Apatite Phase Research Articles

Synthesis, Characterization, and Biological Performances of Magnesium-Substituted Dicalcium Phosphate Anhydrous.

Dicalcium phosphate anhydrous (DCPA, CaHPO4) is regarded as an orthopedic material due to its ability to match the generation of new bone to the rate of implant resorption without considering the material's mechanical stability. Additionally, magnesium (Mg) is widely recognized for its essential function in bone metabolism, especially during the initial phases of osteogenesis. Therefore, we explored the influences of Mg ions on DCPA powder, in biological responses, and on the enhancement of osteogenic properties. Mg-DCPA powders with varying substitution levels (0, 3, 5, and 7 mol%) were produced using the co-precipitation method. In the in vitro test, precipitates began to develop on the surface of the Mg-DCPA powders after 7 days. These results indicate that Mg ions in the DCPA powder could enhance the generation of a new apatite phase when subjected to physiological fluids on the surface of the powder. In addition, the osteogenic performance of the DCPA powder was improved by adding Mg ions. The most effective magnesium substitution content in the DCPA powder in order to improve its osteogenic potential was approximately 3 mol%. Consequently, this amount of magnesium in the DCPA powder could control the maintaining time in the implantation operation to produce a new apatite phase.

Occurrence, distribution and fate of iodine during phosphate ore beneficiation process

Numerous beneficiation techniques, such as washing, grinding, flotation, digesting, and calcination, are used to concentrate the minerals found in phosphate rocks, which include apatite, carbonatites, and silicates. Significant iodine levels are often found in phosphate ore minerals, which have a distinctive geochemical occurrence. However, the exact occurrence and distribution of iodine in these minerals are not yet thoroughly understood. A study was carried out to investigate the iodine's distribution, occurrence modes (phases), and release rate in Moroccan phosphate as it undergoes the beneficiation process. The samples underwent a multi-analytical approach combining mineralogical and chemical characterization using ICP-MS, ICP-OES, XRD, elements titration, and Pearson correlation analysis for interelement relationships. Calcination, digestion, and Heavy liquid separation is used to study the fate of iodine. The analysis indicates that iodine is primarily found in fluorapatite, with local concentrations ranging from 35 to 130 ppm. The most enriched grains/zones are associated with fluorapatite, enriched in P2O5, F-. in addition, iodine is positively correlated with its main components, including P2O5, F-, SO3, Na2O, CaO, and REEs. The flotation and heavy liquid separation process used for calcite and silicate removal is acting as an iodine and P2O5 concentrator, given that 99 % of iodine occurs in the apatite phase. However, it has been demonstrated that iodine can be released during the digestion of phosphate rock. Where the initial iodine content is distributed among phosphoric acid, PG, and the gaseous phase, constituting 35 %, 25 %, and 40 %, respectively. Furthermore, the calcination of phosphate rock between 800–1000 °C shows that total iodine is released with gases in I2 form, leading to an increase in the concentration of iodine in the surrounding area. In this regard, an integrated pyrometallurgical process has been proposed for the valorization of iodine as silver iodide. This process involves trapping gaseous iodine in an alkaline solution, followed by precipitation, thereby contributing to the overarching objectives of the circular economy and environmental protection.

First widespread occurrence of rare phosphate chladniite in a meteorite, winonaite Graves Nunataks (GRA) 12510: Implications for phosphide–phosphate redox buffered genesis in meteorites

Abstract The first widespread occurrence of rare Na-, Ca-, and Mg, Mn, Fe-bearing phosphate chladniite was observed in meteorite Graves Nunataks (GRA) 12510, which is a primitive achondrite that sits within the winonaite class. Numerous 1–500 µm chladniite grains were found, often on the margins between silicate clasts and the kamacite portions of the large metal veins that permeated through the sample. The largest chladniite grains are associated with merrillite, kamacite, taenite, troilite, albite, forsterite, diopside, and enstatite, with a few tiny chladniite grains and an apatite grain enclosed within merrillite. GRA 12510s average chladniite composition is Na2.7Ca1.25(Mg10.02Mn0.69Fe0.20)Σ10.91(PO4)9. Electron backscattered diffraction (EBSD) patterns indicate varying degrees of nucleation and growth of chladniite grains. Additionally, the first pure Raman spectrum of chladniite is described here, revealing primary ν1 bands at 954, 974, and especially 984 cm–1. The co-occurrence and close association of merrillite, apatite, chladniite, and P-bearing metallic phases within GRA 12510 suggests that the fO2 of IW-2 to IW-4 is an intrinsic property of the precursor chondritic material, and the phosphate-phosphide reaction may have buffered the final winonaite and IAB iron meteorite phase assemblages. Altogether, chladniite appears to form alongside other phosphates, with their chemistries reflecting the diverse environment of their formation. Meteoritic chladniite likely formed through subsolidus oxidation of schreibersite, scavenging Na from albite, Ca from diopside, Mg from enstatite/forsterite, Fe from kamacite/taenite, and Mn from alabandite/chromite when available. A P0-P5+ redox-buffered environment also has implications for thermometry and fast cooling rates, although more experiments are needed to extrapolate powder reaction rates to those of larger crystals. Furthermore, phosphide-phosphate buffered experiments may aid in investigating equilibrium chemistry at fO2 values between IW-2 and IW-4, which have been challenging to explore experimentally due to the limited availability of solid metal-metal oxide buffers between IW (Fe-FeO) and IW-5 (Cr-Cr2O3) at temperatures and pressures relevant to planetary interiors. Future investigations of phosphide-phosphate redox-buffered genesis at fO2 values between IW-2 and IW-4 have important implications for primitive meteorite constituents (e.g., CAI values), partially differentiated planetesimals and planets, including Mercury and core formation on Earth.

3D-printed silicate porous bioceramics promoted the polarization of M2-macrophages that enhanced the angiogenesis in bone regeneration.

The failure of bone regeneration has been considered as a serious problem that troubling patients for decades, most of which was resulted by the poor angiogenesis and chronic inflammation after surgery. Among multiple materials applied in the repair of bone defect, silicate bioceramics attracted researchers because of its excellent bioactivity. The purpose of this study was to detect the effect of specific bioactive glass ceramic (AP40, based on crystalline phases of apatite and wollastonite) on angiogenesis and the subsequent bone growth through the modulation of macrophages. Two groups were included in this study: control group (macrophages without any stimulation, denominated as Control) and AP40 group (macrophages incubated on AP40). This study investigated the effect of AP40 on macrophages polarization (RAW264.7) and angiogenesis in vitro and in vivo. Additionally, the changes of angiogenic ability regulated by macrophages were explored. AP40 showed excellent angiogenesis potential and the expression of CD31 was promoted through the modulation of macrophages toward M2 subtype. Additionally, the macrophages incubated on AP40 synthesized more PDGF-BB comparing to macrophages without any stimulation, which contributed to the improved angiogenetic ability of human umbilical vein endothelial cells (HUVECs). Results of in vivo studies indicated increased bone ingrowth along the implants, which indicated the potential of bioceramics for bone defect repair clinically.

Tuning Mg Doping and Features of Bone-like Apatite Nanoparticles Obtained via Hydrothermal Synthesis.

Nanocrystalline apatites have been intensively studied for decades, not only for their well-known mimesis of bone apatite but also for applicative purposes, whether as biomaterials for skeletal repair or more recently for a variety of nanomedical applications enabled by their peculiar surface characteristics. Particularly, ion-doped apatites are of great interest because the incorporation of foreign ions in the composition of apatite (nano)crystals alters the bulk and surface properties, modifying their ability to interact with the external environment. This is clearly seen in the physiology of bone tissue, whose mineral phase, a low crystallinity apatitic phase, can dynamically exchange ions with cells, thus driving bone metabolism. Taking bone mineral as a model, the present work describes the development of Mg-doped hydroxyapatite nanoparticles, exploiting hydrothermal synthesis to achieve extents of Mg2+ doping hardly achieved before and using citrate to develop stable apatite colloidal dispersions. Morphological and physicochemical analyses, associated with in-depth investigation of ions populating the apatitic lattice and the nonapatitic surface layer, concurred to demonstrate the cooperative presence of Mg2+ and citrate ions, affecting the dynamic ion retention/release mechanisms. Achieving high Mg2+ doping rates and understanding how Mg doping translates into surface activation of apatite-based nanoparticles is expected to foster the design of novel smart and tunable devices, to adsorb and release ionic species and cargo molecules, with potential innovations in the biomedical field or even beyond, as in catalysis or for environmental remediation.

Multifunctional Biocomposites: Synthesis, Characterization, and Prospects for Regenerative Medicine and Controlled Drug Delivery.

This article presents a new method for preparing multifunctional composite biomaterials with applications in advanced biomedical fields. The biomaterials consist of dicalcium phosphate (DCPD) and bioactive silicate glasses (SiO2/Na2O and SiO2/K2O), containing the antibiotic streptomycin sulfate. Materials were deeply characterized by X-ray diffraction and attenuated total reflectance Fourier transform infrared spectroscopy, and zeta potential analysis, UV-visible spectrophotometry, and ion-exchange measurement were applied in a simulating body fluid (SBF) solution. The main results include an in situ chemical transformation of dicalcium phosphate into an apatitic phase under the influence of silicate solutions and the incorporation of the antibiotic. The zeta potential showed a decrease in surface charge from ζ = -24.6 mV to ζ = -16.5 mV. In addition, a controlled and prolonged release of antibiotics was observed over a period of 37 days, with a released concentration of up to 755 ppm. Toxicity tests in mice demonstrated good tolerance of the biomaterials, with no significant adverse effects. Moreover, these biomaterials have shown potent antibacterial activity against various bacterial strains, including Listeria monocytogenes, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa, suggesting their potential use in tissue engineering, drug delivery, and orthopedic and dental implants. By integrating the antibiotic into the biomaterial composites, we achieved controlled release and prolonged antibacterial efficacy. This research contributes to advancing biomaterials by exploring innovative synthetic routes and showcasing their promise in regenerative medicine and controlled drug delivery.

Multiscale investigation on the formation path of the apatite phase in bioactive glasses

Mesoporous bioactive glasses (MBGs) have been reported as promising biomaterials to stimulate and promote the growth of bones. When exposed to Simulated Body Fluid (SBF), MBGs develop an apatite phase called carbonate hydroxyapatite (H(C)A) on their surfaces that closely mimics the mineral phase of bones. In order to gain deeper insights into the key stages of the surface reactions of two different types of MBGs (58S and 70S30C) soaked in SBF, we have used high energy total X-ray scattering coupled to Pair Distribution Function (PDF) analysis, along with Raman spectroscopy and scanning electron microscopy. This type of coupled analytical approach can ultimately help to unravel the details of the reaction kinetics in the complex calcium phosphate environment around the BGs surfaces. The data obtained in our in-vitro study point to the formation of other intermediate phases like amorphous calcium phosphate (ACP) and calcite (CC), that transform after a specific time into H(C)A depending on the composition of the MBGs, their surface properties and their interaction times with SBF.

Systematic investigation and controlled synthesis of Ag/Ti co-doped hydroxyapatite for bone tissue engineering

Hydroxyapatite (HA) is a cornerstone bio ceramic in bone tissue engineering applications, prized for its inherent biocompatibility and structural resemblance to natural bone tissue. However, both porous and dense, conventional HA formulations face notable stability and mechanical robustness constraints, impeding their broader utility. We introduce an innovative biomaterial synthesized via a straightforward and efficient sol-gel method to surmount these challenges and imbue novel scaffolds with multifunctional capabilities. Leveraging a double doping strategy, our approach seeks to enhance mechanical performance and incorporate antibacterial features, maintaining the biocompatibility of HA-based scaffolds for advanced tissue engineering applications. In pursuit of this objective, we synthesized Ag-doped, Ag, Ti-doped, and Ti-doped HA samples to explore the impact of varying dopant types and concentrations on various structural, thermal, crystallographic, chemical, morphological, mechanical, and biocompatibility characteristics. X-ray Diffraction (XRD) analysis confirmed the presence of apatitic phase compositions across all samples, while Fourier-transform Infrared Spectroscopy (FTIR) data corroborated phosphate formation and functional group identification. Scanning Electron Microscopy (SEM) studies revealed a correlation between particle size and dopant concentration, consistent with XRD findings. Nanoindentation results indicated optimal mechanical performance was achieved with balanced incorporation of Ag and Ti ions despite increased Vickers microhardness with higher Ti concentrations. All doped samples exhibited effective antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), except for the Ti-doped HA sample. Moreover, the HA sample co-doped with equal amounts of Ag and Ti demonstrated noncytotoxicity for human lung cancer (A549) cells. In contrast, all doped samples exhibited cytotoxicity towards human prostate cancer cell (PC3) cells. Statistical analysis confirmed a synergistic enhancement of biocompatibility and mechanical performance in HA samples doped with Ag and Ti ions in equal proportions. In conclusion, our study presents a simple and effective approach for enhancing HA's mechanical and antibacterial properties through co-doping with Ag and Ti. This innovative biomaterial holds significant promise for advancing bone tissue engineering applications.

Environmental assessment of phosphogypsum: A comprehensive geochemical modeling and leaching behavior study

Understanding the variations in the geochemical composition of phosphogypsum (PG) destined for storage or valorization is crucial for assessing the safety and operational efficacy of waste management. The present study aimed to investigate the environmental behavior of PG using different leaching tests and to evaluate its geochemical behavior using geochemical modeling. Regarding the chemical characterization, the PG samples were predominantly composed of Ca (23.03–23.35 wt%), S (17.65–17.71 wt%), and Si (0.75–0.82 wt%). Mineralogically, the PG samples were primarily composed of gypsum (94.2–95.9 wt%) and quartz (1.67–1.76 wt%). Moreover, the automated mineralogy revealed the presence of apatite, fluorine and malladrite phases. The overall findings of the leaching tests showed that PG could be considered as non-hazardous material according to US Environmental Protection Agency limitations. However, a high leachability of elements at a L/S of 2 under acidic conditions ([Ca] = 166.52–199.87 mg/L, [S] = 207.9–233.59 mg/L, [F] = 248.62–286.65 mg/L) is observed. The weathering cell test revealed a considerable cumulative concentration over 90 days indicating potential adverse effects on the nearby environment (S: 8000 mg/kg, F: 3000 mg/kg, P: 700 mg/kg). Based on these results, it could be estimated that the surface storage of PG could have a serious impact on the environment. In this context, a simulation model was developed based on weathering cell results showed encouraging results for treating PG leachate using CaO before its disposal. Additionally, PHREEQC was used to analyze the speciation of major elements and calculate mineral phase saturation indices in PG leaching solutions. The findings revealed pH-dependent speciation for Ca, S, P, and F. The study identified gypsum, anhydrite, and bassanite as the key phases governing the dissolution of these elements.

Fabrication and Properties of the Montmorillonite/Nanobioglass Hybrid Reinforcement from Agroindustrial Waste for Bone Regeneration.

Nowadays, bone systems have a series of consequences that compromise the quality of life mainly due to wear and decreased bioactivity, generally in elderly people and children. In this context, the combination of montmorillonite (MMT-NPs) in a vitreous system such as nanobioglass facilitates the adsorption of biomolecules on the surface and within the interlamellar spaces, enabling the entry of ions by a cation exchange process focusing on increasing the rate of bone formation. This work aims to synthesize and characterize an eco-friendly hybrid reinforcement containing MMT-NPs with nanobioglass doped with magnesium nanoparticles (MgNPs-BV). In this way, MMT-NPs@MgNPs-BV was synthesized by the impregnation method, where an experimental design was used to verify the synthesis conditions. The ideal condition by experimental design was carried out in terms of the characterization and biological activity, where we demonstrated MMT-NPs of 30% w w-1, MgNPs-BV of 6% w w-1, and a calcination temperature of 1273.15 K with a cell viability around 66.87%, an average crystallite diameter of 12.5 nm, and a contact angle of 17.7°. The characterizations confirmed the impregnation method with an average particle size of 51.4 ± 13.1 nm. The mechanical tests showed a hardness of 2.6 GPa with an apparent porosity of 22.2%, similar to human bone. MMT-NPs@MgNPs-BV showed a cell proliferation of around 96% in osteoblastic cells (OFCOL II), with the formation of the apatite phase containing a relation of Ca/P of around 1.63, a biodegradability of 82%, and rapid release of ions with a Ca/P ratio of 1.42. Therefore, the eco-friendly hybrid reinforcement with MMT-NPs and MgNPs-BV shows potential for application with a matrix for biocompatible nanocomposites for bone regeneration.

Nano round polycrystalline adsorbent of chicken bones origin for Congo red dye adsorption

Nano round polycrystalline adsorbent (NRPA) of chicken bones origin was utilize as effective adsorbent in Congo red dye removal via aqueous media. The NRPA adsorbent was prepared via thermal decomposition and its structure was investigated with the aids of Transmission Electron Microscopy, Fourier Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy, Energy Dispersive X-ray Analysis (EDX), and X-ray Diffractometer (XRD). A monophasic apatite phase was confirmed from XRD investigation, while functional groups analysis showed that NRPA possessed CO32−, PO43− and OH− absorption bands. The maximum adsorption capacities derived from Langmuir isotherm is 98.216 mg g−1. From the combined values of n from Freundlich and separation factor (RL) of Langmuir models, the adsorption of CR by NRPA is favourable. Thermodynamic values of 5.280 kJ mol−1 and 16.403 kJ mol−1 K−1 were found for ΔH° and ΔS° respectively. The entire values of ΔG° which ranges from − 35.248 to − 459.68 kJ mol−1 were all negative at different temperatures. Thus, nano polycrystalline adsorbent of chicken bone origin can serve as excellent adsorbent in Congo red dye removal from waste water.

Phosphate uptake is an essential process for rapid bone mineralization during early diagenesis – evidence from bone alteration experiments

Bones and teeth are often the only fossil remains of vertebrates that are preserved over geological time in sedimentary rocks. They render valuable archives for geochemical proxies which are commonly used for paleo-reconstructions. However, the fossilization mechanisms of bone are not yet well understood. Crucial processes are the transformation of bioapatite into and the replacement of collagen by thermodynamically more stable apatite phases, such as fluorapatite. In the present study, aqueous alteration experiments on cortical bone samples were performed under simulated early diagenetic conditions in order to investigate whether and how an external phosphate (PO4) source affects post mortem bone mineralization. Additionally, abiotic oxygen isotope exchange mechanisms between bioapatite and aqueous solutions were assessed by using either 18O-enriched water or PO4 as a tracer. The presence of an external sedimentary 18O-labeled PO4 source led to a rapid formation of new fluorapatite crystallites at the sample’s margin that was highly enriched in 18O. Meanwhile, in the interior of the samples carbonate-poor hydroxylapatite formed through a dissolution-precipitation process without incorporating significant amounts of the 18O tracer. These two processes appear to act independently from each other. In samples exposed to 18O-labeled aqueous solutions lacking a PO4 source, no newly grown apatite crystallites were found, however in the interior of these samples, nano-crystalline carbonate-poor or -free hydroxylapatite precipitated. A comparatively low but uniform 18O-enrichment was measured from the sample’s margin towards its interior, which is assumed to have resulted from the adsorption of H218O onto crystallite surface sites and collagen. Overall, our results suggest that a fast incorporation of 18O-doped PO4 from the sediment source accelerated bone mineralization and consequently changed the oxygen isotope composition of the PO4 group in the bone mineral phase more rapidly and to a greater extent than in a diagenetic setting lacking additional external PO4. Dissolved PO4 from the taphonomic setting thus seems to be an important factor fostering bone fossilization and preservation as well as oxygen isotope alteration.

On the role of vanadium in the structure and properties of calcium-bismuth-sodium oxyapatite

This study explores the possibility of obtaining solid solutions with the composition Ca8BiNa(PO4)6-x(VO4)xO (0 < x ≤ 6) and investigating their physicochemical and medicobiological properties. Using solid-state synthesis method, only the composition Ca8BiNa(PO4)5·5(VO4)0·5O was obtained, while for other values of x, mixtures of apatite and secondary phases or mixtures of various vanadates and phosphates without the target apatite structure were obtained. The study considers the dimensional crystal chemical factors influencing the possibility of forming solid solutions in a wide range of compositions. The crystal structure of Ca8BiNa(PO4)5·5(VO4)0·5O was refined by the Rietveld method (a = 9.45154(37) Å, c = 6.93659(28) Å, V = 536.638(47) Å3, R-Bragg = 3.718 %) and confirmed by group analysis of the IR spectrum. Standard MTT test showed that this substance is not cytotoxic at dilutions of 1:2 and higher. No bactericidal activity against S. aureus and E. coli cultures was observed.

Coupled carbon‑iron‑phosphorus cycling in the Rainbow hydrothermal vent field

Hydrothermal venting has been shown to play a role in the global biogeochemical cycles of three bio-essential elements: iron (Fe), carbon (C) and phosphorus (P). However, our insight into the coupled cycling of Fe and associated C and P in hydrothermal plumes as well as their long-term fate in the underlying sediments remains limited. We present a detailed study, tracing the biogeochemical pathways of hydrothermally sourced Fe and the associated C and P from a buoyant to a neutrally buoyant plume and to the underlying sediments. Combining chemical and micro(spectro)scopic methods, we characterize particulate and dissolved phases recovered from the water column and sediment at two sites: one located directly in the active Rainbow hydrothermal vent field at 36°N on the mid-Atlantic ridge (MAR) and one located 3 km NE of the active vents. Our results show that the precipitates in one of the largest hydrothermal plumes on the MAR consist of aggregates of Fe nanoparticles, comprising poorly-ordered Fe oxyhydroxides and polycrystalline Fe sulfides, coated with carbon that is likely of organic origin. The sediments underlying the hydrothermal plume show enrichments in organic C, Fe, P and vent-derived trace metals such as Cu that decrease with distance from active vents. The enrichment in organic C and persistence of apparently highly-reactive Fe phases after sediment burial may reflect enhanced preservation potential of both phases as a result of the formation of organic-mineral complexes. We further demonstrate that the scavenging of dissolved seawater phosphate (PO43−) by Fe nanoparticles is constrained to early stages of particle formation and sorption reactions in the buoyant hydrothermal plume and that P burial close to the vent field is driven by the deposition of the Fe nanoparticles. In the sediment, P is then efficiently retained through sink-switching from Fe-bound to more stable, authigenic apatite phases. As such, the sediments underlying the Rainbow vent seem to faithfully record coupled emission, scavenging and burial of essential elements and therefore offer potential for reconstruction of past venting activity. The deposition and burial of partly reduced plume material (e.g., Fe sulfides) in an oxic deep-sea sediment results in sediment chemistry and diagenesis that is very specific to the hydrothermal environment, while the redox signature of the plume is gradually lost. Beyond its role as a potential source of bioavailable Fe, we highlight how hydrothermal venting represents an efficient sink for organic C and bioavailable P. The findings contribute to understanding the profound impact of geological episodes of increased hydrothermal activity on ocean biogeochemistry and the coupled ocean-climate system.

Unraveling the CMAS corrosion mechanism of APS high-yttria-stabilized zirconia thermal barrier coatings

In this study, the CMAS corrosion behavior of two high-yttria-stabilized zirconia thermal barrier coatings (38YSZ and 55YSZ) deposited by air plasma spraying is investigated and compared with a typical 8YSZ coating at 1250 °C to unravel the underlying corrosion mechanism. The 8YSZ coating undergoes severe CMAS attack driven by dissolution-reprecipitation and intergranular corrosion. However, the 38YSZ and 55YSZ coatings can react with CMAS melt vigorously to form a dense reaction layer with CMAS-resistant apatite phase at the CMAS/coating interface, thereby resisting the CMAS infiltration. The apatite phase can be formed only when the yttria content in c-ZrO2 precipitated from CMAS attains the critical value (∼20 at%). Moreover, compared to the 38YSZ coating, apart from the high yttria content, the low zirconia content in the 55YSZ coating also allows higher free Y3+ available to form apatite phase via inhibiting the formation of c-ZrO2, thus facilitating the formation of more apatite phase.

Resistance of (Dy0.2Ho0.2Er0.2Tm0.2Lu0.2)2Hf2O7 top-coat material in thermal/environmental barrier coatings to calcium-magnesia-alumina-silicon attack at 1300 °C and 1500 °C

Rare earth elements (Dy, Ho, Er, Tm, and Lu), characterized by low-diffusivity in silicate melts, were designed as defect-fluorite structure high-entropy material (Dy0.2Ho0.2Er0.2Tm0.2Lu0.2)2Hf2O7 to determine its resistance to calcium-magnesia-alumina-silicon (CMAS) attack. The results indicate that corrosion reactions preferentially crystallize anorthite and garnet phases in the front of molten CMAS at 1300 °C, which alleviates rapid infiltration of CMAS. The reaction between the melt and (Dy0.2Ho0.2Er0.2Tm0.2Lu0.2)2Hf2O7 forms mixture layers comprising apatite and fluorite phases at 1500 °C, which are accompanied by the prompt exhaustion of CMAS. The capability of intaking RE determines the formation mechanisms of apatite with two different structures. The study reveals that the high-entropy material effectively resists molten CMAS attack at 1300 °C; however, its effectiveness in preventing rapid corrosion decay diminishes at 1500 °C. Factors affecting reaction control were discussed at each condition to elucidate the interactions between the multi-cation hafnate material and silicate deposits. This study represents a significant stride towards advancing high-entropy hafnate thermal barrier coating material applications in aerospace engineering.

Reaction mechanisms of (RE0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 (RE = La or Yb) under CaO-MgO-Al2O3-SiO2 (CMAS) attack

In this study, two high-entropy ceramics, namely (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 (LaHZ) and (Nd0.2Sm0.2Eu0.2Gd0.2Yb0.2)2Zr2O7 (YbHZ), were prepared and investigated, in comparison to La2Zr2O7 (LZ). This investigation focused on their interactions with calcium-magnesium-alumina-silicate (CMAS), revealing noteworthy findings. High entropy samples particularly YbHZ exhibit significantly reduced infiltration depths compared to LZ. After CMAS corrosion, the reaction zones of LaHZ and LZ show a similar microstructure characterized by the presence of apatite and fluorite embedded in CMAS residue. In contrast, YbHZ forms a dense and nanoscale dual-phase zirconia (fluorite + pyrochlore) layer, with no visible CMAS residue. The different corrosion behavior is associated with the competition between fluorite and apatite phases, which is strongly related to the ionic radius of RE3+. Apart from the apatite, the formation of a dense and continuous fluorite Ca&RE-ZrO2 layer could also provide excellent CMAS resistance. These findings provide a viable strategy for designing CMAS-resistant materials.

Probing the influence of strontium doping and annealing temperature on the structure and biocompatibility of hydroxyapatite nanorods.

Among numerous biologically important metal cations, strontium (Sr2+) has received much attention in bone tissue regeneration because of its osteoinductive properties combined with its ability to inhibit osteoclast activity. In this study, strontium-doped hydroxyapatite (Sr-HAp) nanorods with varying molar ratios of Ca : Sr (10 : 0, 9 : 1, 5 : 5, 3 : 7 and 0 : 10) were synthesized using the chemical precipitation technique. The synthesized Sr-HAp nanostructures were characterized using powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy, energy dispersive X-ray spectroscopy, and Raman and Fourier transform infrared (FTIR) spectroscopies to understand their structural and morphological features, and composition. XRD results revealed the formation of HAp nanostructures, whose unit cell volume increased as a function of the dopant level. The reaction process investigation showed the formation of hydroxyapatite (HAp), strontium apatite (SAp) and various Sr-HAp phases. FESEM micrographs displayed the morphological transformation of Sr-HAp from nanorods to nanosheets upon increasing the dopant level. In the FTIR spectra, the bands of the PO43- group shifted towards a lower wavenumber upon increasing the dopant concentration in Sr-HAp that signifies the structural distortion due to the presence of a large amount of strontium ions. The peaks of PO43- and OH- vibrations in the Raman spectra were further analysed to corroborate the structural distortion of Sr-HAp. Selected area electron diffraction patterns obtained using TEM reveal the reduced crystallinity of Sr-HAp due to Sr-doping, which is in line with the XRD results. Finally, the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay showed that the synthesized Sr-HAp has no toxic effect on the survival and growth of mesenchymal stem cells. In summary, the synthesized novel Sr-HAp nanorods exhibit great promise for bone tissue engineering applications.

Bio-response of copper-magnesium co-substituted mesoporous bioactive glass for bone tissue regeneration.

Mesoporous bioactive glass (MBG) is widely acknowledged in bone tissue engineering due to its mesoporous structure, large surface area, and bioactivity. Recent research indicates that introduction of metallic ions has beneficial impacts on bone metabolism and angiogenesis. Thus, the features of MBG can be modified by incorporating combinations of ions, such as magnesium (Mg) and copper (Cu), which can play a considerable role in bone formation, influencing angiogenesis, osteogenesis, as well as antibacterial properties. In this study, Mg and Cu were co-doped for the first time (in a ratio of 1 : 1) in 80SiO2-5P2O5-(15 - 2x)CaO-xMgO-xCuO glass composition with x = 0, 0.5, 1, and 2 mol%, synthesized using the sol-gel and evaporation-induced self-assembly method. X-ray diffraction analysis confirmed the amorphous nature of the powders, while inductively coupled plasma-optical emission spectrometry verified the existence of dopant ions in the respective amounts. The nitrogen sorption method indicated the formation of uniform cylindrical mesopores which are open at both ends and a high surface area of the powders. TEM images show fringes, indicating an ordered mesoporous structure in all MgCu co-doped systems. In vitro bioactivity was observed in all MBG powders, confirmed by the formation of an apatite phase when placed in simulated body fluid (SBF). Flake-like microstructure characteristics of HAp crystals found on the surface of MBG powders were visualized using FESEM. Cytotoxicity tests at lower concentrations (0.1 and 1 wt/vol%) of co-doped 2MC MBG (co-doping up to 2 mol%) showed cell proliferation and viability of osteoblast-like MG-63 cells and normal human dermal fibroblast (NHDF) cells similar to the basic glass 80S. Antibacterial study of MBG pellets showed an increment in the zone of inhibition with the sequential addition of doping ions. The turbidity measurement of bacterial cultures revealed that the optimal concentration for effectively inhibiting bacterial growth was 1 wt/vol% (i.e., 10 mg mL-1) concentration of MBG extracts. The result suggested that the incorporation of Mg and Cu ions in MBG in lower concentrations of up to 2 mol% can be useful in bone regeneration owing to bioactivity, cell proliferation, and antibacterial characteristics.

Iodine-substituted hydroxyapatite nanoparticles and activation of derived ceramics for range verification in proton therapy.

Osteosarcoma is a radioresistant cancer, and proton therapy is a promising radiation alternative for treating cancer with the advantage of a high dose concentration in the tumor area. In this work, we propose the use of iodine-substituted hydroxyapatite (IHAP) nanomaterials to use iodine (127I) as a proton radiation tracer, providing access to range verification studies in mineralized tissues. For this purpose, the nanomaterials were synthesized at four iodine concentrations via hydrothermal synthesis. The materials were characterized via different microstructural techniques to identify an optimal high iodine concentration and pure apatite phase nanomaterial. Finally, such pure IHAP powders were shaped and irradiated with proton beams of 6 and 10 MeV, and their activation was demonstrated through subsequent decay analysis. The materials could be integrated into phantom structures for the verification of doses and ranges of protons prior to animal testing and clinical proton therapy treatments of tumors located deep under combined soft and calcified tissues.