This PhD thesis, entitled "Smart microdevices for nutraceutical-delivery", is focused on the design and evaluation of organic-inorganic hybrid systems for the protection and controlled release of bioactive molecules. These systems are based on (i) silica materials, mainly mesoporous particles, as inorganic support to store and protect the bioactive cargo; and (ii) in an outer layer of biomolecules that regulate the payload release triggered by certain stimuli. The first chapter of the thesis

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... ls with the use of oleic acid as a molecular gate capable of regulating the confinement and release of the encapsulated compounds under the presence of a specific stimulus (surfactants like bile salts). This chapter is subdivided into three different articles, in which different objectives are pursued for the same molecular gate. In the first article, a new molecular gate based on oleic acid has been developed, and its ability to entrap cargo molecules inside the pore voids and release them exclusively in the small intestine has been validated. The system consists of an inorganic support (SBA-15), loaded with the rhodamine B model molecule, and functionalized with amine groups on which oleic acid is anchored by covalent bonding. The designed material is capable of protecting the cargo under the conditions present in the mouth and stomach, and inducing its release in the small intestine. Finally, the system has been used for the release of vitamin B2, thus demonstrating the validity of the system for the protection and controlled release of bioactive molecules in the conditions of the small intestine. The second article evaluates the effectiveness of this molecular gate in different types of mesoporous silica particles, with different sizes and pore structures (MCM-41, MCM-48, SBA-15 and UVM-7). In all the systems studied, the molecular gate is able to keep the molecules confined and protected into the porous structure, and only release them in the presence of bile salts. Also, these experiments have evidenced the dependence of the release profile on the structure of the inorganic material used. Finally, the solid based on the structure of UVM-7 Abstract was validated in an in vivo model of Wistar rat, observing a delay in the intestinal absorption of rhodamine B when administered using the designed system compared with the administration of the free compound. Lastly, the third article included in this chapter has studied the possibility of incorporating molecular gates onto phyllosilicates. These materials have been used for passive release, but they had not been protected with molecular gates that allow the payload's active release triggered by the action of a specific stimulus. In this work, the protection and controlled release of both model molecules (rhodamine B) and large biomolecules involved in human metabolism (vitamin B12 and hematin) have been achieved using phyllosilicates functionalized with oleic acid as molecular gate. The second chapter describes new systems in which the protein zein (corn prolamin) is used for the first time as molecular gate. This biomolecule, despite its wide use in the food sector, has not been used in the development of controlled release systems based on molecular gates. A set of mesoporous silica particles loaded with different essential oil components (EOCs) and functionalized with zein has been prepared. In the designed systems, the presence of the corn prolamin inhibits the release of encapsulated EOCs (thymol, carvacrol and cinnamaldehyde), whose release is exclusively allowed in the presence of proteolytic enzymes excreted during bacterial growth, capable of degrading the protein that blocks the pores. Among all the developed materials, the cinnamaldehyde-loaded system has shown much greater inhibition of E. coli growth than the free compound. Finally, the third chapter studies the effectiveness of lactose as a molecular gate capable of protecting essential oils and releasing them only in the conditions present in the small intestine. Three different materials have been prepared, based on MCM-41 inorganic support, loaded with thymol, eugenol and cinnamaldehyde and functionalized with lactose to inhibit the exit of EOCs. Thus, only the enzymatic action of the lactase secreted by the intestinal microvilli is capable of hydrolyzing the molecular gate into the corresponding monosaccharides, removing the steric hindrance that keeps the payload encapsulated, and thus allowing its release along Abstract the intestinal lumen. The designed microdevices have been validated in in vitro models with Caco-2 cells, where the internalization of the particles by the cells has been observed, and the increase in the cytotoxic capacity of cinnamaldehyde thanks to its encapsulation. It has also been observed in vitro that the encapsulation of EOCs in the lactose-protected microdevices decreases their permeability through the intestinal membrane-model, thus increasing the residence time of the compound in the lumen and its progressive release with the triggering action of the secreted lactase. Finally, the cinnamaldehyde-loaded microdevice has been validated in an in vivo model (Wistar rat), which has confirmed the decrease in permeability of cinnamaldehyde previously observed in vitro and a greater permanence of the EOC in the gastrointestinal lumen. Thus, the present PhD thesis has demonstrated the possibility of using simple food-grade biomolecules as gatekeepers on a wide variety of silica materials. These new systems have allowed the encapsulation of different nutraceutical compounds, both volatile and large, for their protection and controlled release, thus improving their bioactivity and bioavailability. In this way, a further step has been taken in the use of nanotechnology to enhance the properties of natural biomolecules for pharmacological purposes. Abbreviations and Acronyms Abbreviations and Acronyms A ATCC American Type Culture Collection ACN Acetonitrile ap Apical side (cell insert) APTES (3-Aminopropyl)triethoxysilane B B2 Riboflavin (vitamin B2) B12 Cyanocobalamin (vitamin B12) BET Brunauer, Emmett and Teller model BJH Barret, Joyner and Halenda model bl Basolateral side (cell insert) BSA Bovine Serum Albumin