Physicochemical Properties of Egg-Box-Mediated Hydrogels with Transiently Decreased pH Employing Carbonated Water

Abstract

Anionic polysaccharides, including low-methoxy (LM) pectin, are extensively used in biomaterial applications owing to their safety, biocompatibility, and feasibility in constructing supramolecular assemblies by forming egg-box structures with divalent cations. Mixing an LM pectin solution with CaCO3 spontaneously forms a hydrogel. The gelation behavior can be controlled by adding an acidic compound to change the solubility of CaCO3. CO2 is used as the acidic agent and can be easily removed after gelation, thereby reducing the acidity of the final hydrogel. However, CO2 addition has been controlled under varied thermodynamical conditions; therefore, specific CO2 effects on gelation are not necessarily visualized. To evaluate the CO2 impact on the final hydrogel, which would be extended to control hydrogel properties further, we utilized carbonated water to supply CO2 into the gelation mixture without changing its thermodynamic conditions. The addition of the carbonated water accelerated gelation and significantly increased the mechanical strength, promoting cross-linking. However, the CO2 volatilized into the atmosphere, and the final hydrogel became more alkaline than that without the carbonated water, probably because a considerable amount of the carboxy group was consumed for cross-linking. Moreover, when aerogels were prepared from the hydrogels with carbonated water, they exhibited highly ordered networks of elongated porosity in scanning electron microscopy, proposing an intrinsic structural change by CO2 in the carbonated water. We also controlled the pH and strength of the final hydrogels by changing the CO2 amounts in the carbonated water added, thereby validating the significant effect of CO2 on hydrogel properties and the feasibility of using carbonated water.

Polymeric Surfactants Bearing Divalent Carboxy Pendants for Stable Color Dispersions with High Redispersibility

“…Several reasons for changing viscosity are possible. The interaction between the molecular aggregates, 36 formation of network structures, 37 change in the polarity of the surface, 38 and change in the local environment 39 should be considered as the main causes for the changes in the viscosity.…”

Mechanical properties of poly(N‐acryloyl‐glycinamide) hydrogels dependent on initiation number of the polymerization reaction

“…Hydrogels, which are composed of polymer network structures containing large numbers of water molecules, have attracted increasing attention as biomaterials, including cell-culturing scaffolds and wound dressings. [1][2][3][4] The polymer networks are divided into two main types: those formed by the chemical crosslinking of polymers through covalent bonds [2,[5][6] and those formed by physical interactions among polymers, including electrostatic interactions, hydrophobic interactions, and hydrogen bonding. [2,[6][7][8] Generally, hydrogels based on physical interactions have the benefit of self-healing properties and stimuli-responsive sol-gel transitions, but are more fragile than those based on chemical cross-linking.…”