Title: Optimization of properties of Ti based alloys for biomedical and structural applications Author: Josef Stráský Department / Institute: Department of Physics of Materials Supervisor of the doctoral thesis: Assoc. Prof. Miloš Janeček, Ph.D. Abstract: Titanium alloys belong to the mostly used biomaterials for orthopaedic implants. Advanced surface treatments of Ti alloys for orthopaedic use and newly developed biomedical beta-Ti alloys are investigated in this thesis. Wide spectrum of experimental techniques was employed in order to correlate material processing, microstructure and mechanical properties. Electric discharge machining was used as a biocompatibility enhancing surface treatment of Ti-6Al-4V alloy, but the treated material suffered from the poor fatigue performance. Two subsequent surface treatments - chemical etching and shot- peening - were proposed and it was shown that their combination significantly improves the fatigue performance of the material making it applicable in orthopaedics. This process was patented in the Czech Republic. The thesis further reviews complex problematic of biocompatible beta-Ti alloys. Several new biocompatible beta-Ti alloys were designed on the basis of Ti-Nb-Zr-Ta quaternary alloy. The effect of Fe, Si and O additions on microstructure, elastic modulus and...

As diversas aplicações tecnológicas de nanopartículas magnéticas (NPM) vêm intensificando o interesse por materiais com propriedades magnéticas diferenciadas, como magnetização de saturação (MS) intensificada e comportamento superparamagnético. Embora MNP metálicas de Fe, Co e bimetálicas de FeCo e FePt possuam altos valores de MS, sua baixa estabilidade química dificulta aplicações em escala nanométrica. Neste trabalho foram sintetizadas NPM de Fe, Co, FeCo e FePt com alta estabilidade química e rigoroso controle morfológico. NPM de óxido metálicos (Fe e Co) também foram obtidas. Dois métodos de síntese foram empregados. Usando método baseado em sistemas nanoheterogêneos (sistemas micelares ou de microemulsão inversa), foram sintetizadas NPM de Fe3O4 e Co metálico. Foram empregados surfactantes cátion-substituídos: dodecil sulfato de ferro(III) (FeDS) e dodecil sulfato de cobalto(II) (CoDS). Para a síntese das NPM, foram estudados e determinados a concentração micelar crítica do FeDS em 1-octanol (cmc = 0,90 mmol L-1) e o diagrama de fases pseudoternário para o sistema n-heptano/CoDS/n-butanol/H2O. NPM esferoidais de magnetita com3,4 nm de diâmetro e comportamento quase-paramagnético foram obtidas usando sistemas micelares de FeDS em 1-octanol. Já as NPM de Co obtidas via microemulsão inversa, apesar da larga distribuição de tamanho e baixa MS, são quimicamente estáveis e superparamagnéticas. O segundo método é baseado na decomposição térmica de complexos metálicos, pelo qual foram preparadas NPM esféricas de FePt e de óxidos metálicos (Fe3O4, FeXO1-X, (Co,Fe)XO1-X e CoFe2O4) com morfologia controlada e estabilidade química. O método não mostrou a mesma efetividade na síntese de NPM de FeAg e FeCo: a liga FeAg não foi obtida enquanto que NPM de FeCo com estabilidade química foram obtidas sem controle morfológico. NPM de Fe e FeCo foram preparadas a partir da redução térmica de NPM de Fe3O4 e CoFe2O4, as quais foram previamente recobertas com sílica. A sílica previne a sinterização inter-partículas, além de proporcionar caráter hidrofílico e biocompatibilidade ao material. As amostras reduzidas apresentaram aumento dos valores de MS (entre 21,3 e 163,9%), o qual é diretamente proporcional às dimensões das NPM. O recobrimento com sílica foi realizado via hidrólise de tetraetilortosilicato (TEOS) em sistema de microemulsão inversa. A espessura da camada de sílica foi controlada variando-se o tempo de reação e as concentrações de TEOS e de NPM, sendo então proposto um mecanismo do processo de recobrimento. Algumas amostras receberam um recobrimento adicional de TiO2 na fase anatase, para o qual foi empregado etilenoglicol como solvente e ligante para formação de glicolato de Ti como precursor. A espessura da camada de TiO2 (2-12 nm) é controlada variando as quantidades relativas entre NPM e o precursor de Ti. Ensaios de hipertermia magnética foram realizados para as amostras recobertas com sílica. Ensaios de hipertermia magnéticas mostram grande aumento da taxa de aquecimento das amostras após a redução térmica, mesmo para dispersões diluídas de NPM (0,6 a 4,5 mg mL-1). Taxas de aquecimento entre 0,3 e 3,0oC min-1 e SAR entre 37,2 e 96,3 W g-1. foram obtidos. A atividade fotocatalítica das amostras recobertas foram próximas à da fase anatase pura, com a vantagem de possuir um núcleo magnético que permite a recuperação do catalisador pela simples aplicação de campos magnéticos externos. Os resultados preliminares dos ensaios de hipertermia magnética e fotocatálise indicam um forte potencial dos materiais aqui relatados para aplicações em biomedicina e em fotocatálise. / The most diverse technological applications of magnetic nanoparticles (MNP) have intensifiedthe interest for materials with different magnetic properties such as enhanced saturationmagnetization (MS) and superparamagnetic behavior. Despite the high MS values of metalparticles of Fe, Co, FeCo and FePt, their low chemical stability hinders most applications at thenanoscale. This thesis reports the synthesis of metallic Fe and Co and bimetallic FeCo and FePtMNP with high chemical stability and strict morphological control. MNP of iron oxide and mixediron-cobalt oxide were also synthesized. Two methods were employed. The first method, basedon nanoheterogeneous systems (micellar or reverse microemulsion systems), was used toprepare magnetite and metallic Co NPM. The method applies cation-substituted surfactants:iron(III) dodecyl sulfate iron (FeDS) and cobalt(II) dodecyl sulfate (CoDS). Before the MNPsyntheses, it were studied e determined the critical micelle concentration of FeDS in 1-octanol(cmc = 0.90 mmol L-1) and the pseudo-ternary phase diagram of n-heptane/CoDS/nbutanol/H2O. Spheroidal MNP of magnetite with 3.4 nm in diameter and quasi-paramagneticbehavior were prepared in octanolic FeDS micellar systems. Despite their broad sizedistribution and low MS, metallic Co MNP were produced in reverse microemulsions withchemical stability and superparamagnetic behavior. The second synthesis method, based onthermal decomposition of metal complexes, was employed to prepare spherical FePt and metaloxides (Fe3O4, FeXO1-X, (Co, Fe)XO1-X and CoFe2O4) MNP. Strict morphological control and highchemical stability were reached. Such method does not show the same effectiveness tosynthesize FeAg and FeCo MNP: the FeAg bimetallic alloy was not obtained while FeCo MNPwith chemical stability and compositional control were prepared with no morphological control.Fe and FeCo MNP were produced by thermal reduction of silica-coated Fe3O4 and CoFe2O4 MPN. The coating, beyond to prevent inter-particle sintering, provides biocompatibility andhydrophilic character. The reduced samples showed a significant increase in MS values(between 21.3 and 163.9%), which is directly proportional to MNP size. The silica coating wasaccomplished by tetraethylorthosilicate (TEOS) hydrolysis in reverse microemulsions. Thethickness of the silica layer is controlled by varying the reaction time and concentration of TEOSand NPM. The observations during coating process allowed to propose its probable mechanism.An additional coating of TiO2 (anatase phase) was performed onto silica layer for somesamples. Anatase coating was achieved by using ethylene glycol as both solvent and ligand toproduce an intermediate complex Ti precursor. The variation of the relative amounts of NPMand the Ti precursor allows to control the thickness of the anatase layer between 2 and 12 nm. Assays of magnetic hyperthermia were performed for silica-coated samples. The heating rate of the reduced samples increases after thermal reduction, even for dilute MNP dispersions (0.6 to4.5 mg mL-1). Heating rates between 0.3 and 3.0o C min-1 and SAR in the range of 37.2 96.3 Wg-1 were obtained. The photocatalytic activities of pure anatase particles and TiO2 -coated MNPwere close, but the magnetic samples has the advantage of being recovered from reactionmedia by applying the external magnetic fields. The preliminary results of magnetichyperthermia and photocatalysis assays indicate such materials have strong potential forapplications in biomedicine and photocatalysis.

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Multifunctional superparamagnetic iron oxide nanoparticles (SPIONs) coated with silica are a promising research field for lots of biomedical applications. The scope of this work is a preparation of SPIONs and coating them with silica to form core-shell structured nanoparticles for nanomedicine applications. SPIONs were synthesized by two chemical methods – co-precipitation and thermal decomposition of organic iron precursor. Prepared nanoparticles were carefully characterized –average size, size distribution, morphology, crystallinity, colloidal stability and magnetic properties were studied. After comparing SPIONs synthetized by two routes the most suitable method for biomedical applicable nanoparticles preparation is determined. The nanomedicine requires nanoparticles of the highest quality. The next step was coating SPIONs with silica shell. For this purpose inverse microemulsion method was chosen. TEOS was used as a silica precursor. Mean size, size distribution, magnetic properties, structure of silica shell were studied.

no / This review summarises the recent developments in the synthesis and applications of polymers derived from malic acid. There has been an increased interest in the design of sustainable and biodegradable polymers as a result of the drive to use renewable feedstocks as an alternative to petrochemicals in addition to their significant potential in biomedical applications. Synthetic strategies to access polymers from malic acid based on both condensation and ring-opening polymerization, across a broad range of conditions, are reviewed along with their advantages and limits. The role that such materials are studied for in biomedical applications is discussed, and their environmental impact based on the biodegradability of the malic polymer backbone is outlined. / The Royal Society, EPSRC, BBSRC

Η ανίχνευση των δυναμικών δραστηριότητας συμβάλλει στη μείωση των δεδομένων προς αποστολή από ένα εμφυτεύσιμο σύστημα ασύρματης καταγραφής της νευρωνικής δραστηριότητας ενός ζώντα οργανισμού. Η παρούσα Mεταπτυχιακή Διπλωματική Εργασία έχει ως στόχο την σχεδίαση ενός ανιχνευτή δυναμικών δραστηριότητας σε νευρωνικές κυματομορφές ικανό να λειτουργεί σε περιβάλλον χαμηλής τάσης τροφοδοσίας για την επίτευξη μειωμένης κατανάλωσης ισχύος. Για το σκοπό αυτό, προτείνεται η σχεδίαση συστημάτων στο πεδίο του λογαρίθμου με τη χρήση MOS τρανζίστορ που είναι πολωμένα στην περιοχή υποκατωφλίου. Αρχικά, μελετώνται τα φυσικά χαρακτηριστικά των δυναμικών δραστηριότητας, δηλαδή το συχνοτικό τους περιεχόμενο και το σχήμα τους στο πεδίο του χρόνου. Επίσης, παρουσιάζεται ο μη-γραμμικός τελεστής ενέργειας και ο λόγος για τον οποίο αυτός καθίσταται σημαντικός στην επεξεργασία νευρωνικών σημάτων. Στη συνέχεια, παρουσιάζονται οι βασικές αρχές για τη σχεδίαση κυκλωμάτων στο πεδίο του λογαρίθμου. Ακόμα, κάνοντας χρήση των βασικών δομικών μονάδων του λογαριθμικού πεδίου, των μη-γραμμικών διαγωγών Ε Cells, υλοποιούνται τόσο οι συμπληρωματικοί τελεστές όσο και οι δομές επεξεργασίας σήματος που είναι απαραίτητες για την πραγματοποίηση του μη-γραμμικού τελεστή ενέργειας. Οι δομές αυτές είναι διαφοριστές και πολλαπλασιαστές τεσσάρων τεταρτημορίων τρόπου ρεύματος. Τέλος, δίνεται η ολοκλήρωση του συστήματος με την σχεδίαση ενός συγκριτή ρεύματος που επιτελεί την λειτουργία της κατωφλιοποίησης. Για την εξομοίωση του συστήματος, χρησιμοποιείται μια νευρωνική κυματομορφή, το Analog Design Environment του λογισμικού Cadence και οι παράμετροι της τεχνολογίας TSMC 130nm. / The detection of action potentials contributes to the reduction of data to be transmitted by an implantable wireless neural activity recording system. The goal of the present M.Sc. Τhesis is the design of an action potential detector capable of operating in a low-voltage environment, in order to achieve reduced power dissipation. For this purpose, the log-domain designing technique is suggested by using MOS transistors operating in the subthreshold region. Initially, the physical characteristics of action potentials are studied, i.e. the frequential content and time-domain shape. Moreover, the nonlinear energy operator is presented in addition to the reason that makes this system crucial for neural signal processing. Thereafter, the basic principles of designing log-domain circuits are presented. Furthermore, the complementary operators as well as the signal processing blocks that are necessary for the realization of NEO are implemented by using the main log-domain building units, the nonlinear transconductors E cells. The blocks required for the NEO implementation are current-mode differentiators and four-quadrant multipliers. Finally, the complete system is given after the design of a current comparator which is responsible for the operation of thresholding. The simulation of the system has been performed through the utilization of the Analog Design Environment of Cadence software and the design kit of TSMC 130nm process in addition to a neural waveform.

Partículas poliméricas com propriedades magnéticas podem ser utilizadas tanto em aplicações terapêuticas in vivo, como agentes de liberação controlada de princípios ativos, ex vivo, na extração de células cancerígenas do organismo, ou ainda in vitro, em diagnósticos. A necessidade de materiais inteligentes e biocompatíveis, como agentes de encapsulação destas partículas magnéticas, leva ao uso de polímeros sensíveis a estímulos. Em aplicações terapêuticas, esta tecnologia é baseada na localização das partículas através da aplicação de um campo magnético e na concentração da droga na área de interesse. Esta etapa é seguida pela liberação da droga, utilizando-se as propriedades sensíveis dos polímeros. Dessa forma, este trabalho de tese se dedica ao estudo da obtenção de nanopartículas constituídas de uma matriz polimérica sensível a estímulos e de partículas de óxido de ferro (?-Fe2O3 e Fe3O4). Inicialmente, nanogéis à base de poli(NVCL-co-AA) foram obtidos através do método de polimerização por precipitação. A Poli(Nvinilcaprolactama) (PNVCL) é um polímero termo-sensível, que possui temperatura crítica inferior de solubilização (LCST) próxima à temperatura fisiológica (35-38 ºC) e é conhecida, ainda, por possuir maior biocompatibilidade, em comparação a outros polímeros do gênero. O poli(ácido acrílico) (PAA), por sua vez, é um polímero que apresenta sensibilidade ao pH. Nesta etapa estudou-se a influência de alguns parâmetros de síntese nos diâmetros de partículas, na polidispersidade e na sensibilidade à temperatura dos nanogéis. A sensibilidade ao pH também foi estudada em função da concentração de ácido acrílico adicionado nas sínteses. Em seguida, realizou-se o estudo da encapsulação de nanopartículas magnéticas complexadas com dextrana em nanogéis de PNVCL, utilizando-se a técnica de polimerização em miniemulsão inversa. Os nanogéis magnéticos sensíveis à temperatura foram caracterizados quanto ao diâmetro de partículas (DP) e distribuição do diâmetro de partículas (DDP), pela técnica de espalhamento de luz. A sensibilidade à temperatura dos nanogéis magnéticos também foi estudada por espalhamento de luz, através de medidas de diâmetro de partículas em diferentes temperaturas. As medidas de magnetização foram obtidas em um magnetômetro de amostra vibrante (MAV). Análises de infra vermelho (FTIR) e de difratometria de raios X revelaram qualitativamente a encapsulação das nanopartículas magnéticas. A eficiência de incorporação das nanopartículas de óxido de ferro foi estudada através de análises termogravimétricas (TGA) e medidas de magnetização. As características morfológicas dos nanogéis magnéticos foram observadas por microscopia eletrônica de transmissão (TEM). / Polymeric particles with magnetic properties can be useful for in vivo therapeutic applications, as agents for controlled drug release, for ex vivo applications, as agents for the extraction of cancer cells, and finally, for the diagnosis in vitro. The search for biocompatible and smart materials as agents for the encapsulation of magnetic particles, leads to the use of stmuli-responsive polymers. In therapeutic applications, this technology is based on the localization and the concentration of the particles containing the drug in the area of interest by applying a magnetic field. This step is followed by the release of the drug, using the sensitive properties of the polymers. In this context, this thesis is devoted to the preparation of nanoparticles constituted by a stimuli-responsive polymer matrix and particles of iron oxide (?-Fe2O3 e Fe3O4). First of all, we performed the synthesis of poly(NVCL-co-AA)-based nanogels using the precipitation polymerization method. Poly(N-vinilcaprolactama) (PNVCL) is a thermo-responsive polymer which presents the lower critical solution temperature (LCST) near the physiological temperature (35-38 °C) and it is well known by its greater biocompatibility, in comparison with other themallysensitive polymers. On the other hand, the poly(acrylic acid) (PAA) is known by its sensibility to changes in the enviromental pH. In this stage, the influence of some synthesis parameters on the particles diameter, polydispersity and themally-sensitive behavior of the nanogels was evaluated. The pH-sensibility behavior was also studied as a function of the AA concentration in the synthesis. As a second step, the study of the incorporation of dextran-coated magnetic nanoparticles in the PNVCL-based nanogels using the inverse miniemulsion polymerization was preformed. The thermo-responsive magnetic nanogels were characterized in terms of particles diameter (PD) and particles size distribution (PSD) using light scattering. The temperature sensitivity of the magnetic nanogels was also studied by light scattering, with measurements of particles diameter as a function of temperature. The magnetization measurements were obtained on a vibrating sample magnetometer (VSM). Analysis of infra-red (FTIR) and X-ray diffraction revealed qualitatively the incorporation of magnetic nanoparticles. The incorporation efficiency of iron oxide nanoparticles was studied by thermo-gravimetric analysis (TGA) and magnetic measurements. The morphological characteristics of the magnetic nanogels were observed by transmission electron microscopy (TEM).

Depuis quelques décennies, les nanomatériaux et tout particulièrement les nanoparticules d’oxyde de fer (magnétite/maghémite) superparamagnétiques ont connus un intérêt croissant en nano-médecine. Leur biocompatibilité et leurs propriétés magnétiques permettent notamment leur utilisation à des fins de diagnostic (IRM, Imagerie optique et nucléaire…) et de thérapie (Hyperthermie, nano vectorisation…). Au cours de cette thèse, la première étape a consisté à étudier en détails l’influence de plusieurs paramètres de synthèse sur les propriétés finales des nanoparticules d’oxyde de fer magnétique. Cette étude avait pour but de développer et d’optimiser une méthode de synthèse dérivée de la méthode de synthèse classique dite de co-précipitation mais modifiée par ajout de ligand citrates au cours de la synthèse. Des nanoparticules d’oxyde de fer d’une taille pouvant être contrôlée entre 4 et 13 nm recouvertes par une couronne de ligands citrates ont ainsi été synthétisées, celles-ci présentent une aimantation à saturation atteignant jusqu’à 75 emu/g d’oxyde de fer qui est une valeur particulièrement haute pour des nanoparticules de cette taille. Tout au long de ce travail, la caractérisation de ces nanoparticules par un panel étendu de techniques (MET, DRX, Mössbauer, IRTF, XPS, mesures magnétiques, DLS …) à permis notamment d’étudier de façon précise les relations existantes entre la taille, le taux de ligand, la composition et les propriétés magnétiques des nanoparticules synthétisées. Ces nanoparticules fonctionnalisées par des citrates ont ensuite été testées en milieu biologique afin d’évaluer leur internalisation dans les cellules et leur cytotoxicité. Dans un deuxième temps, d’autres travaux ont été menés sur les nanoparticules d’oxyde de fer. Notamment le remplacement des ligands citrates par un polymère bio-inspiré pouvant, selon les fonctions chimiques qui lui sont adjointes, avoir de multiples applications dans le domaine biomédical / From decades now, nanomaterials and especially superparamagnetic iron oxide nanoparticles are studied for their numerous applications in nanomedecine area. The biocompatibility and the magnetic properties of such nano-objects allow their utilization for diagnostic (MRI, optical imagery, PET…) and for therapy application (nanovectorization, hyperthermia…) During this thesis work, the first step was to study the influence of several synthesis parameters on the final properties of the magnetic iron oxide nanoparticles. The aim of this study was the development and the optimization of the widely used way of synthesis by co-precipitation modified by a ligand addition during the growth step of the synthesis. Citrate capped iron oxide nanoparticles with a controlled size between 4 and 13 nm have been synthesized, the saturation magnetization of these nanoparticles reach 75 emu/g of iron oxide, this value is particularly high for nanoparticles of such sizes. During this work, the large panel of characterizations performed on these nanoparticles (TEM, XRD, Mössbauer, FTIR, XPS, DLS, Magnetic measurement) allowed to study precisely the relations between size, ligand ratio, composition and magnetic properties of the synthesized nanoparticles. The interaction between the synthesized citrate capped nanoparticles and biological materials such as human cells have been investigated in-vitro notably to evaluate cells internalization and citotoxicity. In a second step, some additional works have been performed on the citrate capped iron oxide nanoparticles in order to replace the citrate ligand by a bio-inspired polymer (poly-oxazoline). This polymer can have multiple biomedical applications depending of the pendent chemical groups that have been fixed on it

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-07-27T23:02:40Z No. of bitstreams: 1 BASÍLIO SERRANO DE SOUSA FILHO – DISSERTAÇÃO (UAEMa) 2015.pdf: 6550059 bytes, checksum: df64991899dee3033f0a17c6e1047024 (MD5) / Made available in DSpace on 2018-07-27T23:02:40Z (GMT). No. of bitstreams: 1 BASÍLIO SERRANO DE SOUSA FILHO – DISSERTAÇÃO (UAEMa) 2015.pdf: 6550059 bytes, checksum: df64991899dee3033f0a17c6e1047024 (MD5) Previous issue date: 2015-08-31 / CNPq / O objetivo deste trabalho é produzir ligas de titânio-nióbio (Ti-Nb) pelo processo de fusão a plasma seguido d emoldagem por injeção em molde metálico (PSPP, plasma skull push-pull). As ligas de Ti-Nb foram produzidas com teores crescentes de nióbio correspondentes a 5, 10, 15, 20 e 30% (em peso). Essas ligas foram caracterizadas quanto a sua composição química, microestrutura, propriedades mecânicas e resistência à corrosão, visando futuras aplicações biomédicas. A microestrutura observada nestas ligas variou em função da concentração de Nb, manifestando-se na variação dos tamanhos de grãos, estando presentes nos contornos de grãos camadas de fase α nucleadas, placas de Widmanstatten e inclusas na matriz intragranular lamelas da fase α ou fase β nucleadas. As análises de difração de raios X revelaram picos característicos das fases α, α’, α” e β. Nas concentrações entre 5 a 10%p de Nb, observou-se predominantemente as fases α e α’. Nas concentrações entre 15 e 20%p de Nb se alternaram as fases α, α’, α” e β. A concentração de 30%p de Nb apresentou as fases α” e β, sendo a β em maiores proporções. Os resultados de microdureza registraram a dependência quanto à microestrutura, presente em cada composição. O módulo de elasticidade (E) foi influenciado pelas fases constituintes, por alterações da microestrutura, apresentando correlação direta com o teor de Nb. As ligas Ti-Nb foram submetidas a ensaios eletroquímicos de corrosão segundo a norma ASTM F2129-15, e utilizando fluido corporal simulado (SBF), à temperatura corpórea (37ºC). Avaliou-se a influência dos teores de Nb sobre as medidas de polarização potenciodinâmica linear (PPL) e a espectroscopia de impedância eletroquímica (EIE). A resistência à corrosão das ligas Ti-10Nb e Ti-30Nb foi superior à das outras composições, embora haja ocorrência de formação de filmes de passivação em todas as ligas estudadas. O circuito elétrico equivalente, obtido dos diagramas de impedância, confirma a formação dos filmes de passivação, mais evidentes nas concentrações anteriormente citadas. / The objective of this work is to produce titanium alloys, niubium (Nb-Ti) by plasma fusion process followed by injection molding metal mold (PSPP, plasma push-pull skull). The Ti-Nb alloys were produced with increasing levels of niobium corresponding to 5, 10, 15, 20 and 30% (by weight). These alloys were characterized for their chemical composition, microstructure, mechanical properties and corrosion resistance, aiming future biomedical applications. The microstructure observed in such alloys varies with the concentration of Nb, manifesting itself in the range of grain sizes being present in the contours of grain layers of α nucleated phase Widmanstätten plates and included in the intragranular array plates of the α phase or phase β nucleated. The analysis of X-ray diffraction showed the characteristic peaks of phases α, α’, α” and β. At concentration of 5 to 10 wt% of Nb, it was observed predominantly the α phase and α’. In concentrations between 15 and 20 wt% Nb alternated phases α, α’, α” and β. The concentration of 30wt% Nb presented phases α’ and β, with the β in higher proportions. The microhardness results reported in dependence on the microstructure present in each composition. The modulus of elasticity (E) is influenced by the constituent phases, changes the microstructure, having a direct correlation with the Nb content. The Ti-Nb alloys were subjected to electrochemical corrosion tests according to ASTM F2129-15, and using simulated body fluid (SBF) at body temperature (37ºC). We evaluated the influence of N levels on linear potendiodynamic polarization measurements (PPL) and electrochemical impedance spectroscopy (EIS). The corrosion resistance of Ti-10Nb and Ti-30Nb alloy was superior to other compositions, although there is occurrence of formation of passivating films on all studied alloys. The electoral equivalent circuit obtained from the impedance diagrams, confirms the formation of passivating films on all studied alloys. The electrical equivalent circuit obtained from the impedance diagrams, confirms the formation of passivation films, most evident in the concentrations mentioned above.

Submitted by Erika Demachki (erikademachki@gmail.com) on 2017-04-27T17:01:46Z No. of bitstreams: 2 Tese - Luis Cesar Branquinho - 2014.pdf: 6091709 bytes, checksum: 2c59441af9866c02cd7a2cc3cc667b3e (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-05-03T11:40:46Z (GMT) No. of bitstreams: 2 Tese - Luis Cesar Branquinho - 2014.pdf: 6091709 bytes, checksum: 2c59441af9866c02cd7a2cc3cc667b3e (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-05-03T11:40:46Z (GMT). No. of bitstreams: 2 Tese - Luis Cesar Branquinho - 2014.pdf: 6091709 bytes, checksum: 2c59441af9866c02cd7a2cc3cc667b3e (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2014-12-09 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Magnetic nanoparticles can generate heat when submitted to alternating magnetic fields of adequate amplitude and frequency. This phenomenon is named magnetic hyperthermia and has several therapeutic applications, as for example, in the treatment of cancer. In general, the theoretical models used to describe this neglect the effect of interparticle interaction. In this thesis we investigate the effect of magnetic dipolar interaction in the magnetothermal efficiency (named specific loss power – SLP) of bicompatible magnetic nanoparticles. Firstly, we develop a chain of magnetic particles model, where we prove that the interaction leads to a contribution to the uniaxial anisotropy. This term in the free energy density allowed us to extract from the electron magnetic resonance technique (EMR) information about the mean chain size in the colloid. Further, this additional magnetic nanoparticle anisotropy term was used to develop an analytical theoretical model that takes into account the effect of the dipolar interaction between nanoparticles to SLP, considering the case where the magnetization responds linearly to the field (Linear Response Theory). Our calculations indicate that depending on the particle parameters, specially the anisotropy, the effect can be to enhance or decrease the heat generation. Moreover, we showed that increasing the chain size (number of particles in the chain) the optimal particle size for hyperthermia can decrease up to 30% in comparison with non-interacting particles. This result has several clinical implications, which allowed us to suggest some strategies for improving the therapeutic efficacy. In order to investigate experimentally the effect, two magnetic fluids, one containing spherical nanoparticles based on manganese ferrite (MnF-citrate) in the superparamagnetic regime, and another commercial one (BNF-starch) magnetite-based with a shape of a parallellepiped and blocked, were selected and deeply characterized. We found a decrease of SLP increasing the chain size for the MnF sample, while for BNF-starch no effect was found at the same experimental conditions. The decrease of SLP in the MnF sample, within the particle concentration range, was explained considering in the model not only the effect in the anisotropy but also by an increase in the damping factor parameter, a term correlated to spin-phonon interaction. Data obtained using EMR and Monte Carlo simulations corroborate our hypothesis. The absence of concentration effect for the BNF sample was attributed to the higher anisotropy value and to the probable influence of brownian relaxation. In addition, the same chain model was used to investigate the behavior of blocked nanoparticles of Stoner-Wohlfarth type. In this case, we demonstrate that the chain formation increases the magnetic hyperthermia, as found in magnetosomes. Finally, we showed that a fluctuation of the dipolar interaction field between particles in the chain, which does not destroy the symmetry of this term, shows a Vogel-Fulcher behaviour in the weak coupling regime. / Nanopartículas magnéticas são capazes de gerar calor quando submetidas a campo magnético alternado de amplitude e frequência adequadas. Este fenômeno é conhecido como magnetohipertermia e possui aplicações terapêuticas como, por exemplo, no tratamento de câncer. Em geral, os modelos teóricos que descrevem o fenômeno não levam em conta efeitos associados à interação partícula-partícula. Nesta tese investigamos o efeito da interação dipolar magnética na eficiência magnetotérmica (SLP) de nanopartículas magnéticas biocompatíveis. Primeiramente desenvolvemos um modelo de cadeia de nanopartículas magnéticas, aonde provamos que a interação entre partículas que formam uma cadeia linear equivalem a uma contribuição uniaxial a anisotropia. Essa contribuição à densidade de energia permitiu que obtivéssemos por meio da técnica de ressonância magnética eletrônica (RME) informações acerca do tamanho médio de aglomerado na suspensão coloidal. Posteriormente utilizamos esse termo adicional da anisotropia efetiva da nanopartícula para propor um modelo teórico analítico que leve em consideração o efeito de tal interação na eficiência de aquecimento de nanopartículas magnéticas em um fluido para o caso em que a magnetização das nanopartículas responde linearmente ao campo (Teoria da Resposta Linear). Nossos cálculos indicaram que, dependendo de parâmetros da nanopartícula, em particular da anisotropia, este efeito pode aumentar ou diminuir a geração de calor. Além disso, mostramos que o aumento do número de partículas formando cadeias lineares reduz o diâmetro ótimo para hipertermia em até 30% em relação ao valor esperado para partículas isoladas. Este resultado possui fortes implicações clínicas, e permitiu que sugeríssemos algumas estratégias para aumentar a eficiência terapêutica. No intuito de investigar experimentalmente este efeito, dois fluidos magnéticos, um contendo nanopartículas esféricas de ferrita de Mn (MnF-citrato) no regime superparamagnético e outra comercial (BNF-starch) à base de magnetita com forma de nanoparalelepípedos e contendo partículas bloqueadas, foram selecionados e amplamente caracterizados. Observamos uma diminuição no SLP com o aumento de partículas na cadeia para a amostra MnF-citrato, para todos os valores de campo, enquanto que para a amostra BNF-starch não percebemos alteração do SLP. O decréscimo do SLP da amostra MnF, na faixa de concentração investigada, foi explicado incluindo não apenas o efeito na anisotropia efetiva, mas também o aumento no valor do fator de amortecimento. Dados de RME e simulação de Monte Carlo corroboraram tal hipótese. A ausência de efeito para amostra BNF-starch foi atribuída à alta anisotropia e provável influência de relaxação browniana. Adicionalmente, o modelo de cadeia foi usado para explicar o comportamento de nanopartículas bloqueadas do tipo Stoner-Wohlfarth. Neste caso demonstramos que a formação de cadeias aumenta a hipertermia magnética, como verificado em magnetossomos. Finalmente, mostramos que uma flutuação no campo dipolar interpartículas na cadeia, que não destrua a simetria desta contribuição, fornece um comportamento do tipo Vogel-Fulcher no regime fracamente interagente.