Tuning Pluronic F127 phase transitions by adding physiological amounts of salts: A rheology, SAXS, and NMR investigation
Giovanni Russo, Giulia Rossella Delpiano, Cristina Carucci, Massimiliano Grosso, Claudia Dessì, Olle Söderman, Björn Lindman, Maura Monduzzi, Andrea Salis
Abstract
Specific ion (Hofmeister) effects in colloid and biological systems represented a scientific challenge for more than 100 years. Recently, possible applications, based on their rationalization, are emerging. Here, Cl-, SO42-, SCN- anions and Na+, K+, Mg2+ cations are added at physiological concentration (∼0.15 mol/kg) to Pluronic F127 20 wt% aqueous solutions to suitably tune phase transitions for a smart drug delivery platform. Rheological measurements, along with SAXS and NMR self-diffusion experiments, are used to carefully characterize the prepared F127/salt-based formulations. The critical micellar temperature (cmt), the hard-gel formation temperature (Thg), liquid crystal structures, and self-diffusion coefficients are determined. The cmt and Thg values of F127/salt formulations are lower than that of F127 20 wt% sample, following an anionic Hofmeister series: SO42- < Cl- < SCN-. All added salts significantly increase storage modulus and complex viscosity with maximum values occurring at T around 40 °C. SAXS data confirm that added salts preserve cubic liquid crystal phases. NMR self-diffusion analysis highlights that the intermolecular interactions and mobility of F127 unimers/aggregates are ion specific at 16 °C but not at 40 °C. These findings suggest that F127/salt-based formulations may constitute a versatile thermosensitive platform for drug delivery able to assure sustained release in topical or surgery administrations, in the range of temperatures 30–45 °C.