Comparative Large Amplitude Oscillatory Shear (LAOS) Study of Ionically and Physically Crosslinked Hydrogels

Hydrogels are highly versatile and widely applicable materials within various scientific, technological, and food sectors. Alginate and gelatin hydrogels, along with their crafted variations, are possibly the most common ones. However, the ionic crosslinking of alginate-Ca++ is a different gelation mechanism than the physical crosslinking of gelatin. In this work, we prepare alginate-Ca++ hydrogels using individual layer gelation and experimentally evaluate LAOS rheological behavior. We apply shear-stress decomposition using the MITlaos software and obtain the elastic and viscous contributions within the nonlinear response of the individual alginate-Ca++ layer. We compare these results with the nonlinear responses of the gelatin-alginate ex situ individual layer. The strain-sweep patterns are similar, with loss modulus overshoot. The applied shear can destroy the larger-scale structural units (agglomerate/aggregates), resulting in analogous patterns. However, the critical strain points are different. Based on the shear-thickening ratio T of the LAOS analysis, it can be assumed that the common feature of ex situ preparation, i.e., gelation as individual layers, provides a matching bulk microstructure, as the hydrogels differ significantly at a molecular-binding level.

Automated summary

Hydrogels are versatile and widely used materials in various fields. Alginate and gelatin hydrogels are among the most common ones. The gelation mechanisms of alginate-Ca++ and gelatin are different. In this study, we prepared alginate-Ca++ hydrogels using individual layer gelation and analyzed their rheological behavior. We compared the results with gelatin-alginate hydrogels prepared ex situ. The strain-sweep patterns were similar, but the critical strain points were different, indicating differences in the microstructure at a molecular level.