium concentration either at the time of gelation or during culture maintenance. Our data show that increasing the concentration of the CaCl2 solution used at the time of gelation, thus increasing the strength of the alginate gel network, impedes the growth characteristics of betaTC3 cells encapsulated in a high guluronic acid content alginate. This effect is amplified by maintaining a constant supply of calcium ions during culture thus sustaining the interaction between guluronic acid residues and calcium ions. However, preparations of betaTC3 cells encapsulated in an alginate with high mannuronic acid content are not affected by changes in CaCl2 concentration due to the low percentage of consecutive guluronic acid residues. Therefore, the present data show that the strength of the alginate gel network is an important factor that influences the growth characteristics of encapsulated cell preparations.