1,720,978 research outputs found
Doped calcium phosphate bone cements and real-time monitoring of their hardening mechanism
No full textNowadays, considerable efforts have been focused on various calcium phosphate
based cement compositions (CPC), developed to restore the damaged human hard
tissues, like vertebras and osteoporotic bone. Furthermore, CPC materials are widely
used as synthetic substitutes for non-load bearing fractures, bone defects and teeth
reconstruction, due to their chemical similarity to the mineral component of the
natural hard tissue. However, the proposed up to now cement formulations can be
improved by endowing cements with additional properties, requested for a certain
application field. For example, the bone graft associated infections can be prevented
by doping the synthetic materials with Ag+ ions at low (non cytotoxic) concentrations.
This way seems to be more appropriate, because the antimicrobial agents could be
provided directly at the implantation site. Another interesting functionalization option
are Zn2+ ions - an essential trace element participating in a variety of cellular processes,
including DNA synthesis, behavioural responses, bone formation and growth and
wound healing. Moreover, zinc plays an important role in gene expression and in
the regulation of cellular growth and differentiation. To this end, Zn2+ is known to
possess antibacterial, osteo- and angiogenetic properties, enhancing the proliferation
of osteoblastic cells.
The aim of this research is to develope functionalized cements for several bone
grafting applications, among them those mentioned above. In order to monitor in real time
all these processes, the Energy Dispersive X-Ray Diffraction (EDXRD)
technique is applied, being very suitable for this task
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Artificial aging of monoazo and isoindoline yellow pigments
No full textUV- and humidity-related aging effects on two yellow synthetic organic pigments, known for their good lightfastness, were investigated: Pigment Yellow 1 (PY 1, Monoazo) and Pigment Yellow 139 (PY 139, Isoindoline). The work considers the reactivity of these pigments, as individual pigments, in combination with linseed oil, and in presence of highly reactive inorganic white pigments: basic lead carbonate, titanium dioxide, and zinc oxide. Accelerated aging was induced via UV irradiation and high humidity rate in a custom-built chamber using both simple and bilayer paint mock-ups to simulate the technique of overlaying films in paintings. After aging, physicochemical variations were analysed using colorimetry, Fourier-transform infrared spectroscopy, Raman spectroscopy, and photoluminescence spectroscopy. The results show that the accelerated aging induces a greater colour change in monoazo yellow pigment than in isoindoline one when in powder form. Conversely, when oil is present in the samples as binder, the colour variations are similar for both samples suggesting that the large part of the chemical/physical changes occur in the organic binder. For the bilayer systems, photoluminescence spectroscopy suggests that the substrates can induce a larger drying activity on the binder and could follow the contribution of fluorescence in the variation of the perceived colour
Metals and Environment: Chemical Outputs From the Interaction Between Gilded Copper-Based Objects and Burial Soil
No full textThree-dimensional chemical mapping was adopted to investigate an ancient fire-gilded
buckle found in Rome. Time-of-flight secondary ion mass spectrometry (ToF-SIMS)
and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS)
were used to detect and locate degradation products aiming to identify the alteration
processes. Inorganic and organic compounds present in the outermost part of such a
class of cultural heritage objects can be considered the result of long-term interaction
with the burial environment. ToF-SIMS depth profiling experiments can provide chemical
information at the molecular level and high resolved spatial information (about 1μm
laterally, and 1 nm in depth). In this work, the attention was focused on the identification
and localization of the ionic and molecular species involved in the degradation process.
Results showed the presence of copper oxides, chlorides, and sulfides as common
corrosion products but also the presence of species related to copper and bronze
corrosion process, such as atacamite and its polymorphs. 3D maps for all the
relevant molecular species allowed to visualize at the same time the eruption of
copper chlorides throughout the micro/nanochannels present on the gold surface,
the recrystallization of compounds of minor elements from the substrate, a pathway
followed by silico-aluminates from the surface toward the internal corrosion layers, but
mostly the evidence of biological activity of Sulfur Reducing Bacteria (SRB) living in
anaerobic conditions
Preliminary study on Sharpey's fibers in a dental hominin sample from the Middle Pleistocene
No full textDefinizione di un protocollo analitico per lo studio archeometrico di materiali piro-metallurgici del sito di Auoam (Marocco)
No full textThe purely archaeometric de nition of historical and technological background of extraction techniques and pyrometallurgical processing of metals in Morocco of punic-mauritanian requires the creation of an analytical protocol covering every stage of the metallurgical process.
These analysis started in 2011 and involved the development of particular procedure, in order to obtain results in broad-spectrum. The present work is related to the identi cation of metallurgical slags trough different analytical techniques that allow to inve- stigate the individual physical-chemical features of the material. The data where obtained by petrographic analysis, thin-layer investigation, scanning electron microscope (SEM) coupled to the energy dispersion system (EDS), X-ray diffraction (XRD), ther- mogravimetric analysis (TGA) and metallographic investigation.
The compendium of the analytical results, are the basis for a development of this procedure working with the open-source GIS sof- tware quantumgis (QGIS). Considering the special input data, it was necessary to have additional information related to satellite images, used to de ne different micro-areas of interest
Ag-, Zn-doped calcium phosphate bone cements for tissue engineering
No full textCalcium phosphate cements (CPC) are biocompatible materials, nowadays widely used for non-load bearing small bone fractures, maxillo- and craniofacial defects. Being compositionally affinitive to the mineral part of the bone tissue, these biomaterials are non-cytotoxic and able to promote a suitable host bone/material interface. When proposing a new synthetic calcium phosphate material, it should be considered that natural bone tissue is composed of the substituted hydroxyapatite, containing a number of cations and anions, each one of them playing a particular role in the new tissue formation and growth chemistry. Therefore, trying to improve the properties of CPC, one might introduce into their composition ionic additives naturally occurring in the human body with the scope to improve or to induce a certain property. Ag+ and Zn2+ are known to possess antibacterial properties, moreover, the latter has also osteogenetic and angiogenetic ones, enhancing the proliferation of osteoblastic cells and activating the large group of enzymes, such as MatrixMetalloProteinases, involved in the process of construction of new blood vessels.
The aim of this work was to perform an X-Ray diffraction insight into the hardening process of three cement compositions: TCP (tricalcium phosphate), Ag- and Zn-containing TCP (both in 0.6 wt% and 1 wt%). The Energy Dispersive X-Ray Diffraction (EDXRD) technique was proved to be a suitable tool for in situ real-time monitoring of the hardening process of CP bone cements. By means of this technique it is possible to obtain information about phase transformations (new phases and intermediate products) and amorphous-into-crystalline conversion (primary and secondary crystallization processes). Moreover, characteristic setting and hardening times and grain size evolution can be followed. Different reagents-to-products rate of conversion, hardening times and crystallinity were registered for doped and non-doped cement samples, and a number of intermediate phases, evidencing the complex hardening mechanism were observed for the Zn-TCP cement. The role of doping elements is discussed
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