FCT: DCM - Teses de Doutoramento
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- Multifunctional magnetic nanoparticles for targeted Alzheimer's Disease theranosticsPublication . Chaparro, Catarina Isabel Parente; Soares, Paula; Neves, Vera; Borges, JoãoA doença de Alzheimer (DA) é uma doença neurodegenerativa caracterizada pela acumulação de oligómeros de β-amiloide (OβA) e fibrilas, sendo ainda limitadas as estratégias eficazes para o seu diagnóstico precoce e tratamento. Um dos principais desafios na nanomedicina reside na capacidade limitada dos agentes terapêuticos e de diagnóstico em transpor a barreira hematoencefálica (BHE), restringindo a sua entrega no cérebro. Esta tese de doutoramento explora o desenvolvimento de nanopartículas multifuncionais superparamagnéticas de óxidos de ferro (SPIONs), encapsuladas em nanopartículas poliméricas e funcionalizadas com ligandos para combinar tanto a translocação através da BHE, como o reconhecimento de OβA. O péptido PepH3, um “shuttle” da BHE, e o domínio de cadeia leve variável (VL) de um anticorpo anti-OβA, usados individualmente ou no complexo VL-PepH3, foram conjugados a SPIONs encapsulados em nanopartículas de PLGA-PEG (NPs), de modo a integrar funções de transporte através da BHE e reconhecimento específico de OβA. As nanoformulações obtidas foram amplamente caracterizadas quanto às suas propriedades físico-químicas, estabilidade coloidal e relaxação magnética. Todas demonstraram aplicabilidade como agentes de contraste para ressonância magnética de imagem (RMI), apresentando valores de relaxação transversal (r2) superiores aos de formulações utilizadas clinicamente. A atividade biológica de todas as formulações de NPs foi avaliada in vitro em células endoteliais cerebrais humanas (HBEC-5i), com foco na toxicidade, internalização celular e translocação através da BHE. As proteínas VL e VL-PepH3 foram igualmente testadas quanto à sua capacidade de inibir a fibrilização de OβA, revelando efeitos moderados e limitados, respetivamente. A conjugação com o PepH3 e o complexo VL-PepH3 aumentou significativamente a internalização das NPs em células endoteliais, ao passo que o VL isolado manteve níveis de internalização semelhantes aos controlos não conjugados. Estes resultados demonstram a capacidade do PepH3 em potenciar a interação das NPs com a BHE. Apesar disso, a eficiência de translocação através da BHE permaneceu baixa, provavelmente devido ao sequestro intracelular das NPs; contudo, a integridade da barreira foi preservada, confirmando a biocompatibilidade dos nanosistemas. Em suma, este trabalho estabelece, como prova de conceito, o desenvolvimento de uma nanoplataforma de teranóstico que alia o potencial de contraste por RMI à capacidade de reconhecimento precoce de β-amiloide. No entanto, evidencia a necessidade de otimizações adicionais para reforçar a translocação através da BHE e o direcionamento específico para a ligação a OβA.
- Zinc-tin oxide devices for sustainable electronic systemsPublication . Silva, Carlos Miguel de Castro; Kiazadeh, Asal; Deuermeier, Jonas; Zhang, WeidongSustainable, earth-abundant materials offer a promising route toward addressing the economic, environmental, and energy challenges of modern computing. This thesis explores zinc-tin oxide (ZTO), an amorphous semiconductor, as a versatile platform for energy-efficient and scalable neuromorphic computing systems. Initially, ZTO memristors were designed to show the necessary qualities for their use as in-memory computing units in neural network accelerating applications. However, with the aim of more faithfully emulating biological neuronal structures, the research of physical reservoir systems (PRC) was pursued. By exploiting the inherent non-linear mechanisms of tailor designed memristors, the resulting PRC implementations were able to achieve considerable improvements in both network size and accuracy in a practical digit recognition task. ZTO-based diodes were also developed in tandem with the previously mentioned systems. With potential use as sneak-path-preventing selective devices in active crossbars for neuromorphic applications or other high-frequency tasks, the Schottky diodes showed record breaking metrics when compared with the vertically stacked solution-based oxide structures currently available in the literature.
- Conjugated Polymers for Energy Harvesting and Smart Sustainable ElectronicsPublication . Ferreira, Guilherme Mendes; Pereira, Luís; Nandy, SumanTriboelectric nanogenerators (TENGs) are devices for converting mechanical energy into electricity by a conjunction of triboelectrification and electrostatic induction. In this work, Polyaniline (PANi) and Polypyrrole (PPy) were explored as active materials for energy harvesting, pressure sensing and humidity sensing. Conjugated Polymer based (CP) inks were used for the functionalization of natural substrates including paper, textiles and foams through drop-casting, dip-coating and later for printing of functionalized substrates through Doctor Blade and 3D extrusion Bioprinter. The usage of water-based inks and natural substrates allow for the integration of sustainable and cost-effective wearable devices. The CPs functionalized substrates were built into energy harvesting and pressure sensing blocks. The MTRCTM model is proposed for exploring the charge generation mechanism. The energy harvesting devices were tested for different factors: force and frequency of mechanical input, area of active layer, type of coupled electrode material, introduction of triboelectric enhancers and conductive particles. The best results achieved so far for CP’s based energy harvesters were the textile functionalized fibers with PDMS cover. A maximum voltage peak of VOC and ISC of 244 V and 15 μA were obtained, respectively (2.29 W m−2 and 19.5 mA m−2 of power density and current density with a load resistance of 5 MΩ) when applying an impact force of 30 N. The output is stable even after 2000 cycles and this set of TENG yarns is also able to light at least 50 LEDs when tapping by hand. In this work, the final prototypes were also integrated with an ADC and microprocessor unit coupled with an embedded Wi-Fi module, for IoT implementation. The circuits employed were designed for security, smart packaging, tracking and ID validation applications.
- Development of a new magneto-thermoresponsive implantable 3D device for localized cancer treatmentPublication . Gonçalves, Adriana Maria Louro; Soares, Paula Isabel; Borges, João PauloThe high complexity and the wide variation of cancer types make it impossible to find an optimal and generally applicable treatment. Conventional approaches, such as chemotherapy, radiotherapy, and surgery, remain the standard of therapy but are often limited by their severe side effects, cancer recurrence, and treatment resistance. These challenges underscore the importance of innovative therapeutic strategies, including stimuli-responsive systems that can provide localized and controlled cancer treatments. The combination of multiple stimuli-responsive mechanisms can yield multifunctional platforms with a broader range of applications, enabling more personalized and effective therapies. This PhD project aims to develop a magneto-thermoresponsive 3D-printed device that combines magnetic hyperthermia and controlled drug release for cancer treatment, offering the possibility of localized treatment tailored to individual needs. This device consists of a thermoresponsive core with a transition temperature slightly above human body temperature, embedded with a chemotherapeutic drug, allowing for controlled and localized release. Drug release profiles can be adjusted by modifying crosslinking conditions, pH, and media temperature. The device’s shell is produced using stereolithography, incorporating magnetic nanoparticles that can induce localized hyperthermia to damage cancer cells and trigger the release of chemotherapeutic drugs from the thermoresponsive polymer. The proposed system enables synergistic and tailored treatment, aiming to minimize side effects on healthy tissues while offering the possibility of implantation with minimal invasion, improving patient care. The obtained results are essential for understanding how such systems can be designed and optimized for targeted therapeutic applications in the treatment of solid tumors.
- Bioactive glass composition and macrophage polarizationPublication . Pádua, Ana Sofia Tomaz Teixeira de; Silva, Jorge Alexandre; Graça, Manuel PedroBioactive glasses (BGs) have emerged as promising materials in regenerative medi-cine. Recent research has focused on enhancing BG performance by incorporating metal oxides to improve antibacterial, osseointegrative, and pro-regenerative capabilities. This study investigates the properties of 45S5 BGs doped with metallic oxides, including tanta-lum, copper, zinc, magnesium, and niobium at concentrations of 1, 2, and 4 mol%. These BGs were evaluated for their antibacterial properties, ability to enhance osseointegration, and overall pro-regenerative potential. Results showed that 4 mol% concentration of all doping agents yielded the most favourable outcomes, except copper that showed opti-mal performance at 1 mol%. For BG integration into coatings produced using CoblastTM deposition, two formulations were used: one combining BG and hydroxyapatite (HAp) at a 60:40 ratio, and another using co-doped BGs with two doping oxides. The CoBlastTM method ensured homogeneous coating application with uniform coverage and strong adhesion. The first formulation did not enhance biofilm prevention. Coatings containing only BGs showed significant antibacterial efficiency compared to undoped BG coating and exhibited favourable cell response in vitro. The optimized BGs were integrated into composite scaffolds comprising polycaprolactone (PCL) and varying concentrations of ceramics, including undoped BG. These scaffolds, fabricated using solvent casting, hot pressing, and salt-leaching, showed highly porous architecture with interconnected pores, supporting increased mechanical loads as ceramic content increased, with no variations from doping agents. In vitro analysis showed non-cytotoxic responses, enhanced cell ad-hesion, promoted proliferation, and improved alkaline phosphatase (ALP) activity. The Zn-doped BG/PCL composite scaffold displayed the most favourable properties for bone tis-sue engineering applications. These results are important for understanding the applica-tion and improvements of these biomaterials for next generation bone tissue engineer-ing.
- Microwave-assisted syntheses of sustainable TiO2-based platforms for water remediationPublication . Matias, Maria Leonor; Gomes, Daniela; Rodrigues, Joana; Machado, Ana MariaThe widespread contamination of aquatic ecosystems poses critical environmental challenges, spurring intensive global research into advanced sustainable water remediation technologies. Titanium dioxide (TiO2) nanostructures have emerged as prominent photocata- lysts due to their physical/chemical stabilities, cost-effectiveness, and catalytic efficiency. However, TiO2 has a wide band gap, restricting its utilization to the ultraviolet region. To en- hance spectral responsiveness under visible light, various strategies were explored, including the creation of a heterostructure (graphitic carbon nitride/TiO2), multi-dimensional defect en- gineering, as well as doping with two abundant elements: Fe and Ca. To overcome the limita- tions associated with the recovery and recyclability of nanopowders, TiO2-based nanostruc- tures synthesized under microwave irradiation were either incorporated into or directly syn- thesized onto green substrates, floating and non-floating. These substrates included cork, cel- lulose-based materials, resin, and polyurethane foams. The TiO₂-based nanopowders and platforms demonstrated excellent performance, achieving up to ~85 % combined adsorption and degradation of methyl orange and rhodamine B, and ~80 % for tetracycline, within 180– 240 min, depending on the substrate type and synthesis conditions. These breakthroughs show that TiO₂-based nanostructures can be synthesized at mild temperatures (90–230 °C) using microwave-assisted methods and be easily integrated into eco-friendly substrates while ena- bling sustainable water purification. Moreover, this PhD thesis aligns with the United Nations Sustainable Development Goals by promoting circular economy principles through the devel- opment of reusable and eco-friendly materials, fine-tuned to improve water quality.
- Colloidal Lithography for Light Trapping in Flexible Thin Film Solar CellsPublication . Boane, Jenny Luis Nhaliguangue; Águas, Hugo; Mendes, ManuelThe demand for more efficient, reliable, and economical optoelectronic and photovoltaic (PV) devices has led researchers to explore nano/microtechnological solutions. These solu- tions aim to enhance PV performance without significantly increasing production costs. Among these, photonic structures based on wavelength-sized transparent conductive oxides (TCOs) are particularly promising. They improve efficiency by reducing reflection and opti- mizing light absorption inside the solar cells, as well as in other photodetector devices like UV sensors. In this work, we developed a simple, low-cost, versatile, and highly scalable colloidal lithography process to fabricate and optimize three different microstructures: indium zinc ox- ide (IZO), indium tin oxide (ITO), and titanium dioxide (TiO2). These microstructures, with wavelength-sized features, were smoothly modelled on flexible ITO substrates coated with polyethylene terephthalate (PET), parylene C membranes, and rigid substrates (glass) coated with ITO. The ITO micro-mesh demonstrated enhanced transparent electrode properties, showing significant light interaction with a pronounced light scattering performance (diffuse transmission up to ~50%). Additionally, the microstructured photonic mesh of TCOs allowed for a greater volume of material in the electrode while maintaining desired transparency, lead- ing to a reduction in sheet resistance (~14%) and improved electrical benefits due to enhanced contact conductance. When integrated into perovskite solar cell test devices, these microstruc- tured photonic meshes provided excellent optical improvements, yielding short-circuit pho- tocurrent gains of up to ~20% and efficiency gains of up to ~17%, closely matching the values predicted by modelling optimizations. In view of exploring other promising applications, the microstructuring of test parylene- C membranes was investigated in UV sensors. This resulted in a pronouncedly enhanced pho- tocurrent response when compared with non-structured devices. These findings pave the way for a new class of transparent photonic electrodes with mechanical flexibility. They hold strong potential not only as advanced front contacts for thin- film foldable solar cells but also for a wide range of optoelectronic applications.
- Sustainable Materials Applied To Flexible Electronics Using A Laser-Induced Modular PlatformPublication . Silvestre, Sara; Coelho, João; Pereira, LuísWearable electronics and miniaturized devices have become integral to modern life. The next step is scaling these innovations for larger systems while maintaining efficiency, flexibility, and energy performance, especially as smart cities expand and demand eco-friendly solutions to reduce electronic waste and environmental impact. This thesis bridges advanced electronics and sustainability by using renewable materials and low-cost, eco-friendly methods for large-scale applications. Through a one-step direct laser writing (DLW) technique, three-dimensional porous green laser-induced graphene (gLIG) is produced. Optimization strategies, including precursor selection, substrate pretreatment, and laser parameter tuning, yield robust, thin, and flexible conductive patterns of high quality with low sheet resistances: 55.4 ohm sq-1 (for paper), 45.5 ohm sq-1 (for lignin-enriched paper), and 10.6 ohm s-1 (for cork). These properties make gLIG suitable for applications such as energy storage devices, sensors, and energy harvesting systems. Micro-supercapacitors (MSCs) developed in this work achieved capacitance values of 1.35–10 mF cm-2 and energy densities of 0.13–0.85 μWh cm-2, with power densities up to 80 μW cm-2. Stability tests revealed a capacitance retention of ≈80–85% over extended charge-discharge cycles, highlighting their reliability during prolonged operation. Additionally, these devices maintained stable performance under mechanical deformation, demonstrating their versatility for dynamic applications. Cork-based piezoresistive sensors further enhance this work, showcasing exceptional pressure sensitivity (0.38 mV Pa-1 at 15–35 kPa and 0.286 mV Pa-1 at ≥35 kPa) and functionality as triboelectric nanogenerators (TENGs), efficiently charging 0.47 and 4.7 μF capacitors. These results highlight their potential for powering small electronics and supporting sustainable energy solutions. Finally, this work underscores the importance of integrating sustainable, high-performance technologies into future infrastructure, paving the way for eco- friendly, self-sustaining platforms in smart cities and beyond.
- Skin Interfaced, Graphene-based Bioelectronics for Biomedical ApplicationsPublication . Pinheiro, Tomás Pinto e Cruz de Oliveira; Fortunato, Elvira; Sales, Maria Goreti; Almeida, HenriqueCarbon nanomaterials, more specifically graphene, have become highly valuable re- sources in the development of soft conductors, for highly conformable, epidermic biomedical devices. From the different graphene synthesis and processing techniques available nowadays, Direct Laser Writing (DLW) has become increasingly investigated, for the simultaneous synthe- sis and patterning of three-dimensional, porous graphene geometries, through the synthesis of Laser-Induced Graphene (LIG). Significant advancements have been made in the synthesis and translation of LIG derived from petroleum-based aromatic polymers, towards wearable device fabrication. However, the exploration of more accessible, less environmentally impactful materials derived from vegetable biomass, such as paper substrates, is lacking in comparison. In this thesis, a longitudinal study is presented, aiming at developing LIG synthesis strat- egies on paper substrates, to determine their potential as suitable substrates for high efficiency graphitization and patterning, towards on-skin biomedical applications. At a first stage, focus is given on the study and optimizations of LIG synthesis and laser processing strategies to develop paper-based electrochemical sensors. At a second stage, novel strategies to develop conformable, paper-based LIG soft conducting architectures, through the development of ma- terial transfer methods, is explored. Finally, these flexible, conformable LIG architectures are translated into functional devices, where LIG bioelectrodes are explored for the acquisition of electrophysiological signals, iontophoresis-based stimulation for sweat secretion and electro- chemical sweat sensing applications, for non-invasive glucose sensing. Overall, novel laser processing strategies developed in this work include paper in the toolbox of highly efficient LIG precursors, with the developed manufacturing approaches demonstrating compatibility for on-skin, bioelectronics applications for different biomedical applications.
- DESIGN OF 2D AND 3D METAMATERIALS WITH TAILORED THERMOMECHANICAL PROPERTIESPublication . Cardoso, João Oliveira; Velhinho, Alexandre; Borges, JoãoMetamaterials are a method of organizing materials according to different architectures to obtain properties not usually found in nature. These materials have the potential of addressing complex and nuanced engineering problems. Although originally metamaterials were confined to electro-optical properties, the scope has broadened to encompass all fields including structural metamaterials, which are the subject of this work. Herein, several 2D and 3D architectures were studied via modelling, simulation, and experimental characterization, comparing results to obtain insights regarding the achievement of negative/null values for the Poisson's ratio (NPR), resulting in the so-called auxetic behavior; and the obtention of similarly negative/null values for the thermal expansion coefficient (NTE), which when coupled with NPR corresponds to a behavior dubbed anepectic. Ultimately, the objective was to find means to tailor both parameters' values to specific targets by modifying the metamaterial's architecture. All the structures were produced via additive manufacturing, and can be resumed as: ● A 2D re-entrant metallic auxetic mesh. This didn't result in success, but several milestones were reached, and possible strategies were laid out for future work. ● A 2D polymeric auxetic mesh obtained via topology optimization. In the case of these 2D structures, a valid design and validation methodology has been established, to be adopted in subsequent research. ● A 3D re-entrant polymeric anepectic lattice. As a follow-up from previous results obtained with 2D re-entrant meshes, their 3D counterparts represented the most immediate approach to achieve the desired NPR and NTE behavior. ● 3D polymeric lattices based on the double-elliptic ring unit cell. With this architecture, an auxetic structure, ultimately intent on mimicking the behavior of inter-vertebral disks, was designed, and tested. Also, by adequate partial substitution of the constituting material, a functional anepectic prototype was designed and its behavior validated experimentally. ● 3D auxetic architectures based on triple periodic minimal surface (TPMS) geometries, ultimately chosen as a way to match the properties of femoral bone. Among these TPMS architectures, the gyroid geometry was the object of extensive studies, which apart from the determination of its properties led to the development of different metamaterial design methodologies. As a complement, a different TPMS, the Schwarz P geometry, served as a means to explore the viability of additively manufactured auxetic metallic structures.