PEG-based amphiphilic copolymers such as PLGA-PEG-PLGA (PLGA: poly(D,L-lactide-co-glycolide) and PEG-PPO-PEG (PPO: poly(propylene oxide)) are promising candidates for biomedical applications due to the thermoresponsive sol-gel transition properties and the biocompatibility originating from the PEG block. For the maximum utilization of the highly biocompatible PEG block, the hydrophilic PEG block should be relatively longer than the hydrophobic block, in other words the PEG/hydrophobic block ratio should be higher. However, it was reported that PEG-based copolymers with high PEG/hydrophobic block ratio lack the thermoresponsive sol-gel transition properties. In fact, the aqueous solution of PLGA-PEG-PLGA with the high PEG/PLGA ratio (above 0.5) would not exhibit thermoresponsive sol-gel transitions.<br/>In this work, PLGA-PEG-PLGAs with higher PEG/PLGA ratios were synthesized and laponite clay nanoparticles were added to the PLGA-PEG-PLGA solutions to realize the thermoresponsive sol-gel transition in the temperature range between 25 and 37°C. Furthermore, considering the drug delivery system (DDS) as an application of the aqueous laponite/PLGA-PEG-PLGA nanocomposite gel, we also studied the decomposition behavior and attempted to regulate the decomposition behavior. We comprehensively studied the sol-gel transition behavior by varying the molecular weight of PLGA-PEG-PLGA, the PEG/PLGA block ratio of PLGA-PEG-PLGA, and the solute concentration. The sol-gel transition behavior was studied by the test-tube inversion method and the dynamic mechanical analysis (DMA). It was found that the PLGA-PEG-PLGA with the high PEG/PLGA ratio of ~0.8 could exhibit the sol-gel transition by adding 1.0 wt% of laponite. It was also found that the sol-gel transition temperature and the rheological behavior were effectively regulated by changing the molecular weight of PLGA-PEG-PLGA from 2.0 k to 6.0 k and the laponite concentration from 0.75 wt% to 1.5 wt%. As for the decomposition behavior, we comprehensively studied the decomposition behavior by varying D,L-lactide/glycolide (LA/GA) ratio from 1.1 to 8.8 in the PLGA block. The molecular weight of PLGA-PEG-PLGA triblock copolymers was fixed to 600-1000-600. It was found that the thermoresponsive sol-gel transition behavior was almost constant regardless of the LA/GA ratio. It was also found that the decomposition rate of the nanocomposite gels with LA/GA: 1.1 was higher than those with LA/GA: 4.0 and LA/GA: 8.8.

PEG-based nanocomposite hydrogels with controlled thermoresponsive gelation and hydrolytic degradation

2019 Spring National Meeting

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