Amorphous Tricalcium Phosphate Research Articles

Comparison of Antibacterial Properties of an Orthodontic Composite Containing Silver and Amor-phous Tricalcium Phosphate Nanoparticles against Streptococcus mutans: An In Vitro Study

Comparison of Antibacterial Properties of an Orthodontic Composite Containing Silver and Amor-phous Tricalcium Phosphate Nanoparticles against Streptococcus mutans: An In Vitro Study

Comparison of the Shear Bond Strength of Orthodontic Composites Containing Silver and Amorphous Tricalcium Phosphate Nanoparticles: an ex vivo Study.

It is important to use orthodontic composites with favorable properties, which are easily removed after the end of the treatment but not easily debonded during treatment. Nanoparticles have drawn attention for their antibacterial properties when added to composite resins. However, the effect of addition of nanoparticle on shear bond strength is not broadly discussed. The present study was designed to compare the shear bond strength of orthodontic brackets bonded by orthodontic composite containing silver nanoparticles with orthodontic composite containing amorphous tricalcium phosphate nanoparticles. In this ex vivo study, 36 sound extracted human premolars were used and randomly divided into three groups. The brackets were bonded in the first group by composite without nanoparticles, in the second group by composite containing 3% amorphous tricalcium phosphate nanoparticles and in the third group by composite containing 0.3% silver nanoparticles at the buccal surface of the teeth. The shear bond strengths of the samples were measured 24 hours after preparation by a universal testing machine. Data were analyzed using SPSS 21 software through one-way ANOVA and Tamhane's T2 multiple comparison tests. pValues under 0.05 were considered significant. There was no significant difference between the mean shear bond strength of composite containing amorphous tricalcium phosphate nanoparticles with composite without nanoparticles (p= 0.142). However, the mean shear bond strength in the composite containing silver nanoparticles was significantly lower than the other two groups (p< 0.001). According to the results of this study, the addition of amorphous tricalcium phosphate nanoparticles to orthodontic composite does not significantly decrease the shear bond strength while silver nanoparticles reduce the shear bond strength of orthodontic composite.

Modification of physicochemical properties and bioactivity of oxide coatings formed on Ti substrates via plasma electrolytic oxidation in crystalline and amorphous calcium phosphate particle suspensions

One way to improve characteristics of oxide coatings prepared by plasma electrolytic oxidation (PEO) method in suspensions lies in variation of solid particle properties. In this study, the effect of particle crystallinity on different physicochemical properties and bioactivity of coatings prepared on Ti and Ti6Al4V substrates was studied, and repeatability of resulting characteristics was assessed depending on selected substrates. PEO was performed in direct current mode at a voltage of 350 V in electrolytes containing 0.1 M KH2PO4 and 100 g.L-1 of stoichiometric crystalline hydroxyapatite or amorphous tricalcium phosphate particles with average size of ∼ 450 nm. Series of measured physical parameters included coating thickness, as well as surface wettability, roughness and topography. Surface and cross-sectional chemical composition was studied by Raman and EDX spectroscopy, while bioactivity was evaluated with simulated body fluid tests. Results showed specific influence of particle crystallinity on surface morphology and repeatable particle incorporation pattern depending on the substrate utilized. It was found that amorphous particles lead to the increased amount of incorporated calcium phosphate phases followed by improved coating bioactivity and possible explanation of this phenomenon was suggested. Variation of particle crystallinity was proposed as a new potential instrument for the adjustment of PEO coating properties.

RETENTION OF CU(II) IONS BY AMORPHOUS AND APATITIC TRICALCIUM PHOSPHATES: AN UNDEMANDING ROUTE TO PRODUCE LIBETHENITE

The retention of copper ions by amorphous and apatitic tricalcium phosphates was studied using X-ray photoelectron spectroscopy, X-ray diffraction, infrared spectroscopy, and induction-coupled plasma atomic emission spectroscopy. The experimental results of this study show that the amorphous tricalcium phosphate exposed for 48 hours to a 2.10-2 M copper ion solution with the initial molar ratio Cu(solution)/Ca(phosphate) = 1 retains 96% of the initial amount of copper. It also completely converts to copper hydroxyphosphate, the mineral known as libethenite. The research revealed that apatitic tricalcium phosphate subjected to a similar treatment removed only 38% of the initial amount of copper and was only partially transformed into libethenite. In this case, it turned out that by extending the exposure time of the phosphate or by increasing the initial molar ratio Cu(solution)/Ca(phosphate), the conversion of the apatitic phosphate becomes complete and leads to a retention capacity of 595 mg/g. X-ray photoelectron spectroscopy analysis of libethenite produced by the conversion of tricalcium phosphates confirms the chemical purity of this mineral. It reveals that the Cu2p core level exhibits a multiple structure that can be deconvoluted into five peaks at binding energies of 934.5 eV, 954.5 eV, 940.6 eV, 943.1, and 961.5 eV. The first two peaks were attributed to the Cu2p3/2 and Cu2p1/2 photoelectrons and are consistent with the divalent state of copper, while the other peaks, not all previously reported, were assigned to shake-up satellites arising from Cu+2 with d9 configuration in the ground state.

α-tricalcium phosphate synthesis from amorphous calcium phosphate: structural characterization and hydraulic reactivity

In the present study, amorphous tricalcium phosphate (TCP) has been synthetized by a wet route to obtain low temperature α-TCP at 650 °C (LT-αTCP) and compare its structural, physical–chemical and thermal properties with those of α-TCP obtained by the conventional solid-state reaction method at 1400 °C (HT-αTCP). Even if no significant differences were observed concerning the values of lattice parameters measured by Rietveld refinement, LT-αTCP presented lower crystallinity and higher crystal strains than HT-αTCP. The reactivity in water of the α-TCP obtained by the two different routes was assessed. Both raw samples appeared relatively inert in solution and did not favour the nucleation of calcium deficient apatite (CDA); the LT-αTCP and HT-αTCP were converted into apatite only after milling. The mechanical process leads to a decrease in crystallinity and the formation of an amorphous phase, which is supported in this work by Raman spectroscopy. The faster rate of conversion of milled LT-αTCP compared to HT-αTCP can be assigned to its higher specific surface area, lower crystallinity and higher residual crystal strain; these favour the dissolution of the α-TCP phase. Finally, the setting properties of α-TCP-based bone cements were compared regarding their synthesis route. Although the synthesis route does not significantly affect the setting times, the kinetic of conversion into CDA was faster for LT-αTCP than for HT-αTCP. Thus, the modulation of the dissolution rate of α-TCP-based cement determined by the preparation route and the grinding process allows control of the overall setting reaction.

Bioceramic powders for bone regeneration modified by high-pressure CO2 process

Non-stoichiometric nanocrystalline apatites present enhanced bioactivity compared to stoichiometric hydroxyapatite. The purpose of this work was to modify the calcium phosphates (CaP) generally used to prepare bioactive ceramics in the aim of obtaining a biomimetic apatite powder. Hydroxyapatite (HA) powder, amorphous tricalcium phosphate (amTCP) powder and a blend of these two were modified by means of an innovative, simple, “green” carbonation process, involving water and high-pressure CO2 (80 bar). This process induced a modification of the CaP, which is sensitive to the environment in which it is located and, in particular, to the pH variations that occur during the treatment phase (decrease in the pH) and during the degassing phase (return to neutral pH). FTIR and Raman spectroscopy, XRD and SEM analyses showed that, depending on the type of initial CaP powder, high-pressure CO2 treatment led to the formation of different types of calcium phosphate phases. This process allowed partial dissolution of the initial powder, mainly of TCP when present, and precipitation of a new CaP phase. HA and HA/amTCP powders were transformed into a mixture of OCP and immature carbonated apatite (PCCA) phases, including OCP maturation/transformation into PCCA. In the case of amTCP powder, a DCPD phase was also present due to the high TCP solubility and an earlier precipitation during the degassing step. This work shows the great potential of such an innovative low-temperature and high-pressure process to transform HA, HA/TCP and TCP powder into bioactive biphasic ceramics composed of OCP and PCCA similar to bone mineral.

Living phosphatic stromatolites in a low-phosphorus environment: Implications for the use of phosphorus as a proxy for phosphate levels in paleo-systems.

In the geological record, fossil phosphatic stromatolites date back to the Great Oxidation Event in the Paleoproterozoic, but living phosphatic stromatolites have not been described previously. Here, we report on cyanobacterial stromatolites in a supratidal freshwater environment at Cape Recife, South African southern coast, precipitating Ca carbonate alternating with episodes of Ca phosphate deposition. In their structure and composition, the living stromatolites from Cape Recife closely resemble their fossilized analogues, showing phosphatic zonation, microbial casts, tunnel structures and phosphatic crusts of biogenic origin. The microbial communities appear to be also similar to those proposed to have formed fossil phosphatic stromatolites. Phosphatic domains in the material from Cape Recife are spatially and texturally associated with carbonate precipitates, but form distinct entities separated by sharp boundaries. Electron Probe Micro-Analysis shows that Ca/P ratios and the overall chemical compositions of phosphatic precipitates are in the range of octacalcium phosphate, amorphous tricalcium phosphate and apatite. The coincidence in time of the emergence of phosphatic stromatolites in the fossil record with a major episode of atmospheric oxidation led to the assumption that at times of increased oxygen release the underlying increased biological production may have been linked to elevated phosphorus availability. The stromatolites at Cape Recife, however, form in an environment where ambient phosphorus concentrations do not exceed 0.28μM, one to two orders of magnitude below the previously predicted minimum threshold of >5μM for biogenic phosphate precipitation in paleo-systems. Accordingly, we contest the previously proposed suitability of phosphatic stromatolites as a proxy for high ambient phosphate concentrations in supratidal to shallow ocean settings in earth history.

Quadrifunctionality Variation of Aluminosilicate Silicon Nucleus on Solid State Geopolymerisation Observed by 29Si Magic Angle Spinning Nuclear Magnetic Resonance Studies

Solid state 29Si MAS NMR is a versatile spectroscopic technique to study anisotropic interactions of Si in geopolymeric cement systems. This article is concerned with the analysis of structural information and mechanism for evolution of tailored geopolymeric precursor powder originated after mechanical co-grinding of fly ash, NaOH and amorphous tricalcium phosphate. The solid state 29Si MAS NMR of geopolymeric precursor material shows distinguishable chemical shifts. Results indicated that developed geopolymeric precursor contain Si/Al tetrahedral network in which SiQ4(3-4Al) dominated among Q0, Q1 and Q2. The evolution of green phosphatic geopolymer cement material takes place after addition of water to developed precursor material. Results also provide an insight about -Si-O-Si- interactions in geopolymer precursor formation, due to reorganization and structural disordering, as a noteworthy greener solid state mechanism. Another eminent finding of this study is the occurrence of significant change in chemical shift values caused by grinding. These shifts are accompanied by incorporation of Al in Si-O-Si linkages and 3D crosslinking into the matrix in geopolymeric precursor material itself, leading to formation of transient Si/Al containing species following solid state mechanism.

27Al NMR MAS Spectral Studies Inferring the Initiation of Geopolymerization Reaction on Together Mechanochemical Grinding of Raw Materials

Chemical shifts and intensities of the 27Al NMR signals provide structural information about the environment of Al nuclei in presence of an external magnetic field. This paper analyzes the structural information of the aluminum nuclei present in the precursor material after mechanochemical co‐grinding of the raw materials, namely fly ash, NaOH, and amorphous tricalcium phosphate [Ca3(PO4)2], with the help of 27Al MAS NMR spectral studies. The results indicate transformation of the sixfold coordination Al ions with oxygen AlQ6 present in aluminosilicate material fly ash to fourfold AlQ4 and fivefold AlQ5 in the precursor material. The variation in chemical shift is between δ 64 and 65 ppm. This indicates that, in addition to direct bonding to the oxygen atom, the Al tetrahedron is also bonded to Si as [AlQ4(4Si)]. Thus, the mechanochemical co‐grinding of the raw materials initiates a solid‐state chemical reaction among them. The addition of water alone to this precursor material results in the formation of the geopolymeric material unlike the conventional geopolymeric system which requires the addition of a highly alkaline aqueous solution to fly ash. This study helps in the determination of the reaction mechanism during the mechanochemical transformation of raw materials into the geopolymeric product by a novel process.

Hydration enthalpy of amorphous tricalcium phosphate resulting from partially amorphization of β-tricalcium phosphate

AbstractAs it was recently shown that β-tricalcium phosphate (β-TCP), similar to α-TCP, can be mechanically activated by prolonged ball milling, partially amorphized β-TCP is promising for the development of new bone cement formulations. Hence in the present study the hydration of partially amorphized β-TCP with different contents of an amorphous phase (amorphous tricalcium phosphate, ATCP) was investigated by isothermal calorimetry and quantitative X-ray diffraction (XRD) to obtain the hydration enthalpies of β-TCP and ATCP. Measurements were conducted at 23 °C, a 0.1 M Na

Novel preparation route of stable amorphous calcium phosphate nanoparticles with high specific surface area

Novel and effective method for preparation of nanosized and stable calcium phosphates (CaPs) is developed. Amorphous or partially crystalline CaP nanoparticles are rapidly reprecipitated from synthesis solution due to fast change of pH. Basic steps of the proposed approach are: to dissolve CaP salt (e.g. hydroxyapatite) with acid and add base thus inducing reprecipitation of new CaP nanoparticles. It is well known that pH of synthesis medium has a significant effect in CaP precipitation, therefore we varied synthesis pH from 8 to 11. Study reveals impact of synthesis pH on chemical structure (FT-IR), phase composition (XRD) for as-synthesized and heat-treated (300–1100 °C) CaPs and specific surface area (BET). Partially crystalline CaPs form at pH 8 and pH 9, while amorphous calcium phosphate precipitates at pH 10 and pH 11. CaPs prepared by the novel technology have high specific surface area (133–154 m2/g). Their amorphous state corresponds to amorphous tricalcium phosphate with carbonate ion substitutions depending on pH of the synthesis. Effectiveness of technology is the use of conventional drying instead of lyophilisation.

The removal of N and P in aerobic and anoxic-aerobic digestion of waste activated sludge from biological nutrient removal systems

Biological nutrient removal (BNR) activated sludge (AS) systems produce a waste activated sludge (WAS) that is rich in nitrogen (N) and phosphorus (P). When this sludge is thickened to 3-6% total suspended solids (TSS) and digested (aerobic or anaerobic), a high proportion of N and P are released to the bulk liquid resulting in high concentrations of ammonia/nitrate and orthophosphate up to several hundred mg/l (without denitrification or P precipitation). This research investigates P removal by P precipitation in anoxic-aerobic digestion of P-rich BNR system WAS. The experimental setup for this work was a lab-scale membrane UCT BNR system fed real settled sewage with added acetate, orthophosphate, and cations Mg and K to increase biological excess P removal. This WAS was fed to batch aerobic digesters at various TSS concentrations, and to two 20-day retention time continuous anoxic-aerobic digesters (AnAerDig) with aeration cycles of 3-h air on and 3-h air off, one fed concentrated WAS (20 g TSS/l ) and the other fed diluted WAS (3 g TSS/l). Nitrogen removal has been discussed in the previous paper. This paper focuses on the P removal by P precipitation observed in the batch tests and continuous systems. The rate of polyphosphate release (bGP) during batch aerobic digestion at low TSS without P precipitation was found to be 2.5 times faster than the endogenous respiration rate (bG) of phosphorus accumulating organics (PAO), i.e. bGP = 0.1/d. This rate was then applied to the high-TSS aerobic batch tests and continuous anoxic-aerobic digesters to estimate the P precipitation at various TSS concentrations, with and without additional Mg or Ca dosing. Newberyite (MgHPO4-3H2O) and amorphous tricalcium phosphate (ACP or TCP, Ca3(PO4)2-xH2O) are found to be the most common phosphate precipitates.

Microwave sintering of fine grained MgP and Mg substitutes with amorphous tricalcium phosphate: Structural, and mechanical characterization

Abstract

Formation of Calcium-Deficient Hydroxyapatite via Hydrolysis of Nano-Sized Pure α-Tricalcium Phosphate

Nano-sized pure α-tricalcium phosphate (α-TCP) fabricated by a novel synthesis approach shows great potential for a faster transformation into calcium-deficient hydroxyapatite (CDHA) than conventionally prepared α-TCP. In this work, amorphous tricalcium phosphate precursors were precipitated and treated with a solvent (water or ethanol), and dried (freeze-dried and oven-dried) before heating at 775 °C. Nanosized α-TCP powders were investigated for their phase composition and crystallinity, particle shape and size, reactivity and cellular biocompatibility. Reaction with water showed faster CDHA formation for freeze-dried powder, at 6 hours, compared to ethanol treated powders, whereas a higher biocompatibility was found for pure α-TCP.

Calorimetry investigations of milled α-tricalcium phosphate (α-TCP) powders to determine the formation enthalpies of α-TCP and X-ray amorphous tricalcium phosphate

One α-tricalcium phosphate (α-TCP) powder was either calcined at 500°C to obtain fully crystalline α-TCP or milled for different durations to obtain α-TCP powders containing various amounts of X-ray amorphous tricalcium phosphate (ATCP). These powders containing between 0 and 71wt.% ATCP and up to 2.0±0.1wt.% β-TCP as minor phase were then hydrated in 0.1M Na2HPO4 aqueous solution and the resulting heat flows were measured by isothermal calorimetry. Additionally, the evolution of the phase composition during hydration was determined by in situ XRD combined with the G-factor method, an external standard method which facilitates the indirect quantification of amorphous phases.Maximum ATCP hydration was reached after about 1h, while that of crystalline α-TCP hydration occurred between 4 and 11h, depending on the ATCP content. An enthalpy of formation of −4065±6kJ/mol (T=23°C) was calculated for ATCP (Ca3(PO4)2), while for crystalline α-TCP (α-Ca3(PO4)2) a value of −4113±6kJ/mol (T=23°C) was determined.

The removal of N and P in aerobic and anoxic-aerobic digestion of waste activated sludge from biological nutrient removal systems

Biological nutrient removal (BNR) activated sludge (AS) systems produce a waste activated sludge (WAS) that is rich in nitrogen (N) and phosphorus (P). When this sludge is thickened to 3–6% total suspended solids (TSS) and digested (aerobic or anaerobic), a high proportion of N and P are released to the bulk liquid resulting in high concentrations of ammonia/nitrate and orthophosphate up to several hundred mg/ℓ (without denitrification or P precipitation). This research investigates P removal by P precipitation in anoxic-aerobic digestion of P-rich BNR system WAS. The experimental setup for this work was a lab-scale membrane UCT BNR system fed real settled sewage with added acetate, orthophosphate, and cations Mg and K to increase biological excess P removal. This WAS was fed to batch aerobic digesters at various TSS concentrations, and to two 20-day retention time continuous anoxic-aerobic digesters (AnAerDig) with aeration cycles of 3-h air on and 3-h air off, one fed concentrated WAS (20 g TSS/ℓ ) and the other fed diluted WAS (3 g TSS/ℓ). Nitrogen removal has been discussed in the previous paper. This paper focuses on the P removal by P precipitation observed in the batch tests and continuous systems. The rate of polyphosphate release (bGP) during batch aerobic digestion at low TSS without P precipitation was found to be 2.5 times faster than the endogenous respiration rate (bG) of phosphorus accumulating organics (PAO), i.e. bGP = 0.1/d. This rate was then applied to the high-TSS aerobic batch tests and continuous anoxic-aerobic digesters to estimate the P precipitation at various TSS concentrations, with and without additional Mg or Ca dosing. Newberyite (MgHPO4·3H2O) and amorphous tricalcium phosphate (ACP or TCP, Ca3(PO4)2·xH2O) are found to be the most common phosphate precipitates.Keywords: biological excess phosphorus removal, waste activated sludge, anoxic-aerobic digestion, phosphaterelease, mineral precipitation

Modeling phosphate transport and removal in a compact bed filled with a mineral-based sorbent for domestic wastewater treatment

Phosphorus filter units containing mineral-based sorbents with a high phosphate (PO4) binding capacity have been shown to be appropriate for removing PO4 in the treatment of domestic wastewater in on-site facilities. However, a better understanding of their PO4 removal mechanisms, and reactions that could lead to the formation of PO4 compounds, is required to evaluate the potential utility of candidate sorbents. Models based on data obtained from laboratory-scale experiments with columns of selected materials can be valuable for acquiring such understanding. Thus, in this study the transport and removal of PO4 in experiments with a laboratory-scale column filled with a commercial silicate-based sorbent were modeled, using the hydro-geochemical transport code PHREEQC. The resulting models, that incorporated the dissolution of calcite, kinetic constrains for the dissolution of calcium oxide (CaO) and wollastonite (CaSiO3), and the precipitation of amorphous tricalcium phosphate, Ca3(PO4)2, successfully simulated the removal of PO4 observed in the experiments.

Crystallization behavior of nanostructured amorphous tricalcium phosphate under thermal treatment

The crystallization behavior of mechanosynthesized amorphous tricalcium phosphate nanoparticles was investigated under thermal treatment. The main product of milling for 10h was nanostructured amorphous tricalcium phosphate. During the heating cycle, the crystallization of amorphous phase occurred and the fraction of crystalline phase reached a maximum after annealing at 1100°C for 1h. According to SEM and TEM images, the 10 h milled sample was composed of spheroidal particles with a mean particle size of about 20nm. After annealing at 1100°C, the microstructure showed a bimodal grain size distribution characterized by the presence of coarse grains with a mean particle size of around 2μm along with finer grains with an average particle size of about 300nm.

Mechanochemical synthesis and structural characterization of nano-sized amorphous tricalcium phosphate

Abstract Nano-sized amorphous tricalcium phosphate powders were synthesized through different mechanochemical reactions. The influence of milling parameters and chemical composition of reagents on the formation of amorphous tricalcium phosphate was investigated. In all the experiments, the mole ratio of calcium to phosphorous oxide was 3:1, i.e. the stoichiometric Ca/P content in the composition of amorphous tricalcium phosphate (Ca/P=1.5). Results revealed that the phase purity, structural features, and morphological characteristics of products were significantly influenced by the chemical composition of raw materials and milling parameters. For all the reactions, amorphous tricalcium phosphate was formed as the main product of mechanical activation after 10 h. After annealing at 1100 °C, crystallization of amorphous phase occurred, and consequently high crystalline β-tricalcium phosphate was generated. According to FT-IR findings, the synthesized powders had high chemical purity. After 10 h of milling, the obtained nanopowders through four distinct reactions exhibited crystallite sizes about 20, 69, 58 and 55 nm. The results from scanning electron micrographs showed that the mean size of agglomerate was in the range of 1–5 μm. Detailed study of morphological features by using transmission electron microscopy confirmed the formation of nano-sized amorphous tricalcium phosphate with spheroidal and ellipse-like morphologies.

Enhancing CaP Biomimetic Growth on TiO2 Cuboids Nanoparticles via Highly Reactive Facets

Pure decahedral anatase TiO(2) particles with high content of reactive {001} facets were obtained from titanium(IV) tetrachloride (TiCl(4)) using a microemulsions droplet system at specific conditions as chemical microreactor. The product was systematically characterized by X-ray diffraction, field-emission scanning and transmission electron microscopy (FE-SEM, TEM), N(2) adsorption-desorption isotherms, FT-IR and UV-vis spectroscopy, and photoluminescence studies. The obtained cuboids around 90 nm in size have a uniform and dense surface morphology with a BET specific surface area of 11.91 m(2) g(-1) and a band gap energy (3.18 eV) slightly inferior to the anatase dominated by the less-reactive {101} surface (3.20 eV). The presence of reactive facets on titania anatase favors the biomimetic growth of amorphous tricalcium phosphate after the first day of immersion in simulated human plasma. The results presented here can facilitate and improve the integration of anchored implants and enhance the biological responses to the soft tissues.