Effect of electrolytes on the sol-gel phase transitions in a Pluronic F127/ carboxymethyl cellulose aqueous system: Phase map, rheology and NMR self-diffusion

This investigation aims to obtain a thermosensitive platform useful for specific nanomedicine applications through the addition of suitable salts. An aqueous mixture consisting of the copolymer Pluronic F127 and sodium carboxymethyl-cellulose, in a ratio of 20/4 by weight, in the presence of different concentrations of Na2SO4, NaCl, and NaSCN, was investigated using the visual inversion tube approach to estimate a phase map, and then characterized through rheological measurements. The formation of a cubic liquid crystalline phase at temper-atures higher than 37 degrees C was suggested in all systems. The complex viscosity, decreases in the presence of salts in the order Na2SO4 > NaCl > NaSCN with more marked effect for lower concentrations. Salt addition allows to tune the crowding effect of NaCMC. For the polymer mixture and for a sample containing NaCl, 1H NMR self -diffusion experiments display a non-mono-exponential decay of the echo signals of Pluronic F127, caused by the polydispersity of commercial Pluronic F127. The rheological properties along with the diffusion behaviour of the liquid crystal micelles suggest that a sample containing NaCl 0.07 mol/kg, with a sol-hard gel transition temperature around 35 degrees C, close to that of the body, may be a suitable and biocompatible thermosensitive platform to administer both hydrophobic and hydrophilic drugs such as antibiotics, anticancer drugs or growing factors.