PLGA-PEG-PLGA Solutions with Thermoresponsive Features and the Observation of a Sol-Gel Transition

Hydrogels are three-dimensional polymeric networks absorbing a significant amount of water. Hydrogels can be prepared from amphiphilic copolymers of the ABA-typetriblock copolymers. A typical example [1] is poly(D,L-lactic acid-co-glycolic acid)-block-poly(ethylene glycol)-blockpoly(D,L-lactic acid-co-glycolic acid) (PLGA-PEGn-PLGA), which exhibits a reversible temperature-induced sol-gel transition at higher polymer concentrations in aqueoussolution. This type of system constitutes an important material in the development of drug delivery systems. In the presentwork, the length of the hydrophobic PLGA block was kept constant, whereas the length of the hydrophilic PEG block was altered and this variation has a pronounced impact on thephase behavior of the aqueous samples. In this study, the poly(ethylene glycol) block length waschanged from n = 1000 to n = 1500 and this alteration wasfound to significantly tune the phase behavior of the system, as well as the gelation power. A short PEG block promotesgelation, whereas a longer PEG block (n = 1500) prevents gelation over the considered temperature domain. By mixingthe two copolymers, the mixing ratio can be utilized to modulate the phase separation behavior as well as the gelation temperature. In this paper, we examine how the length of the PEG block and the composition of the two copolymers will affect the phase separation behavior and the gelation properties.