In situ evaluation of alginate-Ca²⁺ gelation kinetics

A thorough assessment of gelation progress requires real-time recording of biopolymer kinetics. In this study, an in situ investigation with a customized parallel-plate rheometric setup examines how the initial distribution of CaCl₂ to alginate through micro-holes affects the process. At constant volume and concentration of reactants, stiffer gels are produced at the same probing time by increasing the number of suppliers (2–12). Due to the oscillation and the different local distribution of the cations into the biopolymer solution, the development of gel front is affected, which is for the first time in situ rheologically investigated by the temporal evaluation of complex modulus, G*. The alternative configurations of the same number of micro-holes have drastically contribution to this regard, too. Moreover, a two-kernel equation is introduced predicting the alginate-Ca²⁺ gelation kinetics. It represents the initial fast increase in G*, determined by the concentration of cross-linker, and the slow diffusion of cations to the assembled gelling structures depicted on the successive evolution of G* in longer times. Finally, a continuous and an intermittent oscillatory time sweep influence the diffusion of the cross-linking solution resulting in considerably different gelation curves for the same concentration of reactants.