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

Abstract

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.