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In this work, we present two novel nanostructured hybrid materials based on a chitin matrix loaded with increasing amounts of graphene oxide and reduced graphene oxide nanosheets (nGO and rGO respectively). Both kind materials (Chi:nGO and Chi:rGO) were studied using different spectroscopic and rheological techniques with the aim of understanding the interaction mechanism between chitin and nGO/rGO and explaining how the type of filler and its proportion affects its reinforcement. The production of these hybrids represents not only the obtention of low-cost materials with mechanical resistance but also a good opportunity for developing materials with several applications according to their composition. The nGO and rGO were characterised through FT-IR and ESR for the determination of oxidation degree of each nanofiller. Then, the hybrids were spectroscopically analysed with FT-IR, ESR and SAXS which demonstrated that the components do not interact through covalent bondings and the nanosheets are well-dispersed among the chitin matrix. Finally, a rheological behavior assay results was performed and its results were analysed in terms of G' and η*. In short, all the results allowed us to conclude that nGO acts as a more efficient reinforcer than rGO due to the higher amount of hydrogen bondings established with chitin.

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The oxidation of keratin hydrogels was optimized aiming to obtain keratose hydrogels while maintaining the original 3D structure and pH-responsive behaviour. In addition, we present a comparative study of their dual-stimuli responsive behaviour regarding the pHresponsiveness and their previously non-described ion selective responsiveness. Keratose and keratin hydrogels showed similar swellings when contracted at low pH, and the former showed steeper expansion and higher swelling than the latter at high pH. In addition, both hydrogels showed selective responsiveness toward Ca 2+ ions when expanded, and toward Cu 2+ ions when contracted. IR, Raman, ss-NMR, HRMAS NMR, SAXS, and thermal characterization demonstrated that oxidation does not interfere with the stimuli-responsive mechanisms related to protein conformation. The higher swelling of keratose hydrogels would be originated in the increase of the mobility of the chains after oxidation coupled to the hydration of sulfonic acid groups.

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