Effect of the HA/β-TCP Ratio on the Biological Performance of Calcium Phosphate Ceramic Coatings Fabricated by a Room-Temperature Powder Spray in Vacuum

Four calcium phosphate ceramic coatings, the less soluble hydroxyapatite (HA) coating, the more soluble β-tricalcium phosphate (β-TCP) coating, and two biphasic calcium phosphate (BCP) coatings with HA/β-TCP ratios of 70/30 and 30/70 were fabricated by spraying each corresponding powder onto a titanium substrate at room temperature (RT) in a vacuum, in order to investigate the effect of the HA/β-TCP ratio on the dissolution behavior and the cellular responses of the coating. No secondary phases, except for HA and β-TCP, were observed for the coatings in the X-ray diffraction results. The coating compositions were almost the same as those of the starting powders because the coating was conducted at RT. Microscopic examination of the coatings revealed crack-free and dense microstructures. The BCP coatings exhibited dissolution rates intermediate between those of the pure HA and β-TCP coatings. The dissolution rate of the coatings was largely dependent on their HA/β-TCP ratio. The cell proliferation and differentiation results indicated that the cellular responses of the coatings were not proportional to their dissolution rates. The 3HA–7TCP (HA/β-TCP ratio of 30/70) coating exhibited an optimal dissolution rate for excellent biological performance.     

Effect of CO32− Incorporation on the Mechanical Properties of Wet Chemically Synthesized β-Tricalcium Phosphate (TCP) Ceramics

Calcium-deficient hydroxyapatite (CDHA) powders were synthesized by a wet chemical precipitation method using Ca(OH)₂ and H₃PO₄ solutions. Single-phase β-tricalcium phosphate (β-TCP) powder with a molar (Ca+Mg)/P ratio of 1.5 was obtained after calcination of CDHA synthesized under vacuum. During synthesis in air, CO₂ can be adsorbed and HBO₄²⁻ is partly substituted by CO₃²⁻, resulting in a lower phosphorous content and consequently an increase of the molar (Ca+Mg)/P ratio to 1.53. A two-phase β-TCP powder containing 20 wt% hydroxyapatite (HA) was obtained after calcination. Samples prepared from β-TCP powders synthesized under vacuum achieved a compressive strength of 301±23 MPa at 99.6% fractional density, while TCP/HA samples prepared in air achieved a maximum compressive strength of 132±29 MPa at 91.7% fractional density. This decrease in strength can be correlated to the porosity retaining due to CO₂ release during sintering and residual tensile stresses in the TCP matrix caused by the thermal expansion mismatch of β-TCP and HA.     

Effect of Co-Precipitation on the Low-Temperature Sintering of Biphasic Calcium Phosphate

Three types of biphasic calcium phosphate (BCP) powders were prepared and their sintering behavior was investigated. The specific surface area and HA/TCP ratio were similar in all three specimens. Most of the densification in the co-precipitated s-BCP occurred before the β- to α-TCP phase transformation, and a maximum density of ∼95% was obtained at 1100°C. The mixture of separately precipitated and calcined hydroxyapatite (HA) and tricalcium phosphate (TCP) (m-BCP) showed a poor sintering behavior, and the apparent density was below 70% at temperatures up to 1200°C. In the commercial HA and TCP mixture (c-BCP), the low temperature sintering was poor, but densification continued without the phase transformation due to the presence of MgO, achieving almost full densification at 1200°C.     

Preparation of Porous Ca10(PO4)6(OH)2 and β-Ca3(PO4)2 Bioceramics

Submicrometer-sized, pure calcium hydroxyapatite (HA, (Ca₁₀(PO₄)₆(OH)₂)) and β-tricalcium phosphate (β-TCP, Ca₃(PO₄)₂) bioceramic powders, that have been synthesized via chemical precipitation techniques, were used in the preparation of aqueous slurries that contained methyl cellulose to manufacture porous (70%–95% porosity) HA or β-TCP ceramics. The pore sizes in HA bioceramics of this study were 200–400 μm, whereas those of β-TCP bioceramics were 100–300 μm. The pore morphology and total porosity of the HA and β-TCP samples were investigated via scanning electron microscopy, water absorption, and computerized tomography.     

多孔双相钙磷钛合金微弧氧化膜层的制备及生物相容性

为克服钛合金生物膜层单一相的缺陷,以Ti6A14V合金为基体,用微弧氧化法制得具有双相钙磷复合陶瓷膜层(BCP)的钛合金器件.通过控制工作液成分制得由不同比例的β-磷酸三钙(β-TCP)和羟基磷灰石(HA)组成的多孔性复合膜层.研究了电源占空比对BCP膜孔隙率和孔径大小的影响.采用能谱仪和X射线衍射仪分析了BCP膜层的...     

Synthesis of β-TCP and CPP containing biphasic calcium phosphates by a robust technique

Biphasic calcium phosphate (BCP) compositions consisting of β-tricalcium phosphate (β-TCP) and calcium pyrophosphate (CPP) are potential biodegradable ceramics for bone regeneration. The present work demonstrates the formation of such dense ceramics by first preparing the precursors of nano-sized, amorphous, and equiaxed calcium pyrophosphate particles, and then sintering the precursors at 900 °C to transform them into desired BCP. However, if the complex of calcium tripolyphosphate was used, only CPP could be generated. It was also observed that the incorporation of Mg²⁺ had several effects on the resulting products including: (1) promoting the generation of meso-porous precipitates; (2) favoring the formation of β-TCP instead of CPP; (3) reducing the grain size and increasing the density of the sintered ceramics, and (4) enhancing the negative electric charge of the BCP surface. Thus, the as-prepared BCP ceramics can serve as potential bone substitute materials in orthopedic applications.     

Effect of Substitutional Monovalent and Divalent Metal Ions on Mechanical Properties of β-Tricalcium Phosphate

β-tricalcium phosphate (β-TCP) powder doped with monovalent or divalent metal ions was hot pressed at 1100°C, and the effect of substitutional monovalent and divalent metal ions on mechanical properties of β-TCP was investigated. The sinterability of β-TCP would be enhanced by the substitution of monovalent and divalent metal ions for β-TCP. Sintered β-TCP doped with 7.6 mol% of Mg²⁺ ion showed a bending strength of 160 MPa. It was found that the substituition of Mg²⁺ ion up to 9.6 mol% and a small amount of monovalent metal ions for β-TCP is effective to improve the mechanical strength of β-TCP.     

MgO–Na2O–P2O5-Based Sintering Additives for Tricalcium Phosphate Bioceramics

Effects of MgO–Na₂O–P₂O₅-based sintering additives on densification, microstructure, hardness, compression strength, and biodegradability of β-tricalcium phosphate (β-TCP) ceramics were studied. Three additive compositions were prepared and introduced into β-TCP. Uniaxially compacted ceramic structures, sintered at 1250°C in air, were characterized. Scanning electron microscopy was used to study the microstructure. The X-ray diffraction technique was used for phase analysis. Results showed that these additives modified the microstructure and improved the sintered density and mechanical properties. An increase of 9% in density, 40% in hardness and 38% in compression strength were achieved. Biodegradation analysis revealed that these additives could tailor the rate of resorption and hardness degradation of 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.     

Porous Photocatalytic TiO2 Thin Films by Aerosol Deposition

Porous photocatalytic TiO₂ thin films were fabricated by the leaching technique, followed by aerosol deposition. Mixed powders of TiO₂ and β-tricalcium phosphate (TCP) were aerosol deposited at room temperature for the initial fabrication of composite films. After the β-TCP phases were leached out from the composite films in a diluted HCl aqueous solution for 24 h, porous TiO₂ films remained on the substrate. To fabricate these porous films, the β-TCP content was varied from 10 to 45 wt% and submicrometer-sized pores were formed after leaching. The porous TiO₂ films showed strong initial photocatalytic activities due to the adsorption effect of the pores and the enlarged surface area.     

Preparation and characterisation of HA/TCP biphasic porous ceramic scaffolds with pore-oriented structure

Porous hydroxyapatite/tricalcium phosphate (HA/TCP) ceramic scaffolds with a uniform unidirectional pore structure were successfully fabricated by an ice-templating method by using Ca-deficient HA whiskers and phosphate bioglass. HA whiskers showed good dispersibility in the slurry and favoured the formation of interconnected pores in the scaffolds. Addition of bioglass powders enhanced the material sintering process and the phase transformation of Ca-deficient HA to β-TCP. Calcium-phosphate-based scaffolds with a composition from HA to an HA/β-TCP complex could be obtained by controlling the freezing moulding system and slurry composition. The fabricated scaffolds had a porosity of 75–85%, compressive strength of 0.5–1.0 MPa, and a pore size range of 130–200 µm.     

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。     

The preparation and characterization of HA/β-TCP biphasic ceramics from fish bones

The aim of this research is to observe the physicochemical characterization and evaluate the biocompatibility of the HA/β-TCP biphasic calcium phosphate ceramics (BCP) produced from fish bones. In addition, the mechanism of the formation of BCP after calcination of fish bones was discussed. Three kinds of fish bones (Salmo salar, Anoplopoma fimbria and Sardine) were prepared and calcined for one hour at different temperatures ranging from 600 °C to 1100 °C in a muffle furnace. The calcined bones were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (GTA), inductively coupled plasma optical atom emissions spectroscopy (ICP-OES), X-ray fluorescence (XRF) and scanning electron microscopy (SEM). The in vitro cytotoxicity assessment was used to evaluate the biocompatibility of the biphasic ceramics. BCP materials were produced from all kinds of fish bones by calcination above 700 °C, the carbonated hydroxyapatite and multiple trace element were also found in the calcined bones. With the increase of temperature, the ratio of HA/β-TCP varied and the major organic components were progressively removed. The carbonated hydroxyapatite disappeared when temperature rises above 900 °C. Rising temperature also caused crystal growth that eventually gave rise to the increase of the BCP grain size and influenced the mesoporous structure. The BCP materials were confirmed to have no obvious cytotoxicity to mesenchymal stem cells (MSC) in the in vitro cytotoxicity assessment. Calcium-deficient hydroxyapatite(CDHA) may make up the major inorganic constituent of fish bones that could decompose to HA and β-TCP when calcined above 700 °C. 800–900 °C is considered to be the optimal temperature to fabricate BCP materials which contain more β-TCP, carbonated hydroxyapatite and retain distinct mesoporous structure while has good biocompatibility. With the unique composition and structure, these three kinds of fish-bone-derived BCP materials can be further applied to fabricate bioceramic scaffolds for biomedical applications.     

Research of phase transformation induced biodegradable properties on hydroxyapatite and tricalcium phosphate based bioceramic

Biodegradable calcium phosphate composites consisting of tricalcium phosphate (α-TCP) and hydroxyapatite (HA) were prepared using a two-step sintering method. The ratio of α-TCP/HA was controlled by modulating the sintering temperature. The initial calcination process at 800 °C causes HA dehydroxylation and induces the early transformation of HA into α-TCP in subsequent sintering processes. At the optimum sintering temperature of 1300 °C, the material is comprised of a moderate ratio of α-TCP to HA (3:7) and possesses a hardness of 5.0 GPa. The high temperature phase transformation from HA to α-TCP accompanied by bonded water loss, which results in the formation of nano-pores within the α-TCP matrix, hardly deteriorated the mechanical strength of the composite. This pore-containing structure also provided a convincing evidence for the origin of the high degradability of α-TCP in a biological environment.     

Preparation and characterization of single phase,biphasic and triphasic calcium phosphate whisker-like fibers by homogenous precipitation using urea

Whisker-like calcium phosphate fibers were prepared by a homogenous precipitation method under refluxing conditions in solutions with a Ca/P molar ratio of 1.67 at 90 °C and pH 3.0 using urea as additive. The precipitates were characterized by XRD, FTIR, SEM, and FE-SEM. The ICP spectroscopy and elemental analyzer were used to determine Ca/P ratio and carbonate content of products, respectively. The results indicate that the morphology and structural characteristics of the precipitates depend on the urea concentration and reaction time. Whisker-like biphasic monetite/hydroxyapatite (HA) fibers with a mean length of 60 µm and a mean width of 1.0 µm were obtained with the use of a low concentration of urea. Calcination of the biphasic calcium phosphate at 800 °C led to the formation of a triphasic mixture of HA/whitlockite (β-TCP)/calcium pyrophosphate (CPP) with a whisker-like morphology. The use of a higher concentration of urea was caused to form a mixed morphology of spherulites/whisker-like fibers consisting of octacalcium phosphate (OCP) and HA phases. When the reaction time was increased to 10 days, both the above biphasic calcium phosphates transformed to a single phase HA which its morphology and growth pattern were similar to those of a whisker, according to FE-SEM images. The HA whiskers produced by a lower amount of urea had a lower carbonate content compared to those obtained using a higher urea concentration.     

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。     

Processing and properties of biphasic calcium phosphates bioceramics obtained by pressureless sintering and hot isostatic pressing

Calcium phosphate powders were obtained from coprecipitation method using diammonium phosphate and calcium nitrate solutions. The adjustment of experimental parameters and Ca/P initial ratio allowed synthesizing stoichiometric HA and β-TCP powders and four biphasic calcium phosphates (BCP) with compositions equal to 20/80, 40/60, 60/40, 80/20, of HA and TCP respective in mass. Two sintering techniques, pressureless sintering and hot isostatic pressing (HIP) were performed to compare the sinterability of the stoichiometric and biphasic compounds. By pressureless sintering, densities higher than 98% were obtained. Results illustrate the negative impact of hydroxyapatite on the densification of BCP but its benefit effect on grain growth inhibition. After HIP treatment, transparent ceramics were obtained. The mechanical behavior of these fully densified compounds was examined in order to determine the role of the chemical composition on mechanical properties.     

In vitro biodegradable and mechanical performance of biphasic calcium phosphate porous scaffolds with unidirectional macro-pore structure

In this study, porous biphasic calcium phosphate (BCP) scaffolds were fabricated by a freeze–gel casting technique using a tertiary-butyl alcohol (TBA) based slurry. After sintering, unidirectional macropore channels of scaffolds aligned regularly along the TBA ice growth direction were tailored simultaneously with micropores formed in the outer wall of the pore channels. The synthesized porous BCP scaffolds (two different sintering temperatures) exhibit compressive strength of 46.8 MPa for 43.0% porosity and 33.1 MPa for 45.9% porosity, respectively. After immersion in Hank's balanced salt solution (HBSS) for 1, 2, 4, 8 weeks, a precipitation started to be formed with individual small granules on the scaffolds surface. In the case of BCP scaffolds sintered at 1200 °C, β-TCP were slowly degraded with increasing the immersing time; on the other hand, α-TCP (from BCP scaffolds sintered at 1300 °C) was extremely degraded within 1 week of immersing. This behavior could be due to a fast hydrolysis (dissolution–reprecipitation) as a phase transformation from α-TCP to brushite or apatite compared to the β-TCP. After immersion in HBSS, overall the compressive strength of the scaffolds reduced by the gradual degradation in biological environment solution. This behavior is consistent with the degradation behavior of scaffolds after immersion in HBSS.     

Regulating the multifactor during wet chemical synthesis to obtain calcium phosphate powders with controllable phase purity for bone repair

Calcium phosphate ceramics are widely used as bone repair materials owing to their excellent biocompatibility, bone conductivity, bone induction, and degradability. Although there are many methods for synthesizing calcium phosphate and controlling its phase composition, it is necessary to explore effective preparation methods by understanding the formation of calcium phosphate and its influencing factors. In this study, calcium phosphate powders with controllable phase compositions were synthesized using a wet chemical precipitation method by adjusting the process parameters (aging time, bipolar solution, initial Ca-P molar ratio, capping agent concentration, and system concentration). Subsequently, a certain biphasic proportion of (biphasic calcium phosphate, BCP) products was prepared, and pure (β-tricalcium phosphate, β-TCP) can be obtained according to the customer's requirements. BCP ceramics with desired phase compositions were obtained by pressing and sintering different calcium-deficient powders. Specifically, β-TCP powder with a purity of 99.83 wt% was obtained when the aging time, bipolar solution, initial Ca-P molar ratio, capping agent concentration, and system concentration were 0 h, 50% ethanol, 1, 0.27 M, and 0.0135 M, respectively. The BCP synthesized in this study shows great application potential in the field of bone tissue repair materials.     

The threonine effect on calcium phosphate preparation from a solution containing Ca/P = 1.33 molar ratio

In this study, calcium phosphate materials were prepared by a modified precipitation method using high-speed dispersing equipment. A solution with a Ca/P molar ratio of 1.33 (octacalcium phosphate stoichiometry) was transferred into the reactor vessel with different concentrations of threonine at temperature 97 °C. A white precipitant was collected after the addition of condensed ammonium solution and the samples were subsequently calcined at 900 °C. From the XRD patterns and FT-IR spectra of the uncalcined samples, three phases of octacalcium phosphate (OCP), monetite (DCP) and hydroxyapatite (HA) were obtained. Calcined samples showed two phases of β-tricalcium phosphate (β-TCP) and calcium pyrophosphate (CPP). SEM micrographs showed the different morphology of samples. The specific surface areas (ssa) were 45–53 m²/g for and 5–6 m²/g for calcined samples. From the obtained results, we found that threonine added in various amounts in the initial solution inhibits the formation of HA and consequently creates OCP and DCP.