Thermo-responsive peptide-based triblock copolymer hydrogels

A series of novel thermo-responsive peptide-based triblock copolymers, poly(L-glutamic acid)-b-poly(N-isopropylacrylamide)-b-poly(L-glutamic acid) (PLGA-b-PNIPAM-b-PLGA), were successfully synthesized via ring opening polymerization (ROP) of the gamma-benzyl L-glutamate derivative (BLG-NCA) using a diaminoterminated PNIPAM as a macroinitiator, followed by de-protection of the benzyl groups. These triblock copolymers form physically crosslinked networks after complexation with a diamino-terminated poly(ethylene oxide) (PEO) in an organic solvent through acid-base proton transfer and successive ionic-bonding confirmed by Fourier transform infrared (FTIR) spectroscopy. The secondary structure of the peptide block, before and after complexation, was confirmed by circular dichroism (CD) experiments, showing an alpha-helix conformation of the PLGA segments. Swelling experiments on the ionic-bonded networks showed that the water uptake process strongly depends on the temperature and relative humidity conditions. Thus, higher humidity and temperatures below the lower critical solubility temperature (LCST) of the PNIPAM block increase the amount of water absorbed into the network. These swollen ionic complexes contract and reject water when these thermo-responsive peptide-based hydrogels are heated up above their LCST, making them promising for biomedical applications and drug delivery systems.