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

Abstract

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.

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

“…Similar changes were observed in the case of cellulose derivatives such as HPC [20,21], MC, and HPMC [23] as well as in the authors' earlier works on chitosan systems [32,50]. In order to quantify the phase transition conditions, the experimental data were normalized to obtain the relative transmission parameter (Figure 3b); the time in which this parameter reached 50% determines the characteristic time of the phase transition [20,21,50]. The dependence of the T50 time on the shear rate occurring in injection needles is shown in Figure 3c.…”

“…It can be seen that regardless of the needle used during the injection preceding the actual sol-gel phase transition, the experimental curves assume the shape typical of progressive aggregation accompanied by an increase in opacity limiting light transmission. Similar changes were observed in the case of cellulose derivatives such as HPC [20,21], MC, and HPMC [23] as well as in the authors' earlier works on chitosan systems [32,50]. In order to quantify the phase transition conditions, the experimental data were normalized to obtain the relative transmission parameter (Figure 3b); the time in which this parameter reached 50% determines the characteristic time of the phase transition [20,21,50].…”

“…Despite the satisfactory mapping of the experimental data and consequently shape of the approximating function, when using the It should be noted that due to the use of classic literature methods for determining the gelation time, it is not possible to directly compare the obtained results for different aggregation regimes. This is due to the fact that both methods used define points located in other areas of the generalized dynamics curve of characteristic quantity changes during the sol-gel phase transition [50].…”

“…This means that completely different states of the structure would be compared, and the time T 50 itself, by definition, will be longer. Owczarz et al [50] suggested the possibility of replacing the relative transmission value by the total destabilization index TSI, the shape of which takes the form of the letter S, characteristic of dynamic changes of selected rheological or optical values during the gelation process. The influence of the injection needle used on the kinetics of changes of the TSI parameter versus time is presented in Figure 5.…”

“…In order to take into account the kinetics of changes in the fast gelation region as well as to avoid onepoint analysis, it was decided to further develop the above methods. For this purpose, the fast gelation region was described by an exponential function which in most theoretical models describes the area of rapid changes during progressive aggregation [50,52]. Contrary to the literature, the initial changes were described by a linear function, not by In previous studies, for the quantitative analysis of the sol-gel phase transition condition using TSI curve, the authors proposed a method of determining the characteristic time in analogy to the one presented by Rwei [20] and Gosecki [21] in which the relative TSI reaches 50% [50], or a graphical method based on the intersection point of two lines passing through the induction area and the fast gelation region [32].…”