Amorphous Apatite Research Articles

Mechanochemical synthesis and characterization of strontium substituted apatite for biomedical application

Strontium-substituted apatite has been proposed as a promising material for osteoporosis treatment. Several synthesis methods have been attempted in the past. In this study, we investigated a method known as the mechanochemical synthesis method. Characterization was carried out using different amounts of strontium ions in the hydroxyapatite (HAp) matrix with FT-IR spectral analysis, X-ray diffraction, lattice constant measurements, differential thermal analysis (DTA), terahertz spectroscopy, and investigation of the basic morphology using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX). We report that the development and performance of mechanochemical synthetic pathways are more efficient and economical than other substituted apatite formation methods and are useful in the biomedical field to produce calcium phosphate-based clinical materials. The FTIR spectra, terahertz spectra, and XRD analysis results revealed that the mixture of dicalcium phosphate dihydrate (DCPD), Ca(OH)2 and Sr(OH)2 8H2O was phase-transformed into strontium-containing carbonate amorphous apatite by this simple and economical mechanochemical synthesis method.

In vitro biomineralization potential in simulated wound fluid and antibacterial efficacy of biologically-active glass nanoparticles containing B2O3/ZnO

In the present study, SiO2-CaO-B2O3-ZnO (SCBZ), SiO2-CaO-B2O3 (SCB), SiO2-CaO-ZnO (SCZ) and SiO2-CaO (SC) silicate-based glasses were synthesized by the sol-gel method to elucidate the influence of B2O3 and ZnO substitution on glass characteristics aiming to further use in wound healing applications. The amorphous nature, spherical-shaped morphology and nano-sized primary particles of glasses were revealed by XRD and SEM analysis. Moreover, investigating the antibacterial activity of glasses against E.coli and S.aureus bacteria indicated the improved antibacterial properties of SCBZ glass against both bacterial strains compared with SCB and SCZ glasses. Assessment of ion release revealed that the incorporation of zinc induces a more stable glass network with a lower tendency to dissolution contrary to the incorporation of boron, which facilitated the dissolution of glass by the formation of more reactive SiOB and BO bonds. Glasses were immersed in Simulated Wound Fluid (SWF) to predict their mineralization susceptibility. Morphological studies and FTIR analysis showed the formation of cauliflower-like hydroxy-carbonated apatite on the surface of SCB and SC glasses after 14 days. In contrast, the presence of Zn in SCBZ and SCZ glasses inhibited the formation of crystalline apatite and induced the deposition of spherical-shaped amorphous apatite. Our study suggests that the co-incorporation of B and Zn in SCBZ glass make this material a potential multifunctional candidate for accelerating the healing of skin wounds.

Enrichment of rare earth elements in the early Cambrian Zhijin phosphorite deposit, SW China: Evidence from francolite micro-petrography and geochemistry

The Zhijin phosphorite deposit is a giant early Cambrian rare earth element (REE) deposit, with particular enrichment in heavy REEs, and is of high economic significance. The REEs of the deposit occur almost entirely in apatite, which, on the basis of petrographic characteristics, can be divided into francolite grains (90%), amorphous apatite, and phosphate fossils. In this paper, we report an investigation into francolite grains in different types of phosphorite from ore sections of the Zhijin deposit. Detailed petrographic and transmission electron microscopy observations reveal that the francolite grains are composed of nano-apatite crystals measuring 120–160 nm long. Trace-element contents of pyrite and whole-rock geochemical indicators (such as Cr/Zr and V/Ni ratios and Th/U–Co/Ni plots) suggest that the Zhijin phosphorite formed in an anoxic hydrothermal sedimentary environment. However, the negative Ce/Ce* and Eu/Eu* anomalies indicate that the diagenetic environment of the francolite grains was oxidic. Different diagenetic redox environments and the presence of transportation fractures in francolite grains identified under back-scattered electron imaging reveal that the francolite grains underwent prolonged abrasion and transportation in seawater before sedimentation. Petrographic observations and laser ablation–mass spectrometry element surface scanning analyses indicate that the REEs are uniformly distributed in nano-apatite in isomorphic form, and no nano-inclusions or REE minerals were found, implying that late mineralization was not the cause of REE enrichment. The higher (La/Yb)N ratios of francolite grains relative to seawater indicate that the francolite grains captured abundant REEs during the early diagenetic stage. We infer that prolonged exposure to seawater and the high specific surface area of francolite grains are the key factors that led to the enrichment in REEs. Combining the timing of the metallogenic epoch (543 Ma), Sr–Nd isotopic data, and the Y/Ho ratio, which is close to those of modern seawater, indicates that the REEs were sourced from paleo-seawater. Paleogeographic information suggests that during the early Cambrian, extensive continental collisions caused great amounts of continental weathering products to enter the paleo-ocean, leading to the production of abundant amounts of hydrothermal–sedimentary phosphorus and REEs in shallow seas, thus forming an ideal sedimentary environment for generating the REE resources of the Zhijin phosphorite deposit.

A novel photocrosslinked phosphate functionalized Chitosan-Sr5(PO4)2SiO4 composite hydrogels and in vitro biomineralization, osteogenesis, angiogenesis for bone regeneration application

The natural polysaccharide-based hydrogels have gained significant interest to use as 3D scaffolds for bone repair and reconstruction owing to their excellent biocompatibility, biosafety, and biodegradability. Yet, these hydrogels have major obstacles in terms of insufficient properties such as mechanical, osteogenic, angiogenic, and biomineralization. Therefore, this study mainly aims to develop an innovative water-soluble phosphate functionalized chitosan (CSMAP) through consequent modification with methacrylic anhydride (MA), then alteration by phosphonopropionic acid (P). Further, a novel photocrosslinked composite hydrogel was fabricated with a combination of CSMAP and synthesized strontium phosphosilicate (SPS, Sr5(PO4)2SiO4) bioceramic nanoparticles with a photoinitiator under UV irradiation. The various concentrations of nanosized SPS particles (0.5, 2.5, 5, and 10 mg/mL) were incorporated into the CSMAP matrix and the swelling, mechanical, morphological, physiochemical, osteogenic, angiogenic properties were investigated. The CSMAP-SPS composite hydrogels possessed a well-arranged porous network structure. The composite hydrogel was restricted to swell in distilled water with the increased concentration of SPS particles. The compressive strength and modulus of CSMAP hydrogel were improved by the inclusion of SPS particles. The bioactive Sr, P, and Si ions were released from CSMAP-SPS hydrogels in a sustained and controlled manner at a non-toxic level. The composite hydrogels promoted in vitro amorphous apatite deposition, revealing a superior biomineralization activity. In vitro results demonstrated that the composites hydrogels showed no toxicity to preosteoblast MC3T3-E1 cells, induced MC3T3-E1 osteogenic differentiation with detection of bsp, ocn and opn osteogenic genes, and also promoted the endothelial tube formation with increased capillary length, branch points, and angiogenic gene vegf expression. Thus, the obtained results proved that the fabricated novel CSMAP-SPS hydrogel could act as an attractive candidate for bone regeneration.

Influence of preferred orientation on the bioactivity of hydroxyapatite: a potential tooth repair and implant surface coating material

Abstract Bioactive hydroxyapatite (HAp) material was synthesized using a simple wet chemical precipitation and heat-treatment method from snail (Achatina achatina) shells and a phosphate-containing solution. According to X-ray diffraction patterns obtained, the heat-treatment caused a crystallographic preferred orientation along the HAp c-axis and thus, affected the material mineralization and bioactivity modeled in vitro using simulated body fluid (SBF) for 7 and 21 days. After 21 days of immersion, calcium and phosphate mineral concentrations in SBF decreased by 66% and 83%, respectively. This corresponded to a transformation from a poor calcium amorphous apatite phase (calcium phosphate) to a resorbing crystalline calcium apatite indicated by scanning electron microscopy micrographs. The material crystallite size (~15 nm), lattice parameters, physicochemical properties, and morphological characteristics were all typical of the human enamel apatite and, therefore, could be considered ideal for use in tooth repairs and implant surface coatings.

Assembly Mechanism of Highly Crystalline Selenium-Doped Hydroxyapatite Nanorods via Particle Attachment and Their Effect on the Fate of Stem Cells.

Hydroxyapatite is the main inorganic component of human bone. Synthetic hydroxyapatite and its different modified forms, which have been shown to be biocompatible and osteoconductive, have been widely used in bone tissue engineering. It is still challenging to controllably synthesize hydroxyapatite with a targeted morphology. In this work, we synthesized highly crystalline selenium-doped hydroxyapatite nanorods (SeHAN) via a two-step alcohol thermal method and provided a complete explanation of the synthesis mechanism. Tracing the crystals obtained from the solvated phase to the crystal phase with high-resolution microscopy, the nanorod formation route can be briefly described as follows: as a basic unit, ∼30 nm amorphous apatite initially formed in the first step and partly crystallized in early part of the second step; after a period of alcohol thermal reaction, immature nanorods appeared, which were composed of nanocrystals; finally, immature nanorods transformed into single-crystal nanorods through crystallization by particle attachment. Since few works have focused on the osteogenesis ability of SeHAN, whose antitumor effect has been widely studied, we investigated the influences of SeHAN on rat-bone-marrow-resident mesenchymal stem cells (MSCs). Surprisingly, SeHAN exhibited excellent biocompatibility for MSCs, enhanced their osteogenic differentiation, and inhibited their adipogenic differentiation. This work provides not only a general method to controllably synthesize hydroxyapatite nanorods/SeHAN but also an insight into understanding the hydroxyapatite formation mechanism. The current study also highlights the effects of SeHAN on MSCs that could furnish a significative strategy for manufacturing functional biomaterials for biomedical applications and tissue engineering by enhanced ossification and reduced marrow adiposity.

Physiological and genetic characterization of calcium phosphate precipitation by Pseudomonas species

Microbial biomineralization is a widespread phenomenon. The ability to induce calcium precipitation around bacterial cells has been reported in several Pseudomonas species but has not been thoroughly tested. We assayed 14 Pseudomonas strains representing five different species for the ability to precipitate calcium. Calcium phosphate precipitated adjacent to the colonies of all the Pseudomonas strains tested and also precipitated on the surface of colonies for several of the Pseudomonas strains assayed. The precipitate was commonly precipitated as amorphous calcium phosphate, however seven of the 14 Pseudomonas strains tested precipitated amorphous apatite in agar adjacent to the colonies. Out of the seven Pseudomonas strains that precipitated amorphous apatite, six are plant pathogenic. The formation of amorphous apatite was commonly observed in the area of the agar where amorphous calcium phosphate had previously formed. A transposon mutagenesis screen in Pseudomonas syringae pv. tomato DC3000 revealed genes involved in general metabolism, lipopolysaccharide and cell wall biogenesis, and in regulation of virulence play a role in calcium precipitation. These results shed light on the common ability of Pseudomonas species to perform calcium precipitation and the underlying genetic regulation involved in biomineralization.

A zinc oxide-modified hydroxyapatite-based cement facilitated new crystalline-stoichiometric and amorphous apatite precipitation on dentine.

To evaluate the remineralization ability of two endodontic sealer cements. Mid-coronal dentine surfaces were subjected to: (i) 37% phosphoric acid (PA) or (ii) 0.5mol L-1 ethylenediaminetetraacetic acid (EDTA) conditioning prior to the application of two experimental hydroxyapatite-based cements, containing sodium hydroxide (calcypatite) or zinc oxide oxiapatite respectively. Samples were stored in simulated body fluid for 24h or 21days. Remineralization of the dentine surfaces were studied by Raman spectroscopy (mapping with K-means cluster and hierarchical cluster analysis) was undertaken. Nanoroughness and collagen fibril width measurements were performed with an atomic force microscopy. ANOVA and Student-Newman-Keuls test were performed (α=0.05). Phosphoric acid+oxiapatite promoted both the highest dentine mineralization (P<0.05) and crystallographic maturity at the dentine surface. Noncrystalline amorphous-like apatites were also formed. Dentine treated with PA+calcypatite attained the roughest surface (P<0.05) with minimal fibril width (P<0.05). Cross-linking of collagen only became greater in the group PA+oxiapatite after 21days. The maximum relative mineral concentration and structure of collagen linked to the amide I and ratio amide III/AGEs was obtained after using PA+calcypatite at 21-days time-point (P<0.05). EDTA produced a lower stoichiometric hydroxyapatite (P<0.05) with decreased maturity, at the expense of carbonate band widening, although it favoured the nucleation of carbonated calcium phosphate. Dentine surfaces treated with PA+oxiapatite attained the highest dentine remineralization with both crystalline-stoichiometric and amorphous apatites, at 21days. EDTA conditioning facilitated amorphous-bulk mineral precipitation. The amorphization was more intense after using oxiapatite and provided an ion-rich environment favouring insitu dentine remineralization.

The chitosan coating and processing effect on the physiological corrosion behaviour of porous magnesium monoliths

Abstract The present study evaluates the corrosion resistance effect of chitosan coating onto porous magnesium (Mg) monoliths with porosities of 14–40 vol.%, prepared by sintering of Mg powder with NH 4 HCO 3 used as spacer particles. The dip-coated chitosan was found to interact with corrosion products (Mg(OH) 2 and MgO) via hydrogen bonding, providing the physiological stability and the corrosion resistance, at the same time affecting the mineralization process towards amorphous apatite with a small contribution of crystalline hydroxyapatite(HAP). The electrochemical studies reveal that porosity increases, and that the coating process affects the corrosion resistance positively. However, the values for compression strength (17–72 MPa) and elastic modulus (12–26 MPa) of chitosan-coated monolith indicate its applicability as a supporting, rather than self-standing implantation material.

Strontium-Containing Apatite/Poly Lactide Composites Favoring Osteogenic Differentiation and in Vivo Bone Formation

Strontium was shown to enhance bone growth; however, its oral administration may lead to severe side effects. The application of strontium in orthopedic biomaterials may therefore be an alternative to achieve targeted and sustained strontium treatment to the surgery site in aid of bone growth locally. In this study, strontium-containing composites were prepared by introducing various levels of strontium into amorphous apatite and extruding the obtained apatite powders into polylactide in a weight ratio of 1:1. Strontium substitution increased apatite dissolution and enhanced the degradation behavior of the resulting composites. Sustained and dose-dependent strontium release from the composites was observed for up to 24 weeks in simulated physiological solution, indicating that strontium release can be tuned by its substitution level in the embedded apatite. Strontium-containing composites enhanced the osteogenic differentiation of murine mesenchymal stromal cells in vitro in a dose-dependent fashion. After heterotopic implantation with the combination of rhBMP-2, bone formation on strontium-containing composites was enhanced. These results suggest that strontium-releasing composites provide a local ion-rich (i.e., Sr2+ as well as Ca2+ and PO43–) environment that favors osteogenic differentiation and in vivo bone formation

Textured fluorapatite bonded to calcium sulphate strengthen stomatopod raptorial appendages

Stomatopods are shallow-water crustaceans that employ powerful dactyl appendages to hunt their prey. Deployed at high velocities, these hammer-like clubs or spear-like devices are able to inflict substantial impact forces. Here we demonstrate that dactyl impact surfaces consist of a finely-tuned mineral gradient, with fluorapatite substituting amorphous apatite towards the outer surface. Raman spectroscopy measurements show that calcium sulphate, previously not reported in mechanically active biotools, is co-localized with fluorapatite. Ab initio computations suggest that fluorapatite/calcium sulphate interfaces provide binding stability and promote the disordered-to-ordered transition of fluorapatite. Nanomechanical measurements show that fluorapatite crystalline orientation correlates with an anisotropic stiffness response and indicate significant differences in the fracture tolerance between the two types of appendages. Our findings shed new light on the crystallochemical and microstructural strategies allowing these intriguing biotools to optimize impact forces, providing physicochemical information that could be translated towards the synthesis of impact-resistant functional materials and coatings.

Double layer bioglass-silica coatings on 316L stainless steel by sol–gel method

Abstract The application of bioglass coatings on metallic implants provides link between bone and materials and prevents corrosion of metallic implants in body fluid. Therefore, in this research, 45S5 bioglass-silica coatings on 316L stainless steel were prepared by the sol–gel method and were characterized by different techniques. According to X-ray diffraction (XRD) results, by sintering 45S5 bioglass at 600 °C for 5 h, coatings containing both amorphous phase and Na2Ca2Si3O9 crystalline phase were obtained. Scanning electron microscopy (SEM) results showed that coatings prepared via appropriate sol aging and substrate preparations are crack-free. Potentiodynamic polarization tests in simulated body fluid (SBF) showed that coatings improve corrosion resistance of substrates, significantly. Further, bioactivity was considered during 30 days of immersion in SBF at 37 °C by atomic absorption spectroscopy (AAS), XRD, SEM and potentiodynamic polarization tests that demonstrated the growth of amorphous apatite, hydroxyapatite (HA) and CaSiO3 film on coatings.

Reactivity kinetics of 52S4 glass in the quaternary system SiO2–CaO–Na2O–P2O5: Influence of the synthesis process: Melting versus sol–gel

A new composition of bioactive glass, in the quaternary system SiO2–CaO–Na2O–P2O5, was synthesized using melting and sol–gel routes. The prepared glass, 52S4: (wt.%) 52% SiO2–30% CaO–14% Na2O–4% P2O5, was soaked in Simulated Body Fluid (SBF) in order to evaluate the kinetic reactivity of this glass versus the synthesis mode. The obtained results have shown that 52S4 is a bioactive glass if it is prepared either by melting or sol–gel methods. The bone-like apatite was formed at the glass surface prepared by sol–gel route after 2h. However, the formation of this apatite was delayed to 1day when the glass was prepared by melting method. In addition, this apatite was crystallized, after 30days soaking in SBF, only if the glass is prepared by melting route. The glass prepared by sol–gel method was more resorbable and leads to silica gel formation up on amorphous apatite layers at any time. So, this silica gel inhibited the crystallization of amorphous apatite.

Raman spectroscopic monitoring of the osteogenic differentiation of human mesenchymal stem cells

The differentiation of stem cells into multi-lineages is essential to aid the development of tissue engineered materials that replicate the functionality of their tissue of origin. For this study, Raman spectroscopy was used to monitor the formation of a bone-like apatite mineral during the differentiation of human mesenchymal stem cells (hMSCs) towards an osteogenic lineage. Raman spectroscopy observed dramatic changes in the region dominated by the stretching of phosphate groups (950-970 cm(-1)) during the period of 7-28 days. Changes were also seen at 1030 cm(-1) and 1070 cm(-1), which are associated with the P-O symmetric stretch of PO(4)(3-) and the C-O vibration in the plane stretch of CO(3)(2-). Multivariate factor analysis revealed the presence of various mineral species throughout the 28 day culture period. Bone mineral formation was observed first at day 14 and was identified as a crystalline, non-substituted apatite. During the later stages of culture, different mineral species were observed, namely an amorphous apatite and a carbonate, substituted apatite, all of which are known to be Raman markers for a bone-like material. Band area ratios revealed that both the carbonate-to-phosphate and mineral-to-matrix ratios increased with age. When taken together, these findings suggest that the osteogenic differentiation of hMSCs at early stages resembles endochondral ossification. Due to the various mineral species observed, namely a disordered amorphous apatite, a B-type carbonate-substituted apatite and a crystalline non-substituted hydroxyapatite, it is suggested that the bone-like mineral observed here can be compared to native bone. This work demonstrates the successful application of Raman spectroscopy combined with biological and multivariate analyses for monitoring the various mineral species, degree of mineralisation and the crystallinity of hMSCs as they differentiate into osteoblasts.

Comparative Bioactivity Study of 45S5 and 58S Bioglasses in Organic and Inorganic Environment

Melt derived bioactive glasses and sol-gel derived glasses have been extensively investigated and are reported to be bioactive. Investigation of the bioactivity was conducted in different media, like conventional Simulated Body Fluid (c-SBF), Dulbecco's Modified Eagle's Medium (DMEM) and Tris buffer solution. The aim of this work is to investigate and evaluate thein vitro bioactivity assessment of two commonly used bioactive glasses- 45S5 and 58S-soaked in DMEM and c-SBF, in order to compare the biological response of both glasses in organic and inorganic environ- ments. For the samples immersed in c-SBF, the onset of apatite formation on the surface of 45S5 grains was slightly delayed in comparison to 58S. After 3 days in DMEM 58S powders revealed the formation of a crystalline HCAp phase on the surface of all grains in contrary to 45S5, where a sparsely developed amorphous apatite phase was developed.

Articular cartilage calcification in osteoarthritis: Insights into crystal‐induced stress

Osteoarthritis (OA) is the most common form of rheumatic disease, leading ultimately to chronic pain, restriction of joint mobility, and disability. OA affects millions of people worldwide, and its prevalence is expected to increase with the concomitant prevalence of obesity and aging (1). OA is a disease affecting the whole joint and is characterized by articular cartilage destruction along with changes occurring in other joint components including bone, menisci, synovium, ligaments, capsule, and muscles (2). Multiple parameters contribute to the pathogenesis and progression of OA, including hereditary factors, mechanical overload, intraarticular calcium-containing microcrystal (Ca crystals) deposition, and aging. Ca crystals, which encompass calcium pyrophosphate dihydrate (CPPD) and basic calcium phosphate (BCP) crystals, have been associated with severe OA for many years. However, the role of CPPD and BCP crystals in OA remains controversial (3,4). BCP crystals, a heterogeneous group of apatite crystals including carbonated apatite, octacalcium phosphate, immature amorphous apatite, tricalcium phosphate (5), and magnesium-substituted apatite (whitlockite) crystals (6), are considered by some investigators to be “innocent bystanders” and/or markers of end-stage disease, because they can be released from bone as apatite mineral (4). Similarly, CPPD crystal deposition is considered to be a common aging-related process (4,7). However, numerous clinical and experimental data provide strong evidence that cartilage calcification occurs as an active process, and that calcification clearly plays a pathogenic role in OA, a phenomenon referred to as “microcrystal-induced stress.” This is different from the previously described and well-known mechanical, oxidative, or cytokine stresses in OA. The aim of this review is to highlight this old but forgotten and neglected concept. Ultimately, cartilage calcification could be considered as a potential therapeutic target in OA. As such, several therapeutic strategies will be discussed.

Preparation and characterization of novel alkali‐activated nano silica cements for biomedical application

The major goal of this study was to investigate and characterize novel Ca(OH)(2)-activated nano silica (SiO(2)) cements for the potential application as a bone cement. Novel Ca(OH)(2)-activated nano-SiO(2) powders composed of Ca(OH)(2) and nano-SiO(2) were easily prepared, and the deionized water was used as the liquid phase. The initial and final setting times of Ca(OH)(2)-activated nano-SiO(2) cements with liquid to powder (L/P) ratios of 1.00-1.33 mL g(-1) range from 50 ± 1 to 120 ± 3 min and 96 ± 2 to 190 ± 5 min, respectively. The calorimetric curves indicate that the heat liberations of Ca(OH)(2)-activated nano-SiO(2) cements (105.57-138.01 J g(-1)) are lower than that of C(3)S (about 150 J g(-1)). The Ca(OH)(2)-activated nano-SiO(2) pastes are injectable under general extrusion force of 100 N, and their compressive strengths with suitable L/P ratios are 5-9 MPa, which is comparable with that of cancellous bone. The in vitro bioactivity of the Ca(OH)(2)-activated nano-SiO(2) cement pastes were investigated by soaking in simulated body fluid for various periods. The results show amorphous apatite deposits on the paste surfaces after soaking in simulated body fluid for 2 h. With the prolonged soaking time, amorphous apatite transforms into crystalline apatite after soaking for 1 day. The Ca(OH)(2)-activated nano-SiO(2) cements have short setting times, low heat liberation, injectability, suitable compressive strength, and excellent in vitro bioactivity, and may be used as bioactive bone cements for bone regeneration.

Formation of carbonated apatite particles from a supersaturated inorganic blood serum model

Pathological calcification is common among for instance dialysis patients, and this causes an increase in mortality risk. An elevated serum phosphate concentration among those patients strongly correlates to this increase. In this work investigations of the conditions, composition, crystallinity and morphology of in vitro calcification are performed and related to results from in vivo studies. The study was performed under conditions mimicking physiological ones, i.e. a pH around 7.40, a temperature of 37 degrees C, an ionic strength of 150 mM and ion concentrations close to those in human serum including the effects of elevated phosphate concentrations. The course of precipitation involves an initial precipitate that subsequently re-dissolves to give another precipitate, in accordance with the well-known Ostwald ripening theory. The final bulk precipitate consists of a macroscopically amorphous carbonated apatite. The amorphous apatite is formed from assemblies of spherical particles in the mum range, in turn composed of nano-crystalline needles of about 10 x 100 nm. Even the initially formed precipitate, as well as a small amount of precipitate that occurs on the liquid surface, consist of a carbonated calcium phosphate. The in vitro observed carbonated apatite bears strong resemblance to in vivo cardiovascular calcification known from literature.

Characterization of biominerals in the radula teeth of the chiton, Acanthopleura hirtosa

Understanding biomineralization processes provides a route to the formation of novel biomimetic materials with potential applications in fields from medicine to materials engineering. The teeth of chitons (marine molluscs) represent an excellent example of a composite biomineralized structure, comprising variable layers of iron oxide, iron oxyhydroxide and apatite. Previous studies of fully mineralized teeth using X-ray diffraction, Raman spectroscopy and scanning electron microscopy (SEM) have hinted at the underlying microstructure, but have lacked the resolution to provide vital information on fine scale structure, particularly at interfaces. While transmission electron microscopy (TEM) is capable of providing this information, difficulties in producing suitable samples from the hard, complex biocomposite have hindered progress. To overcome this problem we have used focused ion beam (FIB) processing to prepare precisely oriented sections across interfaces in fully mineralized teeth. In particular, the composite structure is found to be more complex than previously reported, with additional phases (goethite and amorphous apatite) and interface detail observed. This combination of FIB processing and TEM analysis has enabled us to investigate the structural and compositional properties of this complex biocomposite at higher resolution than previously reported and has the potential to significantly enhance future studies of biomineralization in these animals.

Ionization-induced effects in amorphous apatite at elevated temperatures

Electron-beam-induced effects in preamorphized Sr2Nd8(SiO4)6O2 were investigated in situ using transmission electron microscopy with 200-keV electrons at temperatures ranging from 380 to 780 K. Within the electron-irradiated area, epitaxial recrystallization was observed from the amorphous/crystalline interface toward the surface, with the rate of recrystallization increasing as temperature increased from 380 to 580 K. Structural contrast features (i.e., O deficient amorphous material), as well as recrystallization, were observed outside of the irradiation area at temperatures from 680 to 780 K. Ionization-induced processes and local nonstoichiometry induced by oxygen migration and desorption are possible mechanisms for the electron-beam- induced recrystallization and for the formation of the structural contrast features, respectively.