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[Hypothesis] The internal organization of polyelectrolyte layers deposited on colloidal templates plays a very important role for the potential applications of these systems as capsules for drug delivery purposes., [Experiments] The mutual arrangement of oppositely charged polyelectrolyte layers upon their deposition on positively charged liposomes has been studied by combining up three different scattering techniques and Electronic Spin Resonance, which has provided information about the inter-layer interactions and their effect on the final structure of the capsules., [Findings] The sequential deposition of oppositely charged polyelectrolytes on the external leaflet of positively charged liposomes allows modulating the organization of the obtained supramolecular structures, impacting the packing and rigidity of the obtained capsules due to the change of the ionic cross-linking of the multi-layered film as a result of the specific charge of the last deposited layer. The possibility to modulate the properties of the LbL capsules by tuning the characteristics of the last deposited layers offers a very interesting route for the design of materials for encapsulation purposes with their properties controlled almost at will by changing the number of deposited layers and their chemistry.

This work presents a simple methodology for coating small unilamellar liposomes bearing different degrees of positive charge with polyelectrolyte multilayers using the sequential layer-by-layer deposition method. The liposomes were made of mixtures of 1,2- dioleyl-sn-glycero-3-phosphocoline and dimethyl dioctadecyl ammonium bromide (DODAB) and coated by alternated layers of the sodium salt of poly(4-styrenesulfonate) (PSS) and poly(allylamine) (PAH) as polyanions and polycations, respectively. The results show that the zeta potential of the liposomes was not very sensitive to the mole fraction of DODAB in the membrane, XD, in the range 0.3 ≤ XD ≤ 0.8. We were able to coat the liposomes with up to four polymer bilayers. The growth of the capsule size was followed by dynamic light scattering, and in some cases, by cryo-transmission electron microscopy, with good agreement between both techniques. The thickness of the layers, measured from the hydrodynamic radius of the coated liposome, depends on the polyelectrolyte used, so that the PSS layers adopt a much more packaged conformation than the PAH layers. An interesting finding is that the PSS amount needed to reach the isoelectric point of the capsules increases linearly with the charge density of the bare liposomes, whereas the amount of PAH does not depend on it. As expected, the preparation of the multilayers has to be done in such a way that when the system is close to the isoelectric point, the capsules do not aggregate. For this, we dropped the polyelectrolyte solution quickly, stirred it fast, and used dilute liposome suspensions. The method is very flexible and not limited to liposomes or polyelectrolyte multilayers; also, coatings containing charged nanoparticles can be easily made. Once the liposomes have been coated, lipids can be easily eliminated, giving rise to polyelectrolyte nanocapsules (polyelectrosomes) with potential applications as drug delivery platforms., Unión Europea. Horizonte 2020, Ministerio de Economía y Competitividad (MINECO), Ministerio de Ciencia e Innovación (MICINN), Universidad Complutense de Madrid/Banco de Santander, Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

CRUE-CSIC (Acuerdos Transformativos 2021), Magnetic colloids adsorbed at a fluid interface are unique model systems to understand self-assembly in confined environments, both in equilibrium and out of equilibrium, with important potential applications. In this work the pearl-chain-like self-assembled structures of superparamagnetic colloids confined to a fluid–fluid interface under static and time-dependent actuations are investigated. On the one hand, it is found that the structures generated by static fields transform as the tilt angle of the field with the interface is increased, from 2D crystals to separated pearl-chains in a process that occurs through a controllable and reversible zip-like thermally activated mechanism. On the other hand, the actuation with precessing fields about the axis perpendicular to the interface induces dynamic self-assembled structures with no counterpart in non-confined systems, generated by the interplay of averaged magnetic interactions, interfacial forces, and hydrodynamics. Finally, how these dynamic structures can be used as remotely activated roller conveyors, able to transport passive colloidal cargos at fluid interfaces and generate parallel viscous flows is shown. The latter can be used in the mixture of adsorbed molecules and the acceleration of surface-chemical reactions, overcoming diffusion limitations., Unión Europea. Horizonte 2020, Ministerio de Ciencia e Innovación (MICINN), Ministerio de Economía y Competitividad (MINECO), Universidad Complutense de Madrid/Banco de Santander, Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

Las investigaciones relacionadas con el transporte y liberación controlada de principios activos se encuentran en constante evolución, debido a la creciente demanda social de alternativas a las terapias y sistemas que se han venido empleando en los últimos años. En este sentido, el empleo de sistemas coloidales se presenta como una opción prometedora debido a su versatilidad y biocompatibilidad. Sin embargo, el desarrollo de nuevas plataformas de encapsulación, cada vez más específicas y eficientes, requiere de un conocimiento profundo de los mecanismos que intervienen en la formación y transporte de estos sistemas. Englobada en este contexto, en esta tesis se estudia, desde un enfoque químico-físico, la formación de nuevas plataformas basadas en cápsulas coloidales micro y nanométricas y su transporte a través de fluidos viscosos..., The research lines related to the transport and controlled release of drugs are in continuous evolution, due to the growing social demand for improved systems and strategies, alternative to the ones employed in the last decades. In this sense, remotely controlled biocompatible colloidal systems emerge as promising designs for the encapsulation and transport of active compounds. For the development of these advanced platforms is necessary a deep understanding of the mechanisms involved in the construction and propulsion...