Custom-made rheological setup for in situ real-time fast alginate-Ca²⁺ gelation

There is a growing interest in the in situ gelation of the alginate-Ca²⁺ system due to its remarkable applications. In this work, we record and evaluate the fast gelation kinetics of alginate-Ca²⁺ using a custom-made rheometric setup. This enables us to inject CaCl₂ into the alginate while we perform the rheological measurements. We successfully measure the in situ gelation reaction from the early stages. As the alginate concentration is increased up to 3 wt.%, we observe a systematic increase of the elastic modulus, G′. Similarly, higher concentrations and injected volumes of CaCl₂ increase the magnitude and initial growth rate of G′. At longer times, the growth rate of G′ is lower. It decreases further very slowly, indicating that the chemical reaction requires quite a considerable amount of time to be completed. Finally, from the rheometric data, we estimate the average rates of the elastic modulus during the initial and quasi-steady-state stages.