Arbetet syftar till att skapa en prototyp av en textil trycksensor som kan känna av och skilja på olika typer av belastning. En lämplig metod för att på ett vetenskapligt sätt testa sagda prototyp har också utvecklats. Prototypen har tillverkats för hand på en datoriserad vävstol och de ingående materialen är piezoelektrisk poly(vinyldifluorid), PVDF, tvinnad tillsammans med ett konduktivt garn, Shieldex®, samt polyester. När PVDF-fiber utsätts för töjning genererar de en spänning, vars storlek står i relation till töjningen. Den vävda konstruktion som valdes till prototypen är en distansvara där väftinläggen lagts in i 7 olika lager för att skapa volym. Därmed möjliggörs en töjning av PVDF-fibern som relaterar till trycket strukturen utsätts för. För att utvärdera strukturen skapades tre likadana trycksensorer innehållandes fyra PVDF-fiber som lagts in med ett mellanrum på ca 1,5 cm. Dessa prototyper har sedan fästs på en egentillverkad ramp och PVDF- samt Shieldex®-garnet har kopplats in till ett oscilloskop. Därefter har vikter rullats över prototypen för att generera spänning, vilken har kunnat uppmätas med oscilloskopet. De uppmätta resultaten har analyserats och utvärderats med hjälp av Excel. Testerna visade tydligt att spänningen som uppmättes stod i relation till vikternas storlek; högre vikter gav en mätbart större spänning. Det finns dock stor varians bland resultaten och utvärdering av samtliga prover visar på stora standardavvikelser hos samtliga fiber. Detta innebär att även om det är tydligt att ökad vikt medför ökad signal så kan det finnas svårigheter i att avgöra storleken på vikten utifrån den uppmätta spänningen. / The aim of this project was to create a sensor in textile material which can register and recognize different kinds of pressure. A suitable method has been developed in order to scientifically investigate and evaluate the sensitivity of the prototypes. The prototypes have been produced with a computerized hand weave machine and the materials used were polyester and piezoelectric PVDF-fiber, twisted with a conductive yarn, Shieldex®. When a force is applied to the PVDF-fiber, causing an extension of the fiber, a voltage is generated directly related to the applied force. The final prototype is a woven textile with integrated monofilaments and weft inserted in seven different layers to create a voluminous structure. An extension by the PVDF-fiber is there by enabled to occur which is related to the force applied onto the structure. Three equable prototypes were produced, each consisting four separated PVDF-fibers which were inserted with a distance of 1, 5 cm from each other. The prototypes were further attached one by one on a homemade ramp and the PVDF- and Shieldex®-fibers were connected to an oscilloscope. Different weights were then rolled from the top of the ramp, generating a voltage each time it pressures a fiber, which were seen on the computer software of the oscilloscope. The results were afterwards analyzed and evaluated using Excel. A clear relationship between applied force and generated voltage is shown although there is a great variety among the test results on each weight along with large standard deviations. The exact weight generating a specific voltage is therefore difficult to determine.

The objective of this research is to develop a new class of miniaturized sensors on-catheter technology through the integration of functional nanomaterials and flexible microsystems, with high sensitivity, fast recovery time, reduced form factor, for in situ blood pressure and flow monitoring with minimal invasiveness. Real-time endovascular pressure measurement techniques are crucial to evaluate the hemodynamics, which indicates the physiological state of the cardiovascular system. Current technology relies on fluid filled catheter coupled to remote transducers to measure endovascular pressures and gradients. The fluid filled catheters are bulky, inherently inaccurate due to the tubing mechanical resonance, and with low signal integrity due to the vibration noises from the environment. Silicon based conventional pressure sensors have complications due to issues of catheter stiffness, biocompatibility or small form factor integration. We propose a paradigm shift in designing the endovascular pressure sensing technology, through developing compact flexible sensing structures using nanoengineered piezoelectric polymers which can be integrated on catheters without consuming the internal lumen space. We focused on designing novel nanostructures using PVDF-TrFE (Polyvinyledene fluoride trifluoroethylene), with well controlled [Beta]-crystalline phase to significantly improve the resulting sensor performance. The research objectives include: (1) Thin-film structures for higher piezoelectric effect without any mechanical stretching or poling requirements, (2) High density highly-aligned electrospun nanofibers through electrospinning towards enhanced sensitivity; (3) Core-shell electrospun nanofiber for tapping the near [Beta]-crystalline phase formation and high cyrstallinity by virtue of inherent stress and stretching involved in the fabrication procedure. For pressure sensor design and characterization, we worked on two main form factors designs: thin-film, and aligned electrospun nanofiber based sensors patterned on catheter tips which are ready to be deployed in intra-vascular environment. Testing results showed promising results from PVDF based pressure sensors. The average sensitivity of the PVDF sensors was found to be four times higher than commercial pressure sensor while the PVDF sensor had five fold shorter response time than commercial pressure sensor, making the PVDF sensors highly suitable for real-time pressure measurements using catheters. / text

Orientador: Luiz Francisco Malmonge / Resumo: Nanocompósitos com matriz de fibras em escala micro e nanométrica de poli(fluoreto de vinilideno) – PVDF com adição de argila montmorilonita ou zeólita faujasita – FAU, nas concentrações de 3%, 5%, 10%, 20% e 30%, foram produzidas pela técnica de fiação por sopro em solução e submetidas a caracterizações morfológica e estrutural (Microscopia Eletrônica de Varredura – MEV, Difratometria de Raios X – DRX e Energia Dispersiva de Raios X – EDX). As análises térmicas foram feitas por Calorimetria Exploratória Diferencial – DSC e Análise Termogravimétrica – TGA; as mecânicas por análises de Tensão – Deformação; e de molhabilidade por Ângulo de Contato. As amostras foram submetidas a testes de remoção de metais pesados através da adsorção em banho e em membrana. Os resultados demonstraram queda da espessura dos nanocompósitos, que passaram de 500 μm do polímero puro, para 251 μm e 315 μm para os nanocompósitos com 30% de argila e FAU, respectivamente. A técnica de MEV evidenciou amostras com grande quantidade de fibras lisas, uniformes, cilíndricas e pouco aglomeradas, cujos diâmetros foram inferiores a 200 nm. A ferramenta de EDX confirmou a presença dos elementos da argila e da FAU dispersos por todo o filme, porém surgem aglomerados com o aumento de sua concentração. A técnica de DRX demonstrou a presença das fases cristalinas α e β da matriz, além disso, o aumento da quantidade de argila e FAU nos nanocompósitos intensificou seus picos característicos. A técnica DSC revelou que ... (Resumo completo, clicar acesso eletrônico abaixo) / Doutor

Le but de cette thèse était d’étudier des solutions innovantes pour la récupération d’énergie pour pouvoir alimenter de manière autonome les futurs capteurs et nœuds communicants sans fil de l’Internet des Objets (IoT pour Internet of Things). Le travail s’est focalisé sur des matériaux piézoélectriques souples et sur une approche composite et multiphysique. L’objectif est de récupérer de l’énergie à partir de déformations directes ou induites provenant de sources à la fois mécaniques et thermiques et en particulier de sources négligées jusqu’alors (lentes et de faibles intensités). L’idée maitresse est l’hybridation de plusieurs matériaux fonctionnels avec un cœur du système constitué par des microgénérateurs piézoélectriques (et pyroélectriques) imprimés nécessaires à la génération de charges électriques. L’originalité de ce travail est d’avoir réalisé un système de récupération d’énergie entièrement flexible, au format d’une carte de crédit et compatible avec de plus grandes dimensions, en utilisant des copolymères piézoélectriques de P(VDF-TrFE) sous forme d’encres. Ce matériau est flexible et particulièrement résistant, ce qui le rend attractif pour desapplications mettant en jeu formes complexes, notamment, courbes. Un autre avantage du copolymère de P(VDF-TrFE) est qu’il ne nécessite pas de pré-déformation mécanique comme pour le polymère PVDF et il commence à être aujourd’hui disponible sous forme d’encres pour l’électronique imprimée, ce qui simplifiera et réduira les coûts de fabrication à termes.En premier, nous décrivons le procédé de fabrication par sérigraphie des microgénérateurs en P(VDF-TrFE), suivi par les caractérisations ferroélectriques puis piézoélectriques des dispositifs. A cet effet, nous avons développé des techniques de mesures originales en circuit ouvert qui ont été testées et validées au préalable avec des échantillons dePVDF commercial. La dernière étape a été de réaliser un prototype de récupération d’énergie thermique flexible de faible encombrement (sans radiateur). Cela a été réalisé en hybridant les microgénérateurs précédemment fabriqués avec des feuilles d’alliages à mémoire de forme thermique à base de NiTi, qui est un matériau sensible à un seuil de température donnée.Les résultats phares de cette étude sont : 1) le dépôt multicouches de P(VDF-TrFE)combiné au dépôt d’une électrode souple en PEDOT:PSS, β) l’établissement des caractéristiques ferroélectriques et piézoélectriques en fonction de l’épaisseur de P(VDFTrFE) et enfin γ) la détermination d’un coefficient g31 supérieur à la normale avec0.15 V·m/N. Aussi, nous avons démontré la capacité de ces microgénérateurs à délivrer des tensions utiles de l’ordre de 10 V avec ici une densité d’énergie de proche de 500 μJ/cm3, ces valeurs étant limitées aux conditions de test utilisées.Nous concluons ce travail sur une preuve de concept fonctionnelle de récupérateur d’énergie thermique flexible apte à détecter ou utiliser des variations lentes et faibles de température à partir de sources élémentaires, produisant pour l’instant γ7 V (correspondant à95 μJ) à 65 ºC, et qui à termes pourront être l’air ambiant (chaud ou froid) ou la chaleur de la peau. / This work aims to study innovative solutions for energy harvesting applicable toautonomous wireless sensors for IoT (Internet of Things). It is focused on flexiblepiezoelectric composite materials and a multi-physical approach. The objective is to harvestenergy via strain-induced phenomena from both mechanical and thermal sources, andparticularly sources neglected so far (slow and low). The main idea is the hybridization ofdifferent functional materials with the core of the system being screen printed piezo/pyroelectricmicrogenerators, mandatory to generate electrical charges. The originality of thiswork is to realize large area flexible energy harvesting systems by using ink-basedpiezoelectric copolymers of polyvinylidene fluoride P(VDF-TrFE). This material is veryflexible and durable which makes it attractive for applications in systems with complexshapes. Another benefit of P(VDF-TrFE) is that it does not need to be pre-stretched as PVDFand it is now available in inks for printable electronics which can simplify and reduce theprice of the fabrication process.We first describe the fabrication process of the screen printed P(VDF-TrFE)microgenerators, followed by ferroelectric and piezoelectric characterizations. For thispurpose we have developed optimized methods in open-circuit conditions adapted for flexiblesystems tested and validated on commercial bulk PVDF. The last step was to realize a lowprofile thermal flexible energy harvester prototype (no radiator). It was done by hybridizationof the fabricated microgenerators and foils of shape memory NiTi-based alloy, which is afunctional material sensitive to a given temperature threshold.The key outcomes of this work are: 1) the successful deposition of multilayers ofP(VDF-TrFE) and organic PEDOT:PSS electrode, 2) dielectric, ferroelectric and directpiezoelectric constants reported as a function of film thickness, and 3) the g31 direct voltagecoefficient, measured for the first time, and showing the record value of 0.15 V·m/N. Also,we have demonstrated that in open-circuit conditions, the microgenerators can produce auseful strain-induced voltage of 10 V with an energy density close to 500 μJ/cm3, these valuesbeing limited by the experimental set-up.The concept of thermal energy harvesting composite based on thin film screen printedP(VDF-TrFE) microgenerators was realized and demonstrated to be effective. We concludewith a functional prototype of flexible energy harvester, able to detect non-continuous slowthermal events and producing 37 V (corresponding to 95 μJ) at 65 ºC.

A técnica do triodo de corona com corrente constante foi utilizada para carregar amostras de PVDF na fase &#945, acompanhando a evolução do potencial de superfície durante o carregamento. Com essa técnica foi possível não só obter a fase &#945p a partir da fase &#945 como também analisar o comportamento elétrico de ambas as fases. Os resultados obtidos em ambiente úmido mostram que a forma geral das curvas de potencial nas amostras carregadas com corona positiva e negativa são similares, ou seja, no início do carregamento tem-se um salto inicial, continua crescendo numa taxa mais lenta até alcançar um valor máximo de potencial e a partir deste valor decai para um regime estacionário. Os valores de potenciais alcançados na superfície da amostra não foram suficientes para gerar campos elétricos da ordem 1.5MV/cm, requeridos para induzir uma transição para a fase &#945p. Apesar de ocorrerem mudanças no comportamento elétrico durante os carregamentos, nenhuma mudança na estrutura das amostras foi detectada, usando a técnica de difratometria de raios-X. Em ambiente seco foi verificado que, durante o carregamento, o potencial na superfície da amostra alcançava valores altos quando comparado aos obtidos em ambiente úmido. Verificou-se também, que as amostras apresentavam enrugamento, característicos de materiais poliméricos. As mudanças ocorridas devido ao carregamento foram detectadas pela técnica de raios-X, confirmando a mudança de estrutura para &#945p. O comportamento ferroelétrico das amostras na fase &#945p, foi identificado pela curva de evolução do potencial de superfície, onde se avalia a quantidade de polarização ferroelétrica adquirida. As mudanças de estrutura e das propriedades elétricas em ambiente seco foram irreversíveis. / The constant current corona triode was used for charging &#945-PVDF samples and monitoring their surface potential buildup during poling. It is shown that the method allows one to obtain the polar &#945p form of PVDF from the non-polar &#945-form and also to analuse electrical characteristics of both forms. The experimental results obtained with samples under humid conditions show a similar behavior for positive and negative corona. There is na initial steep increase in the surface potential which then increases passing through a maximum value, and decreases until a steady state is reached. The maximum values attained are not sufficiently high to attain electric fields of around 1.5MV/cm required for causing a phase change from &#945 to &#945p. Furthermore, no change in the structure of the samples is noted in X-ray diffractograms. For measurments carried out under dry conditions, on the other hand, the sample surface potential attain much higher values. The samples become wrinkled after being submitted to these high electric fields (&#62 1.5MV/cm), and this is characteristic of ferroelectric materials. The change to &#945p from samples is confirmed by the structural changes exhibited in X-ray diffractograms. The ferroelectric behavior of the &#945p samples is further identified by the surface potential buildup, from which the remanent polarization can be inferred. The structural as well as the electric changes caused by the corona charging are found to be irreversible.

Foi desenvolvido um novo método para a determinação da polarização ferroelétrica de polímeros ferroelétricos, em particular do PVDF estirado biaxialmente. A técnica consiste em manter constante a corrente através da amostra e medir a evolução da tensão (V versus t) entre os eletrodos da mesma. As medidas foram realizadas em ambiente com atmosfera de ar superseco o que permite desprezar a condução elétrica das amostras, simplificando sobremaneira as equações do problema. Considera-se a existência de dois tipos de polarização: a ferroelétrica, com tempo de chavamento desprezível, e uma polarização elétrica foram realizados em duas situações distintas: com chaveamento e sem chaveamento ferroelétrico. O procedimento permite avaliar a dependência da polarização ferroelétrica com o campo, determinada a partir da equação geral da corrente. Para se descrever a resposta da polarização elétrica dependente do tempo, usa-se o princípio da superposição e assume-se que ela está em fase com o campo elétrico aplicado (processo lento). Será mostrado que é possível determinar a polarização ferroelétrica do polímero PVDF estirado biaxialmente sem a necessidade de determinar a formas funcionais da polarização dependente do tempo e de se conhecer o valor da capacitância da amostra. / In this work a novel method was developed for the determination of the ferroelectric polarization of ferroelectric polymers, in particular of biaxially stretched PVDF. The technique consists of maintaining constant the current through the sample and to measure the evolution of the bias voltage (V versus t) on the electrodes. Measurements were performed in super-dry air, which allows one to neglect the electric surface and volumetric conduction of the samples, simplifying the equations of the problem. It is considered the existence of two polarization types: the ferroelectric, with a very short switching time, and a another polarization dependent of the time. The processes for studying the electric polarization were accomplished in two different situations: with switching and without ferroelectric switching. The procedure allows evaluating the dependence of the ferroelectric polarization on the electric field, determined starting from the general equation of the current. To describe the time dependent polarization it is used the principle of superposition and the polarization value assumed to be in phase with the applied electric field (slow process). It will be shown that it is possible to determine the ferroelectric polarization of the material without the need of the functional form of the polarization and the value of the capacitance of the sample.

O uso de biomateriais para acelerar reparos de fraturas ósseas tem aumentado nos últimos anos. Neste estudo, as propriedades piezelétricas do fluoreto de polivinilideno foram utilizadas com a finalidade de mimetizar os potenciais bioelétricos associados à deformação óssea, que são diminuídos quando ocorre fratura óssea. Estudos histomorfométricos foram efetuados para verificar a influência do polímero. Testes de biocompatibilidade e de esterilização permitiram avaliar os riscos da utilização do polímero como material de implante. O polímero piezelétrico associado à placa de osteossíntese resultou em uma maior quantidade de matriz óssea mineralizada na lesão quando comparado ao implante da placa sem o polímero. / The use of biomaterials to promote accelerated bone fracture repair has been improved in the recent years. In the present study, the piezoelectric properties of poly(vinylidene fluoride) were used with the aim of mimetizing bioelectrical potentials associated to bone strain which decrease when a bone fracture occurs. Histomorphometric studies were accomplished to verify the influence of the polymer. Biocompatibility and sterilization tests assessed any risk related to the use of a polymer as an implantable material. The piezoelectric polymer associated to an osteosynthesis plate resulted in a larger amount of mineralized bone matrix in the lesion when compared to a plate implanted without the polymer.

L'ingénierie tissulaire vise à réparer les tissus endommagés et à récupérer les fonctions biologiques correspondantes. Afin de restaurer un tissu endommagé tel que le système nerveux, la conception et la fabrication de nouveaux types d’échafaudages tissulaires sont nécessaires. Dans ce travail, nous avons développé plusieurs techniques de microfabrication pour le polyfluorure de vinylidène (PVDF), un fluoropolymère thermoplastique, non réactif et piézoélectrique, qui peut être utilisé pour la culture cellulaire et l'ingénierie tissulaire. Nous avons tout d'abord étudié l'adhésion et la croissance cellulaire sur des substrats en PVDF avec des motifs micro et nanométriques en utilisant différentes techniques de fabrication telles que la micro-photolithographie, la lithographie douce, l’impression par microcontact, etc. L'influence de la micro-structuration sur les activités piézo-électriques du PVDF a été caractérisée par différentes méthodes d'analyses de surface (FTIR, XRD). Par la suite, nous avons effectué une étude systématique sur la fabrication de nanofibres de PVDF et leur compatibilité avec la culture cellulaire. Enfin, nous avons démontré la possibilité de doper ces nanofibres avec des nanoparticules magnétiques ce qui les rends excitables à distance par un champ magnétique / Tissue engineering aims at repairing damaged tissues and recovering the lost or degraded biological functions with artificial scaffolds. In order to meet the requirement for more complex functionality such as peripheral nerve reconstruction, new types of scaffold materials are needed. In this work, we developed several micro- and nanofabrication techniques to pattern polyvinylidene fluoride (PVDF), a highly non-reactive, piezoelectric, thermoplastic fluoropolymer, which can serve as new constituents for advanced tissue engineering. We first studied the feasibility of PVDF patterning using conventional photolithography, soft lithography and microcontact printing. The fabricated patterns were systematically characterized by surface analysis techniques (FTIR, XRD) and used for cell culture studies. Then, we developed a study on electrospinning of PVDF nanofibers. Our results showed that the fabricated PVDF nanofibers were compatible with cell-based assays. Finally, we doped electrospun PVDF nanofibers with magnetic nanoparticles, which should make them excitable with a remote magnetic field

Electrospinning was examined for its potential to create functional materials. Three distinct electroactive materials were electrospun into fibers and fiber mats and then characterized with the intent of determining their utility in aerospace and biomedical applications such as micro-air vehicles and the cardiovascular system. Electrospun Graft Elastomers demonstrated potential as actuators, as electromechanical strain testing showed comparable response to the film form of this material. Further improvement of electroactive response was realized with high dielectric inclusions and fiber orientation. Electrospin processing imparted piezoelectric properties to the fibers of poly(vinylidene fluoride). Differential scanning calorimetry and infrared spectroscopy indicated a degree of control over crystalline phase in poly(vinylidene fluoride) fibers based on electrospinning conditions. An increase in dielectric constant in the direction of fiber orientation proved that electrospinning also caused alignment of single-walled carbon nanotubes within the fibers. Ultem®/aligned single-walled carbon nanotube fiber nanocomposites were also fabricated; these showed evidence of enhanced piezoelectric strain response relative to fibers composed of the matrix alone. Thermal and static mechanical testing of all three types of fibers revealed no significant findings that would limit their use in abovementioned applications. Extract biocompatibility tests did not indicate severe adverse reaction of L929 mouse fibroblast cells to fiber mats for either Graft Elastomers or poly(vinylidene fluoride). These contributions prove that functional electroactive materials can be produced utilizing electrospinning as the processing method. This technique is simpler and cheaper to carry out, and resulting fiber mats showed comparable or improved properties and performance compared to other physical forms of the same materials.

Trauma caused by grasping during laparoscopic surgery is something which will never be fully eradicated however efforts should be taken to reduce the potential to cause trauma by grasping. Tissue is often grasped with excessive forces for long periods of time during surgeries such as cholecystectomies and colectomies. This along with failed grasping actions and the occurrence of slip has been shown to damage the tissue. Design features often employed within graspers such as profiling and the occlusion mechanism of the instrument cause areas of high, uneven distribution of pressures on the tissue which can result in perforation or tissue tearing. By investigating these contributing factors, development of graspers with a low risk to cause damage this combined with actuating the grasping force should reduce the incidence of grasping trauma, currently at estimated at one incidence per procedure. These trauma events can lead to conversion to open surgery, peritonitis and even death. Development of an autonomous grasping instrument to detect and prevent slip by actuating the grasping force is reported. Piezoelectric sensors are used to detect incipient slip and slip events. A closed loop control system then reacts to these perceived slip events to prevent slip occurring by actuating the applied force by small increments to increase or decrease grasping force. This leads to a system in which only the required amount of force necessary to overcome pull force is applied to the tissue. Other areas of investigation to reduce tissue trauma are presented. In chapter 3 design features such as surface profiling and fenestrations are evaluated to determine the potential to cause damage. A variety of profiles and fenestrations are studied and each is reported by representing the applied force to retention force ratio which indicates how good the profile is at retaining tissue against a pull force. The aim of this study was to develop surface profiling which had a high retention force but a reduced number of high stress areas which can lead to tissue damage. Three new parallel action grasping designs are presented and evaluated using finite element analysis. Parallel action grasping is important in reducing tissue trauma as it distributes pressure evenly across the active grasping area as opposed to more conventional pivot style graspers which have high stress concentration areas in the proximal opening. Each area of study within the thesis addresses areas of concern which have been shown to cause tissue trauma and postulates viable solutions to reduce the incidences of tissue trauma during laparoscopic surgery with the ultimate aim of developing a deployable and autonomous grasping device which will detect and prevent slip.