Novel poly(ethylene glycol) hydrogels from silylated PEGs

Poly(ethylene glycol) (PEG) and Pluronic(R) F-127 (PF127) were silylated with 3-isocyanatopropyltriethoxysilane to synthesize PEG-based hydrogels by sol-gel transition of silane. Silanes on different PEG molecules formed covalent bonds by acid-catalyzed hydrolysis and condensation. Addition of monosilylated PEG resulted in the incorporation of dangling PEG chains, which increased the swelling ratio of the hydrogels slightly. PEG hydrogels in microspheres were prepared by emulsifying aqueous silylated PEG solution in oil followed by curing. Crosslinked PF127 hydrogels displayed inverse thermosensitivity. The previously swollen PF127 hydrogels shrank immediately at high temperatures (e.g., 60 degrees C), but the welling of shrunken hydrogels at low temperature (e.g., 5 degrees C) took much longer. The release of fluorescein from the PF127 hydrogels was dependent on the temperature of the environment. The release of fluorescein from the PF127 hydrogels was faster at 45 degrees C than at 5 degrees C. This was most likely due to shrinking of the hydrogels leading to squeezing of the incorporated fluorescein. The ability of hydrogel formation by simple sol-gel transition of silylated PEG can be used to prepare new drug delivery systems and biomaterials.