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Hydroxyapatite (HA) is a biomaterial widely used in biomedical applications. Many studies have shown that ionic substituents can be incorporated into HA to produce a mineral composition more similar to natural bone tissue with more favorable biological characteristics for application in bone regeneration. However, its potentially toxic effects need to be evaluated before full approval for human use. For this purpose, an embryotoxicity test was performed on zebrafish according to OECD guideline 236. Zebrafish embryos were exposed to 1 or 3 microspheres of alginate containing nanoparticles of HA and carbonate (CHA), strontium (SrHA), and zinc-substituted HA (ZnHA) from 4 to 120 h post-fertilization (hpf). Lethality and developmental endpoints were evaluated. In addition, larval behavior at 168 hpf was also analyzed to observe whether biomaterials adversely affect optomotor and avoidance responses (neurotoxicity), as well as the oxidative stress pattern through qPCR. After 120 h exposure to all microspheres with different patterns of crystallinity, porosity, nanoparticle size, surface area, and degradation behavior, there was no mortality rate greater than 20%, indicating the non-embryotoxic character of these biomaterials. All experimental groups showed positive optomotor and avoidance responses, which means that embryo exposure to the tested biomaterials had no neurotoxic effects. Furthermore, larvae exposed to one SrHA microsphere showed a better optomotor response than the control. Furthermore, the biomaterials did not change the pattern of mRNA levels of genes related to oxidative stress even after 120 hpf. The growing number of new HA-based biomaterials produced should be accompanied by increased studies to understand the biosafety of these compounds, especially in alternative models, such as zebrafish embryos. These results reinforce our hypothesis that ion-substituted HA biomaterials do not impose toxicological effects, cause development and neuromotor impairment, or increase oxidative stress in zebrafish embryos being useful for medical devices and in the process of bone regeneration.

Hydroxyapatite (HA), Ca 10 (PO 4 ) 6 (OH) 2 , is a key material used to manufacture thin, bioactive coatings on metal implants for hard tissue regeneration. Technical challenges in their fabrication include control of the coating structure and chemical composition, as well as managing surface activation via ionic substitution. In this study, 15 – 216 nm-thick zinc-doped HA (ZnHA) thin films were grown via magnetron sputtering at room temperature. The effect of substituting Zn 2+ for Ca 2+ on the ultrastructures of the HA films was analyzed during several stages of film growth. Infrared vibrational scattering scanning near-field optical microscopy (s-SNOM) using the ultra-broad-band IR beam from synchrotron radiation was compared with Fourier transform infrared spectroscopy in attenuated total reflectance (FTIR/ATR) to reveal the close relationships between local topography and the chemical compositions of the film surface and the bulk of the film. The energy delivered via ionic bombardment induced the formation of complex structures: island-shaped nanoparticles of amorphous zinc-doped calcium phosphate, coalescent islands, disordered non-stoichiometric ZnHA nanoparticles, and long-range structures of nearly stoichiometric and crystalline ZnHA. Grazing incidence X-ray diffraction (GIXRD) from synchrotron radiation, X-ray photoelectron spectroscopy (XPS), focusing ion beam (FIB), and high-resolution transmission electron microscopy (HRTEM) confirmed Zn substitution into the HA lattice. Zinc was distributed homogeneously within the film structure (1.6 at%) but its concentration increased slightly on the film surface. The bulk of the film consisted of crystalline, columnar ZnHA domains oriented perpendicular to the substrate surface while the regions near the film/substrate interface were preferentially disordered and non-stoichiometric.

X-ray photoelectron spectroscopy (XPS) is one of the main tools for hydroxyapatite (HA) surface characterization in developing materials for biomedical and heterogeneous catalysis. Despite the XPS technique's potential to correlate binding energies with existing photo-emitter sites on near-surfaces, few previous studies analyzed this aspect for HA and metal-substituted HA surfaces. In this work, we theoretically reconstructed the XPS spectra of stoichiometric HA and lead-substituted hydroxyapatite (PbCaHA, Ca10-xPbx(PO4)6(OH)2; x = 2, 10) using a first-principles linear combination of atomic orbitals embedded cluster approach and periodic supercell band structures within the framework of Density Functional Theory (DFT). We take into account photoemission lines contributions from Ca(1), Ca(2), Pb(1) and Pb(2) sites located on surface and near-surface depths (up to ∼15 A) along the (0 0 1) and (1 0 0) surfaces. The calculated DFT spectra of HA and PbCaHA were compared with high-resolution XPS spectra previously characterized by synchrotron X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS). A combined theoretical and experimental approach enables decoding of the complex structure of HA and PbCaHA in XPS spectra. It was found that XPS binding energies profiles depend significantly on photo-emitters from near-surface sites and surface crystallographic orientation. The main Ca 2p3/2 envelope peak in HA is predominantly from Ca(1) and Ca(2) sites (∼347.4 eV), while the weaker peak is due to the Ca(2) site only (∼345.0 eV). Variations on HA nanoparticle morphology could be a critical factor for changes in XPS binding energies' profile.

Calcium phosphate (CP) has been used as biomaterial to regenerate bone defects. In order to improve its biological properties, substitutions in the calcium phosphate chemical structure have been investigated. Zinc has stimulatory effects on in vitro and in vivo bone formation and an inhibitory effect on in vitro osteoclastic bone resorption. The aim of this systematic review (SR) was to assess the effect of zinc incorporation into calcium phosphate on bone repair. This SR was performed in accordance with the PRISMA guidelines and Preclinical Systematic Review & Meta-analysis Facility. An electronic search was conducted using the MEDLINE/PubMed, Cochrane, Scopus, and Scielo databases. Eligibility criteria included only animal studies that compared the effect of zinc incorporation into CP–based materials on bone repair. The selection process yielded 18 studies among 335 retrieved. The ARRIVE guidelines checklist was used to assess the articles’ quality. It was observed that zinc incorporation into CP did not affect its biocompatibility, tends to reduce the resorption rate and was considered to be osteoconductive. Most of the manuscripts suggested that zinc incorporation can enhance bone repair. The results indicate that zinc-doped CP has potential for increasing bone repair, being an interesting option for bone regeneration biomaterial.

The non-equilibrium electro-thermodynamic properties of magnetized plasma produced by a modified radio-frequency magnetron sputtering system were investigated in detail. The plasma was analyzed using Hall, Langmuir, and Faraday probes and optical emission spectroscopy, and numerical simulations were conducted to determine the electric and magnetic field profiles. It is found that the occurrence of lower hybrid resonance and excitation of helicon waves are satisfied locally along the plasma profile (Z). This unusual effect in magnetron sputtering systems plays an important role in the increase of the electrons and ions temperature improving the quality of the films produced. Films of complex structure as hydroxyapatite that have biomedical applications were produced along the Z to confirm our plasma results. The films were characterized by performing grazing incidence X-ray diffraction using synchrotron radiation, X-ray photoelectron spectroscopy and atomic force microscopy. The microstructure analysis of hydroxyapatite films produced at different Z revealed that films with high crystallinities and with ideal stoichiometries (Ca/P = 1.67 ± 0.05) were produced within a magnetic cusp region (26 mm

Insulin-loaded calcium phosphate nanoparticles have been proposed as a potential drug delivery system for the oral treatment of diabetes and to stimulate bone cell proliferation and bone mineralization. The kinetics of insulin incorporation onto hydroxyapatite (HA) and Sr (SrHA)- and Zn (ZnHA)-substituted hydroxyapatite nanoparticles was investigated using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, zeta potential measurements and circular dichroism (CD) spectroscopy. The increase in insulin concentration on HA, SrHA and ZnHA was a typical physical adsorption process controlled by electrostatic forces and followed a Freundlich isotherm model. Zn substitution enhanced the capacity of the apatite surface to adsorb insulin, whereas Sr substitution inhibited insulin uptake. The surface stoichiometry and mesopore specific area induced by Zn and Sr substitution are proposed as the main causes of the difference in insulin adsorption. Despite the weak interaction between insulin and the apatite surface, the CD spectra revealed a decrease in the insulin ellipticity when the protein was adsorbed on the HA, SrHA and ZnHA nanoparticles. A reduction in alpha-helical structures and an increase in beta sheets were observed when insulin interacted with the HA surface. A less pronounced effect was found for ZnHA, for which a subtle decrease in alpha-helical structures was followed by an increase in turn structures. Interaction with the SrHA surface did not change the native insulin conformation. In vitro cell culture experiments lasting 24h using F-OST stromal cells showed that the insulin loaded on HA and ZnHA did not affect cell proliferation but the insulin loaded on SrHA improved cell proliferation. These results suggest that the stability of the native protein conformation is an important factor to consider when cells interact with insulin adsorbed on metal-substituted HA surfaces.

Background Bone tissue is capable of self-healing in the event of injuries. However, situations such as the patient‘s age or size of the damage can compromise natural healing, bringing to the fore the need for interventions to treat bone injuries. Tissue engineering presents treatment alternatives involving the use of cells and associated biomaterials. In this context, studies using biomaterials claim that carbonated hydroxyapatite (CHA) is more resorbable than hydroxyapatite (HA) and has biological similarity to bone hydroxyapatite. Methods Parameters of indirect contact (cytotoxicity, proliferation, and migration) of the extract obtained from spheres of carbonated hydroxyapatite associated with murine bone marrow stem cells (BMSCs) in vitro were evaluated. Then the osteogenic potential of CHA extract in murine BMSCs in vitro was assessed by quantification of calcium matrix, alkaline phosphatase levels and gene expression Col1A1 and Bglap. Non-critical size bone defects were performed in rat femur. After 14 days of healing, bone blocks were obtained for analysis from treated animals and compared to non-treated animals by histological and histomorphometric evaluation. Results The CHA extract showed osteoinductive properties in vitro without the need to add osteogenic inducing medium. The ability to induce osteogenic differentiation in undifferentiated cells was confirmed by increased activity of alkaline phosphatase, formation of mineralized nodules and increased expression of the Col1A1 and Bglap genes after 7 and 14 days of differentiation. All groups presented bone neoformation at the injury site 14 days after the operation. Histomorphometric analysis showed no statistical difference between groups in the parameters of bone formation, biomaterial and connective tissue. Conclusion The CHA spheres have in vitro osteoinductive properties and, when loaded with murine BMSCs, have the potential for bone repair and regeneration in vivo, presenting biocompatibility and osteoconductive, making it a promising alternative for bone tissue engineering applications.

In the present work, we investigated the nanostructure of calcium phosphate films formed during the initial stages of deposition (between 30 and 240 s; deposition rate of 3.7 nm/min) by radio-frequency magnetron sputtering. The sputtering deposition parameters and the plasma energy were previously adjusted to produce nearly stoichiometric nanocrystalline hydroxyapatite films after 180 min. Grazing-incidence X-ray diffraction and X-ray photoelectron spectroscopy analyses revealed that the films formed in the initial stages were composed of an amorphous calcium phosphate phase with a Ca/P ratio Ca/P = 1.60 ± 0.12, which is close to that of hydroxyapatite. Using high-resolution transmission electron microscopy, we demonstrated that the films were not a unique amorphous phase. An additional phase composed of dense calcium phosphate nanospheres was found in all periods and investigated. The nanospheres grew in size as the deposition time increased, and small nanospheres were always observed. This observation suggests the continuous formation of nanospheres at the surface of the film. Nanocrystalline regions were revealed by electron diffraction and high-resolution electron microscopy after a deposition of 60 s with a corresponding film thickness of 3.7 nm. Electron energy-loss spectroscopy analysis comparing individual nanospheres to the amorphous calcium phosphate layer showed differences in the oxygen K edge, suggesting a difference in the chemical bonding of the oxygen species. Nanospheres were observed in association with isolated crystals, suggesting that the nanospheres may participate in the crystallization of hydroxyapatite according to a heterogeneous nucleation process.

A radio-frequency magnetron sputtering technique operating in right-angle geometry (RAMS) with high plasma confinement was revised to produce thin films (15–570 nm) of fluorine-substituted hydroxyapatite, FHA, adapted to be used as nano-coatings for biomedical implants. An electron temperature of T eff ≈ 9.0 eV and a plasma electron density of 1.2 × 10 15 m − 3 assured the nucleation of an amorphous fluorine-substituted hydroxyapatite phase on Si and Ti surfaces. With the aid of a Langmuir probe, the RAMS plasma energy was tuned to control the coating stoichiometry and the ratio between the crystalline and amorphous phases. The energy delivered over time from the bombardment of ions and electrons transformed the amorphous calcium phosphate phase into crystalline fluorine-substituted hydroxyapatite. The crystalline films were obtained at room temperature. The partial substitution of OH − for F − in the HA structure was confirmed by X-ray diffraction using synchrotron radiation in grazing-incidence mode, X-ray photoelectron spectroscopy and attenuated total reflection Fourier transform infrared spectroscopy. High-resolution transmission electron microscopy carried out on cross-section film samples prepared by a focused ion beam (FIB) technique revealed that the film ultrastructure was composed of columnar crystals oriented perpendicularly to the substrate surface. The crystals were connected to the substrate surface by ordered nanolayers, indicating the existence of a continuous binding between the two materials. This work demonstrates that the RAMS technique is able to produce FHA nano-coatings with controlled chemical compositions and structures on metallic implants for clinical applications.

We report the ultrastructure of regenerated bone surrounding two types of biomaterials: hydroxyapatite–alginate composite and sintered hydroxyapatite. Critical defects in the calvaria of Wistar rats were filled with micrometer-sized spherical biomaterials and analyzed after 90 and 120 days of implantation by high-resolution transmission electron microscopy and Fourier transform infrared attenuated total reflectance microscopy, respectively. Infrared spectroscopy showed that hydroxyapatite of both biomaterials became more disordered after implantation in the rat calvaria, indicating that the biological environment induced modifications in biomaterials structure. We observed that the regenerated bone surrounding both biomaterials had a lamellar structure with type I collagen fibers alternating in adjacent lamella with angles of approximately 90°. In each lamella, plate-like apatite crystals were aligned in the c-axis direction, although a rotation around the c-axis could be present. Bone plate-like crystal dimensions were similar in regenerated bone around biomaterials and pre-existing bone in the rat calvaria. No epitaxial growth was observed around any of the biomaterials. A distinct mineralized layer was observed between new bone and hydroxyapatite–alginate biomaterial. This region presented a particular ultrastructure with crystallites smaller than those of the bulk of the biomaterial, and was possibly formed during the synthesis of alginate-containing composite or in the biological environment after implantation. Round nanoparticles were observed in regions of newly formed bone. The findings of this work contribute to a better understanding of the role of hydroxyapatite based biomaterials in bone regeneration processes at the nanoscale.

High-resolution transmission electron microscopy (HRTEM) and ab initio quantum-mechanical calculations of electronic structure were combined to investigate the structure of the hydroxyapatite (HA) (0 1 0) surface, which plays an important role in HA interactions with biological media. HA was synthesized by in vitro precipitation at 37 °C. HRTEM images revealed thin elongated rod nanoparticles with preferential growth along the [0 0 1] direction and terminations parallel to the (0 1 0) plane. The focal series reconstruction (FSR) technique was applied to develop an atomic-scale structural model of the high-resolution images. The HRTEM simulations identified the coexistence of two structurally distinct terminations for (0 1 0) surfaces: a rather flat Ca(II)-terminated surface and a zig-zag structure with open OH channels. Density functional theory (DFT) was applied in a periodic slab plane-wave pseudopotential approach to refine details of atomic coordination and bond lengths of Ca(I) and Ca(II) sites in hydrated HA (0 1 0) surfaces, starting from the HRTEM model.

The kinetic of chlorhexidine digluconate (CHXDG) uptake from aqueous solution by hydroxyapatite (HA) was investigated by ultraviolet (UV) analysis performed in HA powder (UV-solid) after the CHX adsorption. Adsorption isotherm of chlorhexidine (CHX) uptake was modeled by a combination of Languimir and Langmuir–Freundlich mechanisms. Strong molecule–molecule interactions and positive cooperativity predominated in the surface when CHX concentration was above 8.6 μg CHX /mg HA . UV-solid spectra (shape, intensity and band position) of CHX bound to HA revealed that long-range molecular structures, such as aggregates or micelles, started to be formed at low CHX concentrations (1.52 μg CHX /mg HA ) and predominated at high concentrations. Grazing-incidence X-ray diffraction (GIXRD) analysis from synchrotron radiation discarded the formation of crystalline structures on HA surface or precipitation of CHX crystalline salts, as suggested in previous works. The effect of the HA/CHX association on HA in vitro bioactivity, cytotoxicity and CHX antimicrobial activity was evaluated. It was shown that CHX did not inhibit the precipitation of a poorly crystalline apatite at HA/CHX surface after soaking in simulating body fluid (SBF). Cell viability studies after exposure to extracts of HA and HA/CHX showed that both biomaterials did not present significant in vitro toxicity. Moreover, HA/CHX inhibited Enterococcus faecalis growth for up to 6 days, revealing that binding to HA did not affect antimicrobial activity of CHX and reduced bacterial adhesion. These results suggested that HA/CHX association could result in a potential adjuvant antimicrobial system for clinical use.

Bovine serum albumin (BSA) may have an inhibitory or promoter effect on hydroxyapatite (HA) nucleation when apatite is precipitated in a medium containing the protein. In this study we evaluated the influence of BSA on the precipitation of calcium phosphate phases (CP) from simulated body fluid (SBF) when the protein was previously bounded to HA surface. The kinetics of BSA immobilization onto hydroxyapatite surface was performed in different buffers and protein concentrations in order to adjust experimental conditions in which BSA was tightly linked to HA surface for long periods in SBF solution. It was shown that for BSA concentration higher than 0.1mg/mL the adsorption to HA surface followed Langmuir–Freundlich mechanisms, which confirmed the existence of cooperative protein–protein interactions on HA surface. Fourier Transformed Infrared Attenuated Total Reflectance Microscopy (FTIRM-ATR) evidenced changes in BSA conformational state in favor of less-ordered structure. Analyses from high resolution grazing incident X-ray diffraction using synchrotron radiation (GIXRD), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) showed that a poorly crystalline calcium phosphate was precipitated on the surface of HA discs coated with BSA, after the immersion in SBF for 4 days. The new bioactive layer had morphological characteristics similar to the one formed on the HA surface without protein. It was identified as a carbonated apatite with preferential crystal growth along apatite 002 direction. The GIXRD results also revealed that BSA layer bound to the surface inhibited the HA dissolution leading to a reduction on the formation of new calcium phosphate phase.

Well characterized kaolin samples from different deposits of Brazil were studied by electron paramagnetic resonance. Three paramagnetic species attributed to iron in different chemical environments were identified in raw samples. A very intense and broad line with 0.2 mT linewidth was typical of large particles of iron oxides/hydroxides. A species at g = 2.0 with 0.04 mT line width was associated with superparamagnetic particles adsorbed to kaolinite surfaces or trapped between its lamellae. An isotropic and/or orthorhombic species in the g = 4.2 region belongs to structural Fe 3+ replacing Al 3+ in sites with different crystal-field symmetries. It was verified that large iron oxide particles were responsible for keeping the kaolin whiteness at levels below 50%. Superparamagnetic iron particles mainly affect whiteness in the range of 50% 86%) were determined by Fe 3+ iron content in the kaolinite structure. However, only a small part of this species can be removed from the kaolinite structure by traditional industrial processing techniques. These results showed that EPR is a powerful technique to assist in controlling kaolin quality in industrial processes.

The corrosion resistance of Ti and Ti–6Al–4V was investigated through electrochemical impedance spectroscopy, EIS, potentiodynamic polarisation curves and UV–Vis spectrophotometry. The tests were done in Hank solution at 25 °C and 37 °C. The EIS measurements were done at the open circuit potential at specific immersion times. An increase of the resistance as a function of the immersion time was observed, for Ti (at 25 °C and 37 °C), and for Ti–6Al–4V (at 25 °C), which was interpreted as the formation and growth of a passive film on the metallic surfaces.

In this work we applied a new route to synthesize magnetic iron oxide nanoparticles into alginate polymer for future application as drug delivery system activated by magnetic external stimuli. Calcium-alginate was used to encapsulate iron oxide nanoparticles, and as scaffold for particle nucleation and its influence on particles size and magnetic properties were studied. The iron oxide mean sizes were between 4.3 and 9.5 nm. Iron is dispersed throughout the polymer matrix mainly as iron oxide particles, and a small fraction as iron (III) occupying calcium sites in the polymer network. The temperature dependence of the Mossbauer spectra is typical of superparamagnetic particles in agreement with the magnetic susceptibility data.

Spin–lattice relaxation times, T 1 , for EPR signals created by irradiation of tooth enamel or carbonate-doped hydroxyapatite were studied by three-pulse inversion recovery and long-pulse saturation recovery. The recovery curves were modeled as the sum of two log-normal distributions of relaxation times. The dominant component in the EPR signal for tooth samples is assigned to CO 2 - replacing phosphate (B-sites) in the hydroxyapatite matrix. For this component the center of the T 1 distribution was 1.4 – 1.6 μ s at 294 K, and did not vary significantly with radiation dose or the source of the sample. The smaller, slower relaxing, component of the signals from the tooth samples had a T 1 distribution centered at 30 – 60 μ s and is assigned to an organic radical ( g ∼ 2.0045 ) . At 294 K the spin–spin relaxation time T 2 measured by two-pulse echo decay was dominated by motion of the CO 2 - and was independent of dose. The dose independence of T 1 and T 2 at ambient temperature provides the basis for using dose-independent microwave powers to record dosimetric tooth signals at microwave powers above the linear response regime.

Hydroxyapatite (HA) films have been widely recognized for their biocompatibility and utility in promoting biointegration of implants in both osseous and soft tissue. Conventional sputtering techniques have shown some advantages over the commercially available plasma spraying method; however, the as-sputtered films are usually amorphous which can cause some serious adhesion problems when post-deposition heat treatment is necessitated. In this paper we present an opposing radio frequency (RF) magnetron sputtering approach for the preparation of HA thin films on various substrates at low power levels. Using this alternative RF magnetron geometry, as-sputtered HA films are nearly stoichiometric, highly crystalline, and strongly bound to the substrate. Post-deposition heat treatment under 800 °C did not result in a marked improvement in the degree of crystallinity of the films. In addition, dissolution experiments show that as-sputtered films are more stable than annealed ones. As-sputtered films grown on amorphous silica substrates exhibit X-ray diffraction (XRD) patterns similar to those of randomly orientated HA powder. On the other hand, films deposited on oriented substrates such as Si(100) and Si(111) show a polycrystalline HA XRD pattern but with some strongly preferred orientations, indicating that HA crystallization is sensitive to the nature of the substrate. The results suggest that the opposing RF magnetron sputtering approach has some potential to produce high quality HA films on metallic implants.

Isolated iron ions and iron oxide nanoparticles entrapped in alginate microspheres were studied by 57 Fe Mfssbauer spectroscopy (MS), electron paramagnetic resonance (EPR) and magnetization measurements. Ferric alginate beads were prepared by dropping sodium alginate solution into ferric chloride solution (0.1 and 0.5 M) with stirring under Ar atmosphere. MS and EPR spectroscopy show that iron is absorbed in alginate as Fe(III). The EPR suggests that isolated Fe(III) substitutes sodium in the polymeric structure (narrow line paramagnetic species at g=4.23). This mechanism induces the linking of the alginate units and the formation of the alginate microspheres. During this process, superparamagnetic iron hydroxide particles (broad line species at g=2.22) are precipitated inside the polymer network. MS measurements performed in diluted and concentrated Fe(III) samples displays a paramagnetic doublet at 300 K, and two components at 4.2 K due to a paramagnetic site and blocked superparamagnetic particles. D 2004 Published by Elsevier B.V.

Immobilization of toxic metals by calcium phosphates is a promising technology for treating contaminated soil, water and wastes. A detailed study on the mechanisms of lead immobilization by hydroxyapatite has been carried out using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). For this, synthetic hydroxyapatite powder were submitted to a sorption process through exposure to an aqueous solution containing 917 mg L−1 of lead for times that varied from 3 min to 54 h. The results obtained reinforce the hypothesis that hydroxypyromorphite formation is the end of a kinetic process in which the hydroxyapatite crystals are continuously dissolved and recrystallized in order to form more stable structures with higher lead content. Consequently, the use of calcium phosphates to immobilize lead ions seems to be technically viable.

Archaeological artefacts made of obsidian are all the more precious for archaeologists as they are witnesses of cultural, social or 'economic' relationships between prehistoric populations. The main obsidian sources reachable in these times have been identified and characterized by chemical analysis and fission track dating. Because of iron presence (from 1% to 10% expressed in Fe 2 O 3 ) it is possible to use Mossbauer spectroscopy and electron spin resonance (ESR) on geological samples to characterize different sources. We studied by electron spin resonance about seventy obsidians coming from six Mediterranean volcanic islands. The complex spectra are mainly due to iron in different states and site location (and sometimes isolated Mn 2+ ions). X-band (9 GHz) spectra exhibit a signal at g = 4.3 with a shoulder at 9.8 ascribed to isolated Fe 3+ in the glassy matrix with a rhombic environment (C 2y ). Condensed clusters of Fe 3+ ions give rise to a resonance line at g = 2.0 whose position and width do not depend on temperature and in addition to this signal broad resonance lines are ascribed to micro-crystallites of mixed iron oxides (hematite, magnetite and related spinels, titanates, silicates) as inclusions into the amorphous matrix of obsidian. When temperature decreases from 300 to 5 K these signals shift towards weak fields. The contribution of every signal to ESR spectrum is different from one source to the other according to the different thermodynamic conditions that occurred during obsidian formation. It is thus possible to discriminate a priori one geological source using ESR spectra. At room temperature the first differences appear at X-band, low temperatures experiments may allow to remove some ambiguities.

The magnetization and anisotropy of Ni 81 Fe 19 /W 90 Ti 10 multilayers prepared by DC sputtering are presented. At high-angle X-ray diffraction, weak superlattice peaks appear around the NiFe (1 1 1) diffraction line, which indicate a fiber texture 〈1 1 1〉 for NiFe. The magnetization decreases with NiFe layer thickness t NiFe and the analysis of the results at 300 K indicates the presence of 6 A thick dead Ni 81 Fe 19 layer. The ferromagnetic resonance (FMR) spectra are obtained with the applied magnetic field parallel and perpendicular to the film plane at 300 K. Complicated spin-wave resonance spectra were observed and analyzed. From FMR, a negative value for Ni 81 Fe 19 /W 90 Ti 10 interface anisotropy is obtained.

The structural and magnetic properties of Fe/Zn films prepared by thermal evaporation have been studied by means of X-ray diffraction, vibrating-sample magnetometry and ferromagnetic resonance (FMR). For Fe layer thickness smaller than 20 A the saturation magnetization decreases with decreasing Fe thickness, which is an indication of the island growth of Zn and Fe–Zn interdiffusion at the layer interfaces. The effective field magnetization 4 πM eff of the Fe/Zn multilayers was determined from the FMR data in a rotating external magnetic field. The interface anisotropy constant of the Fe/Zn multilayers, K S , is found to be 1.0 erg/cm 2 at 300 K. This indicates the presence of a large perpendicular interface anisotropy and this may suggest that the largest part of K S originates from lattice misfit strain.

We studied by 57 Fe Mossbauer spectroscopy and EPR 11 obsidian samples from the islands of Lipari, Palmarola, Pantelleria and Sardinia (Western Mediterranean), 26 obsidian artefacts from Italian Neolithic sites of known origin and eight artefacts from the two sites of the Lipari and Filicudi islands whose origins were not previously determined. We show that structural fingerprinting may be considered a viable alternative to formation age or geochemical characterization in obsidian provenance studies in the Neolithic of Western Mediterranean and brings provenance attributions to archaeological obsidians from the Filicudi Eolian island.

Synthetic A-type carbonated apatite samples were irradiated at room temperature with 60Co gamma rays. Their ESR spectra consist of the lines of CO2- and CO3- radicals of orthorhombic and axial symmetry. The measurements carried out immediately after sample irradiation showed that CO2- species are produced by decomposition of CO3- radicals. Intensity of the CO2- lines in the synthetic and enamel samples increases during the first 400 and 200 h after irradiation, respectively. The dependence of the EPR signal on the dose varies with carbonate content of the sample. The dose response curve for tooth enamel is steeper for the synthetic material.

Several irradiated biocarbonates were studied by magnetic resonance techniques. Seven paramagnetic species, attributed to CO 2 − , SO 2 − and SO 3 − were identified. Comparison between radiation induced defects in bioaragonites and aragonite single-crystals shows that isotropic and orhorhombic CO 2 − centers with broad line spectra are not produced in the latter samples. Vibrational and rotational properties of isotropic CO 2 − centers were studied from low temperature Q-band spectra. Vibrational frequency is determined from the 13 CO 2 − hyperfine spectrum and yielded v =1.54 × 10 13 s −1 . The correlation time for isotropic CO 2 − , τ c =1.2 × 10 −11 s ( T =300 K), is typical of radicals rotating in liquids. ENDOR and General Triple spectroscopy show that orthorhombic CO 2 − centers are surrounded by water molecules located in the second nearest CO 3 2− sites at 5.14, 5.35 and 6.02 A. Water molecules replacing carbonates or as liquid inclusion of growth solution in local crystal imperfections may be responsible for the variety of orthorhombic and isotropic CO 2 − species, respectively.

In this work we combine electron paramagnetic resonance (EPR), high-resolution electron nucleus double resonance (ENDOR) and general triple resonance (GTR) spectroscopies, to study the local environment of the CO2− groups created by ionizing radiation in fossil tooth enamel. We demonstrate that the CO2− groups occupy slightly modified phosphate sites in the hydroxyapatite lattice. In quaternary shark enamel we found these groups to be interacting with water molecules in the apetite channels. The absence of water molecules as first neighbors in mammalian samples indicate, however, that these molecules are not significantly responsible for the stabilization of CO2− dating centers in enamel.

Irradiated A-type carbonated apatites with carbonate content ranging from 1.45% to 4.84% are studied by using electron paramagnetic resonance (EPR). The EPR spectra are mainly constituted of lines associated to axial CO 2 − species ( g ⊥ =2.0028 and g ∥ =1.9973) and orthorhombic CO 3 − species ( g 1 =2.0170, g 2 =2.0090 and g 3 =2.0041). The production of CO 2 − species on gamma irradiation depends on the carbonate concentration and the hydroxyapatite stoichiometry. The lowest dose detection limit was achieved with stoichiometric samples and carbonate concentration of 3.7%.

We have studied the ESR spectrum of enamel from fossil vertebrate teeth

The ESR natural spectrum of humic-free speleothem calcite single crystals in the region of g = 2.0000 is a composite of lines from 4 radiogenic species, in addition to Mn2+ lines. Laboratory irradiation causes appearance of 3 more species. Use of isotropic F species (g = 2.0003) for dating is possible if specific cautions are followed.