Programa de Pós-graduação em Física

URI Permanente desta comunidade

http://200.137.215.59/tede/handle/tde/276

Navegar

Agora exibindo 1 - 8 de 8

Efeito da interação dipolar magnética na eficiência de aquecimento de nanopartículas: Implicações para magnetohipertermia
(Universidade Federal de Goiás, 2014-12-09) Branquinho, Luis Cesar; Bakuzis, Andris Figueiroa; http://lattes.cnpq.br/3477269475651042; Bakuzis, Andris Figueiroa; Pelegrini, Fernando; Franco Junior, Adolfo; Morais, Paulo Cesar de; Landi, Gabriel Teixeira
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.
Propriedades magneto-ópticas de colóides magnéticos á base de nanopartículas de magnetita recobertas com prata
(Universidade Federal de Goiás, 2010-05-17) Lopes Junior, José Carlos Campello; Bakuzis, Andris Figueiroa; http://lattes.cnpq.br/3477269475651042
In this work we investigated, theoretically and experimentally, the magneto-optical properties of a magnetic fluid consisting of core-shell nanoparticles, where the core is made of magnetite, while the shell is silver. The theoretical model used was based on Mie s theory, under the electrostatic approximation, i.e. for nanoparticles with diameters much less than the incident wavelength (lambda). A Clausius-Mosotti for a core-shell system was used to calculate the electrical susceptibility of the core-shell nanoparticle for equals to 632 nm. The susceptibility was shown to be strongly dependent on the core diameter and the shell thickness. Nevertheless, a maximum value of 7.20 (greater than isolated nanoparticles of silver, which has 0 = 4.30, or magnetite with 0 = 1.47) was obtained for a fraction f, defined as f = (Dcore/Dcore−shell)3, equal to 0.36. This result suggest that there exist an ideal fraction f for nanocomposites with enhanced optical properties. In order to compare our theoretical results with experimental data a core-shell magnetic fluid was synthesized on the Institute of Chemistry of UFG by the group of Dr. Em´ılia Celma de Oliveira Lima. The nanoparticles were suspended in water at fisiological pH and recovered by a double layer of lauric acid (dodecanoic acid). The nanoparticles were characterized by X-ray diffraction, high resolution electron transmission, energy dispersive X-ray spectroscopy, and vibrating sample magnetometer. The Sturges method was used to obtain the nanoparticle diameter histogram. The data revealed the existence of a bimodal nanoparticle distribution. Both distributions were curve fitted using a lognormal function. The modal diameter of one of them was 9.24 ± 0.03 nm with a dispersity of 0.27 ± 0.02, while for the other one we found a modal diameter of 23.0 ± 0.2 nm with disperisty 0.2 ± 0.1. The energy dispersive X-ray spectroscopy confirmed the existence of magnetite and silver only for larger particle diameters, while the lower ones only magnetite was found. From the experimental analysis we confirmed the synthesis of a magnetic fluid containing 10% of core-shell nanoparticles. Magnetization data was used to estimate the magnetic particle volume fraction. The magneto-optical properties were obtained using a magnetotransmissivity technique, where the polarizer and analyser axis are positioned on the magnetic field direction. The sample containing 10% of core-shell nanoparticles, with a total particle volume fraction of 0.18%, had shown an extinction of light of 100% for a magnetic field of only 500 Oe, while a magnetic fluid with 100% of core nanoparticles, at a similar particle concentration (0.15%), had shown a 50% extinction of light at the same field range. The magnetotransmissivity data were curve fitted with a theoretical model containing only two parameters, one related to the electrical susceptibility and the other to the formation of self-organized nanostructures in the colloid. The mean agglomerate size (nanoparticles forming linear chains) had changed from 2.09 to 3.36 for a particle volume fraction increasing from 0.06% to 0.18%. Using the estimative of the double layer lenght of lauric acid, approximately 2 nm, and analyzing the magnetotransmissivity data for several particle concentrations, we were able to obtain the fraction f of core-shell nanoparticles of 0.17. This result, together with TEM data, allowed us to calculate the core diameter of the core-shell nanoparticle as 13 nm. Indeed such result suggest that in order to be suscessful in coating the nanoparticle with the shell element one might need monodisperse-like nanoparticle systems.
Hipertermia magnética in vivo com nanopartículas de MnFe2O4 no tratamento de tumores sólidos e subcutâneos de Sarcoma 180
(Universidade Federal de Goiás, 2017-04-19) Rodrigues, Harley Fernandes; Lacerda, Elisângela de Paula Silveira; http://lattes.cnpq.br/9390789693192751; Bakuzis, Andris Figueiroa; http://lattes.cnpq.br/3477269475651042; Bakuzis, Andris Figueiroa; Lacerda, Elisângela de Paula Silveira; Silva, Carlos Jacinto da; Reis, Rui Manuel Vieira; Pontes, Renato Borges
In this thesis a methodology of real-time monitoring of magnetic hyperthermia (HM) in vivo was developed in the murine tumor model Sarcoma 180 using infrared thermography technique. Magnetic nanoparticles (NPM) consisted of Mn ferrites capable of generating heat at low magnetic field amplitude at the 300 kHz frequency within the safety limit determined by Atkinson. It has been shown that the apparent surface temperature value measured with the infrared camera underestimates the real skin temperature value of the mice if the camera objective does not form an angle 0 ° with the normal direction to the animal's skin in the region of interest on the tumor, with the error reaching more than 7.0 ° C (for 60 °). A new theoretical model to estimate the error in the temperature of curved surfaces was developed and proved valid even in the case where the surface temperature diverges significantly from the environment. Preclinical treatment results indicated a complete remission condition in animal that was submitted to 150 min of hyperthermia and other cases with partial remission, suggesting that biological response analyzes need to be done in a long time (> 60 days). Measurements of the intratumoral temperature monitored by three fiber-optic thermometers during the therapeutic procedure of HM with NPM indicated an inhomogeneous heat delivery within the tumor. Additionally, a new methodology for calculating the thermal dose (CEM43) evaluated at the surface, considering each pixel of the thermographic image as a thermometer in the tumor region, indicated that the value T10(t) of the temperature detected in vivo at the surface of the skin over subcutaneous tumors can report, with an error of the order of 5%, the mean intratumoral temperature value during the therapeutic procedure of HM.
Magnetohipertermia em nanopartículas core-shell
(Universidade Federal de Goiás, 2016-05-04) Santos, Marcus Carrião dos; Bakuzis, Andris Figueiroa; http://lattes.cnpq.br/3477269475651042; Bakuzis, Andris Figueiroa; Knobel, Marcelo; Jadim, Renato de F.; Silva, Hermann F. F. Lima e; Pelegrini, Fernando
The phenomenon of heat dissipation by magnetic materials interacting with an alternating magnetic field, known as magnetic hyperthermia, is an emergent and promising therapy for many diseases, mainly cancer. The scientific community has endeavored to identify the properties that lead to maximum efficiency dissipation of magnetic nanoparticles. However, the diameter in which this efficiency reaches maximum is sometimes bigger than 10 nm, presenting several incompatibilities with biomedical aplications. On the other hand, small nanoparticles (< 8 nm}) do not suffer from the same disadvantages. On the contrary, they benefit from a biodistribution convenient for cancer treatment, affinity for the lymphatic system, further penetration of tumor tissue and renal clearance. However, the use of small nanostructures as heat centers never received much attention, in part because the model most used to describe the magnetic hyperthermia phenomenon, the linear response theory (LRT), provides a very small dissipation in these systems. Recently, experimental results have questioned this inefficiency and evidences that it is possible to produce a biological response (including cell death) without necessarily measuring a temperature variation opened up new possibilities for small nanostructures. This research, therefore, proposes a change in magnetic nanostructure tailoring strategy for biomedical applications of hyperthermia: to make more efficient dissipation in small nanoparticles. Therefore, it is necessary to rebuild the theoretical framework of hyperthermia, making the description of these small systems more accurate. This thesis deals with the development of modeling tools to enable a distinction between the most superficial and internal region of the nanoparticle, recognizing that many of the properties at the nanoscale has its origin in surface effects and the surface-to-volume ratio. A model for the description of core-shell system magnetization was developed, based on the Heisenberg Hamiltonian and a mean field theory in which different parameters may be assigned to each region. The combination of this model with the LRT has given rise to a new description of hyperthermia phenomenon in which the importance of surface effects and can be explicitly considered, making also possible the description of heterogeneous systems. The model was compared with original (homogeneous nanoparticles) and literature (heterogeneous nanoparticles) experimental data, with good qualitative agreement with the results. In an attempt to verify the influence of effects of nonlinearity in these systems, a non-linear response theory was developed from the generalization of the LRT, and applied to core-shell systems. The fundamental role of these theoretical tools is to point the direction in which the nanomaterials tailoring should advance to make viable the proposed hyperthermia with small nanostructures. The models proposed here suggest that a higher dissipation efficiency in small systems is obtained with a combination of materials which lead to the reduction ratio of shell-to-core damping factors, increasing of the exchange constant in the interface and maximizing the shell-to-core anisotropy constants, indicating that better results should be found in Soft@Hard systems.
Estudo magnético e magneto-ótico do internalização de nanopartículas magnéticas biocompatíveis de γ-F e2O3 recobertas com dextrana por células tumorais de sarcoma
(Universidade Federal de Goiás, 2010) Silva, Anderson Costa da; Bakuzis, Andris Figueiroa; http://lattes.cnpq.br/3477269475651042
In this work we investigated the internalization process of magnetite nanoparticles, surface coated with dextran, by mice tumour cells of Sarcoma 180 (S180) through the tech- niques of vibrating sample magnetometer (VSM) and static magnetic birefringence (SMB). The magnetic fluid sample, stable in physiological conditions, was prepared by the coprecip- itation method. The growth of nanoparticles occurred in conjunction with the nanoparticle surface coating process by dextran. The crystal structure was confirmed by X-ray diffraction. The nanoparticles were characterized by high resolution transmission electronic microscopy. The Sturges method was used to obtain the polydispersity in diameter, which was fitted by a lognormal size distribution obtaining a modal diameter of 5.5 ± 0.1 nm and dispersity of 0.18 ± 0.02.The mice tumour cell sarcoma 180 was obtained using protocol established by the American Type Culture Collection (ATCC, Rockville, MD, USA). Studies of cytotoxicity, using the MTT method, were obtained for a nanoparticle volumetric fraction of φ = 0.00065 after one and five hours of exposure of cells S180 to the nanoparticles. In particular, we found a cellular viability of 87 ± 11 % after one hour of exposure proving that there was no appreciable cell death in the time interval in which the measurements of MAV and BME were performed. Magnetization measurements were performed to obtain the volume fraction of nanoparticles. Tests regarding the effect of centrifugation of nanoparticles suspended in cell culture medium RPMI 1640 showed a extremely low sedimentation of magnetic nanoparticles. A procedure, using a acceleration of 260×g for 10 minutes, was used to separate cells containing internalized nanoparticles from nanoparticles suspended in RPMI 1640. Measurements of magnetization of S180 cells containing nanoparticles were performed in a wide range of exposure time (100 iv minutes). Between 10 and 70 minutes the amount of nanoparticles in mass unit increased from 52 ± 20 pg/cell to 110 ± 15 pg/cell. Indeed magnetometry data indicate that the process of internalization had achieved saturation between 30 to 40 minutes. Magneto-optical technique of SMB was also used to investigate the process of inter- nalization of nanoparticles. Firstly, SMB measurements were performed in control samples consisting of magnetic nanoparticles suspended in RPMI 1640. We investigated the effects of nanoparticle concentration and aging time (related to the dynamics of nanoparticle agglom- eration). In particular, the average size of the agglomerate (Q), associated with the number of nanoparticles forming a linear chain, remained basically constant, Q = 4.8 ± 0.2 for a full- time of 70 minutes. Magnetic birefringence saturation data also remained stable in this time interval. Additionally, analysis of the measurements of SMB were also used to estimate the thickness of the coating layer (dextran), from which we found 1.70 ± 0.02 nm. Unlike VSM data, SMB measurements were obtained on samples containing both S180 cells and magnetic nanoparticles inside the RPMI medium 1640. Data were obtained in a wide range of time (120 min.). Initially it was observed that the SMB signal decreases in a time range and then increases again (between 30-40 min.). The fit of the experimental data indicate that the mag- netic birefringence saturation (∆ns) decreases in the first 30 minutes and then increases again smoothly, while the average size of the cluster has the opposite behavior, i.e. increases in the first 30 minutes and then decreases. In particular, for a exposure time, t(exp), of 10 min. the average size of the agglomerate (magnetic birefringence saturation) changed from 4.18 ± 0.04 (∆n(s) = 3.41 ± 0.02 ×1018 cm−3 min. As the birefringence saturation is proportional to the number of nanoparticles contribut- ing to the magneto-optical signal one can conclude that the decrease in the magneto-optical signal was due to the process of internalization of magnetic nanoparticles by cells S180. On the other hand, the analysis of the aging time dependence of the mean size of the agglomerate also suggests that the process of internalization occurs primarily with anisometric nanoparticles or nanostructures forming small agglomerates. Finally, after reaching saturation of the process ) to 5.22 ± 0.08 (∆ns = 2.75 ± 0.02 ×1018 cm−3 ) at texp = 30 v of nanoparticle internalization we found a formation of small agglomerates in the RPMI 1640 medium, which is responsible for the increased intensity of the magneto-optical signal, as well as the decrease of the mean size of the agglomerate for times longer than 30 minutes.
Avaliação dos efeitos das hipertermias magnética e fototérmica na síntese de heteroestruturas à base de nanopartículas de MnFe2O4 e Au
(Universidade Federal de Goiás, 2015-12-14) Sousa Júnior, Ailton Antônio de; Bakuzis, Andris Figueiroa; http://lattes.cnpq.br/3477269475651042; Bakuzis, Andris Figueiroa; Lima, Emília Celma de Oliveira; Castro, Marcos Antônio de; Mendanha Neto, Sebastião Antônio
The purpose of this project is to synthesize and characterize heterostructures composed by manganese ferrite nanoparticles (MnFe2O4 NPs) and gold nanoparticles (Au NPs) able to: 1) respond to external alternating magnetic fields, what would enable their use in cancer diagnostic as contrast agentes for magnetic resonance imaging, as well as in cancer treatment via magnetic hyperthermia; 2) respond to eletromagnetic radiation, what would enable their use in cancer diagnostic as contrast agents for X-ray computed tomography (CT), as well as in cancer treatment via photothermal hyperthermia. We evaluate four MnFe2O4-Au heterostructures synthesis protocols. On Protocol 1, we use part of the energy of a laser beam (808 nm, 800 mW) to promote the nucleation of Au NPs at the surface of previously synthesized MnFe2O4 NPs covered by DMSA (dimercaptosuccinic acid). On Protocol 2, we use part of the energy of an alternating magnetic field (333,8 kHz, 17 mT) to promote this nucleation. We also perform an analysis of the influence of MnFe2O4 NPs covering layer, by comparing the ionic surfactants DMSA and sodium citrate. On Protocols 3 and 4, both the magnetic cores (MnFe2O4 NPs) and the metalic cores (Au NPs) are previously synthesized. Therefore, three Au NPs synthesis methods are evaluated. On Protocol 3, we promote the coupling between Au NPs and MnFe2O4-DMSA NPs using part of the energy from the same laser beam used on Protocol 1. On Protocol 4, we promote the coupling between cysteine-covered Au NPs and lysine-covered MnFe2O4 NPs via peptidic reaction between these two aminoacids. Finally, we conduct a comparative analysis between magnetic and photothermal hyperthermia, proposing a method for the determination of the optical SLP (Specific Loss Power). Moreover, we submit some of our samples to CT imaging. Protocol 1 is the best one in terms of covering the magnetic core by Au NPs. Protocol 2 allows the nucleation of Au NPs with diameters greater than the ones obtained via Protocol 1. Protocols 3 and 4 offer nanostructures with better potential with respect to their use as contrast agents in CT. However, the final yield of all four protocols is very low. Comparing magnetic and photothermal hyperthermia, we verify that the optical SLP is two to three orders of magnitude greater than the magnetic SLP under the assessed conditions, what suggests that protocols using laser beams have more energy available for the nucleation/coupling of Au NPs at the surface of MnFe2O4 NPs than those using alternating magnetic fields or simple heating on hot plate.
Hipertermia magnética de nanopartículas à base de ferrita de manganês: efeito do recobrimento superficial de nanopartículas por moléculas de citrato
(Universidade Federal de Goiás, 2012-05-31) Zufelato, Nícholas; Bakuzis, Andris Figueiroa; http://lattes.cnpq.br/3477269475651042; Bakuzis, Andris Figueiroa; Silva, Sebastião William da; Pelegrini, Fernando
This work investigated the magneto-thermal properties of manganese ferrite-based nanoparticles. The nanosctructures were synthesized by the coprecipitation method. Three samples were studied, namely: non passivated (2A), passivated (2B), and passivated with citrate coating molecules (2B cit). The particles were characterized by x-ray diffraction (XRD), transmission eléctron microscopy (TEM), vibrating sample magnetometer (VSM) and electron magnetic resonance (EMR). The non-coated samples showed similar diameter and saturation magnetization values, while the citrate-coated sample showed striking diferente values. In particular, the 2B cit sample showed lower values of particle size (determined from Scherrer relation), saturation magnetization and magnetic anisotropy. Those results corroborate with a core-shell nanoparticle model. The magnetic hyperthermia studies, perfomed around 300kHz, revealed that sample 2B had a higher magneto-thermal effiency when compared with the 2B cit one. Dynamic hysteresis curves, obtained within the linear response regime, were capable to explian qualitatively the experimental data. The phenomena was related to a lower magnetic anisotropy for the 2B cit nanoparticles. In addition, the biocompatible magnetic colloid (2B cit) showed SAR values around 50 W/g of MnFe 2 O 4 at the high field limit. However, differently from results reported in the literature, based upon magnetite/maghemite nanoparticles, saturation is achieved at a lower magnetic field amplitude. This suggest that this type of material has great biomedical potential for low-field magnetic hyperthermia applications, which might be necessary in order to inhibit harmful eddy currents inside the patient’s body.
Construção, caracterização e otimização da magnetohipertermia de nanocarreadores multifuncionais fluorescentes: a importância da relaxação coletiva na geração de calor
(Universidade Federal de Goiás, 2018-02-22) Zufelato, Nícholas; Bakuzis, Andris Figueiroa; http://lattes.cnpq.br/3477269475651042; Bakuzis, Andris Figueiroa; Nunes, Wallace de Castro; Silva, Sebastião William da; Pelegrini, Fernando; Bufaiçal, Leandro Felix de Sousa
In this work, we developed a multifunctional nanocarrier that has diagnostics and therapeutic applications in oncology, and evaluated the magnetothermal efficiency (SLP) properties in a comparative manner with respect to magnetic fluids. The nanocarrier consists of Mn-ferrite magnetic nanoparticles, a near-infrared fluorescent molecule IR-780, that are surface-coated with albumin proteins (BSA). The samples were characterized by dynamic light scattering (DLS), electron microscopy (TEM and MEV-FEG), vibrating sample magnetometer (VSM), fluorescence molecular tomography (FMT). FMT data proved the coupling of IR-780 to the protein allowing the fabrication of a magnetofluorescent nanostructure. Magnetic hyperthermia data as function of field amplitude (60-200 Oe) and frequency (170-990 kHz) were obtained for all samples containing the same magnetic particle volume fraction in the liquid carrier, but with distinct agregate sizes. The sizes were controlled by tuning the ionic force, and monitored experimentally using DLS. Magnetization curves revealed a (quasi-static) superparamagneticlike behavior, and was used to extract the particle concentration. The hyperthermia efficiency SLP of the magnetic fluids decreased increasing the hidrodynamic diameter. On the contrary, the nanocarrier showed a maximum of SLP, that can be optimized for hyperthermia and is more efficient than the ferrofluid. SLP data as function of frequency revealed a relaxation time of the order of 10-7 s and an equilibrium susceptibility lower than the Langevin value. A theoretical analysis of SLP at the linear responde regime was developed taking into account the dipolar interaction of nanoparticles organized in distinct arrangements. In magnetic fluids we considered a linear chain using the longitudinal configuration (anisotropy axis aligned), while for the nanocarriers we considered spherical agregates where the anisotropy axis of the nanoparticles are arranged randomly. The theoretical analysis indicate that the relaxation time cannot be explained by brownian relaxation or the Néel relaxation of single particle (even considering the dipolar effect). But instead, a mechanism of collective relaxation, mediated by dipolar interaction, is responsible for heat generation. It also indicates that only a fraction of agregates in the colloid is responsible for heating. In addition, the theoretical model revealed the existence of a transition from single particle relaxation to collective relaxation only if the dipolar interaction for the aggregate is higher than a critical value, which depends on material parameters, as for instance anisotropy field and saturation magnetization. Indeed, the model indicates that collective states are more easily achieved on soft magnets, and therefore suggests enhanced magnetothermal properties for this kind of materials.

Navegar

Navegando Programa de Pós-graduação em Física por Por Orientador "Bakuzis, Andris Figueiroa"

Resultados por página

Opções de Ordenação