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Waterborne polymer coatings have the potential to address the environmental concerns associated with solvent based systems. To improve their performance without using volatile organic compounds, we propose a new approach based on reconfigurable covalent crosslinking that provides mechanical resistance and self-healing properties. The new waterborne polymer coatings are based on mixtures of aldehyde- and amine-functionalized polymer nanoparticles (PNPs) that take advantage of the reversibility of imine bonds in the presence of water. Different degrees of functional monomer incorporation (10 % to 40 %) allowed us to balance crosslinking and interdiffusion during film formation, to obtain mechanically robust and solvent resistant films. A clear structure-properties relation was assessed by following the formation of water resulting from amine-aldehyde condensation crosslinking, measured by differential scanning calorimetry. The resulting polymer coatings further show self-healing properties at room temperature, triggered with residual amounts of water and featuring high recovery rates of the mechanical properties. Our mechanically robust waterborne polymer coatings based in imine reversible crosslinking, featuring self-healing in mild conditions, offer excellent prospects for application in smart coating materials. published

Tese de Doutoramento em Engenharia de Materiais, Os distúrbios a nível do músculo-esquelético têm vindo a crescer continuamente a nível mundial, exigindo novas estratégias para atingir uma regeneração estrutural e funcional. Os polímeros piezoelétricos tem despertado interesse, oferecendo novas oportunidades para a engenharia de tecido do músculo-esquelético, uma vez que estes são electromecanicamente ativos, permitindo a estimulação mecano-elétrica dos tecidos. Neste trabalho, poli(fluoreto de vinilideno) (PVDF), o polímero biocompatível com a maior resposta piezoelétrica foi processado na forma de filmes, fibras e membranas porosas. Biomateriais compósitos foram produzidos com a introdução de nanopartículas de sílica com variação de diâmetro, quantidade e funcionalização, assim como com nanopartículas magnetostritivas (CoFe2O4). Deste modo, foi desenvolvida uma plataforma de polímeros eletroativos com características biomiméticas estruturais e com transdução mecano- e magnetoelétrica até um d33 ≈ |24| pC.N-1 e α33= 16.15 mV.cm-1Oe-1. O efeito da carga superficial dos filmes de PVDF na adesão e diferenciação celular foi investigado. A organização do citoesqueleto de mioblastos C2C12 aderidas a diferentes amostras de PVDF foi estudada por imunofluorescência e as interações entre uma única célula e o PVDF através de Espectroscopia de Força de uma Única Célula. Os mioblastos C2C12 cultivados nas amostras com carga superficial apresentaram uma morfologia mais alongada, independentemente de a carga ser negativa ou positiva. Foi determinado como as propriedades da superfície do material, tanto em termos de polarização (carga superficial positiva ou negativa) como de morfologia (filmes ou fibras) influenciam a diferenciação dos mioblastos, mostrando que o PVDF promove a diferenciação miogénica conforme evidenciado pela fusão e maturação, comprimento, diâmetro e número dos miotubos. As superfícies carregadas melhoram a fusão das células musculares em miotubos diferenciados e o uso de fibras de PVDF orientadas promovem o alinhamento celular. A estimulação dinâmica magnetoelétrica permitiu melhorar o índice de maturação do miotubo comparativamente às condições estáticas, sendo ainda melhorado com a combinação de estímulos químicos (meio de diferenciação) chegando até 70%. A estimulação dinâmica mecano-elétrica direta tem o mesmo efeito que a magnetoelétrica. Assim, este trabalho demonstra que a estimulação mecano-elétrica é uma nova abordagem para aplicações em engenharia de tecido músculo-esquelético., The prevalence of skeletal muscle disorders has been steadily increasing worldwide, requiring new strategies for their structural and functional regeneration. Piezoelectric polymers have attracted interest offering new opportunities for skeletal muscle tissue engineering (TE), since they are electromechanically active, allowing tissue mechano-electric and electro-mechanical stimulation. In this work, piezoelectric poly(vinylidene fluoride) (PVDF), the biocompatible polymer with the highest piezoelectric response, has been processed in the form of films, fibres and porous membranes. Composite biomaterials were also produced with the incorporation of silica nanoparticles with different diameters, functionalization and content, as well as magnetostrictive nanoparticles (CoFe2O4). This allowed a full set of electroactive polymers with biomimetic structural features and mechano- and magnetoelectric transduction up to d33 ≈ |24| pC.N-1 and α33= 16.15 mV.cm-1Oe-1. The effect of the surface charge of PVDF films on cell adhesion and differentiation was investigated. The cytoskeletal organization of C2C12 myoblasts adhered to different PVDF samples was studied by immunofluorescence and the interactions between single live cells and PVDF were analyzed by Single Cell Force Spectroscopy. C2C12 myoblasts seeded on samples with surface charge showed a more elongated morphology, independently of the charge being negative or positive. It was further determined how the surface properties of the material, both in terms of the poling state (positive or negative net surface charge) and their morphology (films or fibres) influence myoblast differentiation, showing that PVDF promotes myogenic differentiation as evidenced by myotube fusion and maturation index, length, diameter and number. Charged surfaces improve the fusion of muscle cells into differentiated myotubes and the use of oriented β-PVDF electrospun fibres scaffolds cell alignment. Magnetoelectric dynamic stimulation allowed to improve myotube maturation index comparatively to the static conditions being further enhanced with the combination of chemical stimuli (differentiation medium) up to ≈ 70%. Further, direct mechanoelectric dynamic stimulation also increases the maturation index of myotubes. Thus, this work convincingly demonstrates that mechano-electrical stimulation is a novel and suitable approach for skeletal muscle TE applications., Foundation for Science and Technology-(FCT), grant SFRH/BD/111478/2015.

Mesoporous silica nanoparticles provide a versatile drug-delivery platform due to their exceptional properties, such as, high payload uptake, tunable pore width and particle size and protection over the guest molecule. The external surface can be functionalize with bioactive molecules and stimuli responsive polymers, improving the biocompatibility and drug bioavailability, increasing the local dose delivered and decreasing the side effects. The objective of this work was to synthesize fluorescent hybrid MSNs, coated with a co-polymeric shell containing pH-responsive and carbohydrate blocks obtained through RAFT polymerization. Such combination opens the possibility of diagnosis, through carbohydrates recognition ability towards cancer cells, and therapy by a pH mediated controlled release. The fluorescent silica nanoparticles were prepared by the Stöber method, incorporating a high quantum yield perylenediimide (PDI) in the silica structure. The nanoparticles were characterized by transmission electronic microscopy, with diameters of 30 nm and 65 nm with low size dispersity. The homo and co-polymers were synthesized by RAFT polymerization and characterized by UV-Vis and size exclusion chromatography (SEC), with a polydispersity below 1.2. The external surface of the MSNs was functionalized to allow the immobilization of the smart polymer. Surface modifications were assessed and quantified using 1H-NMR, UV-Vis and ζ-Potential. Polymer immobilization on the MSNs external surface were performed using four different methods: “transfer to”, “graft to”, “graft from” and a hybrid method. The particles modified with the homo carbohydrate polymer were obtained with polymer weight percentage between 0.5% and 4.3%. The immobilization of the final pH-responsive/carbohydrate co-polymer was achieved with a 2% polymer weight via “graft to” method. The immobilization by the hybrid method was also achieved, with promising results, indicating that our strategy is correct.

In the field of bionanotechnology, the interest in the development of healthcare devices has increased due to their applications on diagnostics and therapeutics. Mesoporous silica nanoparticles (MSNs) have been used in drug delivery systems (DDSs) as nanocarriers due their excellent biocompatibility, high surface areas, large pore volumes, high payload, uniform and tunable pore sizes, and versatile of surface functionalization. The incorporation of a stimuli-responsive polymeric shell allows the drug release control response through a disease-specific physiological conditions, and/or from external applied stimuli. Additionally, it will protect the therapeutic molecules from physiological metabolization and enhance its efficiency and bioavailability in the bloodstream, as well as reduce the side effects. The goal of this work was to prepare a fluorescent core-shell MSNs, coated with a pH-responsive polymeric shell, combining diagnostic and therapeutic properties in a single vector. Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization was used to obtain a homogeneous polymeric shell with a well-defined structure. The hybrid nanoparticles were characterized by Transmission Electronic Microscopy (TEM) and Dynamic Light Scattering (DLS), allowing diameters around 150 nm. The polymeric shell was characterized by Proton Nuclear Magnetic Resonance spectroscopy (1H NMR), Fourier Transform Infrared Spectroscopy (FT-IR) and electrophoretic mobility (ζ-potential). The pH responsive behavior was proven by ζ-Potential with an estimated conformational transition at pH between 6.2 – 6.5. The hybrid nanoparticles indicate being biocompatible tested by cell viability assays in human breast adenocarcinoma (MCF-7), which showed that for a concentration of 125 μg/mL the cell viability is over 70 %.