Novel structural changes during temperature-induced selfassembling and gelation of PLGA-PEG-PLGA triblock copolymer in aqueous solutions

The thermoresponsive amphiphilic block copolymer poly(D,L-lactic acid-co-glycolic acid)-blockpoly( ethylene glycol)-block-poly(D,L-lactic acid-co-glycolic acid) (PLGA-PEGn-PLGA), which exhibits a reversible temperature-induced sol-gel transition at higher polymer concentrations in aqueous solution has attached a great deal of interest because of its potential in biomedical applications. In the present work, the length of the hydrophobic PLGA blocks was kept constant, whereas the length of the hydrophilic PEG block was altered and this variation has a pronounced impact on the phase behavior of the aqueous samples and the structure of the polymer. A short PEG block promotes gelation at a low temperature, whereas a longer PEG block shifts the gelation point to higher temperature. By using a combination of turbidity, rheology, and small angle neutron scattering (SANS) methods, we have revealed dramatic temperature effects. In a broad temperature interval, the transition from spherical core-shell micelles to cylindrical structure and packing of cylinders is observed