Combustion synthesis of heterogeneous calcium phosphate bioceramics from calcium oxide and phosphate precursors

The solid-state reaction of combustion synthesis has been demonstrated to be capable of rapidly producing materials for biomedical applications. Reactant powders of CaO and P₂O₅ were pressed into cylinders and reacted by heating a tungsten filament in either an argon, CO₂ or N₂ atmosphere. Reaction systems examined were: (1) 3CaO + P₂O₅ → Ca₃(PO₄)₂ (TCP) and (2) 4CaO + P₂O₅ → Ca4P₂O₇ + O₂ (TTCP). The product pellets were bright white with a thin glassy appearing outer layer observed with a very porous interior (range of 5–1000 μm pore diameter) regardless of reaction atmosphere. No evidence of sintering is apparent such as intact precursor particles or necking between particles. In the TCP system characteristic XRD peaks for crystalline β-, α-TCP, and HA are noted while in the TTCP system tetracalcium phosphate, α-TCP, and HA are present. DSC analysis indicates the ignition temperature 450°C when P₂O₅ decomposes to PO₃ to react with CaO. SHS is a viable method to manufacture heterogeneous calcium phosphates from CaO and P₂O₅ precursors. The formation of HA and TCP, regardless of stoichiometry or atmosphere is due to thermodynamic energies of the products while other phases are preserved due to limited kinetics in the system’s rapid heating and cooling.     

Combustion synthesis of calcium phosphate bioceramic powders

Calcium phosphate (hydroxyapatite and tri-calcium phosphate) bioceramics closely resembling, in chemical composition, those found in vivo in human bones have been synthesized by using novel synthetic body fluid solutions via the self-propagating combustion synthesis (SPCS) method. Powder characterization was performed by XRD, ICP-AES, FTIR and SEM.     

Influence of carbonation on the low-temperature consolidation by Spark Plasma Sintering of carbonated calcium phosphate bioceramics

Calcium phosphates (CaP) such as biomimetic nanocrystalline apatite or amorphous calcium phosphate are hydrated bioactive compounds particularly suitable for bone repair applications due to their similarity with bone mineral. However, their consolidation in ceramic parts deserves special attention as they are thermodynamically metastable and can decompose into less bioactive phases upon heating. Adapted strategies are needed to obtain bulk bioceramics. Spark Plasma Sintering (SPS) has been shown to allow cold sintering of such compounds at temperatures like 150 °C while preserving the hydrated character and nanosized dimensions of the precursor powders. To this date, however, the role of the degree of carbonation of these precursors on the densification of CO₃-bearing CaP compounds via SPS has not been explored despite the natural carbonation of bone. In this work, several carbonated CaP hydrated compounds were prepared and consolidated by SPS and the characteristics of the obtained ceramics was scrutinized with respect to the starting powders. Two carbonation routes were carried out: via volume carbonation during powder synthesis or via subsequent surface ion exchange. All samples tested led to apatitic compounds after SPS, including amorphous CaP. We show that the degree of carbonation negatively affects the densification rate and propose possible hypotheses explaining this behavior. Evolution in the nature of the carbonate sites (apatitic A-, B-types and labile surface carbonates) before and after SPS is also noticed and commented. The consolidation of such compounds is however proven possible, and gives rise to bone-like apatitic compounds with great potential as bioactive resorbable ceramics for bone regeneration.     

Solubility and freezing point depression (FPD) measurements of Na-1-ethanethiolate,Na-1-propanethiolate,Na-2-propanethiolate,Na-1-butanethiolate,and Na-2-methyl-2-propanethiolate salts in pure water

In this work, we have measured the solubility and the freezing point depression of Na-1-ethanethiolate, Na-1-propanethiolate, Na-2-propanethiolate, Na-1-butanethiolate, and Na-2-methyl-2-propanethiolate salts in pure water within the concentration range of 0–49 wt/wt% at 1?atm. The freezing point curves and solubility curves of five mercaptide salts have been measured at various concentrations of mercaptide salts and further used to find eutectic points.     

Flash sintering of Mg-doped tricalcium phosphate (TCP) nanopowders

β-tricalcium phosphate is a bioceramic with unique osteoinductive and osteoconductive properties. Its processing is limited by the undesired β→α phase transition which occurs upon sintering at 1398 K. The reduction of sintering temperature or the stabilization of β phase (by doping) are therefore of particular interest.In this work, flash sintering was used to consolidate β-tricalcium phosphate nanopowders synthesized by wet chemical methods. Pure and Mg-doped powder was studied, pointing out a strong effect of the dopant on the flash behavior and on the phase transitions. The results point out that tricalcium phosphate can be consolidated in few seconds at relatively low furnace temperature. The sintered pellets contain only the desired β phase in the case of Mg-doped powder, whereas some retained α phase is present in the undoped ones. Starting from the electrical behavior of the material a first processing map to attain β-tricalcium phosphate by flash sintering is proposed.     

A novel rapid synthesis,characterization and applications of calcium phosphate nanospheres from Baltic seawater

Due to the considerable high bio-compatibility, calcium phosphate nanoparticles are widely used in biomedical applications. This study proposes a novel strategy for low-cost manufacturing calcium phosphate nanoporous spheres. The controlled reaction only took less than five minutes, when using Baltic seawater with the dissolved calcium concentration of 2.2?mM as the calcium resources. Porous nanospheres were obtained, with spheres ranging from 50 to 130?nm. The obtained nanospheres possess high drug-loading capacity and exhibit sustained release and pH-dependent properties. In addition, this method provides a general efficient strategy to synthesize other low-cost inorganic nanospheres from seawater.     

Use of cycles of compression to characterize the behaviour of apatitic phosphate powders

A method has been developed to analyse the bulk and mechanical properties of powders under pressure using a uniaxial press. This easy-to-use and rapid method requires small amounts of material and allows different compression parameters to be assessed. Classical parameters, e.g. compaction ratio and tensile strength, are determined. The recording of the compression and rupture cycles allows the energies of compression and of rupture to be calculated. The flowability of the powder is determined during the compression experiment. The energy of compression is linked with the elastic energy to help to explain the energy consumption during compression. It is also correlated to the rupture energy to evaluate the ability of the material to convert the energy of compaction into cohesion. This simple method has been applied to apatitic calcium phosphate powders differing in Ca/P molar ratio and/or crystallinity. It allowed to study the relation between chemical nature and compressibility.     

Investigation of calcium phosphate formation from calcium propionate and triethyl phosphate

Synthetic calcium phosphates are used in for example bone cements and implant coatings to increase biocompatibility. The common method to produce tricalcium phosphate (TCP) uses high temperatures, which creates large crystals with low specific surface areas. In order to investigate new methods to produce TCP at lower temperatures, the reaction between calcium propionate and triethyl phosphate conducted at 220 °C was studied. The method had a near 100% conversion rate, the main synthesis products were calcium phosphate and ethyl propionate. The formed calcium phosphate polymorph could be controlled depending on the water content of the precursor mixture. Anhydrous conditions created amorphous calcium phosphate. As the concentration of water increased, β-TCP was formed, followed by calcium deficient hydroxyapatite and monetite. The particle size increased with the water content, from 20 to 40 nm for amorphous calcium phosphate to tenths of micrometers for monetite. The specific surface areas varied between 209 m²/g for the amorphous product to 3.6 m²/g for the monetite product.     

Biologic potential of calcium phosphate biopowders produced via decomposition combustion synthesis

The aim of this research was to evaluate the biologic potential of calcium phosphate (CaP) biopowders produced with a novel reaction synthesis system. Decomposition combustion synthesis (DCS) is a modified combustion synthesis method capable of producing CaP powders for use in bone tissue engineering applications. During DCS, the stoichiometric ratio of reactant salt to fuel was adjusted to alter product chemistry and morphology. In vitro testing methods were utilized to determine the effects of controlling product composition on cytotoxicity, proliferation, biocompatibility and biomineralization. In vitro, human fetal osteoblasts (ATCC, CRL-11372) cultured with CaP powder displayed a flattened morphology, and uniformly encompassed the CaP particulates. Matrix vesicles containing calcium and phosphorous budded from the osteoblast cells. CaP powders produced via DCS are a source of biologically active, synthetic, bone graft substitute materials.     

Decomposition combustion synthesis of calcium phosphate powders for bone tissue engineering

The aim of this research was to study a potential processing mechanism for the synthesis of biologically active calcium phosphate (CaP) powders. Decomposition combustion synthesis (DCS) is a modified combustion synthesis technique that can be used to produce multiphasic calcium phosphate powders for use in bone tissue engineering applications. During DCS, the stoichiometric ratio of reactant salt to fuel was adjusted to alter product chemistry and morphology, and the resultant CaP powders were analytically characterized. Novel CaP powders produced via DCS represent a potential low-cost/high-efficiency source for mass-produced biomaterials that can be customized for specific biologic manufacturing requirements.     

Inorganic cements for biomedical application: calcium phosphate,calcium sulphate and calcium silicate

Inorganic cements have found utility in tissue replacement since the late nineteenth century, one of the first examples being calcium sulphates in the augmentation of bone defects. In the intervening period of time countless formulations of calcium phosphate, sulphate and silicate cement have been researched and as a result, many are now commercially available for a variety of biomedical applications. This review summarises the applications, formulations, advantages and drawbacks of such inorganic cements, suggesting future work that will drive progress in this area into the future of biomaterials research.     

Comparison of DOPA and DPPA liposome templates for the synthesis of calcium phosphate nanoshells

The aim of this paper is to synthesise calcium phosphate (CaP) nanoshells by controlling their particle size and shape using negatively charged liposomes (1,2 dioleoyl-sn-glycero-3 phosphate sodium salt (DOPA) and 1,2-dipalmitoyl-sn-glycero-3-phosphate sodium salt (DPPA)) as a template. The morphology, particle size, size distribution and zeta potential properties of DOPA and DPPA liposome templates were determined. The results showed that both DOPA and DPPA formed spherical nanoshell structures to be used as templates for the synthesis of CaP nanoshells. By using the DOPA template, spherical CaPs structures with a mean particle size of 197.5 ± 5.8 nm were successfully formed. In contrast, needle or irregularly shaped CaP particles were observed when using the DPPA template.     

Effect of phosphate,calcium, and pH on the dissolution of a phosphate rock in soil

The effect of phosphate (P), calcium (Ca), and pH on the dissolution of Sechura phosphate rock (SPR) in a Typic Dystrochrept was investigated in an incubation study over 90 days. Increasing the P status of the soil had little effect on either the rate or extent of dissolution of SPR, as measured by a single extraction with 0.5M NaOH, or on the amount of plant-available P in the soil as measured by the Bray procedure. This suggests that a reactive PR such as SPR could be effective as a maintenance P fertilizer on soils of medium and high P status.The dissolution of SPR at pH 6.4 was only 4% of total P added, compared to 33.6% of total P added at pH 5.2. Addition of Ca as CaCl₂, at the same rate of Ca as that added in Ca(OH)₂ to raise soil pH from 5.2 to 6.4, reduced the dissolution of SPR to 11% of total P added. The large effect of Ca on the dissolution of SPR contrasts with the small effect of soil P status and probably reflects the fact that the concentration of Ca in the soil solution is generally several orders of magnitude higher than that of P. The results obtained suggest that pH, per se, is of less importance in the dissolution and subsequent plant availability of P from phosphate rock in soil than previously thought.     

Development of calcium phosphate cement

Calcium phosphate cements were prepared by mixing α-type calcium phosphate, aqueous solutions of polyvinyl alcohol and citric acid, and silicate sand. Higher concentration of polyvinyl alcohol and citric acid gave a cured body having higher mechanical strength and 50% aqueous solutions of polyvinyl alcohol and citric acid were the highest concentration to be available in this hardening process. Polyvinyl alcohol gave better mechanical strength to a hard body than citric acid. Smaller particle size of silicate sand gave stronger mechanical strength to a cured body. The highest mechanical strength of a cured body was obtained when the mixing weight ratio of α-type calcium phosphate to silicate sand was1–0.5. The calcium phosphate cement showed very good adhesion strength for cement plates with an analogous component.     

FT-IR characterization of Al-rich Li-, Na- and Ca-HMS

Starting from a micelle-templated material with Si/Al = 2.5 in the H form, three samples have been obtained by means of partial cationic exchange, with LiCl, NaCl and CaCl₂ alcoholic solutions. Their surface properties have been characterized by means of FT-IR spectroscopy of adsorbed probe molecules, namely CO, CO₂ and methylacetylene. Spectroscopic results showed that, though having a chemical composition close to that of cations exchanged Y zeolites, such materials exhibit different basic properties: in particular, no carbonate formation has been detected upon CO₂ adsorption, ruling out the occurrence of basic oxygens at the surface. These features have been ascribed to the amorphous nature of the walls to be contrasted with the crystalline structure of zeolites.     

新型组合式纳米碳酸钙碳化工艺研究

结合中国现有的鼓泡碳化、喷雾碳化以及超重力反应的特点，研制并设计出一套鼓泡和喷雾碳化相结合的新型碳化工艺技术，生产出粒径分布在40～60nm，且结晶规整、分散良好的纳米级碳酸钙产品。     

中国磷酸氢钙标准

中国先后制定了食品添加剂磷酸氢钙国家标准、饲料级磷酸氢钙化工行业标准、牙膏工业用磷酸氢钙化工行业标准、肥料级磷酸氢钙化工行业标准、饲料磷酸氢钙(骨制)轻工行业标准、医药级磷酸氢钙中华人民共和国药典(2000版)。将中国已制定的国家标准和行业标准汇总于一处,见表1～表3。项目GB1889—1992(食品添加剂)GB1889—XXXX(报批稿)HG2636—2000(饲料级)中华人民共和国药典(2000版)HG/T3275—1999　　　(肥料级)　　　优等品一等品合格品QB/T2355—1998　　(饲料)　　一级二级w(CaHPO4·2H2O)/%98.0～103.098.0～103.0≥16.5(…     

Composition of precipitated calcium phosphate ceramics

The composition of the precipitate made by mixing Ca(NO₃)₂ and (NH₄)₂HPO₄ solutions with subsequent drying and firing was studied as a function of reaction conditions. The effects of the initial mixing Ca/P molar ratio, pH of the solution, reaction time and temperature on the phase composition and Ca/P molar ratio of the fired bodies were extensively investigated. Production of hydroxyapatite—β whitlockite ceramics of controlled composition was possible by controlling reaction conditions.