[show abstract][hide abstract] ABSTRACT: Total Scattering Methods are nowadays widely used for the characterization of defective and nanosized materials. They commonly rely on highly accurate neutron and synchrotron diffraction data collected at dedicated beamlines. Here, we compare the results obtained on conventional laboratory equipment and synchrotron radiation when adopting the Debye Function Analysis method on a simple nanocrystalline material (a synthetic iron oxide with average particle size near to 10 nm). Such comparison, which includes the cubic lattice parameter, the sample stoichiometry and the microstructural (size-distribution) analyses, highlights the limitations, but also some strengthening points, of dealing with conventional powder diffraction data collections on nanocrystalline materials.
[show abstract][hide abstract] ABSTRACT: A versatile, rapid and easy synthesis of pure rare-earth-(RE) hexaboride powders was developed, without resorting to hazardous precursors or generating undesired, ineliminable, side products. To this purpose, we employed a metathesis reaction, typically starting from a mixture of a hydrated rare earth trichloride and MgB2, kept at 650 °C for 1 h under vacuum. This methodology affords nanosized RE hexaborides, with average crystallite (domain) sizes down to a few nanometers, useful for tailoring the functional performances of the MgB2 superconducting phase produced by the reactive liquid infiltration method. For the powders showing the lowest average domain sizes (YbB6 and EuB6), an unconventional microstructural analysis, based on Total Scattering methods and on the Debye Function Approach, was also performed, which provided the complete nanocrystal size distributions.
[show abstract][hide abstract] ABSTRACT: Bimodal MRI/OI imaging probes are of great interest in nanomedicine. Although many organic polymers have been studied thoroughly for in vivo applications, reports on the use of poly(amino acid)s as coating polymers are scarce. In this paper, poly-(d-glutamic acid, d-lysine) (PGL) has been used for coating maghemite and gold nanoparticles. An advantage of this flexible and biocompatible polymer is that, once anchored to the nanoparticle surface, dangling lysine amino groups are available for the incorporation of new functionalities. As an example, Alexa Fluor derivatives have been attached to PGL-coated maghemite nanoparticles to obtain magnetic/fluorescent materials. These dual-property materials could be used as bimodal MRI/OI probes for in vivo imaging.
[show abstract][hide abstract] ABSTRACT: The specific routes of biomineralization in nature are here explored using a tissue engineering approach in which bone is formed in porous ceramic constructs seeded with bone marrow stromal cells and implanted in vivo. Unlike previous studies this model system reproduces mammalian bone formation, here investigated at high temporal resolution. Different mineralization stages were monitored at different distances from the scaffold interface so that their spatial analysis corresponded to temporal monitoring of the bone growth and mineralization processes. The micrometer spatial resolution achieved by our diffraction technique ensured highly accurate reconstruction of the different temporal mineralization steps and provided some hints to the challenging issue of the mineral deposit first formed at the organic-mineral interface. Our results indicated that in the first stage of biomineralization organic tissue provides bioavailable calcium and phosphate ions, ensuring a constant reservoir of amorphous calcium phosphate (ACP) during hydroxyapatite (HA) nanocrystal formation. In this regard we suggest a new role of ACP in HA formation, with a continuous organic-mineral transition assisted by a dynamic pool of ACP. After HA nanocrystals formed, the scaffold and collagen act as templates for nanocrystal arrangement on the microscopic and nanometric scales, respectively.
[show abstract][hide abstract] ABSTRACT: appealing characteristics, such as light weight, mechanical flexibility and low-cost production. These advantages make them promising candidates for a wide range of applications such as displays, [10–12] radio-frequency identification (RF-ID) tags,  and sensors. [14–17] To make full use of organic electronic circuitry, it is necessary to combine p-channel and n-channel transistors to produce complementary circuits, which show greater speed, reliability and stability than ambipolar ones. [18–21] While highly pure, stable and solution-processable p-type materials with a charge mobility of 1–10 cm 2 V −1 s −1 are nowadays available in production amounts, [22–27] n-type organic semiconductors of high air-stability and mobility are still a topic of research. Indeed, in the past few years, several high-performance n-type semiconductors have been developed, which also exhibit a high stability in ambient conditions, mostly used as films obtained from vapor deposition methods. [28,29] More recently, solution-processable and printable n-type semiconductors, both small molecules and polymers, [30–33] have been reported, allowing unprecedented OTFT characteristics. Perylene di-imide deriva-tives are considered to be among the most important n-type organic materials because of their relatively strong electron affinities and the tailoring of the charge-transport properties upon changing the substituents on the imide N atoms or on the perylene backbone. [34–42] In this paper, we focus on N,N′-bis(n-ctyl)-x:y,dicyanoperylene-3,4:9,10-bis(dicarboximide), PDI8-CN2, a derivative having two cyano groups directly bound to the aromatic core, which has been proved to be a suitable material for complementary cir-cuits  and shown to yield high-performance devices by subli-mation or from solution methods.  In spite of the potential of PDI8-CN2 and the importance attributed to the control of grain boundary effects in small-molecule device performance and reproducibility, experimen-tally derived knowledge of the crystal structure and molecular conformation and how these factors affect the multiscale organ-ization and microstructure in the film phase are still missing. The packing motif proposed by Rivnay et al.  relies on the combination of the X-ray scattering of thin films and pseudo-potential calculations, which is not as robust or conclusive as A multiscale investigation of N,N′-bis(n-octyl)-x:y, dicyanoperylene-3,4:9,10-bis(dicarboximide), PDI8-CN2, shows the same molecular arrangement in the bulk and in thin films sublimated on SiO 2 /Si wafers. Non-conventional powder diffraction methods and theoretical calculations concur to provide a coherent picture of the crystalline structure. X-ray diffraction (XRD) and atomic force microscopy (AFM) analyses of films of different thickness depos-ited at different substrate temperatures indicate the existence of two temper-ature-dependent deposition regimes: a low-temperature (room temperature) regime and a high-temperature (80–120 °C) one, each characterized by dif-ferent growth mechanisms. These mechanisms eventually result in different morphological and structural features of the films, which appear to be highly correlated with the trend of the electrical parameters that are measured in PDI8-CN2-based field-effect transistors.
[show abstract][hide abstract] ABSTRACT: Nanocrystalline TiO(2) samples, prepared for smart textiles applications by the sol-gel technique in acidic or basic media, have been characterized by synchrotron X-ray powder diffraction and total scattering methods based on a fast implementation of the Debye function and original algorithms for sampling interatomic distances. Compared to the popular and widely used Rietveld-based approaches, our method is able to simultaneously model both Bragg and diffuse contributions and to quantitatively extract either sizes and size distribution information from the experimental data. The photocatalytic activity of the investigated samples is here systematically correlated to the average sizes and size distributions of anisotropically shaped coherent domains, modeled according to bivariate populations of nanocrystals grown along two normal directions.
Journal of the American Chemical Society 02/2011; 133(9):3114-9. · 10.68 Impact Factor
[show abstract][hide abstract] ABSTRACT: The Debye Function Analysis of diffraction patterns from nanosized mineral crystals showing different average degrees of maturity was carried out on engineered bone samples. The analysis relied on a bivariate family of atomistic hydroxyapatite nanocrystal models and provided information about crystal structure, size and shape distributions of the mineral component of the newly formed bone. An average rod-like shape of nanocrystals was found in all samples, with average sizes well matching the collagen I gap region. The diffraction patterns investigated through the Debye Function Analysis were used as signal models to perform the Canonical Correlation Analysis of high resolution X-ray micro-diffraction patterns collected on porous and resorbable hydroxyapatite/silicon-stabilized tricalcium phosphate (Si-TCP) implants. The nosologic maps clearly showed a size gradient in the new formed bone that validates the mechanism (mimicking the bone remodelling in orthotopic bones) of a continuous deposition of bone by osteoblasts, an increasing mineralization of the newly deposited bone, a growth of the new crystals, at the same time that osteoclasts adhere to the scaffold surface and resorb the bioceramic. The comparison of samples at different implantation times proved that the selective resorption of Si-TCP component from the scaffold was already evident after two and almost complete after six months.
[show abstract][hide abstract] ABSTRACT: Pd nanoparticles exhibiting permanent magnetism at room temperature have been prepared within the apoferritin cavity. Pd nanoparticles in air and under an inert atmosphere were synthesized to study the influence of the aerobic and anaerobic conditions in the final magnetic properties. The surface of nanoparticles as well as the type of crystalline phase could determine the magnetic properties. X-ray powder diffraction, including Debye-function analysis, transmission electronic microscopy, and magnetization measurements have been used for characterizing the nanoparticles.
[show abstract][hide abstract] ABSTRACT: DEBUSSY is a new free open-source package, written in Fortran95 and devoted to the application of the Debye function analysis (DFA) of powder diffraction data from nanocrystalline, defective and/or non-periodic materials through the use of sampled interatomic distance databases. The suite includes a main program, taking the name of the package, DEBUSSY, and dealing with the DFA of X-ray, neutron and electron experimental data, and a suite of 11 programs, named CLAUDE, enabling users to create their own databases for nanosized crystalline materials, starting from the list of space-group generators and the asymmetric unit content. A new implementation of the Debye formula is adopted in DEBUSSY, which makes the approach fast enough to deal with the pattern calculation of hundreds of nanocrystals, to sum up their contributions to the total pattern and to perform iterative algorithms for optimizing the parameters of the pattern model. The package strategy uses the sampled-distance database(s) created previously by CLAUDE and combines, for any phase, a log-normal or a bivariate log-normal function to deal with the sample-size distribution; four different functions are implemented to manage possible lattice expansions/contractions as a function of crystal size. A number of output ASCII files are produced to supply some statistics and data suitable for graphical use. The databases of sampled interatomic non-dimensional distances for cuboctahedral, decahedral and icosahedral structure types, suitable for dealing with noble metal nanoparticles, are also available.
[show abstract][hide abstract] ABSTRACT: The hierarchical structure of bone makes the X-ray microdiffraction scanning techniques one of the most effective tool to investigate the structural features of this tissue at different length scales: the atomic/nanometer scale of the X-ray scattering signals and the macroscopic scale of the scanned sample area. The potentiality of the microdiffraction approach has been verified also by investigations on tissue-engineered bone substitutes used to repair large hard bone defects. The aim of this review is to present the most representative and recent results obtained through high-resolution scanning microdiffraction techniques studying both natural and tissue-engineered bone. The rapid evolution of the instrumental set-ups and the advanced methods of data analysis are described. Recent examples in which X-ray microbeams were used for imaging quantitative features of natural bone tissue and engineered bone substitutes are presented along with the qualitative and quantitative information extracted from the two-dimensional patterns collected on bone samples and on ex vivo cell seeded bioceramic implants. Thanks to the microdiffraction approach, several aspects of the mechanisms leading to the generation of the new bone, coupled to the scaffold resorption in the tissue-engineered constructs, have been tentatively interpreted. The potential of X-ray microdiffraction as an imaging tool in the field of bone tissue engineering is discussed and the key role of high-spatial resolution, availability of automatic tools (for dealing with the huge amount of experimental data) and advanced analysis techniques is elucidated. Finally, future perspectives in the field are presented.
Tissue Engineering Part B Reviews 07/2009; 15(4):423-42. · 4.64 Impact Factor
[show abstract][hide abstract] ABSTRACT: The effects of heating-induced crystallization on the structural and mechanical properties of Mg-Ni-Fe amorphous ribbons were studied by anelastic spectroscopy, differential scanning calorimetry (DSC) and X-ray diffraction. DSC results show that the crystallization occurs through several non-reversible steps, which correspond to significant changes in the Young's modulus and concomitant irreversible elastic energy loss peaks. Moreover, an anelastic peak is found at 215 K, which for the first time indicates the presence of some dynamical process related to the simultaneous presence of different phases. The formation of a metastable Mg(6)Ni phase is detected, which transforms into Mg and Mg(2)Ni stable phases. A quantitative analysis of the different phases present at the different steps was also carried out. (C) 2007 Elsevier B.V. All rights reserved.
Journal of Alloys and Compounds 01/2008; 463(1-2):148-152. · 2.39 Impact Factor
[show abstract][hide abstract] ABSTRACT: Resorbable porous ceramic constructs, based on silicon-stabilized tricalcium phosphate, were implanted in critical-size defects of sheep tibias, either alone or after seeding with bone marrow stromal cells (BMSC). Only BMSC-loaded ceramics displayed a progressive scaffold resorption, coincident with new bone deposition. To investigate the coupled mechanisms of bone formation and scaffold resorption, X-ray computed microtomography (muCT) with synchrotron radiation was performed on BMSC-seeded ceramic cubes. These were analyzed before and after implantation in immunodeficient mice for 2 or 6 months. With increasing implantation time, scaffold thickness significantly decreased while bone thickness increased. The muCT data evidenced that all scaffolds showed a uniform density distribution before implantation. Areas of different segregated densities were instead observed, in the same scaffolds, once seeded with cells and implanted in vivo. A detailed muX-ray diffraction analysis revealed that only in the contact areas between deposited bone and scaffold, the TCP component of the biomaterial decreased much faster than the HA component. This event did not occur at areas away from the bone surface, highlighting coupling and cell-dependency of the resorption and matrix deposition mechanisms. Moreover, in scaffolds implanted without cells, both the ceramic density and the TCP:HA ratio remained unchanged with respect to the pre-implantation analysis.