High thermally stable Mg-substituted tricalcium phosphate via precipitation

Tricalcium phosphates incorporating small amounts of Mg show attractive biological performances in terms of enhanced bone apposition, bone in-growth and cell-mediated degradation. A systematic investigation on Mg-stabilized β-TCP (β-tricalcium phosphate, β-Ca₃(PO₄)₂) is presented. Microstructure, composition and thermal behaviour were investigated by means of thermogravimetry and differential thermal analysis (TG-DTA), induced coupled plasma-atomic emission spectroscopy (ICP-AES), Fourier transform infrared spectroscopy (FT-IR), N₂ adsorption isotherms, X-ray diffraction (XRD and HT-XRD), and scanning electron microscopy (SEM). Pure and Mg-substituted tricalcium phosphate precursors consisted of calcium-deficient hydroxyapatite, the specific surface area being 128 m²/g and 87 m²/g, respectively. Tricalcium phosphate nanostructured powders were obtained by thermal treatment above 800 °C. The incorporation of Mg within the calcium phosphate lattice promoted the formation of the β-TCP phase at slightly lower temperature and resulted in the stabilization of the β-polymorph at high temperature (i.e. 1600 °C).     

Synthesis of calcium phosphate-based composite nanopowders by mechanochemical process and subsequent thermal treatment

One-step mechanochemical process followed by thermal treatment has been used to produce calcium phosphate-based composite nanopowders. Effects of milling and subsequent heat treatment on the phase transition as well as structural features were investigated. The products were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM) techniques. The results revealed that the dominant phases after mechanical activation were hydroxyapatite, anatase (TiO₂), and periclase (MgO), while after thermal annealing process at 700 °C hydroxyapatite along with geikielite (MgTiO₃) and periclase (MgO) were the major phases. In addition, decomposition of hydroxyapatite to tricalcium phosphate (β-TCP) occurred after heat treatment in the range 900–1100 °C which resulted in the formation of tricalcium phosphate-based composite nanopowders. Evaluation of structural features of the samples calculated by X-ray diffraction profiles analysis indicated that the average crystallite size of hydroxyapatite after 10 h of milling and subsequent heat treatment at 700 °C were about 21 and 34 nm, respectively. TEM and SEM studies exhibited that the considerable morphological changes at temperatures ≥900 °C had to be ascribed not only to grain growth, but also for the transformation of hydroxyapatite to β-TCP.     

Properties of calcium phosphates ceramic composites derived from natural materials

In this study, ceramics containing mixed phases of hydroxyapatite/beta-tricalcium phosphate (HA/β-TCP) were fabricated by a solid-state reaction technique. The HA powder was synthesized from cockle shells while the β-TCP powder was synthesized from egg shells. Pure HA and β-TCP fine powders were successfully obtained. The HA and β-TCP were mixed and subjected to a thermal treatment up to 1100 °C. To form the mixed phase ceramics, the resulting powders were sintered at 1350 °C. Effects of HA concentration on the properties of the studied ceramic were investigated. X-ray diffraction analysis revealed that all samples presented multiphase of calcium phosphate compounds. Average grain size of the ceramics decreased with the HA additive content. The 75 wt% HA ceramic showed the maximum hardness value (5.5 GPa) which is high when compared with many calcium phosphate ceramics. In vitro bioactivity test indicated that apatite forming increased with the HA additive content. To increase antibacterial activity, selected ceramics were coated with AgNO₃. Antibacterial test suggested that an Ag compound coating on the ceramics could improve the antibacterial ability of the studied ceramics. In addition, the antibacterial ability for the Ag coated ceramics depended on the porosity of the ceramics.     

Dissolution properties of different compositions of biphasic calcium phosphate bimodal porous ceramics following immersion in simulated body fluid solution

Biphasic calcium phosphate (BCP) bimodal porous ceramics were prepared from a mixture of fine powders of hydroxyapatite (HAp) and beta-tricalcium phosphate (β-TCP) with varying HAp/β-TCP ratios. Two types of HAp powders and one type of β-TCP powder were used to produce porous BCP bioceramics with HAp/β-TCP weight ratios of 20/80, 40/60, and 80/20. Dissolution tests were performed to compare the dissolution properties of BCP-based bioceramics with different structural properties. Porous ceramic samples of approximately 0.5 g were individually soaked in 30 ml of simulated body fluid (SBF) solution at 36.5 °C for 1, 3, 7 and 10 days, respectively. The calcium content of the SBF solution was analyzed by ICP. The porous bodies were filtered, dried, and characterized using SEM, XRD, and FT-IR. The results indicate that the sample structural properties seem to have a greater effect than the storage environment on the dissolution properties.     

Effects of strontium substitution on the phase transformation and crystal structure of calcium phosphate derived by chemical precipitation

This study focused on the effects of strontium substitution on the phase transformation and crystal structure of calcium phosphate. Chemical precipitation was used to prepare Sr-doped hydroxyapatite (HA) precursor powders. The phase transformation of the as-prepared samples during sintering was analyzed. The powders were characterized by X-ray diffraction, X-ray fluorescence spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Quantitative analysis of the phase content and fine structure was performed by Rietveld refinement. Sr doping was found to facilitate the phase transformation from HA to beta-tricalcium phosphate (β-TCP) at 1000 °C. The β-TCP content increased with increasing Sr content, causing a decline in the ratio of HA to β-TCP. With Sr contents of ≤5 mol%, HA remained the major phase in the biphasic mixtures; in contrast, with Sr contents of ≥15 mol%, the mass fraction of β-TCP exceeded 50%. The incorporation of Sr²⁺ into HA and β-TCP caused the lattice parameters of both phases to increase. Additionally, Sr incorporation slightly enhanced the binding energy of Ca. The study confirmed that Sr doping could be used to modulate the phase fractions of HA and β-TCP. The effective partial substitution of Sr in both HA and β-TCP makes these materials promising for bone repair.     

Effect of silicon and heat-treatment temperature on the morphology and mechanical properties of silicon - substituted hydroxyapatite

The precipitation method was used to synthesize silicon-substituted hydroxyapatite with different Si contents of 0.4, 0.8 and 1.6 wt.% (0.4, 0.8 and 1.6Si-HA) using silicon acetate [Si(OCOCH₃)₄] as a Si source. As-synthesized hydroxyapatite (HA) and Si-HA powders/bulks were heat-treated at different temperatures of 1150, 1200 and 1250 °C for 1 h. Pure 0.4Si-HA and 1.6Si-HA were obtained after heat-treatment at all temperatures, whilst α-TCP phase was formed in the 0.8Si-HA sample after heat-treatment at 1250 °C. SEM observation clearly showed that the substitution of Si in HA inhibited the grain growth of Si-HA even at high heat-treatment temperatures (1200 or 1250 °C). The highest diametral tensile strength (DTS) of 15.93 MPa was obtained in the 1.6Si-HA sample after heat-treatment at 1250 °C.     

Effects of powder stoichiometry on the sintering of β-tricalcium phosphate

The impact of weak stoichiometry variations on β-TCP sintering behaviour was studied. β-Tricalcium phosphate (β-TCP) powders were synthesised by chemical precipitation through aqueous solution of diammonium phosphate and calcium nitrate. Excess or deficiency of nitrate salt leads to compositions with Ca/P ratios below or over 1.5. These powders, calcined at various temperatures (800–950 °C), were shaped by slip casting process and sintered at 1100 °C. The microstructure, phase composition, specific surface area and density of powders and sintered compacts were analysed by SEM, XRD, FTIR, BET, Archimedes methods and dilatometry.This study shows that the presence of calcium pyrophosphate or the hydroxyapatite phases affects considerably the physical characteristics of the β-TCP powders and in particular specific surface area and consequently their sinterability.A precise determination of the β-TCP chemical composition after synthesis allows to adapt the calcination temperature of the raw powder in order to obtain a maximum densification of the compact. The beneficial role of small quantity of HA phase inside β-TCP powder on their sinterability was also shown in this work.     

医用双相磷酸钙陶瓷的制备工艺研究

医用双相磷酸钙（BCP）陶瓷是β-磷酸三钙（β-TCP）和羟基磷灰石（HA）的复合体,其成分与骨矿物组成类似。它具有良好的生物相容性,在生物医学领域具有非常广阔的应用前景。且在生理环境下能发生不同程度的降解,被组织吸收。通过化学沉淀法制备纳米羟基磷灰石,然后通过可溶性钙盐和磷酸盐反应工艺制得β-磷酸三钙,最后将二者进行机械复合而制得双相磷酸钙,将所得样品用X射线衍射仪（XRD）进行了表征。结果显示：所得的双相磷酸钙中掺杂有β-焦磷酸钙,但是它的结晶较好,并且可以改善双相磷酸钙陶瓷的力学性能。     

Sintering behavior and mechanical properties of hydroxyapatite ceramics prepared from Nile Tilapia (Oreochromis niloticus) bone and commercial powder for biomedical applications

In this work, Nile tilapia (Oreochromis niloticus) bone was calcined at 800 °C for 5 h in an air atmosphere to obtain hydroxyapatite powder (FB powder). The elemental composition, phase structure, and morphology of the FB powder were investigated and compared with commercial hydroxyapatite powder (SM powder). The FB-powder exhibited 1.01 at. % of Mg while the SM-powder showed Mg in ppm-level. Carbonate groups were detected in the two powders. Both HAp and β-tricalcium phosphate (β-TCP) structures were found in the FB powder, but the SM powder exhibit only the HAp phase. Irregular-shaped particles were observed in the FB powder. After the two HAp powders were sintered at 1200 °C and 1250 °C for 2 h (FB-1200, FB-1250, SM-1200, and SM-1250), the β-TCP intensity peaks of the FB-ceramic samples significantly increased with increasing sintering temperature. The highest relative density, well-packed grains, and β-TCP stabilization by Mg at the Ca5 site of the FB-1250 structure were the dominant factors governing the highest mechanical properties. Although high density was observed in the SM-1200 sample, Vickers hardness of the SM-1200 sample is lower than the FB-1250 sample. This may be attributed to the partial decomposition of HAp into β-TCP, α-tricalcium phosphate (α-TCP), and Ca₁₀(PO₄)₆O phases. In addition, the increase of grain size was the main factor that governs the increasing compressive strength and Young's modulus instead of density and phase decomposition of the SM-ceramic samples.     

Chemical preparation of carbonated calcium hydroxyapatite powders at 37°C in urea-containing synthetic body fluids

An important inorganic phase of synthetic bone applications, calcium hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂), was prepared as a single-phase ceramic powder. Carbonated HA powders were formed from calcium nitrate tetrahydrate and di-ammonium hydrogen phosphate salts dissolved in aqueous ‘synthetic body fluid’ (SBF) solutions, containing urea (H₂NCONH₂), at 37 °C and pH of 7·4, by using a novel chemical precipitation technique. These powders were also found to contain trace amounts of Na and Mg impurities in them, originated from the use of SBF solutions, instead of pure water, during their synthesis. The characterization and chemical analysis of the synthesized powders were performed by powder X-ray diffraction (XRD), Fourier-transformed infra-red spectroscopy (FT–IR), and inductively-coupled plasma atomic emission spectroscopy (ICP–AES).     

Effects of manganese doping on properties of sol-gel derived biphasic calcium phosphate ceramics

We have investigated the effect of manganese (Mn) doping on properties of nanosized biphasic calcium phosphate powders and their dense bodies. Manganese levels of 0.6, 1.3, 1.9, 4.3, 7.0 and 11.9 at.% were successfully incorporated into biphasic calcium phosphate via a sol-gel route. The prepared powders were calcined at temperatures of 500-1200 °C. The X-ray diffraction analysis revealed that a mix phase comprising of hydroxyapatite and β-tricalcium phosphate were present, however the content of each phases in the structure was affected by the Mn content. The studies found that the largest portion of β-tricalcium phosphate was detected at 4.3 at.% Mn doping. The incorporation of Mn has also greatly increased the crystallinity of the biphasic calcium phosphate powder due to progressive densification of particles. Characterization on their sintered dense bodies showed that manganese concentration affected the physical properties of the dense bodies. The highest density was found for 4.3 at.% Mn doped biphasic calcium phosphate sintered at 1300 °C.     

Hydroxyapatite,tricalcium phosphate and biphasic materials prepared by a liquid mix technique

The Pechini based liquid-mix technique has been applied to prepare either single phases of hydroxyapatite –Ca₁₀(PO₄)₆OH₂– (OHAp), α and β-tricalcium phosphate –Ca₃(PO₄)₂–, (α-TCP, β-TCP) or biphasic calcium phosphates (BCP). Compositions with a Ca/P molar ratio between 1.5 and 1.667 were synthesized and subjected to a thermal treatment up to 1400 °C. α and β-TCP were both prepared from a Ca/P ratio of 1.5, but while β-TCP is isolated at 900 °C and remains stable up to 1100 °C, it is necessary to anneal at 1400 °C for 72 h to obtain pure α-TCP. OHAp is obtained as a single phase from a 1.667 Ca/P ratio after annealing at 1000 °C for 24 h and starts to decompose at 1400 °C. Between these two extremes a whole range of biphasic calcium phosphates can be prepared by using this technique with an accurate control of the starting reactants. These materials have been characterized by FTIR, XRF, BET, XRD and, based on this technique, a phase quantification determination (QXRD). The solubility of these products was tested in a buffered solution at 37 °C and pH=7.4.     

Wet chemistry approach to the preparation of tantalum-doped hydroxyapatite: Dopant content effects

Tantalum-doped hydroxyapatite (Ta-doped HA) nanopowders with different Ta contents were synthesized by a wet-chemical precipitation route. The structure modification and charge compensation mechanism were investigated by various characterization techniques. Due to the smaller size of tantalum ions compared to the Ca²⁺ size, it was assumed that the tantalum ions occupy either the Ca²⁺ and/or the interstitial positions in the HA lattice, where the charge imbalance from to this substitution was compensated by the Ca²⁺ vacancies. From the XRD patterns, the as-synthesized nanopowders were poorly crystalline apatite in the absence and presence of different dopant contents. The hexagonal HA and tricalcium phosphate (β-TCP) phases as biphasic calcium phosphate mixtures were formed after heating at 900 °C. In addition to the β-TCP phase, minor extra phases such as calcium oxide (CaO) and calcium pyrophosphate (Ca₂P₂O₇) were identified from the HA decomposition. The FTIR results indicated that the decrease of structural hydroxyl groups depended on both tantalum oxyanions and carbonate contents. In the XPS profile, the Ta 4 f peak of the doped sample could be decomposed into four main components, which showed different oxidation states for tantalum (TaO₂ oxide). According to the TEM observations, the doped calcined powder at 900 °C was composed of uniform nanoneedles with an average length and width of 120 ± 50 and 10 ± 5 nm, respectively.     

医用双相磷酸钙陶瓷的制备工艺研究

医用双相磷酸钙（BCP）陶瓷是β-磷酸三钙（β-TCP）和羟基磷灰石（HA）的复合体,其成分与骨矿物组成类似,在生理环境下能发生不同程度的降解,被组织吸收。通过化学沉淀法制备纳米羟基磷灰石,然后通过可溶性钙盐和磷酸盐反应工艺制得的β-磷酸三钙,最后将二者进行机械复合而制得双相磷酸钙,将所得样品用X射线衍射仪（XRD）对样品进行了表征。结果显示：所得的双相磷酸钙中掺杂有β-焦磷酸钙,但是它的结晶较好,并且可以改善双相磷酸钙陶瓷的力学性能。     

The effect of carboxylic acids and phosphate salts additives on the properties of chondroitin sulfate calcium phosphate cements

The use of liquid phase additives is a strategy to improve the physicochemical, mechanical, and biological properties of calcium phosphate cements. In this study, TTCP and α-TCP particles were synthesized using the solid-state reaction method. Apatite cements were prepared by mixing TTCP/DCPD/α-TCP powders and liquid phases containing chondroitin sulfate with various additives of carboxylic acids and phosphate salts. The formation of hydroxyapatite and consumption of raw materials as well as the acceleration and deceleration periods through cementation process were investigated by XRD and DSC experiments, respectively. In addition, the morphology, setting time, porosity, compressive strength, degradation, in-vitro bioactivity and cytotoxicity were studied. The results showed that the approximate amount of hydroxyapatite resulting from the cementation process was divergent in the presence of liquid phase additives. The use of phosphate salt additives presented better results compared to carboxylic acid ones regarding hydroxyapatite cement product formation, compressive strength, hardening, setting, and cytotoxicity. All cements showed, generally a similar tendency to form dense hydroxyapatite on their outer surfaces through immersion in the simulated body fluid. The cement containing Na₂HPO₄ salt exhibited the lowest cytotoxicity and highest strength. The ALP assay and the morphological behavior of MG63 cells indicated the good activity and proper cell adhesion of this cement.     

Properties of hydroxyapatite/zirconium oxide nanocomposites

Effects of zirconium oxide (ZrO₂) nanoparticles additive on the microstructure and physical properties of hydroxyapatite (HA) were investigated. The HA powder was derived from natural bovine bone by a sequence of thermal processes. The composites containing nanoparticles of ZrO₂ (0.2–1.0 vol%) were fabricated by a solid-state reaction mixed oxide method. All samples showed traces of HA, beta-tricalcium phosphate (β-TCP) and alpha-tricalcium phosphate (α-TCP) phases while the x≥0.1 samples also showed ZrO₂ phase. Amount of β-TCP and α-TCP phases tend to decrease with ZrO₂. The additive inhibited grain growth as a result of a decrease in grain size. However, the x=0.2 sample exhibited higher hardness value which is consistent with the density data. In addition, bioactivity test suggested that the additive promoted an apatite forming with the values of Ca/P close to the value obtained from HA.     

Temperature-dependent morphology changes of noble metal tricalcium phosphate-nanocomposites

Calcium phosphates, functionalized with nano-sized metal particles, are a promising material class for the treatment of bone defects. However, a sintering process is required in principle to achieve sufficient strength of calcium phosphate scaffolds. In this work laser-generated nano-sized silver, gold and platinum particles were adsorbed on micro-sized β-tricalcium phosphate particles and further heat treated at temperatures between 600 and 1200 °C. Gold and platinum nanoparticles underwent exponential growth starting at about 600 °C, while sintering of β-tricalcium phosphate started at 800 °C. We hypothesise that this phenomenon is caused by a heat-induced evaporation and growth process where the decrease of the particle number is directly correlated with the size increase. The silver nanoparticles on the other hand formed a new phase with the calcium phosphate (AgCa₁₀(PO₄)₇) during the heat treatments and could not be observed within the ceramic scaffold anymore. Addressing the lack of information in nanoparticle-combined calcium phosphate scaffolds, this study contributes to the further modification of bone replacement materials with biologically relevant functions and molecules.     

Influence of precursor characteristics on properties of porous calcium phosphate-titanium dioxide composite bioceramics

Highly porous (macroporosity 76–90%) bioceramics containing interconnected pores (>100 μm) with compressive strength between 0.54 and 0.32 MPa were prepared by polyurethane foam replica method. Effect of following variables, i.e., calcium phosphate/anatase ratio (30/70, 50/50, 70/30 wt%) in the ceramic slurry, anatase particle size (15 nm, 180 nm), Ca/P molar ratio of calcium phosphate (1.67 and 1.50 for hydroxyapatite and apatitic-tricalcium phosphate (ap-TCP), respectively), on the bioceramics properties was investigated. Bioceramics prepared using anatase and hydroxyapatite consisted of three high-temperature crystalline phases - β-tricalcium phosphate (β-TCP), rutile and CaTiO₃. In case of anatase and ap-TCP, two phases (β-TCP and rutile) were obtained. Interaction of anatase and hydroxyapatite during sintering caused formation of CaTiO₃ at β-TCP and rutile grain boundaries thus contributing to a denser grain packing. Combination of ap-TCP and nanosized anatase facilitated decrease of grain sizes. Correlation was found between compressive strength and calcium phosphate precursor in the ceramic slurry.     

Influence of different chemical treatments on the surface of Al2O3/ZrO2 nanocomposites during biomimetic coating

The objective of this study is to evaluate the influence of different chemical surface treatments (H₃PO₄, HNO₃, and NaOH) in the formation of calcium phosphate phases on the surface of Al₂O₃/ZrO₂ (5 vol%) nanocomposite. For this purpose, Al₂O₃/ZrO₂ samples were shaped, calcined at 400 °C, sintered at 1500 °C, subjected to different chemical treatments, and biomimetically coated from 14 to 21 days. Surface characterization was performed by scanning electron microscopy, atomic force microscopy, confocal microscopy, X-ray diffraction, and infrared spectroscopy. It was observed that the preliminary chemical treatment favored the formation of particular calcium phosphate phases of interest, such as α-TCP (alpha-tricalcium phosphate), β-TCP (beta-tricalcium phosphate), and HA (hydroxyapatite). The differences among the percentages of the phases formed affected the homogeneity of calcium phosphate distribution within the nanocomposites as well as the roughness of the formed layer, effectively contributing to adhesion, proliferation, and desired cell biofixation on bone implant.     

Synthesis of hydroxyapatite fibers using electrospinning: A study of phase evolution based on polymer matrix

Hydroxyapatite (HA) is considered as the most promising biomaterial candidate to replace and regenerate hard tissues. A small amount of β-tricalcium phosphate (β-TCP) phase is advantageous for rapid bonding of the artificial bones to natural ones due to its high solubility compared to hydroxyapatite. Synthesizing HA nanofibers from electrospinning of sol-gel is considered as a widely researched topic. Motivation of the current work was to investigate the influence of polymeric binder in the final phase evolution after heat treatment of electrospun nanofibers. Calcium phosphate nanofibers were fabricated by electrospinning sols using gelatine and polyvinylpyrrolidone as carrier polymers and subjected to heat treatment. It was realized that carrier polymers facilitate preferential calcium phosphate phase formation by forming hydroxyapatite as major phase while PVP was used and β-TCP with HA as secondary phase while gelatine was employed. XRD and thermal analyses were performed to ascertain the reason behind this interesting behaviour.