Rheo-Kinetic Study of Sol-Gel Phase Transition of Chitosan Colloidal Systems

Abstract

Chitosan colloidal systems, created by dispersing in aqueous solutions of hydrochloric acid, with and without the addition of disodium β-glycerophosphate (β-NaGP), were prepared for the investigation of forming mechanisms of chitosan hydrogels. Three types of chitosan were used in varying molecular weights. The impacts of the charge and shape of the macromolecules on the phase transition process were assessed. The chitosan system without the addition of β-NaGP was characterized by stiff and entangled molecules, in contrast to the chitosan system with the addition of β-NaGP, wherein the molecules adopt a more flexible and disentangled form. Differences in molecules shapes were confirmed using the Zeta potential and thixotropy experiments. The chitosan system without β-NaGP revealed a rapid nature of phase transition—consistent with diffusion-limited aggregation (DLA). The chitosan system with β-NaGP revealed a two-step nature of phase transition, wherein the first step was consistent with reaction-limited aggregation (RLA), while the second step complied with diffusion-limited aggregation (DLA).

Injectable Chitosan Scaffolds with Calcium β-Glycerophosphate as the Only Neutralizing Agent

“…The macromolecules are beginning to attract each other and aggregation occurs. The influence of the addition of glycerophosphate on the stability of chitosan (chloride) solutions was confirmed in the study by Owczarz and coworkers [32]. The analysis of Zeta potential curves for samples with the addition of glycerophosphate salts shows that at temperatures below 30 °C, the value decreases with increasing temperature, from 12.8 to 6.9 and from 13.6 to 6.69 mV for sodium and calcium glycerophosphate, respectively.…”

“…The macromolecules are beginning to attract each other and aggregation occurs. The influence of the addition of glycerophosphate on the stability of chitosan (chloride) solutions was confirmed in the study by Owczarz and coworkers [32].…”

“…Chitosan is a cationic polysaccharide that is hydrophobic at neutral pH of the medium, it dissolves only in an acidic environment. Chitosan hydrogel qualify as a physical gel [30] obtained by diffusion limited aggregation (DLA) [31,32]. In this case, the non-covalent interactions (van der Waals and hydrogen bonds) between the polymer chains as a result of the conversion of the polymer from hydrophilic to hydrophobic form, associated with a change in the degree of dissociation of the amino groups, are decisive.…”

“…The phase transition point of such systems is at a temperature above 50 • C. Thus, it prevents their use as injection scaffolds formed in vivo. The addition of disodium glycerophosphate (Na 2 GP) to the chitosan solution in acid results in the formation of an unstable colloidal system (low value of Zeta potential) and a reduction in the temperature of the sol-gel phase transition point [19,[32][33][34]. The chitosan colloidal solutions obtained by dissolving the polymer in hydrochloric acid are commonly described in the literature, however, the role of glycerophosphate is discussed [19][20][21][22]33,35].…”

“…The chitosan colloidal solutions obtained by dissolving the polymer in hydrochloric acid are commonly described in the literature, however, the role of glycerophosphate is discussed [19][20][21][22]33,35]. The process of chitosan aggregation from solutions with glycerophosphate occurs at much lower temperatures and its kinetics depend on the current state of protonation of amino groups-the reaction-limited aggregation (RLA) [20,31,32,35]. Based on the solution of the Poisson-Boltzmann equation for chitosan (polyion) solutions containing disodium glycerophosphate (counterion), Filion and Lavertu [20,35] showed that a sufficient condition for the thermal neutralization of polyion is that dpK 0 /dT < dpK a /dT, where pK 0 is the intrinsic dissociation constant of chitosan and pK a is the dissociation constant of the buffer coupled to chitosan, i.e., counterion.…”