Ethoxysilane-capped PEO-PPO-PEO triblocks: a new family of reverse thereto-responsive polymers

New reverse thereto-responsive polymers systems combining reverse thermal gelation behavior and a gradual increase in the mechanical properties, were created by crosslinking ethoxysilane-capped poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblocks in aqueous solutions at physiological conditions. Pluronic F127 (PEO99<PPO67<PEO99) was functionalized with (3-isocyanatopropyl) triethoxysilane (IPTS) by reacting its terminal hydroxyl groups with the isocyanate. The silane-capped PEO-PPO-PEO triblock was characterized by H-1-NMR, GPC, FT-IR and DSC and the rheological behavior of its aqueous solutions were studied. The silane-containing triblock retained the reverse thereto-responsive characteristics displayed by the original Pluronic. Over time, the ethoxysilane groups hydrolysed and created silanol moieties that subsequently condensated, crosslinking the material and generating hydrogels that exhibited gradually increasing mechanical properties. It was found that the higher the pH, the faster the process and the higher the viscosity levels attained. Finally, the ability of these gels to perform as matrices for drug delivery was exemplified by releasing metronidazole and methylene blue. Findings showed that while a 30% F127 gel at 37 degreesC delivered all the drug within less than 3 days, F127di-IPTS gels completed the process at a much slower rate (up to 15 days). (C) 2003 Elsevier Ltd. All rights reserved.