Sodium alginate (SA) hydrogels have a wide range of applications including tissue engineering, drug delivery and formulations for preventing gastric reflux. The dynamics of sodium ions during the gelation process of SA solution is critical for clarification of the gelation mechanism. In this work, nuclear magnetic resonance (NMR) relaxometry and pulsed-field-gradient (PFG) NMR diffusometry were used to investigate the dynamics of the sodium ions during the gelation of SA alginate. We find that sodium ions are in two different states with the addition of divalent calcium ions, corresponding to the bound-state and free-state. The sodium ions in free-state are those released from the alginate chains via the replacement of calcium ions during the crosslinking. The relative content of sodium ions in bond state decreased with the increase in the content of calcium ions in the system. The relaxation time <i>T</i><sub>2</sub> of sodium ions in bond- and free-states shifts to shorter and longer relaxation time with the increase in concentration of calcium ion, which indicates the closer package of SA chains and the larger space for the diffusion of free sodium ions. This work clarifies the gelation mechanism of SA at molecular level.

New insight into the gelation of Na-alginate aqueous solution

253rd National Meeting (2017)

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