Magnetism and magnetotransport in Core/Shell nanoparticle systems

Este proyecto tiene como objetivo general la fabricación de nuevos materiales magnéticos nanoestructurados con el fin de estudiar las nuevas propiedades que se manifiestan como consecuencia de la reducción del tamaño y avanzar hacia el diseño de materiales bifuncionales y/o con propiedades específicas. La producción de nanopartículas magnéticas con estructura core/shell aumenta las posibilidades para diseñar nuevas nanoestructuras ya que permite combinar materiales de diferentes características: diferentes órdenes magnéticos, con distintas anisotropías, y/ o diferente conductividad eléctrica. Además del efecto de superficie y el desorden estructural debido a la alta relación superficie/volumen, estos sistemas pueden presentar un comportamiento desacoplado de las fases que lo componen o nuevas propiedades como consecuencia del acople en la interfaz. En este marco, se propone fabricar diferentes sistemas de nanopartículas con el fin de sintonizar y optimizar las propiedades magnéticas y el magnetotransporte. En particular se pretende ajustar la anisotropía magnética con el objetivo de estudiar el mecanismo de relajación magnética en presencia de campos oscilantes y optimizar el mecanismo de calentamiento en experimentos de hipertermia magnética de gran interés para futuros tratamientos oncológicos. Por otro lado, considerando que se propone la terapia de hipertermia como tratamiento coadjuvante de la radioterapia, se proyecta fabricar nanopartículas bifuncionales con propiedades magnéticas y sensibles a la irradiación ionizante con el fin de utilizar al mismo material para producir calentamiento local por hipertemia y como sensores de irradiación. Las nanopartículas pueden autoensamblarse y construir arreglos bidimensionales. Esta propiedad, junto con la posibilidad de combinar materiales semimetálicos y aislantes en una única partícula con estructura core/shell, permite diseñar nanoestructuras con el fin de estudiar la magnetorresistencia túnel y diseñar nuevos dispositivos basados en nanopartículas. Finalmente, este trabajo de investigación incluye la formación de recursos humanos en el área de la Ciencia de Materiales y Nanociencia mediante la realización de trabajos de tesis de grado y postgrado.The general objective of this project is the manufacture of new nanostructured magnetic materials in order to study the new properties that are manifested as a consequence of the reduction in size and to move towards the design of bifunctional materials and / or with specific properties. The production of magnetic nanoparticles with core / shell structure increases the possibilities to design new nanostructures since it allows to combining materials with different characteristics: different magnetic orders, with different anisotropies, and / or different electrical conductivity. In addition to the surface effect and the structural disorder due to the high surface / volume ratio, these systems can exhibit a decoupled behavior of the phases that compose it or new properties as a consequence of the coupling at the interface. Within this framework, it is proposed to manufacture different nanoparticle systems in order to tune and optimize the magnetic and magnetotransport properties. In particular, the intention is to adjust the magnetic anisotropy in order to study the mechanism of magnetic relaxation in the presence of oscillating fields and to optimize the heating mechanism in magnetic hyperthermia experiments of great interest for future oncological treatments. On the other hand, considering that hyperthermia therapy is proposed as coadjuvant treatment of radiotherapy, it is planned to manufacture bifunctional nanoparticles with magnetic properties and sensitive to ionizing irradiation in order to use the same material to produce local heating by hyperthermia and as sensors of irradiation. The nanoparticles can self-assembled and construct two-dimensional arrays. This property, together with the possibility of combining semi-metallic and insulating materials in a single particle with core / shell structure, allows the design of nanostructures in order to study tunnel magnetoresistance and design new devices based on nanoparticles. Finally, this research work includes the training of human resources in the area of Materials Science and Nanoscience through the completion of graduate and postgraduate thesis projects

Exchange-coupling in thermal annealed bimagnetic core/shell nanoparticles

In this study we demonstrate that the effective coupling of the magnetic phases in core/shell nanoparticles can be promoted by an appropriate thermal annealing. In this way, the magnetization thermal stability of the hard ferrimagnetic CoFe2O4 oxide can be increased up to room temperature when coupled to a CoO antiferromagnetic core in an inverse core/shell structure. In addition, the results show that, being encapsulated in a ∼2 nm thick CoFe2O4 shell, the CoO core is successfully protected against oxidation which is crucial for the effectiveness of the magnetic coupling at the interface.Fil: Lavorato, Gabriel Carlos. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Lima, Enio Junior. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Troiani, Horacio Esteban. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Zysler, Roberto Daniel. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Winkler, Elin Lilian. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Bifunctional CoFe2O4/ZnO Core/Shell Nanoparticles for Magnetic Fluid Hyperthermia with Controlled Optical Response

Conjugation of optical and magnetic responses in a unique system at the nanoscale emerges as a powerful tool for several applications. Here, we fabricated bifunctional CoFe2O4-core/ZnO-shell nanoparticles with simultaneous photoluminescence in the visible range and ac magnetic losses suitable for hyperthermia. The structural characterization confirms that the system is formed by a ≈7 nm CoFe2O4 core encapsulated in a ≈1.5-nm-thick semiconducting ZnO shell. As expected from its high anisotropy, the magnetic losses in an ac magnetic field are dominated by the Brown relaxation mechanism. The ac magnetic response of the core/shell system can be accurately predicted by the linear response theory and differs from that one of bare CoFe2O4 nanoparticles as a consequence of changes in the viscous relaxation process due to the effect of the magnetostatic interactions. Concerning the optical properties, by comparing core/shell CoFe2O4/ZnO and single-phase ZnO nanoparticles, we found that the former exhibits a broader optical absorption and photoluminescence, both shifted to the visible range, indicating that the optical properties are closely associated with the shell-morphology of ZnO. Being focused on bifunctional nanoparticles with an optical response in the visible range and a tunable hyperthermia output, our results can help to address current open questions on magnetic fluid hyperthermia.Fil: Lavorato, Gabriel Carlos. Centro Brasileiro de Pesquisas Físicas; Brasil. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Lima, Enio Junior. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Vasquez Mansilla, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Troiani, Horacio Esteban. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Zysler, Roberto Daniel. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Winkler, Elin Lilian. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentin

Lower effectiveness of facet joint infiltration in patients with concurrent facet joint degeneration and active endplate changes

BACKGROUND CONTEXT Facet joint degeneration (FJD) and disc degeneration (DD) with associated endplate (EP) changes, specifically Modic 1 changes, might occur concurrently and therefore pose a challenge in the treatment of lower back pain (LBP). PURPOSE The aim of the present study was to investigate if the presence of active EP changes (Modic 1) would alter the effect of facet joint infiltrations (FJI) for the treatment of concurrent FJD. STUDY DESIGN Prospective cohort study, Level III. PATIENT SAMPLE 42 patients (Male:20, Female:22) with an average of 58±14 years with FJD on conventional magnetic resonance imaging (MRI) receiving a FJI for treatment of lower back pain were included. OUTCOME MEASURES The pain score at baseline, 15 min, 1 day, 1 week and 1 month following FJI as well as the reduction of pain were analyzed. Furthermore, active EP changes on conventional MRI and increased EP metabolic activity on PET/MRI were evaluated and compared. METHODS All the patients underwent a (18F)-NaF PET/MRI, conventional MRI and FJI for symptomatic FJD. Active EP changes on conventional MRI and increased EP metabolic activity on PET/MR were analyzed for conformity. The pain score as well as the pain reduction at the above-mentioned time points were compared between patients with and without increased EP metabolic activity in PET/MRI. RESULTS The LBP reduction was significantly different between patients with (n=20) and without (n=22) active EP changes at 15 minutes (1.3±2.4 vs. 2.9±2.4, p=.03) and 1 month (0.9±2.3 vs. 2.8±2.9, p<.001) following FJI. The minimal clinically important difference for LBP reduction was reached significantly more often in the absence of active EP changes (73%) compared with patients with active EP changes (35%) 1 month following FJI (p=.03). CONCLUSIONS FJI is less effective in LBP reduction of patients with FJD and concurrent active EP changes (eg Modic 1)

Temperature evolution of the effective magnetic anisotropy in the MnCr2_2O4_4 spinel

In this work we present a study of the low temperature magnetic phases of polycrystalline MnCr$_2$O$_4$ spinel through dc magnetization and ferromagnetic resonance spectroscopy (FMR). Through these experiments we determined the main characteristic temperatures: T$_C$ $\sim$41 K and T$_H$ $\sim$18 K corresponding, respectively, to the ferrimagnetic order and to the low temperature helicoidal transitions. The temperature evolution of the system is described by a phenomenological approach that considers the different terms that contribute to the free energy density. Below the Curie temperature the FMR spectra were modeled by a cubic magnetocrystalline anisotropy to the second order, with $K_1$ and $K_2$ anisotropy constants that define the easy magnetization axis along the direction. At lower temperatures, the formation of a helicoidal phase was considered by including uniaxial anisotropy axis along the [1-10] propagation direction of the spiral arrange, with a $K_u$ anisotropy constant. The values obtained from the fittings at 5 K are $K_1$=-2.3x10$^4$ erg/cm$^3$, $K^2$=6.4x10$^4$ erg/cm$^3$ and $K_u$=7.5x10$^4$ erg/cm$^3$.Comment: 21 pages, 6 figure

Thickness dependence of exchange coupling in epitaxial Fe 3 O 4/ CoFe 2 O 4 soft/hard magnetic bilayers

Epitaxial magnetic heterostructures of (soft-)Fe3O4/(hard-)CoFe2O4(001) have been fabricated with a varying thicknesses of soft ferrite from 5 to 25 nm. We report a change in the regime of magnetic interaction between the layers from rigid-coupling to exchange-spring behavior, above a critical thickness of the soft magnetic Fe3O4 layer. We show that the symmetry and epitaxial matching between the spinel structures of CoFe2O4 and Fe3O4 at the interface stabilize the Verwey transition close to the bulk value even for 5-nm-thick Fe3O4. The large interface exchange-coupling constant estimated from low-temperature M(H) data confirmed the good quality of the ferrite-ferrite interface and the major role played by the interface in the magnetization dynamics. The results presented here constitute a model system for understanding the magnetic behavior of interfaces in core/shell nanoparticles and magnetic oxide-based spintronic devices.Fil: Lavorato, Gabriel Carlos. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Resonancias Magnéticas; ArgentinaFil: Winkler, Elin Lilian. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Resonancias Magnéticas; ArgentinaFil: Rivas Murias, B.. Universidad de Santiago de Compostela. Facultad de Química; EspañaFil: Rivadulla, F.. Universidad de Santiago de Compostela. Facultad de Química; Españ

Foot Osteomyelitis Location and Rates of Primary or Secondary Major Amputations in Patients With Diabetes

BACKGROUND Diabetic foot osteomyelitis (DFO) often leads to amputations in the lower extremity. Data on the influence of the initial anatomical DFO localization on ultimate major amputation are limited. METHODS In this retrospective analysis, 583 amputation episodes in 344 patients (78 females, 266 males) were analyzed. All received a form of amputation in combination with antibiotic therapy. A multivariate logistic regression analysis with the primary outcome "major amputation" defined as an amputation above the ankle joint was performed. The association of risk factors including location of DFO, coronary artery disease, peripheral artery disease, neuropathy, nephropathy, and Charcot neuro-osteoarthropathy was analyzed. RESULTS Among 583 episodes, DFO was located in the forefoot in 512 (87.8%), in the midfoot in 43 (7.4%), and in the hindfoot in 28 episodes (4.8%). Overall, 53 of 63 (84.1%) major amputations were performed because of DFO in the setting of peripheral artery disease as primary indication. Overall, limb loss occurred in 6.1% (31/512) of forefoot, 20.9% (9/43) of midfoot, and 46.4% (13/28) of hindfoot DFO. Among these, 22 (41.5%) were performed as the primary treatment, whereas 31 (58.5%) followed previously failed minor amputations. Among this latter group of secondary major amputations, the DFO was localized to the forefoot in 23 of 583 (3.9%), the midfoot in 4 of 583 (0.7%) and the hindfoot in 4 of 583 (0.7%). In multivariate logistic regression analysis, initial hindfoot localization was a significant factor (P < .05), whereas peripheral artery disease, smoking, and a midfoot DFO were not found to be risk factors. CONCLUSION In our retrospective series, the frequency of limb loss in DFO increased with more proximal initial foot DFO lesions, with almost half of patients losing their limbs with a hindfoot DFO. LEVEL OF EVIDENCE Level IV, retrospective cohort study

Is routine magnetic resonance imaging necessary in patients with clinically diagnosed frozen shoulder? Utility of magnetic resonance imaging in frozen shoulder

BACKGROUND Shoulder magnetic resonance imaging (MRI) is commonly performed in patients with frozen shoulder (FS). However, the necessity of MRI and its diagnostic value is questionable. Therefore, the purpose of the present study was to clarify whether routine MRI could identify additional shoulder pathologies not previously suspected in the clinical examination and if any change in the treatment plan based on these additional MRI findings in FS patients was observed. MATERIALS AND METHODS The medical records of all patients who presented in our outpatient clinic with a diagnosis of FS from January 2017 to December 2018 were retrospectively reviewed. Patient demographics, the number of patients who received a shoulder MRI, changes in the diagnosis or identification of structural shoulder pathologies following MRI examination (if performed), as well as any alternation in the initially suggested treatment plan were recorded. RESULTS A total of 609 patients (male: 241, female: 368) diagnosed with an FS and an average age of 52 ± 10 (range: 18 to 81) years were identified. In 403 of the 609 patients (66%), a shoulder MRI was performed. An additional structural shoulder pathology was identified in 89 of 403 (22%) patients following the shoulder MRI, mostly rotator cuff tears (partial: 46/403 [11.4%], full-thickness: 30/403 [7.4%], rerupture following reconstruction: 10/403 [2.5%]) and labrum tears (3/403 [0.7%]). At minimum 2-year follow-up, 11 of 403 (2.7%) patients were treated surgically for the additional pathology identified on the MRI scan consisting of an arthroscopic rotator cuff reconstruction in 10 patients and a labrum refixation in one patient. Five of the 609 (0.8%) patients were treated for refractory FS by arthroscopic capsulotomy. CONCLUSIONS Although additional pathologies were identified in 22% of the patients, a change in treatment plan due to the MRI findings was only observed in 2.7% (37 MRIs needed to identify 1 patient with FS requiring surgery for the additional MRI findings). Therefore, routine use of shoulder MRI scans in patients with FS but without suspicion of an additional pathology may not be indicated

Combined Anteversion Threshold to Avoid Anterior Dislocation in Primary Total Hip Arthroplasty Performed Through the Direct Anterior Approach

BACKGROUND Component malposition in total hip arthroplasty (THA) can lead to dislocation, early implant failure, and revision surgery. As the surgical approach might affect the targeted combined anteversion (CA) of THA components, the present study aimed to evaluate the optimal CA threshold to avoid anterior dislocation in primary THA performed through a direct anterior approach (DAA). METHODS A total of 1,176 THAs in 1,147 consecutive patients (men: 593, women: 554) who had an average age of 63 years (range, 24 to 91) and a mean body mass index of 29 (range, 15 to 48) were identified. Medical records were reviewed for dislocation, whereas postoperative radiographs were assessed to measure the acetabular inclination and CA using a previously validated radiographic method. RESULTS An anterior dislocation occurred in 19 patients at an average of 40 days postoperatively. The average CA in patients who did and did not have a dislocation was 66 ± 8° and 45 ± 11°, respectively (P < .001). In 5 of 19 of the patients, a THA was performed for secondary osteoarthritis and 17 of 19 had a 28-mm femoral head. A CA ≥ 60° yielded a sensitivity of 93% and specificity of 90% for predicting an anterior dislocation in the present cohort. A CA ≥ 60° was associated with a significantly higher risk of anterior dislocation (odds ratio = 75.6; P < .001) compared to patients who had a CA<60 points. CONCLUSION The optimal CA to avoid anterior dislocations in THA performed through the DAA should be less than 60°. LEVEL OF EVIDENCE Cross-sectional study, Level III

A novel method for evaluating combined component anteversion in total hip arthroplasty on cross-table lateral hip radiographs

INTRODUCTION Accurate measurement of combined component anteversion (CA) is important in evaluating the radiographic outcomes following total hip arthroplasty (THA). The aim of the present study was to evaluate the accuracy and reliability of a novel radiographic method in estimating CA in THA. MATERIALS AND METHODS The radiographs and computer tomography of patients who underwent a primary THA were retrospectively reviewed, to measure the radiographic CA (CAr), defined as the angle between a line connecting the center of the femoral head to the most anterior rim of the acetabular cup and a line connecting the center of the femoral head to the base of the femoral head to allow a comparison with the CA measured on the CT (CACT). Subsequently, a computational simulation was performed to evaluate the effect of cup anteversion, inclination, stem anteversion, and leg rotation on the CAr and develop a formula that would correct the CAr according to the acetabular cup inclination based on the best-fit equation. RESULTS In the retrospective analysis of 154 THA, the average CAr_cor, and CACT were 53 ± 11° and 54 ± 11° (p > 0.05), respectively. A strong correlation was found between CAr and CACT (r = 0.96, p < 0.001), with an average bias of - 0.5° between CAr_cor and CACT. In the computational simulation, the CAr was strongly affected by the cup anteversion, inclination, stem anteversion, and leg rotation. The formula to convert the CAr to CA_cor was: CA-cor = 1.3*Car - (17* In (Cup Inclination) - 31. CONCLUSION The combined anteversion measurement of THA components on the lateral hip radiograph is accurate and reliable, implying that it could be routinely used postoperatively but also in patients with persistent complaints following a THA. LEVEL OF EVIDENCE Cross-sectional study, Level III