Stimuli-responsive polymers or smart polymers that can react to environmental changes (e.g., temperature, pH) have recently attracted attention in bio-related and food industry applications. One class of stimuli-responsive polymers are thermo-sensitive hydrogels which exhibit thermo-reversible phase transition (sol-gel or gel-sol transformations) in response to temperature changes that makes them appealing for a wide range of multidisciplinary applications such as drug delivery systems, bio-inks, food stabilizing and gelling agents.
κ-Carrageenan is an important class of polysaccharides, and a non-toxic and biocompatible hydrogel that shows an interesting thermo-gelation behavior through a two-step gelation mechanism upon cooling the solution. On the other hand, addition of counterions into the κ-carrageenan solution, particularly potassium ions, can significantly promote gelation and shift the sol-gel transition to higher temperatures. The fact that the viscosity of κ-carrageenan can be tuned by changing temperature is advantageous for extrusion-based bioprinting.
Evaluating thermal phase transition of hydrogels is important in controlling their structure and properties for the above-mentioned applications. There are useful tools for evaluating sol-gel transition of hydrogels including differential scanning calorimetry (DSC), dynamic light scattering (DLS), and rheological measurements (crossover of G’ and G”). An alternative technique that can be used to extract information about sol-gel transition and gelling temperature is based on viscosity measurements.
In our application note, Characterizing Thermal Phase Transition of κ-Carrageenan by Monitoring Viscosity, we show how we use VROC® initium one plus to probe temperature-dependent viscosity and identify gelling temperature of κ-carrageenan during a cooling temperature sweep experiment. In addition, we demonstrate the effect of ionic strength and shear rate on the sol-gel transition of κ-carrageenan solutions.
Written by: Soheila Shabaniverki, PhD, RheoSense Applications Scientist