Synthesis and applications of silanated poly(ethylene glycol)s

For the application of a sol-gel transition property of silane to surface PEG grafting and crosslinking of PEG, PEG with different molecular weights and Pluronic® F-127 (a PEO-PPO-PEO triblock copolymer) were silylated by synthetic routes. The first type of silanated PEG was prepared by direct coupling of m-PEG with 3-isocyanatopropyltriethoxysilane through a urethane bond (silanated PEG I). The second type of silanated PEG (silanated PEG II) contained a long hydrophobic domain between PEG and silane domains. m-PEG was reacted with 1,6-diisocyanatohexane and 10-undecen-1-ol in sequence before silylation with 3-mercaptopropyl trimethoxysflane. Silanated PEGs I and II were grafted onto glass, a model surface used in this study. The PEG-grafted glass surfaces were characterized by contact angle, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). More PEG molecules were grafted onto the surface as the bulk concentration used for grafting was increased. PEG grafting by two different methods, the grafting in 95% ethanol and in anhydrous toluene resulted in different surface topographies as examined by AFM. Glass surfaces modified with silanated PEGs reduced fibrinogen adsorption as compared with the control surface. The surface fibrinogen concentration on PEG-modified surfaces was mainly dependent on the type of silanated PEGs, PEG molecular weight. Silanated PEGs provided a simple method for PEG grafting to the surface containing hydroxyl groups. Crossliking of disilylated PEG by sol-gel transition of end silanes resulted in PEG gels. The PEG gel could be shaped in microspheres as well. Silylated Pluronic® F-127 was crosslinked by the sol-gel process and formed thermoreversible gels. The crosslinked Pluronic® F-127 gels released fluorescein, a model drug used in this study, responding to temperature changes. After swelling at low temperature (5°C), the Pluronic ®F-127 gel release fluorescein fast when it was transferred into the medium of 45°C temperature. Silylated PEG and PEG derivatives can be used for surface modification of biomaterials and for controlled drug delivery.