Tunable transport of glucose through ionically-crosslinked alginate gels: Effect of alginate and calcium concentration

Alginate beads have numerous biomedical applications, ranging from cell encapsulation to drug release. The present study focuses on the controlled release of glucose from calcium-alginate beads. The effects of alginate concentrations (1-6 wt %) and calcium chloride concentrations (0.1-1.0M) on glucose release from beads were examined. It was found that the time required for complete glucose release from beads could be tuned from 15 min to over 2 h, simply by varying alginate and calcium chloride concentrations in beads. For calcium-alginate beads with sodium alginate concentrations of 1-4 wt %, higher sodium alginate concentrations lead to more prolonged release of glucose and thus a smaller value of a rate constant k, a parameter shown to be proportional to the diffusion coefficient of glucose in the alginate gel. For beads with sodium alginate concen-trations of 4-6 wt %, there was no statistically significant difference in k values, indicating a lower limit for glucose release from calcium-alginate beads. Similarly, higher calcium chloride concentrations appear to extend glucose release, however, no conclusive trend can be drawn from the data. In a 50 : 50 mixture of calcium-alginate beads of two different alginate concentrations (1 and 4 wt %), glucose release showed a two-step profile over the time range of 20-50 min, indicating that the pattern and time of glucose release from beads can be tuned by making combinations of beads with varying alginate and/or calcium chloride concentrations.