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 29Si and 13C 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.