Functional nanostructured chitosan-siloxane hybrids

New organic-inorganic hybrids were prepared by a sol-gel method from the biopolymer chitosan and a silane coupling agent, 3-isocyanatopropyltriethoxysilane (ICPTES), in which covalent bridges, essentially composed of urea, bond the chitosan to the poly( siloxane) network. The structural characterization of the advanced chitosan-siloxane hybrids was performed by Fourier transform infrared spectroscopy, X-ray diffraction and Si-29 and C-13 nuclear magnetic resonance. The presence of siloxane nanodomains was detected by small angle X-ray diffraction. The chitosan-siloxane hybrids are bifunctional materials with interesting photoluminescent features and bioactive behaviour. The photoluminescence spectra display an additional high-energy band with longer lifetime, relatively to the characteristic emission of pure chitosan. This band is associated with electron-hole recombinations arising from silicon-related defects at the surface of the siliceous nanodomains. The bioactive behaviour of these materials was also evaluated; the apatite formation was shown to depend on the amount and arrangement of silanol groups.