Influence of Injection Application on the Sol-Gel Phase Transition Conditions of Polysaccharide-Based Hydrogels.

Polysaccharide matrices formed via thermoinduced sol-gel phase transition are promising systems used as drug carriers and minimally invasiveness scaffolds in tissue engineering. The strong shear field generated during injection may lead to changes in the conformation of polymer molecules and, consequently, affect the gelation conditions that have not been studied so far. Chitosan (CS) and hydroxypropyl cellulose (HPC) sols were injected through injection needles (14 G-25 G) or sheared directly in the rheometer measuring system. Then the sol-gel phase transition conditions were determined at 37 °C using rheometric, turbidimetric, and rheo-optical techniques. It was found that the use of low, respecting injection, shear rates accelerate the gelation, its increase extends the gelation time; applying the highest shear rates may significantly slow down (HPC) or accelerate gelation (CS) depending on thixotropic properties. From a practical point of view, the conducted research indicates that the use of thin needles without preliminary tests may lead to an extension of the gelation time and consequently the spilling of the polymeric carrier before gelation. Finally, an interpretation of the influence of an intensive shear field on the conformation of the molecules on a molecular scale was proposed.

Influence of Glycerophosphate Salt Solubility on the Gelation Mechanism of Colloidal Chitosan Systems.

Recently, thermosensitive chitosan systems have attracted the interest of many researchers due to their growing application potential. Nevertheless, the mechanism of the sol-gel phase transition is still being discussed, and the glycerophosphate salt role is ambiguous. The aim of the work is to analyze the possibility of the exclusive use of a non-sodium glycerophosphate salt and to determine its impact on the gelation conditions determined by rheological and turbidimetric measurements as well as the stability of the systems by measuring changes in the Zeta potential value. It was found that ensuring the same proportions of glycerophosphate ions differing in cation to amino groups present in chitosan chains, leads to obtaining systems significantly different in viscoelastic properties and phase transition conditions. It was clearly shown that the systems with the calcium glycerophosphate, the insoluble form of which may constitute additional aggregation nuclei, undergo the gelation the fastest. The use of magnesium glycerophosphate salt delays the gelation due to the heat-induced dissolution of the salt. Thus, it was unequivocally demonstrated that the formulation of the gelation mechanism of thermosensitive chitosan systems based solely on the concentration of glycerophosphate without discussing its type is incorrect.

Thermoinduced aggegation of chitosan systems in perikinetic and orthokinetic regimes.

Thermoresponsive colloidal chitosan systems forming the polymer structure in situ are an example of promising solutions in tissue engineering as an injectable scaffolds or drug carriers. Their application method, and thus shearing, may affect the aggregation process in accordance with the colloidal engineering approach. The aim of the study is to compare the kinetics of chitosan aggregation in the perikinetic regime (limited by Brownian motions) with the orthokinetic process carried out under the influence of an external shear field. The research was carried out using static multiple light scattering (S-MLS) and rheometric measurement techniques coupled with small-angle light scattering (Rheo-SALS). It has been found that the introduction of an external shear field (orthokinetic regime) accelerates the aggregation of chitosan systems. Simultaneously, the rotational measurements can even lead to spontaneous gelation, most likely caused by changes in the conformation of chitosan molecules, their deformation and ordering along the shear field.

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

Low-concentrated colloidal chitosan systems undergoing a thermally induced sol-gel phase transition are willingly studied due to their potential use as minimally invasive injectable scaffolds. Nevertheless, instrumental injectability tests to determine their clinical utility are rarely performed. The aim of this work was to analyze the flow phenomenon of thermosensitive chitosan systems with the addition of disodium ß-glycerophosphate through hypodermic needles. Injectability tests were performed using a texture analyzer and hypodermic needles in the sizes 14G-25G. The rheological properties were determined by the flow curve, three-interval thixotropy test (3ITT), and Cox-Merz rule. It was found that reducing the needle diameter and increasing its length and the crosshead speed increased the injection forces. It was claimed that under the considered flow conditions, there was no need to take into account the viscoelastic properties of the medium, and the model used to predict the injection force, based solely on the shear-thinning nature of the experimental material, showed very good agreement with the experimental data in the shear rate range of 200-55,000 s-1. It was observed that the increase in the shear rate value led to macroscopic structural changes of the chitosan sol caused by the disentangling and ordering of the polysaccharide chains along the shear field.

The effects of sucrose on the sol-gel phase transition and viscoelastic properties of potato starch solutions.

In this paper, starch pastes in the form of solutions and gels were investigated to determine viscoelastic properties and sol-gel phase transition temperatures using rheological methods. The gelatinization process was carried out at a temperature of 95 °C with the use of a pressureless starch cell with a stirrer. Starch pastes obtained were used to determine rheological properties under isothermal conditions (in the temperature range of 45-25 °C) by a cone-plate measurement system. The viscoelastic behavior of the tested medium was confirmed. The range of gelation temperatures was determined and the influence of several factors was discussed, e.g. the effect of sucrose addition and cooling rate on the phenomenon of sol-gel phase transition. In addition, mechanical properties of the obtained starch gel structures were determined using a fractional rheological model.