Search

Dissertação de mestrado em Física, O estudo de nanofibras com diâmetros sub-micrométricos tem atraído, recentemente, grande interesse dada a sua baixa dimensionalidade, que permite criar dispositivos com resolução nanométrica. O conceito de nanofibras magnetoelétricas baseia-se na inserção de compostos ferroelétricos e magnetostritivos, que irão acoplar-se mecanicamente, numa matriz polimérica a partir de uma solução percursora. A técnica de electrospinning apresenta uma grande versatilidade que permite um controlo efetivo da morfologia das nanofibras, sendo possível obter diâmetros inferiores ao mícron e comprimentos muito longos. Assim, neste trabalho são preparadas nanofibras magnetoelétricas compósitas a partir de um acoplamento mecânico de 1 fase de niobato de lítio com 1 fase de ferrite de cobalto, com diferentes percentagens estequiométricas das 2, sendo depois as fibras sujeitas a recozimento. O niobato de lítio (LNO) é um material ferroelétrico que apresenta elevadas propriedades piezoelétricas, piroelétricas, eletro-ópticas, birrefringentes, fotorrefrativas e fotoelásticas. Por outro lado, a ferrite de cobalto (CFO) apresenta uma anisotropia magnetocristalina alta e magnetostricção elevada. Medidas de difração de raios-X mostram que as fibras são policristalinas, com a estrutura cristalina pretendida para as fases de LNO e CFO. A microscopia eletrónica de varrimento, mostrou que grande parte das amostras apresenta estrutura de nanofibras com diâmetros na ordem das centenas de nanómetros, sendo que a temperatura de recozimento selecionada (650°C) terá sido excessiva para amostras com fase de LNO muito predominante. Utilizando o modelo de Havriliak-Negami e incluindo uma contribuição de condutividade, modelizou-se e ajustou-se a componente imaginária do módulo elétrico, obtido com espetroscopia de impedâncias, para obter os tempos de relaxação e energias de ativação. É, então, apresentada a influência da quantidade da fase de LNO e CFO nas propriedades dielétricas das amostras., The study of nanofibers with sub-micrometer diameters has recently attracted great interest given their low dimensionality which allows the creation of devices with nanometric resolution. The concept of magnetoelectric nanofibers is based on the insertion of ferroelectric and magnetostrictive compounds, that will mechanically couple together, in a polymer matrix through a precursor solution. The electrospinning technique has great versatility, which allows an effective control of the morphology of the nanofibers, being possible to obtain diameters smaller than the micron and with long lengths. Thus, in this work, composite magnetoelectric nanofibers are prepared from a mechanical coupling of a lithium niobate phase with a cobalt ferrite phase, with different stoichiometric percentages of the 2, after which the fibers are subjected to annealing. Lithium niobate (LNO) is a ferroelectric material that has high piezoelectric, pyroelectric, electro-optical, birefringent, photorefractive and photoelastic properties. On the other hand, cobalt ferrite (CFO) has a high magnetocrystalline anisotropy and high magnetostriction. X-ray diffraction measurements show that the fibers are polycrystalline, with the desired crystal structure for the LNO and CFO phases. Scanning electron microscopy showed that most samples have a nanofiber structure with diameters in the hundreds of nanometers, and the selected annealing temperature (650°C) was excessive for samples with a very predominant LNO phase. Using the Havriliak-Negami model and including a contribution of conductivity, the imaginary component of the electrical modulus, obtained with impedance spectroscopy, was modeled and adjusted to obtain relaxation times and activation energies. The influence of the amount of the LNO and CFO phase on the dielectric properties of the samples is then presented.

Water is the basis of life in the world. Unfortunately, resources are shrinking at an alarming rate. The lack of access to water is still the biggest problem in the modern world. The key to solving it is to find new unconventional ways to obtain water from alternative sources. Fog collectors are becoming an increasingly important way of water harvesting as there are places in the world where fog is the only source of water. Our aim is to apply electrospun fiber technology, due to its high surface area, to increase fog collection efficiency. Therefore, composites consisting of hydrophobic and hydrophilic fibers were successfully fabricated using a two-nozzle electrospinning setup. This design enables the realization of optimal meshes for harvesting water from fog. In our studies we focused on combining hydrophobic polystyrene (PS) and hydrophilic polyamide 6 (PA6), surface properties in the produced meshes, without any chemical modifications, on the basis of new hierarchical composites for collecting water. This combination of hydrophobic and hydrophilic materials causes water to condense on the hydrophobic microfibers and to run down on the hydrophilic nanofibers. By adjusting the fraction of PA6 nanofibers, we were able to tune the mechanical properties of PS meshes and importantly increase the efficiency in collecting water. We combined a few characterization methods together with novel image processing protocols for the analysis of fiber fractions in the constructed meshes. The obtained results show a new single-step method to produce meshes with enhanced mechanical properties and water collecting abilities that can be applied in existing fog water collectors. This is a new promising design for fog collectors with nano- and macrofibers which are able to efficiently harvest water, showing great application in comparison to commercially available standard meshes.

O aumento dos níveis de emissões de dióxido de carbono (CO2) tem tido consequências graves como as alterações climáticas. Este fator associado ao facto de o CO2 ser também uma matéria-prima abundante e barata, leva à necessidade de desenvolver estratégias que possibilitem a captura e transformação de CO2 em produtos de valor acrescentado, como por exemplo o metanol. O principal objetivo desta tese consiste na conversão de CO2 em metanol, através de um sistema multienzimático imobilizado. No entanto, por se tratar de um sistema complexo, este trabalho foca-se apenas numa parte do sistema. Assim, foi analisada a atividade da enzima álcool desidrogenase (ADH) quando encapsulada. A enzima foi imobilizada numa membrana de fibras produzida pela técnica de eletrospinning. O polímero utilizado para produção das fibras foi o álcool polivinílico (PVA). A atividade desta enzima depende do substrato utilizado, sendo maior em etanol. Deste modo utilizou-se etanol para otimizar os parâmetros reacionais. Para a quantificação/deteção da atividade enzimática utilizou-se um método indireto, através da conversão de NAD+ a NADH (cofatores da enzima), recorrendo à espectroscopia de ultravioleta/visível (UV/Vis). De modo a caracterizar as fibras obtidas utilizaram-se diversas técnicas tais como microscopia eletrónica de varrimento (SEM), testes reológicos (viscosidade), testes mecânicos (ensaios de tração) e espectroscopia de infravermelho (FTIR). A conjugação das informações obtidas permitiu verificar que a enzima consegue estar encapsulada no interior das fibras influenciando a sua formação no processo de electrospinning.

Evidence shows there is no ideal membrane, i.e., biocompatible, biodegradable, with adequate mechanical and physical properties that enable reorganization of periodontal tissues. Eletrospinning technique has demonstrated good processing results on scaffolds made from polymers. Nanofibrous formed by this technique have characteristics that resemble the extracellular matrix. The aim of this study was to evaluate the biocompatibility of nanofibrous polydioxanone scaffolds (PDS II®) containing metronidazole or ciprofloxacin in subcutaneous implantation model in rats Wistar. PDS II® is biocompatible polyester having various applications in the medical field. Our conceptual hypothesis considers that scaffolds with antimicrobials have similar inflammatory behavior when compared to PDS positive control. Sixty adult male rats were randomized into 6 groups: negative control (SHAM) animals with incision and surgical pocket, without scaffold; positive control (PDS) animals with PDS scaffolds; 1MET animals with one PDS scaffold containing 25%wt metronidazole; 2MET animals with two PDS scaffolds containing 25%wt metronidazole, 1CIP animals with PDS scaffolds containing 25%wt ciprofloxacin; 2CIP animals with two PDS scaffolds containing 25%wt ciprofloxacin. Animals were euthanized at 3 days (n=30) and 30 days (n=30), corresponding to initial and late inflammatory responses, respectively. Outcomes measures were the degradation of collagen fibers (Picrosirius Red and Masson´s trichrome), activity of cellular enzyme (Myeloperoxidase activity and N-acetyl-β-D-glucosaminidase activity) and local oxidative profile (reactive oxygen species, lipid peroxidation, protein carbonyl, vitamin C, catalase and reduced glutathione). Dara were analyzed statistically (p

Stents vasculares são dispositivos biomédicos de valor incontestável no tratamento e regeneração de artérias ou veias que ficaram obstruídas ou enfraquecidas. Ao longo dos últimos anos, muito se tem vindo a desenvolver procurando um equilíbrio entre a estabilidade mecânica, biocompatibilidade e o recurso à ação farmacológica de modo a que se combatam as tromboses/embolias vasculares e a ocorrência de complicações como a reestenose após implantes. Atualmente existe no mercado uma elevada variedade de stents vasculares de diversos materiais, desde metálicos a polímeros biodegradáveis com incorporação, ou não, de um fármaco. Os stents metálicos foram os primeiros a serem comercializados, contudo têm problemas inerentes de inflamação ou mesmo incompatibilidade com o organismo dada a durabilidade de aplicação. Por outro lado, os stents vasculares biodegradáveis estão cada vez mais em ascensão, apesar das propriedades mecânicas e sua durabilidade serem ainda um desafio. Polímeros biodegradáveis, sintéticos ou naturais, com grupos terminais fotoreticuláveis têm-se demostrado promissores e úteis em aplicações in situ. Dois dos polímeros mais usados na área biomédica, concretamente na preparação de hidrogéis e scaffolds, são a gelatina e a policaprolactona, respetivamente. A sua mistura pode ser explorada na construção de stents versáteis, com melhores propriedades biológicas para tecidos vasculares ao mesmo tempo que exibem boas propriedades mecânicas. Com esta dissertação pretendeu-se produzir scaffolds por combinação de estratégias de fotoreticulação e electrospinning usando duas abordagens de síntese diferentes, com vista à utilização dos materiais finais como stents vasculares. Em ambas as abordagens de síntese usou-se a gelatina (polímero natural) e a PCL (polímero sintético). A gelatina foi inicialmente funcionalizada com anidrido metacrílico para a formação do hidrogel Gel- MA. Na primeira abordagem, as fibras de PCL foram produzidas por electrospinning sendo de seguida revestidas por hidrogéis de diferentes composições (tendo por base a Gel-MA). Na segunda abordagem, fibras foram preparadas a partir de soluções distintas de PCL e Gel-MA, que foram misturadas e induzidas no electrospinning. Desta forma obteve-se um compósito fibroso. Em ambos os processos, sujeitaram-se os materiais a irradiação UV para garantir a adequada reticulação da gelatina, usando o Irgacure® 2959 como fotoiniciador. Para os scaffolds produzidos foram avaliadas propriedades químicas, físicas, térmicas e biológicas. A análise de ATR-FTIR permitiu observar as ligações características de cada polímero em ambos os scaffolds. Na técnica SEM verificou-se que a disposição das fibras nos scaffolds era aleatória e no caso dos scaffolds revestidos com hidrogel era notório o efeito desse revestimento. A análise TGA mostrou que os scaffolds eram termicamente estáveis. Quando incubados em uma solução tampão fosfato (PBS) durante 28 dias, os scaffolds revestidos com Gel-MA 10% foram os que apresentaram maior diferença de perda de hidrogel. Nos ensaios de hemólise, por contacto direto, só os scaffolds compósitos mostraram valores bastante satisfatórios, revelando-se não hemolíticos. Relativamente aos scaffolds revestidos estes só exibiram esse carácter após uma lavagem prévia do material com PBS. Todavia, os scaffolds apresentaram um carácter trombogénico, o que não é favorável para a aplicação pretendida. Os valores de viabilidade celular, após contacto dos materiais com células endoteliais circulantes foram bastante satisfatórios para os scaffolds compósitos, porém, os scaffolds revestidos de hidrogel com macrómeros apresentaram baixa viabilidade celular. Recomenda-se, neste caso, novos estudos de biocompatibilidade mas também um esforço de síntese para perceber o que pode ser modificado nas formulações. No estudo preliminar de libertação de fármaco para os scaffolds revestidos, obtiveram-se perfis de libertação interessantes tendo em conta a aplicação. Face aos resultados alcançados, pode-se concluir que os scaffolds das duas abordagens apresentam características promissoras para utilização como stents vasculares, podendo ser importantes ferramentas em Engenharia de Tecidos. Vascular stents are biomedical devices of an unquestionable value in the treatment and regeneration of injured and weakened arteries or veins. Over the years, the development of these materials with promising performances requires a thorough understanding and a stringent balance between mechanical stability, biocompatibility and pharmacological activity, fighting against thrombosis, vascular embolism episodes or the possibility of several complications after implant, such as restenosis. Nowadays in the market there are several options of vascular stents, produced from different metals or biodegradable polymers, with or without entrapped drugs. The metallic stents were the first commercially available, nevertheless with inherent issues like inflammations during application or even incompatibility in the body after long usage. On the other hand, biodegradable vascular stents are increasingly in the field, but their mechanical properties and durability remains a challenge. Biodegradable polymers, either synthetic or natural, with photocurable end-groups have proved to be promising and useful for in situ applications. Two of the most commonly used polymers in the biomedical field, particularly in hydrogels and scaffolds development, are gelatine and polycaprolactone (PCL), respectively. Their mixtures may be used and tuned to produce flexible and robust stents with improved biological properties for vascular tissues while exhibiting good mechanical properties. This work aimed at exploring the production of several scaffolds by combination of electrospinning and photocrosslinking strategies. Two different approaches in material synthesis were tested to obtain new materials to be used and characterized as vascular stents. In both synthesis approaches, gelatine (natural polymer) and PCL (synthetic polymer) were used. The gelatine was firstly functionalized with carbon-carbon double bonds by methacrylic anhydride, leading to a Gel-MA hydrogel. In the first approach, PCL fibers were produced by electrospinning and then coated with several hydrogels of different compositions based on Gel-MA. In the second approach, fibers were prepared from diverse PCL and Gel-MA solutions and finally mixed and induced in electrospinning apparatus. In this case, fibrous composites were obtained. In both strategies, the final materials were subjected to UV irradiation, using Irgacure® 2959 as Vascular stents are biomedical devices of an unquestionable value in the treatment and regeneration of injured and weakened arteries or veins. Over the years, the development of these materials with promising performances requires a thorough understanding and a stringent balance between mechanical stability, biocompatibility and pharmacological activity, fighting against thrombosis, vascular embolism episodes or the possibility of several complications after implant, such as restenosis. Nowadays in the market there are several options of vascular stents, produced from different metals or biodegradable polymers, with or without entrapped drugs. The metallic stents were the first commercially available, nevertheless with inherent issues like inflammations during application or even incompatibility in the body after long usage. On the other hand, biodegradable vascular stents are increasingly in the field, but their mechanical properties and durability remains a challenge. Biodegradable polymers, either synthetic or natural, with photocurable end-groups have proved to be promising and useful for in situ applications. Two of the most commonly used polymers in the biomedical field, particularly in hydrogels and scaffolds development, are gelatine and polycaprolactone (PCL), respectively. Their mixtures may be used and tuned to produce flexible and robust stents with improved biological properties for vascular tissues while exhibiting good mechanical properties. This work aimed at exploring the production of several scaffolds by combination of electrospinning and photocrosslinking strategies. Two different approaches in material synthesis were tested to obtain new materials to be used and characterized as vascular stents. In both synthesis approaches, gelatine (natural polymer) and PCL (synthetic polymer) were used. The gelatine was firstly functionalized with carbon-carbon double bonds by methacrylic anhydride, leading to a Gel-MA hydrogel. In the first approach, PCL fibers were produced by electrospinning and then coated with several hydrogels of different compositions based on Gel-MA. In the second approach, fibers were prepared from diverse PCL and Gel-MA solutions and finally mixed and induced in electrospinning apparatus. In this case, fibrous composites were obtained. In both strategies, the final materials were subjected to UV irradiation, using Irgacure® 2959 as Vascular stents are biomedical devices of an unquestionable value in the treatment and regeneration of injured and weakened arteries or veins. Over the years, the development of these materials with promising performances requires a thorough understanding and a stringent balance between mechanical stability, biocompatibility and pharmacological activity, fighting against thrombosis, vascular embolism episodes or the possibility of several complications after implant, such as restenosis. Nowadays in the market there are several options of vascular stents, produced from different metals or biodegradable polymers, with or without entrapped drugs. The metallic stents were the first commercially available, nevertheless with inherent issues like inflammations during application or even incompatibility in the body after long usage. On the other hand, biodegradable vascular stents are increasingly in the field, but their mechanical properties and durability remains a challenge. Biodegradable polymers, either synthetic or natural, with photocurable end-groups have proved to be promising and useful for in situ applications. Two of the most commonly used polymers in the biomedical field, particularly in hydrogels and scaffolds development, are gelatine and polycaprolactone (PCL), respectively. Their mixtures may be used and tuned to produce flexible and robust stents with improved biological properties for vascular tissues while exhibiting good mechanical properties. This work aimed at exploring the production of several scaffolds by combination of electrospinning and photocrosslinking strategies. Two different approaches in material synthesis were tested to obtain new materials to be used and characterized as vascular stents. In both synthesis approaches, gelatine (natural polymer) and PCL (synthetic polymer) were used. The gelatine was firstly functionalized with carbon-carbon double bonds by methacrylic anhydride, leading to a Gel-MA hydrogel. In the first approach, PCL fibers were produced by electrospinning and then coated with several hydrogels of different compositions based on Gel-MA. In the second approach, fibers were prepared from diverse PCL and Gel-MA solutions and finally mixed and induced in electrospinning apparatus. In this case, fibrous composites were obtained. In both strategies, the final materials were subjected to UV irradiation, using Irgacure® 2959 as the radical photoinitiator. In order to evaluate materials feasibility for the intended application, chemical, physical, thermal and biological properties were assessed. The ATR-FTIR analysis allowed a follow up of each polymer bonds in both scaffolds. The SEM technique confirmed a random arrangement of the fibers in the scaffolds, and in the case of the coated materials, the effect of hydrogels coating was noticeably detected. TGA analysis showed that all materials were thermally stable. When the samples were incubated in phosphate buffer solution for 28 days, the scaffolds coated with Gel-MA 10% presented the highest mass loss. In the haemolysis assays, by direct contact, just composite scaffolds exhibited good values of haemolysis percentage, revealing a non-haemolytic nature. The coated scaffolds only presented a non-haemolytic character after washing their by-products with phosphate buffer solution. However, all scaffolds presented a thrombogenic nature, which is not favourable for the purposed application. The results of cell viability studies, after direct contact of the materials with circulating endothelial cells, were quite acceptable for the composite samples. Nonetheless, the coated scaffolds with hydrogels showed poor cell viability. In this case, further biocompatibility studies are recommended in the future but also a research effort must be accomplished to obtain improved formulations. In the preliminary assessment of drug release profiles, the overall performance of the coated scaffolds showed potential in the field, according to therapeutic needs. Altogether, characterization results showed that the produced materials presented a set of properties suitable for Biomedical and Tissue Engineering applications, particularly as vascular stents.

A simple and non-conventional electrospinning technique was employed for producing highly oriented Polyacrylonitrile (PAN) nanofibers. The PAN nanofibers were electrospun from 14 wt% solution of PAN in dimethylformamid (DMF) at 11 kv on a rotating drum with various linear speeds from 22.5 m/min to 67.7 m/min. The influence of take up velocity was investigated on the degree of alignment, internal structure and mechanical properties of collected PAN nanofibers. Using an image processing technique, the best degree of alignment was obtained for those nanofibers collected at a take up velocity of 59.5 m/min. Moreover, Raman spectroscopy was used for measuring molecular orientation of PAN nanofibers. Similarly, a maximum chain orientation parameter of 0.25 was determined for nanofibers collected at a take up velocity of 59.5 m/min.