Biomimetic mineralization of diatom exoskeleton for sustainable pH-sensitive colored chitosan/silica hybrid self-supported films

• A bio-inspired approach mimicking the biosilicification of diatom is described to design hybrid self-supported and cohesive hybrid films. • The sustainable methodology uses chitosan biopolymer to polycondense in-situ silica via a simple sol–gel aqueous route in soft conditions. • This sol–gel route shows considerable results in designing the mechanical and optical properties of the films up to 90 wt% TEOS. • The incorporation of a sustainable pigment does not affect the films properties and shows good pH-sensitivity response under basic environment. A gentle bio-inspired approach to the biosilicification occurring in diatom frustule is proposed to develop, at room temperature and without addition of a co-solvent, self-supported hybrid organic/inorganic films with pH-sensitive properties. It was found that chitosan (CS) biopolymer, a polysaccharide possessing numerous amine groups (–NH 2 ) is capable of mimicking the action of the silaffins proteins of diatom frustule in the polycondensation process of the TetraEthoxyOrthoSilicate (TEOS) silica precursor to form a cohesive self-supported hybrid film under soft conditions in aqueous media. Thanks to its good film-forming property, hybrid chitosan/silica (CS/SiO 2 ) films have been elaborated varying the amount of TEOS to study their optical and mechanical properties. It is shown that increasing the amount of TEOS up to 90 wt% improves the transparency, strength and stability of the films due to the interpenetration of the chitosan and silicaq networks. The incorporation of sustainable pH-sensitive alizarin dye during the elaboration of the films does not affect their mechanical properties whatever the composition. Moreover, these colored hybrid materials show good pH-sensitiveness under basic environment. Therefore, thanks to their antimicrobial properties and their pH-sensitivity, such self-supported films could be designed for applications such as smart sustainable food packaging and food degradation indicator.