Nuovi materiali compositi basati su grafene

The number of possibilities and, hence, examples of composite materials, is huge and varied and depend on the nature of the matrix. However, the evolution of polymers since the beginning of the 19th Century has led to a boost in research on that field, in which the latest advances have provided numerous advantages in nanomedicine, for instance. As a matter of fact, in recent years composites have been made from materials in which the size of at least one of the phases is in the nanometer scale, also called nanomaterials. Among all of them, graphene has unique properties owing to its sp2 hybridised carbon atoms arranged in a 2D honeycomb lattice. Therefore, the incorporation of graphene into polymeric materials offers new options regarding the use of these eventual composites in a wider range of fields (from sensors to biological applications). In this context, the aim of this thesis is the design of new graphene-based composites to be used in several applications regarding the design and the specific features of the final prepared materials. Chapter 1 provides a revision of composite materials, primarily describing important concepts for the understanding of this thesis such as hydrogels, interpenetrating polymer networks (IPNs), and, undoubtedly, graphene; and digging down to more specific literature examples mainly based on this fascinating nanomaterial. In Chapter 2, new composite hydrogels with an autonomous self-healing capacity are described. Semi-IPNs of poly (methacrylic acid) (pMAAc) and poly (vinyl alcohol) are primarily studied. The materials are firstly synthesised and characterised in the presence or absence of graphene, and their healing abilities are subsequently analysed. They show not only an electromechanical behaviour, but also an almost complete auto-reparation after being damaged. Interestingly, graphene does not limit any of the studied properties. The second type of materials were prepared from the MAAc in combination with [2-(acryloyloxy)ethyl]trimethylammonium chloride. The repairing capacity is studied depending on the way in which the material is prepared, and also depending on the presence or not of graphene. In this case, the self-healing is based on ionic interactions. All the materials have demonstrated good repairing ability, even with graphene. Chapter 3 details the synthesis, characterization and different applications of graphene-based composite hydrogels using acrylamide as the main monomer. The composites show excellent mechanical properties, and they are even proved successfully as 3D scaffolds for cell culture, being possible nucleus pulposus replacements for intervertebral disc diseases. De de-swelling behaviour under an external stimulus is also demonstrated, making these composites applicable as probable on-demand drug delivery systems. Finally, a piezoresistive effect is detailed in this chapter due to the presence of graphene into the hydrogel network, obtaining excellent gauge factor values because of the change in the resistivity of the material depending on whether it is being stretched or not. That fact pares the way for the use of our systems as strain sensors. Finally, in Chapter 4, the creation of novel nanostructured systems for neural network regeneration are presented. Firstly, the graphene addition on 2D substrates previously coated with single-wall carbon nanotubes does not show a notable enhancement in the neuron activity, obtaining, for instance, similar values for membrane capacitance with respect to the substrate only coated with the carbon nanotubes. In a second approach, neuron activity is studied in a graphene-based 3D scaffold. The most important fact observed in this study is that neurons are only visualised in the graphene-based hydrogel, but not in the one without nanomaterial, confirming that graphene is taking an important role in the neuronal network.