Diffusion characteristics of different molecular weight solutes in Ca–alginate gel beads

•Quasi-simultaneous and sequential gelation-and-release situations were conducted.•Alginate does not affect the diffusion into the beads of solutes with MW < 20,000.•CaCl2 does not affect the diffusion into the beads of solutes with MW < 20,000.•Alginate decreases diffusion coefficient of solute during release.•CaCl2 increases diffusion coefficient of solute during release.

Diffusion characteristics of cyanocobalamin (Vitamin B12) (VB12) and polyethylene glycol (PEG) in Calcium-alginate (Ca-alginate) hydrogel beads were critically investigated. Quasi-simultaneous and sequential gelation-and-release situations were conducted to determine the sorption and release kinetics of solutes with different molecular weights. In the first case, results were typical of a convection mechanism: high effective PEG diffusion coefficients and no effect of the PEG molecular weight on the overall transfer were observed. An increase in the sodium alginate concentration slightly decreased the diffusion coefficient of VB12, whereas, it had no effect on the PEG diffusion. On the other hand, the lower the calcium chloride concentration is, the higher the release of VB12. The opposite is true for PEG. In the second case, the sorption and release kinetics of VB12 or PEG was monitored after alginate gelation was completed. The diffusion coefficient was found to be strongly affected by the PEG molecular weight. For solute diffusion from the beads: when the alginate concentration increased, diffusivity found a significant decrease; calcium chloride concentration had a negligible effect on diffusivity. For solute diffusion into the beads: neither the alginate concentration nor the calcium chloride concentration had any effect on the diffusion of solutes with MW < 20,000.

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