Apatite Phase Research Articles

Primary human osteoblast and mesenchymal stem cell responses to apatite/tricalcium phosphate bone cement modified with polyacrylic acid and bioactive glass.

In this work, three different modified cements, control apatite/beta-tricalcium phosphate cement (CPC), polymeric CPC (p-CPC), and bioactive glass added polymeric cement (p-CPC/BG) were evaluated regarding their physical properties and the responses of primary human osteoblast cells (HObs) and mesenchymal stem cells (MSCs). Although polyacrylic acid (PAA) increased compressive strength and Young's modulus of the cement, it could cause poor apatite phase formation, a prolonged setting time, and a lower degradation rate. Consequently, bioactive glass (BG) was added to PAA/cement to improve its physical properties, such as compressive strength, Young's modulus, setting time, and degradation. For in vitro testing, HObs viability was assessed under two culture systems with cement-preconditioned medium (indirect) and with cement (direct). HObs viability was examined in direct contact with cements treated by different prewashing conditions. HObs presented a more well spread morphology on cement soaked in medium overnight, as compared to other cements with no treatment and washing in PBS. In addition, the proliferation, differentiation, and total collagen production of both HObs and MSCs adhered to the cement were detected. Cells showed excellent proliferation on PAA/cement and PAA/BG/cement. Furthermore, the higher released Si ion and lower acidosis of PAA/BG/cement-conditioned medium resulted in an increase in osteogenic differentiation (HObs and MSCs) and enhanced collagen production (HObs in osteogenic medium and MSCs in control medium). Therefore, our findings suggest that BG incorporated PAA/apatite/β-TCP cement could be a promising formula for bone repair applications.

Monitoring of alpha-decay radiation damage in a 241Am-doped glass-ceramic material

The evolution under alpha-decay radiation of a 241Am doped aluminoborosilicate glass-ceramic was investigated in hot cells DHA-ATALANTE facility in CEA. The cumulative La2O3 - Am2O3 solubility limit was voluntarily exceeded, leading to the formation of apatite-like silicate crystals. The crystals, with a hexagonal-shaped morphology, that is characteristic of apatite crystals, have a composition and a cell parameter close to those expected for an apatite phase of stoichiometric composition Ca2(La,Am)8(SiO4)6O2. Structural and microstructural evolutions under alpha self-irradiation were followed for 8 years by regularly analyzing the crystals and the residual glassy matrix. The evolution of the X-Ray Diffraction (XRD) patterns is the result of a progressive radiation-induced amorphization in apatite crystals. The fully amorphous state is reached at an alpha-decay dose of around 3 × 1018 α/g. Raman analyses suggest a modification of the connectivity of the SiO4 tetrahedra of apatite crystals, with a transition from isolated SiO4 units in the crystalline state to connected SiO4 units in the metamict state. The crystalline-to-amorphous transformation is accompanied by an increase in macroscopic volume (swelling), highlighted by RAMAN imaging. This macroscopic dimensional change is also associated to a decohesion of the crystals from the glassy matrix, observed by Scanning Electron Microscopy (SEM). However, optical and SEM images of the glass-ceramic surface do not reveal any significant cracks in the residual glass under alpha self-irradiation, thus showing a quite good stability of this glass-ceramic material.

Chitosan-polyethylene oxide/clay-alginate nanofiber hydrogel scaffold for bone tissue engineering: Preparation, physical characterization, and biomimetic mineralization

This study aimed to prepare a novel organic-mineral nanofiber/hydrogel of chitosan-polyethylene oxide (CS-PEO)/nanoclay-alginate (NC-ALG). The effects of NC particles on the mineralization and biocompatibility of the scaffold were investigated. A layer-by-layer scaffold composed of CS-PEO and NC-ALG was prepared. The morphological properties, swelling, biodegradation, and mechanical behaviors of the scaffolds were evaluated. Furthermore, scaffolds were characterized by the Fourier Transform Infrared (FTIR), the Field Emission Scanning Electron Microscope (FE-SEM), and X-Ray Diffraction (XRD) techniques. Bone-like apatite formation ability of the scaffolds was determined by the mineralization test in a simulated body fluid (M-SBF). In addition, the crystalline phase of bone-like apatite precipitates was investigated by XRD analysis. The cell compatibility of the scaffolds was also studied with osteoblastic cell line MC3T3-E1 by MTT assay. Notably, the incorporation of NC particles in CS-PEO/ALG scaffolds is suitable for bone tissue regeneration which enhances bone-like apatite formation. Further, the hemolysis and MTT assays demonstrated that CS-PEO/NC-ALG scaffold was compatible and safe for MC3T3 cells.

Synthesis of transition metal doped lanthanum silicate oxyapatites by a facile co-precipitation method and their evaluation as solid oxide fuel cell electrolytes.

Transition metal doped apatite La10Si6-x Co x O27-δ (x = 0.0; 0.2; 0.8) and La10Si5.2Co0.4Ni0.4O27-δ are synthesized by co-precipitation method followed by sintering. The precursor precipitates and apatite products are characterized by XRD, FTIR, TGA/DTA, Raman Spectroscopy, SEM-EDX and electrochemical impedance spectroscopy. The presence of apatite phase with hexagonal structure is confirmed through the XRD results. The conductivity measurements of the samples sintered at 1000 °C show that the ionic conductivity increases with increasing content of Co2+ doping into apatite that is further increased by co-doping of Ni2+. The Co doped apatite (La10Si5.2Co0.8O27-δ ) exhibited conductivity of 1.46 × 10-3 S cm-1 while Co-Ni co-doped sample (La10Si5.2Co0.4Ni0.4O27-δ ) exhibited highest conductivity of 1.48 × 10-3 S cm-1. The maximum power density achieved is also for Co, Ni co-doped sample i.e., 0.65 W cm-2 at 600 °C. The results represented show that Co and Ni enhances the SOFC performance of apatite and makes it potential electrolyte candidate for solid oxide fuel cell application.

Corrosion behavior of Yb4Hf3O12 ceramics exposed to Calcium-Ferrum-Alumina-Silicate (CFAS) coupled with water vapor at 1400 °C

In this work, the corrosion behavior of Yb4Hf3O12 ceramics under CFAS coupled with water vapor environment at 1400 °C for 2–50 h was investigated. Results show that the CFAS were rapidly dissolved into ceramics under test environment, and then the Yb-Ca-Si apatite and Hf-rich fluorite phases were re-precipitated. Simultaneously, the water vapor corrosion mainly induced grain surface corrosion, resulting in the formation of corrosion pits and ridge-like structures. Moreover, the pores and microcracks caused by water vapor corrosion offer additional penetration path for CFAS melt.

Thermodynamic stabilities of apatite phases in a wetland system: Implications for bone diagenesis

Evaluating the fate and stability of apatite minerals, the largest phosphorus (P) reservoir on Earth's surface, has direct consequences for understanding our vertebrate fossil record as well as biogeochemical cycling. Bone (bioapatite) deposited following the death of an animal represents a potential source of phosphorus in terrestrial and aquatic ecosystems for micro and macrofauna. Exposure of bone to ambient geochemical conditions also represents the first step of the fossilization process. However, the thermodynamic stability of bone in these ecosystems, which are frequently phosphorus-limited, is unknown. The goal of this study was to approach questions related to recrystallization, diagenesis, and fossilization from a thermodynamics perspective, focusing on the role of geochemistry on bioapatite (bone) preservation. By developing thermodynamic models, run using PHREEQC, the stabilities of a range of apatite and other phosphorus-bearing phases were considered under physiochemical conditions measured in a Louisiana wetland and an adjacent river. The models integrated variable temperatures (5–40 °C), concentrations of phosphorus ([PO43-] from 0.0006 to 0.0484 mmol/L), and pH (6.5–9.25) from representative waters collected over 3 years at the wetland. In all models, waters are undersaturated with respect to hydroxylapatite, except under the highest temperatures, [PO43-], and pH conditions. In contrast, fluorapatite approached stability under lower pH and temperatures, and carbonated fluorapatite exhibited a broad range of stable conditions. These results suggest that if bioapatite (bone) were deposited under these present-day conditions, solutions are predicted to be undersaturated with respect to many apatite phases, leading to mineral dissolution. However, if bioapatite undergoes substitutions forming a fluorinated and/or carbonated phase, stability may shift towards preservation. These results have implications for identifying potential biases and mechanisms driving bone preservation over geologic time in a wetland system. The modeling results demonstrate that preservation of bone is favored under subsurface (burial) rather than surface conditions, aligning with long-held views on the formation of our vertebrate fossil record.

The CMAS corrosion behavior of high-entropy (Y0.2Dy0.2Er0.2Tm0.2Yb0.2)4Hf3O12 hafnate material prepared by ultrafast high-temperature sintering (UHS)

High-temperature molten calcium-magnesium-alumina-silicate (CMAS) corrosion has become a fatal factor for the failure of aero-engine thermal barrier coatings. In this study, a promising entropy-stabilized (Y0.2Dy0.2Er0.2Tm0.2Yb0.2)4Hf3O12 (5YH) hafnate was prepared by the emerging ultrafast high-temperature sintering (UHS), and its corrosion and wetting behavior of molten CMAS were investigated. For the corrosion mechanism, the precipitation of the high-entropy apatite phase promotes the formation of the HfO2 phase, and it can improve the density and stability of the slow-growing reaction layer, hindering the further penetration of molten CMAS. At 1300 ℃, a reaction layer with a three-layered morphology is generated, resulting from the decreased viscosity of the molten CMAS. Moreover, computational analysis shows that molten CMAS on the 5YH surface has a larger contact angle (17°) than traditional YSZ (13°), and the spreading area is about 90 % of traditional YSZ, which benefits for its good CMAS corrosion resistance.

Electrical properties of lithium–lanthanum silicate oxyapatites

Lithium–lanthanum silicate oxyapatite exhibits high lithium-ion conductivity at temperatures above 400 °C. To further enhance its ionic conductivity, the relationships among the microstructure, bulk conductivity, and grain boundary conductivity were investigated for Li-rich compositions. LixLa10−xSi6O27−x (x = 1–8), Li5La5Si5O20, Li5La5Si4.5O19, Li6La4Si4.5O18, and Li7La3Si4O16 were synthesized, and their ionic conductivities were determined. Using X-ray diffraction, Li2La8Si6O25, Li5La5Si5O20, Li5La5Si4.5O19, Li6La4Si4.5O18, and Li7La3Si4O16 were analyzed to be close to the apatite phase with few impurities. Scanning electron microscopy/energy-dispersive X-ray spectroscopy and nuclear magnetic resonance analyses revealed that the lithium–silicate glass phase increases with respect to the apatite phase in the following order: Li2La8Si6O25 < Li5La5Si5O20 < Li5La5Si4.5O19 < Li6La4Si4.5O18 < Li7La3Si4O16. Further, as the La/Si ratio of the apatite phase increases, the chemical composition changes from Li1La9Si6O26 to Li3La7Si6O24. Both the bulk (apatite phase) and the grain boundary (glass phase) resistivities at 400 °C decreased in the order Li5La5Si5O20 > Li5La5Si4.5O19 > Li6La4Si4.5O18 > Li7La3Si4O16. The apparent activation energies for the bulk ion conductivity of Li5La5Si5O20, Li5La5Si4.5O19, Li6La4Si4.5O18, and Li7La3Si4O16 were 57.3, 47.6, 43.0, and 40.4 kJ mol−1, respectively. The total conductivities (bulk + grain boundary conductivities) of Li7La3Si4O16 (8.1 × 10−3 S cm−1 at 400 °C) was approximately four times higher than that of Li1.08LaSiO4.04 (2.2 × 10−3 S cm−1 at 400 °C), which has been previously reported to have the highest ionic conductivity.

CMAS corrosion resistance characteristics of RE50TaxZr50-xO175+0.5x thermal barrier oxides in RE2Zr2O7-RETaO4 systems

The corrosion resistance characteristics of RE-rich RE50TaxZr50-xO175+0.5x oxides in RE2Zr2O7-RETaO4 systems to calcium-magnesium-alumino-silicate (CMAS) at 1300 °C, and the influence of RE3+ and Ta5+ on chemical reactions and reactive crystallization of CMAS melts were investigated. The results show that following the thermochemical reactions, apatite, pyrochlore, reprecipitated fluorite and residual Yb(Y)TaO4 phases were the predominant reaction products. Formation abilities of apatite and pyrochlore were found to be proportional to the ionic radius of RE3+. The increase of Ta5+ amount can decrease the number of available RE3+ to form apatite. Moreover, the resistance characteristic to CMAS corrosion in RE50TaxZr50-xO175+0.5x systems was decided by the combined action of apatite and pyrochlore phases. The cohesive mixture of apatite and pyrochlore phases can generate a dense layer near the reaction front, which had a positive effect on suppressing CMAS infiltration. The ability of the fluorite + RETaO4 two-phase field was determined to be sufficient to mitigate CMAS corrosion.

Interaction of ytterbium monosilicate environmental barrier coating material with molten calcium-magnesium-aluminosilicate (CMAS)

The corrosion behaviors and mechanism of CMAS on Yb2SiO5 (YbMS) ceramics were investigated. Results indicated that YbMS was corroded by CMAS to generate various apatite and garnet, whose stability depends on the amounts of doping cations. Noticeably, the Ca2+ acts as an obvious sign of the reaction front diffusing into YbMS along the grain boundaries and volume. The higher diffusion rate of grain boundary than volume results in discontinuous reaction layers. The YbO1.5 formed by the dissolution of YbMS diffuses along the CMAS glass grid until the solubility is saturated to form a cyclic apatite phase, above 1300 ℃.

Rare Earth Element (REE) and Critical Mineral Fractions of Central Appalachian Coal-Related Strata Determined by 7-Step Sequential Extraction

Rare earth elements (REEs) and critical minerals (CMs) are used in many modern industries, including the automotive sector, generation and storage, clean energy, and defense. The demand for REEs is increasing, and the REE supply chain is unpredictable. The US has driven to assess non-conventional sources of REE (such as coal underclay) to identify domestic resources to stabilize this uncertainty in supply. Knowledge of the minerology, distribution, and modes of occurrence of REEs is integral to the assessment of non-conventional sources. Additionally, extraction techniques can be optimized and targeted when REE distribution in different solid fractions from source material is understood. In this study, four bituminous coal-related samples associated with the Lower and Middle Kittanning coal seams in the Appalachian Basin (US) underwent a seven-step sequential extraction procedure, primarily targeting the water-soluble, exchangeable, acid soluble, mildly reducible, moderately reducible, strongly reducible, and oxidizable fractions. The REE and other elements of interest from each extraction step were analyzed, and the percentages of element extracted from raw solids were calculated. REEs extracted from the total seven steps were reported as the extractable fraction, whereas the fractions in the residual solids were reported as the non-extractable fraction. Less than 6% of REE were extracted from three samples. Twenty-one percent of REE was extracted from the fourth sample, mainly from the steps targeting oxidizable and exchangeable phases. Co-extraction of critical metals (Co, Ni, Cu, and Zn) occurred during the oxidizable, exchangeable, acid soluble, and water-soluble steps for the four samples. In the extracted fractions, the four samples all exhibited a middle and heavy REE enrichment relative to light REE. The mobility of major cation (e.g., Ca, Fe, and P) and REE is associated with exchangeable, oxidizable, and acid soluble fractions. Non-extractable REE is likely held in refractory apatitic phases, and/or primary REE-phosphates (e.g., monazite and xenotime).

Bioactive fluorcanasite reinforced magnesium alloy-based porous bio-nanocomposite scaffolds with tunable mechanical properties.

Magnesium (Mg) alloy-based porous bio-nanocomposite bone scaffolds were developed by powder metallurgy route. Selective alloying elements such as calcium (Ca), zinc (Zn) and strontium (Sr) were incorporated to tune the mechanical integrity while, bioactive fluorcanasite nano-particulates were introduced within the alloy system to enhance the bone tissue regeneration. Green compacts containing carbamide were fabricated and sintered using two-stage heat treatment process to achieve the targeted porosities. The microstructure of these fabricated magnesium alloy-based bio-nanocomposites was examined by Field emission scanning electron microscope (FE-SEM) and x-ray micro computed tomography (x-ray μCT), which revealed gradient porosities and distribution of alloying elements. X-ray diffraction (XRD) studies confirmed the presence of major crystalline phases in the fabricated samples and the evolution of the various combinations of intermetallic phases of Ca, Mg, Zn and Sr which were anticipated to enhance the mechanical properties. Further, XRD studies revealed the presence of apatite phase for the immersed samples, a conducive environment for bone regeneration. The fabricated samples were evaluated for their mechanical performance against uniaxial compression load. The tunability of compressive strengths and modulus values could be established with variation in porosities of fabricated samples. The retained compressive strength and Young's modulus of the samples following immersion in phosphate buffered saline (PBS) solution was found to be in line with that of natural human cancellous bone, thereby establishing the potential of the fabricated magnesium-alloy-based nanocomposite as a promising scaffold candidate for bone tissue engineering.

Growth kinetics of apatite layer evolved from calcia-magnesia-aluminosilicate (CMAS) hot corrosion reaction of (Y1-xYbx)2SiO5 ceramics at elevated temperatures of 1673 K and 1773 K

Calcia-magnesia-aluminosilicate (CMAS) corrosion behaviors of hot-pressed (Y1-xYbx)2SiO5 ceramics at 1673 K and 1773 K have been investigated. The main corrosion product of nonstoichiometric Ca-RE-Si-O apatite phase evolves with increasing temperature or prolonging corrosion time. The growth of apatite layer at 1673 K follows approximately a linear rate law, however it follows a proximately parabolic rate law at 1773 K. The growth rate of the apatite layer at 1773 K is lower than that at 1673 K in the process of interaction between CMAS and rare-earth monosilicates. Yb-doping mediates the CMAS corrosion resistance of Y2SiO5 effectively by changing the growth rate of apatite layer and the composition of formed apatite phase. This work provides new insights on compositional regulation of (Y1-xYbx)2SiO5 EBCs materials to resist CMAS corrosion.

دراسات بيوفيزيقية للمحاكاة البيلوجية لإسمنت العظام مع الألجينات لاستخدامه في المجال الطبي

Osteoporosis and many other bone defects are described as the diseases that have attracted attention in the past two decades over worldwide. Because of it is known as a silent disease and with a high commonness rate among the elderly, the battle could be difficult. This paper aims to assess the impact of the inclusion of some additions to the brushite cement and use fluid simulation in the body that contain calcium and free of protein in the laboratory as a stimulant for the apatite formed such as bone apatite samples consisting of brushite cement and various elements that have been added to the roofs. The research paper adopted the experimental approach. The stable phases of calcium phosphate cements depend significantly upon temperatures and the presence of water, either during processing or in the use situation. At body temperature, only two calcium phosphates are stable when in interaction with aqueous media such as body fluids. The samples under investigation are used to select samples which can be considered suitable as a biomaterial in vitro. The samples prepared in the form of two samples each one regards with a group of additives including sodium Alginate, Wollastonite, Titanium Oxide, Hydroxyapatite and Zinc Oxide. Soaking brushite samples with their additives in simulated body fluid for one week may cause presence of a bone-like apatite layer phase (Ca10(OH)2(PO4)6, HA) on the surface of these samples. To sustain the aim of the study, the samples studied by using the X-ray diffraction spectra, scanning electron microscope and Raman spectroscopy. The X-ray diffraction used to ensure the presence of the components used in the preparation of the samples is present in the samples or not. The study of X-ray examination for the samples under investigation after soaking for one week in SBF to help us to recognize new phases appearing after the interaction between the samples surfaces and the components of the SBF.

A Comparative Cyclic Voltametric Study on Rare Earth (Eu, Sm, Dy, and Tb) Ions Doped La10Si6O27 Nanophosphors for Sensor Application

The rare earth (RE = Eu, Sm, Dy, and Tb) ions doped La10Si6O27 nanophosphor was synthesized by a simple solution combustion method. The prepared La10Si6O27:RE3+ nanophosphors (LNPs) were subjected to diverse technical tools for exploring their structural, optical, morphological, and electrochemical features. The structural analysis using powder X-ray diffraction (PXRD) patterns revealed the hexagonal oxy apatite phase for LNPs with a crystallite size in the range of 25–50 nm, and the equivalent was affirmed by image analysis via transmission electron microscopy (TEM). Utilizing DRS data, the bandgap energy (Eg) values were recorded for LNPs. Cyclic voltametric (CV), electrochemical impedance spectroscopy (EIS), and sensor studies were performed using a modified carbon paste electrode of LNPs. The modified LNP electrodes were found to be highly effective in sensing paracetamol in acidic medium with a quick response time of 3 secs for sensing the drugs at 1 mM concentration. All the RE ions Eu3+, Sm3+, Dy3+, and Tb3+ (5 mol%)-doped LNPs exhibited the most promising electrochemical sensing characteristics.

Fabrication of radioactive and non-radioactive titanate and zirconate ceramics for immobilization of used nuclear fuel

The immobilization of used nuclear fuel (UNF) may be desirable for storage and permanent disposal. Ceramics are viable candidates for immobilization for an entire UNF assembly which is rich in U and Zr, as ceramic phases such as pyrochlore and fluorite incorporate target elements (i.e., U, Pu). In this work, titanate and zirconate ceramics were formulated to account for light water reactor UNF compositions. They were fabricated using Ce or Gd as analogues for U and the other actinides in non-radioactive formulations and U or U/Pu for radioactive formulations using similar processing conditions. Ceramics were characterized with powder X-ray diffraction, microscopy techniques (e.g., SEM-EDS, EBSD), and X-ray absorption near edge structure spectroscopy. For non-radioactive titanate ceramics, perovskite, rutile, and zirconolite were detected when Ce was used as an analogue, and pyrochlore and zirconolite were formed when Gd was used. For the radioactive titanate ceramics, pyrochlore, perovskite, and fluorite (including UO2) phases formed. Only pyrochlore was formed for zirconates using Gd analogues but required high temperatures and long dwell times to produce. When Si was added as a sintering aid to lower temperatures and dwell times, fluorite and apatite phases formed on Gd zirconates. Fluorite, perovskite, and pyrochlore phases were observed in a U based zirconate using Si as a sintering aid. Overall, the non-radioactive ceramics were more consolidated than the radioactive ceramics; future work should focus on improving processing conditions for radioactive formulations.

Crystallization and phase evolution in novel (Gd1/6Tb1/6Dy1/6Tm1/6Yb1/6Lu1/6)2Si2O7 environmental barrier coating

AbstractDesign of multiple rare‐earth (RE) principal elements is a practical strategy to optimize key property of RE disilicate environmental barrier coating (EBC). However, multi‐RE component in the feedstocks may also introduce critical fabrication problems due to the different evaporating and crystallizing behaviors of the EBC containing various RE composition. We herein report the preparation of a novel multi‐RE disilicate (Gd1/6Tb1/6Dy1/6Tm1/6Yb1/6Lu1/6)2Si2O7 EBC by atmospheric plasma spraying (APS). The crystallization behavior of the as‐deposited coating annealed at 1100°C–1300°C with different durations (5 and 20 h) in air and argon atmospheres were investigated through comprehensive characterization techniques. RE disilicate, RE mono‐silicate, and RE apatite were detected in the as‐sprayed coatings, and mono‐silicate and apatite transform to RE2Si2O7 with the increment of temperature and extension of annealing duration. Furthermore, the contribution of multiple RE to the formation of apatite phase is discussed. The results provide a fundamental understanding and may guide the controllable preparation of multi‐RE disilicate EBC via APS method.

Facile synthesis, in vitro biocompatibility, and antibacterial activity of porous hollow hydroxyapatite microspheres

AbstractIn this study, porous hollow hydroxyapatite (HAp) microspheres are prepared using chitosan microspheres as novel sacrificial templates and their microstructure, biocompatibility, and drug delivery properties are evaluated. Scanning electron microscope (SEM) observations show that HAp microspheres are spherical in morphology with a diameter of 100–300 μm and have a porous and core–shell structure. X‐ray diffractometer patterns show that HAp microspheres consist of apatite phase. MTT assay indicates that HAp microspheres are biocompatible and have no significant cytotoxicity. SEM observations show that HAp microspheres support attachment and proliferation of osteoblast MC3T3‐E1 cells. After being soaked in the solution of tetracycline hydrochloride (TH, model drug), HAp microspheres adsorb TH with an adsorption capacity of 47% to derive TH‐loaded HAp microspheres. When exposed to two types of representative bacteria: Escherichia coli and Staphylococcus aureus, TH‐loaded HAp microspheres maintain the biological activity of TH to inhibit the growth of bacteria.

Multi-doped apatite: Strontium, magnesium, gallium and zinc ions synergistically affect osteogenic stimulation in human mesenchymal cells important for bone tissue engineering

Functional calcium phosphate biomaterials can be designed as carriers of a balanced mixture of biologically relevant ions able to target critical processes in bone regeneration. They hold the potential to use mechanisms very similar to growth factors naturally produced during fracture healing, while circumventing some of their drawbacks. Here we present a novel phase of carbonated-apatite containing Mg2+, Sr2+, Zn2+ and Ga3+ ions (HApMgSrZnGa). While all dopants decrease the crystallinity, Ga3+ limits crystal growth and enables the formation of a nanosized apatite phase with enhanced specific surface area. Coexistence of the ions enhances degradability and controls solubility of low crystalline, distorted, multi-doped apatite structure, controlled by Ga3+ ions accumulated at the surface. Consequently, HApMgSrZnGa supports the viability of human mesenchymal stromal cells (MSCs) and induces their stimulation along the osteogenic lineage. In addition, the co-released ions has a synergistic antimicrobial effect, particularly within the HApMgSrZnGa-Au(arg) composite with Au(arg) as contact-based antimicrobial. The activity is stable up to two months in vitro. Osteogenic nature and antimicrobial activity, combined in a single biomaterial, are suggesting a well-balanced, multi-doped apatite design applicable as future option in bone regeneration and tissue engineering.

Rapid alteration of cortical bone in fresh- and seawater solutions visualized and quantified from the millimeter down to the atomic scale

It is widely known that post mortem diagenetic alteration processes cause modifications and overprinting of the chemical and isotopic proxies incorporated in vivo in bone apatite and collagen. Understanding the processes occurring during the interaction between fluids and bones in an early diagenetic setting is fundamental to determining the extent to which the commonly-used geochemical proxies in bone get modified during fossilization. The present study experimentally investigates the structural and chemical changes in bone induced by controlled in vitro aqueous alteration experiments under simulated early diagenetic conditions. It is intended to derive a deeper phenomenological and quantitative understanding of the transport and reaction processes that occur in the early stage of fossilization. For this purpose, 3.5 mm-sized cylinders were drilled from modern ostrich cortical bone and immersed in different experimental solutions enriched with tracers such as Zn, Sr, rare earth elements, and U. The experiments ran for several hours to weeks at 30, 60, and 90 °C - the latter two temperatures were chosen to accelerate anticipated early diagenetic modifications of the bone samples. Both the bone samples and the experimental solutions were analyzed using micro-analytical techniques such as Raman spectroscopy, electron microprobe, high-resolution inductively coupled plasma-mass spectrometry, nanoscale ion microprobe, and atom probe tomography to assess mineralogical, chemical, and structural changes from the millimeter to the atomic scale. The results show that element uptake into the bone samples occurs within hours after they have been exposed to an aqueous solution instead of years, as previously assumed. Additionally, distinct modifications of the organic phase were observed, accompanied by the growth of new apatite phases by dissolution-reprecipitation and recrystallization processes. Carbonate-poor or -free hydroxylapatite formed in the sample center and more stable carbonated fluorapatite in the sample rim. From these data, a phenomenological model is derived that explains the interaction between bone and aqueous solutions during the earliest stages of fossilization. This study also demonstrates the importance of using a comprehensive methodological approach when investigating alteration processes whose effects range from the millimeter down to the atomic scale.