SALTS EFFECTS ON RHEOLOGICAL AND HYDRODYNAMIC DIAMETER OF POLYMER-BASED HYDROGELS

Poloxamer (PL) is a synthetic nonionic polymer formed by y blocks of hydrophobic poly(propylene oxide) flanked by x blocks of hydrophilic poly(ethylene oxide). Such molecules tend to organize in micelles and as temperature is increased these micelles are self-assembled in nanostructured thermosensitive gels with ability to retain bioactive molecules and to control their release. It has been demonstrated that the addition of salts can affect their structural organization by augmenting dehydration of the system or by promoting increased intermolecular interactions. Herein, it was studied the behavior of gels composed of PL 407 15%, 20%, 25%, and 30% (w/w), and binary gels containing PL 407/PL 338 15%/15%, 20%/10%, and 25%/5% (w/w) blended with NaCl and KCl (0.05 M, 0.10 M, 0.20 M, 0.30 M, and 0.40 M). The rheological behavior was analyzed as function of temperature, frequency, and shear rate to obtain information about sol-gel transition temperature (Tsol-gel), mechanical stability, consistency and spreadability. The hydrodynamical diameters were analyzed by Dynamical Light Scattering (DLS) at 25 °C and 37 °C to study the salt role on micellar organization. Unique systems tend to be more sensitive to increasing salt concentrations until 0.3 M: as concentration increases the Tsol-gel decreases, and ratio G^'/G'' enhances, pointing that the presence of salts promotes higher structural organization in these formulations. The addition of KCl in poloxamer formulations promotes increased ratio G^'/G'' (~ 20%) and decreased Tsol-gel when compared to formulations with NaCl in same concentrations. Binary formulations tend to exhibit lower Tsol-gel and higher G^'/G'' than isolated ones in the presence of both salts. It is not observed significant modifications in hydrodynamic diameters when NaCl or KCl was added (~ 26 nm in isolated systems, and ~ 29 nm in binary formulations). In conclusion, the presence of NaCl or KCl possibly affect the interactions between supramolecular structures more than micellar dimensions. In addition, the incorporation of KCl promoted pronounced structuring effects, which indicates that cation valence and hydrated radius can alter mechanical properties of hydrogels.
This work was supported by Conselho Nac. Des. Cient. Tecnológico (CNPq 308819/2022-5), FAPESP (2019/20303-4), CAPES (financial code 001).