The Application of Small-Angle Light Scattering for Rheo-Optical Characterization of Chitosan Colloidal Solutions

Abstract

Abstract:In the recent studies on chitosan hydrogels, it was found that understanding both rheological and structural properties plays an important role in their application. Therefore, a combination of two independent techniques was applied to investigate micro-and macroscopic properties of chitosan colloidal system. Studies on viscous properties, as well as the sol-gel phase transition process, were performed using rheological methods coupled with the small angle light scattering (SALS) technique. Based on the anisotropy of scattering patterns obtained during rotational shear tests, it was found that the chitosan solution reveals two different behaviors delimited by the critical value of the shear rate. Below a critical value, chitosan clusters are deformed without breaking up aggregates, whereas after exceeding a critical value, chitosan clusters apart from deformation also breakup into smaller aggregates. The values of the radius of gyration determined by applying the Debye function allow one to state that with an increase of chitosan concentration, molecule size decreases. An analysis of the light scattering data from the temperature ramp test showed that with an increase of temperature, the level of polymer coil swelling increases. Simultaneously, the supply of thermal energy leads to a neutralization of the charge of chitosan chains. As a consequence, the formation of intermolecular links occurs and a gel structure is formed.

Injectability of Thermosensitive, Low-Concentrated Chitosan Colloids as Flow Phenomenon through the Capillary under High Shear Rate Conditions

“…This resulted from the well-known phenomenon in the polymer rheology of the disentanglement of polymer chains and their ordering along the shear field. This phenomenon was also observed for thermosensitive chitosan colloids and described in the previous research of the authors using rheometric measurements combined with small-angle light scattering technique [ 46 ]. This remark is very important since the considered systems must form a polymer network after injection application; changes in their conformation during the flow through the needle may affect both the phase transition conditions and the final mechanical properties of the obtained scaffolds.…”

“…Xu et al [ 45 ] showed that, with increasing shear rate, the end-to-end distance of the polymer chain increases, indicating its disentanglement. This phenomenon was also observed during rheometric measurements with simultaneous analysis using the small-angle light scattering technique [ 46 , 47 , 48 ].…”

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

“…For this reason, the method proposed by Fredrickson and Larson [61] was used. This theory is based on the order-disorder of block copolymers considering the aggregation of hydrophobic acetylated blocks of chitosan chains in systems with glycerophosphate [34,62], and it can be successfully applied even in the case of systems with dominance of elastic properties over viscous ones. As a consequence, the dependence of temperature as a function of the glycerophosphate concentration with the addition of calcium carbonate was determined.…”

“…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 use of only calcium β-glycerophosphate for the preparation of chitosan hydrogels follows from the fact that this compound potentially combines the benefits of the buffering properties of glycerophosphate as well as the replacement of sodium ions unfavorable to organisms, in particular for bone tissues, with calcium ions. The addition of glycerophosphate salt (change in pH of the solution) allows to reduce the sol-gel phase transition temperature [30,34,35], which is extremely important when designing scaffolds formed in vivo.…”