Production of free standing composite membranes or of patterned films after sol–gel reactions in an exponential layer-by-layer architecture

This paper aims at describing that polyelectrolyte multilayer (PEM) films, made of biocompatible molecules, Hyaluronic acid (HA) and Poly(6-lysine) (PLL), can entrap negatively charged precursors of titania or silica. These precursors undergo hydrolysis and polycondensation in contact with the amino groups of PLL leading to the formation of oxides (TiO2 or SiO2) within the films. Moreover, this work shows that these composite thin films, a few μm thick, can be easily detached as free standing membranes containing photoactive TiO2. To this aim the PEM film containing TiO2 was thermally cross-linked to form amide bonds. Immersion of the film in diluted hydrofluoric acid (2% (v/v)) allowed then the formation of a free standing membrane. We extend the concept of sol–gel reaction in PEM films to films made from poly(L-glutamic acid) (PGA) and Poly(allylamine) (PAH) and show that the composition of the multilayer film influences the distribution of the inorganic material in the films: the TiO2 distribution seems homogeneous in (PLL–HA)n films whereas the (PAH–PGA)n films are self patterned with inorganic aggregates tens of micrometers in diameter. The free standing membranes or self patterned composite films obtained in this investigation may present interesting bio-applications.