Construction of free-standing films using graphene for biomedical applications

Abstract

The LbL Electrostatic Self Assembly could be used to produce nano or micrometric thickness multilayer films with several different functionalities and applications. It is based on the alternative dipping of a substrate in positively and negatively charged aqueous solutions giving rise, as could be concluded from the name of the technique, to the self assembly of the charged polymers present in the solutions. Among all the possible applications of this building technique, this research work is focused on the production of a Free Standing Film that could be peeled off from the substrate. Previous research works have revealed the possibility of building a Free Standing Film with asymmetric hydro-response (hydrophilic and hydrophobic surfaces in the same film) that gives rise to a humido-responsive behaviour as the film could wrap around the hydrophobic or the hydrophilic side depending on the environmental humidity. This asymmetric behaviour could make these Free Standing Films very interesting for applications as sensor or detectors. However, its low mechanical strength and high brittleness limit the future uses of this kind of films. In the present work, a higher strength Free Standing Film is tried to develop while maintaining its asymmetric behaviour. Graphene is a novel nanomaterial with outstanding chemical, electrical and mechanical properties that could be used for improving the mechanical strength of these films. Even though it presents outstanding properties, its hydrophobicity makes difficult the incorporation of graphene to the Electrostatic Self Assembly films, reason for which it must be somehow modified. In this research work Free Standing Multilayer Films are satisfactorily built using graphene while maintaining their asymmetric hydro-behaviour that give rise to humido-responsive wrapping as a response to the environmental humidity.