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Ionic substitutions in hydroxyapatite (HA) scaffolds and self-setting cements containing Sr(2+) ions incorporated are particularly of interest in bone regeneration. To date, the approach widely used to incorporate Sr(2+) ions into HA cements has been the addition of Sr(2+) containing salts, such as SrCO3, SrCl2∙6H2O, or SrHPO4. However, this approach is dependent upon the relative solubility of Sr(2+) containing salts with respect to calcium phosphate (CaP) precursors. Therefore, in the current study Sr(2+) substituted dicalcium phosphate dihydrate (DCPD) was first synthesized and directly reacted with tetracalcium phosphate (TTCP) to form Sr(2+) substituted HA forming cements. Rietveld refinement indicated that after one week of aging in phosphate buffered saline, cements prepared with and without Sr(2+) were composed of 75% HA and 25% unreacted TTCP by weight. Cements prepared with 10% Sr(2+) DCPD exhibited increased compressive strengths in comparison to unsubstituted cements. Increased MC3T3-E1 proliferation and differentiation were also observed on the cements prepared with increasing Sr(2+) content. It was concluded that both the scaffold microstructure and Sr(2+) ion release supported osteogenic differentiation. With respect to osteoclastic differentiation, no statistically significant differences in TRAP activity or cell morphology were observed. This suggests that the amount of Sr(2+) released may have been too low to influence osteoclast formation in comparison to unsubstituted cements. The results obtained herein demonstrate that the use of Sr(2+) substituted DCPD precursors rather than individually separate Sr(2+) containing salts may be a useful approach to prepare Sr(2+) containing HA cements.

The development of the calcium phosphate ceramics (CPC) using natural materials such as coral, eggshell, bovine bone, fish bone etc., from Indian origin have been reviewed. The CPCs from natural sources has the benefit that they inherit some of the properties of the raw materials such as the macro-and micro-pore structure, optimal composition, similar morphology etc., as well as the advantage of unlimited world wide availability at a very low raw material cost. Hydroxyapatite (HA), carbonated HA and fluorapatite from natural coral genus "Goniopora” has been obtained. Growth factor loaded coralline HA has been found to significantly accelerate early-stage bone formation in in vivo rabbit model studies. Sea shells have been tested as the source of calcium for electrochemical deposition of HA on titanium implants. Deproteinized hydroxyl carbonate apatite phase was formed by heating adult bovine tibia at 500o C. As eggshell could be easily procured, a great deal of effort has been made to utilize this resource as value-added CPCs including nanocrystalline HA (OHA), calcium deficient HA (CDHA), TCP, tetracalcium phosphate (TTCP) etc., which are the most widely used bone substitutes. Also OHA showed higher antibiotic delivery and more controlled protein release profile compared to the synthetic apatites. Eggshell derived CPCs were also found to have minor amount of Mg, Sr, Si and Na ions inherited from the eggshell. As these ions are crucial for bio-mineralization of eggshell, the influence of multi-ions substituted CPCs as a potential bioceramic for bone regenerative applications has been emphasised.

Apatite cement (AC) is a breakthrough in biomaterials for the reconstruction of the bone defect. However, the replacement of AC to bone up to the present time is still controversial for researchers. Several researchers have reported that AC was replaced by bone while others claimed replacement was limited. The aim of this study is to investigate the transformation mechanism of AC to B-type carbonate apatite (CO3Ap) using different atmosphere. An in vitro study mimicking the body environment was employed in order to examine the effect of setting atmosphere on the composition of set AC. An equimolar of tetracalcium phosphate (TTCP; Ca4(PO4)2O) and dicalcium phosphate anhydrous (DCPA; CaHPO4) mixed with distilled water was enabled to harden at 37°C and 100% of relative humidity under presence of 5% CO2, 100% CO2, and 100% N2 atmospheres. XRD and FT-IR analyses revealed that in the presence of 100% CO2 and 5% CO2, B-type CO3Ap could be determined and only small amounts of TTCP remained unreacted. On the contrary, in the presence of 100% N2, the CO32- bands could not be detected and larger amount of TTCP remained unreacted compared to 5% CO2and 100% CO2 atmospheres. SEM morphology showed that the microstructure of AC was entangled and locked to each other. In addition, the small needle like crystals appeared in the surface of 100% N2, similar to hydroxyapatite. We concluded that the CO32- ions incorporated in AC during setting reaction may be one of the essential factors for CO3Ap formation.

In the present study calcium hydroxyapatites enriched at 0.08 wt% in Mn2+ ions (Mn–HA) and their unsubstituted forms (HA) were synthesized using the same standard wet chemical route. Mn-HA and HA were both calcined at 800°C to give Mn-HAc and HAc, respectively or sintered at 1250°C, to give Mn-HAs and HAs, respectively. The influence of the heat treatment on physicochemical properties of Mn-HA was investigated using powder X-ray diffraction (PXRD), scanning, and transmission electron microscopy (SEM and TEM), and solid-state nuclear magnetic resonance (ssNMR). Mn-HAc and Mn-HAs were compared to each other and to HAc and HAs, respectively. Assignment of the proton ssNMR peaks from high-temperature-treated apatites has been revised. It was found that Mn–HAc and HAc were nanocrystalline, while Mn-HAs and HAs comprised micrometer sized, partially fused particles (SEM and TEM). PXRD and ssNMR demonstrated that the incorporation of Mn2+ into the crystal lattice of hydroxyapatite significantly facilitates its dehydroxylation and decomposition to oxyhydroxyapatite during calcination at 800°C, and induces its transformation to tetracalcium phosphate (TTCP) and alpha-tricalcium phosphate (α-TCP) at 1250°C. Contamination by CaO has also been detected. The 1H→31P NMR cross-polarization experiments have indicated that the Mn2+ ions preferentially occupied the Ca(I) position in the crystallographic unit cell of Mn-HAc. In Mn-HAs, the Mn2+ ions were evenly distributed between the Ca(I) and Ca(II) positions.

Achieving optimal aesthetic appearance is a major objective in dental implant design, and the interaction between the materials and the bone cell progenitors is an important factor in the attainment of this objective. In this study, a novel concept was evaluated by varying the surface modifications on titanium (Ti). Different levels of roughness can be attained by machine grinding (M), sand blasting, and acid etching (SLA) of the samples. The behavior of bone cell progenitors (D1) on the surfaces of Ti disks with different surface modifications was investigated. The surfaces of M or SLA disks were silanized (MS or SLAS group) through treatment with silane/Gly-Arg-Gly-Asp-Ser (GRGDS) peptide (MSP or SLASP group) and anchored particles of tetracalcium phosphate (TTCP) on the specimen surfaces (SLA–TTCP group). Physicochemical analysis was performed by metallographic microscopy, scanning electron microscopy, and contact angle analysis. The proliferation and the quantitative alkaline phosphatase (ALP) production of D1 cells on the surface of different sample groups were determined. The SLASP group had a significantly larger D1 cell proliferation than the other groups after 4 and 7 d of incubation (p

In-vitro and in-vivo studies have been conducted on an in-house-developed tetracalcium phosphate (TTCP)/dicalcium phosphate anhydrous (DCPA)/calcium sulfate hemihydrate (CSH)-derived composite cement. Unlike most commercial calcium-based cement pastes, the investigated cement paste can be directly injected into water and harden without dispersion. The viability value of cells incubated with a conditioned medium of cement extraction is > 90% that of Al2O3 control and > 80% that of blank medium. Histological examination reveals excellent bonding between host bone and cement without interposition of fibrous tissues. At 12 weeks-post implantation, significant remodeling activities are found and a new bone network is developed within the femoral defect. The 26-week samples show that the newly formed bone becomes more mature, while the interface between residual cement and the new bone appears less identifiable. Image analysis indicates that the resorption rate of the present cement is much higher than that of TTCP or TTCP/DCPA-derived cement under similar implantation conditions.

A novel calcium phosphate cement was developed by adding different amount of SrO to tetracalcium phosphate during the fabrication process. The experimental results show that compressive strength of cements based on tetracalcium phosphate doped with SrO significantly increases with the increase of SrO content, approximately 60 MPa, whilst the mechanical behavior of CPC slightly decreases if 0.7wt% SrO is added. X-ray diffraction measurement confirms the setting reaction of doped cements is similar to that of pure calcium phosphate cement (CPC). Low crystalline hydroxyapatite (HA) is found to be the main constituent of set cement. A mechanical reinforcement effect is resulted from the substitution of Sr ion to Ca2+ in tetracalcium phosphate (TTCP), accelerating HA crystal formation and a more cross-linked cement structure. In vitro bioactivity tests showed that CPC added with 0.5wt% SrO had a more rapid degradation compared with pure CPC.

The present study investigates £-radiation effect on structure and selected properties of a tetracalcium phosphate (TTCP)/dicalcium phosphate anhydrous (DCPA)/calcium sulfate hemihydrate (CSH) cement immersed in Hanks’ solution. The results indicate that, at a dosage of 25kGy, the working and setting times of the cement paste derived from £-ray-sterilized TTCP/DCPA/CSH powder did not change significantly. At 50kGy or higher, however, both significantly decreased. A dose of 25kGy caused the 1-d compressive strength of the cement to decrease by 15%. Further increases in £-ray dose did not further change the strength. After immersion for 1 day, the pH values of all non-sterilized and sterilized samples were in the range of 7.6­8.0. The XRD patterns of non-sterilized and sterilized powders were substantially similar. After immersion for 1 day, TTCP phase was still distinguishable, while CSH peaks were largely diminished and apatite phase became dominant. The non-sterilized sample had a significantly higher apatite conversion ratio than those of £-ray-sterilized samples. The average 1-d porosity values of all sterilized and non-sterilized samples were similar (31­33%). The £-ray-sterilized cement samples had coralline type morphology with numerous tiny apatite crystals and micropores. Compared to the sterilized samples, the non-sterilized cement showed a smoother and denser morphology. [doi:10.2320/matertrans.M2013007]

This research was devoted to the investigation of the changes in structure and properties of a tetracalcium phosphate (TTCP)/dicalcium phosphate anhydrous (DCPA)/calcium sulfate hemihydrates (CSH) cement immersed in Hanks’ solution for different periods of time. The cement prepared by mixing TTCP/DCPA/CSH composite cement powder with 0.6 M diammonium hydrogen phosphate ((NH 4 ) 2 HPO 4 ) setting solution at a liquid/powder (L/P) ratio of 0.28 cm 3 g −1 exhibited an average working time and setting time of 6.1 min and 7.1 min, respectively. Experimental results indicated a quick dissolution process of the CSH phase in the solution. After the cement was immersed in Hanks’ solution for 1 day, the TTCP/DCPA-hydroxyapatite (HA) phase transformation had been largely completed and a maximum compressive strength was reached. At this stage, the cement had lost 11% in weight and had a porosity of 26%. After 1 day, the cement gradually decreased its strength, although its weight and porosity level did not change significantly. The long-term pH value of the Hanks’ solution wherein the cement was immersed remained in the range between 6 and 7. The HA phase remained dominant throughout the entire 42 days of immersion. Cytotoxicity test showed that the viability value of the cells incubated with conditioned medium of cement extraction was 88% that of alumina (Al 2 O 3 ) control and 90% that of blank medium.

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.

Investigated in this study are the changes in structure and properties of a tetracalcium phosphate/dicalcium phosphate anhydrous/calcium sulfate hemihydrate (TTCP/DCPA/CSH) cement immersed in Hanks’ solution. Experimental results show that the phase transition involving the hydration of CSH and formation of calcium sulfate dihydrate (CSD) continues up to 7 d of immersion. The phase transition from TTCP/ DCPA to hydroxyapatite (HA) is substantially completed after 14 d; after that, both CSH and CSD phase largely diminished, whereas HA becomes and remains to be the only dominant phase throughout 42 d of immersion. A maximum compressive strength is reached; after that, the cement gradually decreases in strength. After 42 d, its CS value is down to 8 MPa. The long-term pH value of the Hanks’ solution wherein the cement is immersed remains in the range between 5.4 and 7.0. The cytotoxicity test reveals that the viability value of the cells incubated with conditioned medium of cement extraction is 85% that of Al2O3 control and 84% that of blank medium for an extraction ratio of 0.2; and 90% that of Al2O3 control and 93% that of blank medium for an extraction ratio of 0.1. [doi:10.2320/matertrans.M2011152]

In this study the influence of amorphous calcium phosphate (ACP) on the setting of, and the formed apatite crystallite size in, a calcium phosphate cement (CPC) based on alpha-tricalcium phosphate (alpha-TCP) or tetracalcium phosphate (TTCP)/monocalcium phosphate monohydrate (MCPM) was investigated. Setting times at 22 degrees C were measured in air atmosphere; those at 37 degrees C were measured at 100% relative humidity. The phase composition of the set cements was investigated after 1 week using X-ray diffractometry and infrared spectroscopy and the morphology was investigated using scanning electron microscopy. The compressive strength (CS) of the set CPCs was measured after 1 day. Viability of MC3T3-E1 cells on the CPCs was analyzed after 7, 14 and 21 days of incubation using the CellTiter 96 Aqueous Non-Radioactive Cell Proliferation Assay. The alpha-TCP-based cement exhibited long setting times, a high CS and was converted to a calcium-deficient hydroxyapatite (CDHAp). The TTCP/MCPM-based CPC was only partly converted to CDHAp, produced acceptable setting times and had a low CS. Addition of ACP to these two CPCs resulted in cements that exhibited good setting times, CS suitable for non-load-bearing applications and a full conversion to nanocrystalline CDHAp. Moreover, the ACP containing CPCs demonstrated good cell viability, making them suitable candidates for bone substitute materials.

The main goal of the present study was to evaluate the effect of different setting accelerator agents on the developed microstructures of calcium phosphate cements (CPCs) by employing the impedance spectroscopy (IS) technique. Six compositions of CPCs were prepared from mixtures of commercial dicalcium phosphate anhydrous (DCPA) and synthesized tetracalcium phosphate (TTCP) as the solid phases. Two TTCP/DCPA molar ratios (1/1 and 1/2) and three liquid phases (aqueous solutions of Na2HPO4, tartaric acid (TA) and oxalic acid (OA), 5% volume fraction) were employed. Initial (I) and final (F) setting times of the cement pastes were determined with Gillmore needles (ASTM standard C266-99). The hardened samples were characterized by X-ray powder diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and apparent density measurements. The IS technique was employed as a non-destructive tool to obtain information related to porosity, tortuosity and homogeneity of the cement microstructures. The formulation prepared from a TTCP/DCPA equimolar mixture and OA as the liquid phase presented the shortest I and F (12 and 20 min, respectively) in comparison to the other studied systems. XRD analyses revealed the formation of low-crystallinity hydroxyapatite (HA) (as the main phase) as well as the presence of little amounts of unreacted DCPA and TTCP after 24 h hardening in 100% relative humidity. This was related to the proposed mechanisms of dissolution of the reactants. The bands observed by FTIR allowed identifying the presence of calcium tartrate and calcium oxalate in the samples prepared from TA and OA, in addition to the characteristic bands of HA. High degree of entanglement of the formed crystals was observed by SEM in samples containing OA. SEM images were also correlated to the apparent densities of the hardened cements. Changes in porosity, tortuosity and microstructural homogeneity were determined in all samples, from IS results, when the TTCP/DCPA ratio was changed from 1/1 to 1/2. The cement formulated from an equimolar mixture of TTCP/DCPA and OA as the liquid phase presented setting times, degree of conversion to low-crystallinity HA and microstructural features suitable to be used as potential bone cement in clinical applications. The IS technique was shown to be a very sensitive and non-destructive tool to relate the paste composition to the developed microstructures. This approach could be very useful to develop calcium phosphate bone cements for specific clinical demands. Fil: Romeo, Hernan Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Bueno, P. R.. Universidade Estadual Paulista Julio de Mesquita Filho; Brasil Fil: Fanovich, Maria Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina

In the present study, three types of tetracalcium phosphate (TTCP) were prepared by solid-solid reaction or co-precipitation method and by different cooling modes. The effect of TTCP on the performance of calcium phosphate cement (CPC) was investigated. The result showed that the characteristic of TTCP varied with preparation method and played an important role in CPC performance. A solid-solid reacted TTCP yielded smaller particle size and resulted in bad workability and mechanical strength of CPC. The fast cooling of sintering TTCP by liquid nitrogen could avoid the decomposition of TTCP and make pure TTCP. TTCP prepared by wet-precipitation could improve performance of CPC and was promising to optimization of CPC.

Exothermal behavior is always present during the hydration of cements. The biocompatibility and curing effect of a bone cement is in close relationship with its exothermal behavior. The exothermal behavior in the hydration process of the partially crystallized calcium phosphate (PCCP)+dicalcium phosphate anhydrate (DCPA) system cement was studied in this article. The results show that with the decrease of the particle size of DCPA, the heat release rate was greatly increased; whereas, with the decrease of the particle size of PCCP, the heat release rate was not obviously altered. The heat release in the hydration process of the PCCP+DCPA system cement was only 137 J/g, which was quite smaller than that of the tetracalcium phosphate (TTCP)+dicalcium phosphate dihydrate (DPCD) system cement, and the temperature increase was very small for this cement.

In this study, calcium phosphate cements (CPC) were prepared by mixing cement powders of tetracalcium phosphate (TTCP) with a cement liquid of phosphate acid saline solution. Tetracycline (TTC)-CPC, chitosan-CPC and chitosan-TTC-CPC were investigated with different premixed schedule. It was demonstrate that both TTC and chitosan worked on the phase transition and crystal characteristics. TTCP mixed with phosphate acid saline solution had similar features of Fourier transform-infrared spectrometry (FT-IR) no matter it was mixed with chitosan or TTC or both. TTC premixed with cement liquid or powder had significant different features of FT-IR and 876 cm(-1) seemed to be a special peak for TTC when TTC was premixed with cement liquid. This was also supported by XRD analysis, which showed that TTC premixed with cement liquid improved phase transition of TTCP to OCP. Chitosan, as organic additive, regulates the regular crystal formation and inhibits the phase transition of TTCP to OCP, except when it is mingled with cement liquid premixed with TTC in field scanning electron microscope. It was concluded that the premixed schedule influences the crystal formation and phase transition, which may be associated with its biocompatibility and bioactivities in vivo.

Six different tetracalcium phosphate (TTCP) products were synthesized by solid state reaction at high temperature by varying the overall calcium to phosphate ratio of the synthesis mixture. The objective was to evaluate the effect of the calcium to phosphate ratio on a TTCP-dicalcium phosphate dihydrate (DCPD) cement. The resulting six TTCP-DCPD cement mixtures were characterized using X-ray diffraction analysis, scanning electron microscopy, and pH measurements. Setting times and compressive strength (CS) were also measured. Using the TTCP product with a Ca/P ratio of 2.0 resulted in low strength values (25.61 MPa) when distilled water was used as the setting liquid, even though conversion to hydroxyapatite was not prevented, as confirmed by X-ray diffraction. The suspected CaO presence in this TTCP may have affected the cohesiveness of the cement mixture but not the cement setting reaction, however no direct evidence of CaO presence was found. Lower Ca/P ratio products yielded cements with CS values ranging from 46.7 MPa for Ca/P ratio of 1.90 to 38.32 MPa for Ca/P ratio of 1.85. When a dilute sodium phosphate solution was used as the setting liquid, CS values were 15.3% lower than those obtained with water as the setting liquid. Setting times ranged from 18 to 22 min when water was the cement liquid and from 7 to 8 min when sodium phosphate solution was used, and the calcium to phosphate ratio did not have a marked effect on this property.

We have previously prepared spherical-shaped tetracalcium phosphate (s-TTCP) with plasma melting method. We found that apatite cement (AC) containing s-TTCP showed excellent injectability from syringe and handling property when compared with AC that contained irregular-shaped TTCP (i-TTCP). However, transformation of AC containing s-TTCP (s-AC) to apatitic mineral was suppressed and thus mechanical strength of set s-AC was low. In the present study, thermal treatment was attempted on s-TTCP to convert heat decomposition products formed in s-TTCP during plasma melting process to TTCP. X-ray diffraction (XRD) analysis revealed that some heat decomposition products in s-TTCP converted to TTCP when s-TTCP was heated at 1,500°C for four hours and quenched at room temperature (q-TTCP). AC containing q-TTCP transformed to apatitic monolith and showed equivalent mechanical strength similar to AC that contained i-TTCP —without sacrificing excellent injectability from syringe and handling property. Based on these findings, we concluded that AC containing q-TTCP would benefit patients since it delivered excellent injectability without sacrificing basic setting properties of AC.

Effect of added α-tricalcium phosphate (α-TCP) and β-TCP was investigated to understand the setting reaction of apatite cement consisting of tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA). Addition of TCP delayed the initial setting time because TCP was not involved in the initial setting reaction and resulted in the decreased initial mechanical strength. After the initial setting of the cement due to the conversion of TTCP and DCPA into apatite, α-TCP dissolved to supply calcium and phosphate ions and they were consumed for crystal growth of apatite. Therefore, mechanical strength of the apatite cement containing α-TCP was increased. In contrast, added β-TCP showed no reactivity in the cement and thus result in the decreased mechanical strength.

Calcium phosphate was coated from tetracalcium phosphate (TTCP), hydroxyapatite (HA), β-tricalcium phosphate (TCP), β-calcium pyrophosphate (CPP), and β-calcium metaphosphate (CMP) powder targets using radio frequency magnetron sputtering. The composition of the crystal phase of the coated films was changed, depending on the target materials, and the Ca/P molar ratios of the films varied from 0.74 to 2.54, increasing with the Ca/P molar ratio of the target. The solubility of the target, determined using a microwave-induced plasma-mass spectrometer was: TTCP ≈ β-CMP > β-TCP > β-CPP > HA, and the deposition rate from each target showed a similar order to the solubility: TTCP ≈ β-CMP > β-TCP > β-CPP ≈ HA.

Commercial hydroxyapatite (HA) powders were calcined at the temperature range of 1000-1350 °C in air and the calcined powders were immersed in simulated body fluid (SBF) at 37 °C for 3 or 7 days. At 1200°C, HA gradually releases its OH' ions and transforms into oxyhydroxyapatite (Ca 10 (PO 4 ) 6 O x (OH)2-2x, OHAP). HA initiated to decompose to a-tricalcium phosphate (a-TCP) and tetracalcium phosphate (TTCP) phase at 1350°C. The surface dissolution of HA powders was accelerated by non-stoichiometric composition such as a-TCP, TTCP and the powders with smooth surface appeared to be dissolved on the edge showing fiber-like particles, followed by separation of the large particle to small one with the immersion time. The fiber-like particles consisted of new phases such as, carbonated-apatite (CHA) and octacalcium phosphate (OCP).

Stability of hydroxyapatite(HA) structure is influenced by preparation conditions and afterwards heat treatment. In this paper, the powders with different Ca/P molar ratio were calcined to investigate the influence of Ca/P and heat treatment on thermal decomposition and reconstitution of HA. The results show that the Ca/P has little change even calcined at a high temperature of 1500°C. The Ca/P molar ratio close to 1.67 is beneficial to form high purity HA. HA gradually releases its OH- ions in the temperature range of 800-1200°C. The decomposition takes place at about 1200°C and will become more and more severe with the increase of temperature. Cooling with slow rate and post-heat treatment in wet atmosphere are beneficial to both the rehydration and the recovery of HA from the decomposition products (TTCP and α-TCP).

It was a normal phenomena that hydroxyapatite (HA) decomposes into tricalcium phosphate (TCP), tetracalcium phosphate (TTCP), calcium oxide (CaO) and amorphous calcium phosphate (ACP) during the plasma processing step. The present study characterized the phase evolution of calcium phosphates (CaPs) in the nanoparticles synthesized using a radio frequency (RF) induction plasma processing technique. The morphology and microstructure of the CaP nanoparticles were investigated by XRD, SEM, TEM, Raman spectroscopy, FTIR spectroscopy and thermal analysis. It was found that ACP, α-TCP, TTCP and CaO were the main decomposed phases in the nanoparticle. After heat treatment at dicalcium pyrophosphate (β-Ca2P2O7) due to the extreme decomposition of the starting HA during the RF plasma processing step which rapidly solidified into amorphous phase.

A novel route is developed to prepare a new type of Sr-contained hydroxyapatite bone cement. Tetracalcium phosphate, strontium hydrogen phosphate or anhydrous strontium chlorite, dicalcium phosphate, phosphoric and water are used as precursors. XRD, FTIR and EDXS are used to characterize the incorporation of 5% or 10% Sr2+ into the crystal lattice of hydroxyapatite. Results indicate that the Sr-contained CPC system of TTCP/DCPA/DSPA can set in 0.5M diluted phosphate acid with a final product of non-stoichiometric Sr-contained hydroxyapatite.

Tetracalcium phosphate (TTCP) Ca4(PO4)2O is one of the major powder components of self-setting orthopedic and dental cements. Traditionally, TTCP powders are produced by a solid-state process by soaking Ca- and P-containing precursors between 1350° and 1500°C. Such procedures require expensive high-temperature furnaces and subsequent grinding of sintered particulates. Grinding not only introduces contamination but alters the structure of TTCP, thereby reducing its bioactivity. The present paper offers a lower temperature synthesis process for TTCP with several interesting features. First, the synthesis procedure used Ca(CH3COO)2·H2O and NH4H2PO4 as separate sources for Ca and P, respectively. Second, the reactants underwent multiple melting and decomposition stages, thus increasing the reactivity of the synthesis process. NH4H2PO4 melted at 190°C and engulfed the calcium acetate particles. The Ca-acetate component decomposed into CaCO3 at around 400°C while still surrounded by the molten phosphate liquid and an amorphous Ca-metaphosphate phase. Hydroxyapatite, Ca10(PO4)6(OH)2 (HA), and β-Ca3(PO4)2 crystallized upon heating the powder mixture to 700°C. Slightly above 1200°C, the TTCP phase was formed. This sequence of reactions led to a process temperature of 1230°C, the lowest temperature ever reported for the synthesis of TTCP. Third, the resulting powders required much less grinding, which itself is advantageous. Fourth, the resulting powders were in situ seeded with HA. HA-seeded TTCP powders were tested for their apatite-inducing ability by soaking them in synthetic body fluid at 37°C. TTCP powders of this study were readily covered with carbonated apatitic calcium phosphates within the first 72 h.

Prolonged high-energy ball milling of tetracalcium phosphate (TTCP) resulted in a mechanical activation with the formation of nanocrystalline or amorphous domains within the compound. This mechanically activated material demonstrated a completely different thermal behavior compared with highly crystalline TTCP. Differential scanning calorimetry (DSC) measurements indicated the presence of exothermic reactions between 370° and 480°C and between 630° and 930°C for 24 h-milled TTCP, which could be related to conversion to an apatitic phase and calcium oxide (CaO) and crystallization of these products during heating. X-ray diffraction analyses showed that mechanically activated TTCP began converting to an apatitic phase at ∼200°C and fully converted to an apatitic phase and amorphous CaO at 600°C, and a crystalline phase of CaO subsequently appeared around 800°–1200°C. Reconversion to TTCP was observed between 1200° and 1400°C. In contrast, crystalline TTCP remained stable up to 500°C and decomposed to an apatitic phase and CaO around 600°–1000°C.

Due to its superior biocompatibility and osteoconductivity, calcium phosphate cement (CPC) has been suggested for use as a filling material for dental and orthopedic applications [1–4]. The primary reaction product of most CPCs, after being implanted for a while, is various kinds of apatite [5], which is the main inorganic component of human bones and teeth [6, 7]. Tetracalcium phosphate (TTCP), a member of the calcium phosphate family, is known to have a high chemical activity and reacts with aqueous solution at room temperature [8]. The obtained hardened material has a high affinity for the living body and is therefore frequently used as a constituent in CPC powder [9–11]. Despite many advantages, there are problems for CPC during practical application, including working/setting time being too short or too long and dispersion upon early contact with blood or aqueous media. Appropriate working/setting times are critical for surgical applications. In the laboratory, a monolithic TTCP powder with nano-sized whiskers grown on surface was recently developed [12], which demonstrated excellent mechanical properties and biological responses with a relatively short working/setting time. The present work provides a simple heat treatment method for prolonging the working/setting time, while maintaining the strength, of the TTCP cement. The TTCP powder used for the study was fabricated in-house from the reaction of dicalcium pyrophosphate (Ca2P2O7) (Sigma Chem. Co., St. Louis, MO, USA) and calcium carbonate (CaCO3) (Katayama Chem. Co., Tokyo, Japan) by a weight ratio of 1:1.27. The powders were mixed uniformly in ethanol for 12 hr, followed by heating in an oven to let the powders dry. The dried powder mixture was then heated to 1400 ◦C and allowed to react and form TTCP [13]. Since a “whisker treatment” [12] has been very effective in enhancing the properties of TTCP cement, the same treatment was used to treat the TTCP powder for the present study. The whisker-treated TTCP powder was heat-treated in an air furnace (N 7/H, Nabertherm©R, Germany). Different heat-treatment temperatures (140–400 ◦C) and times (30 and 120 min) were used for the study. To form a CPC paste, the TTCP powder was mixed with a diammonium hydrogenphosphate ((NH4)2HPO4) hardening solution with a pH value of 8.6 and liquid/powder ratio of 0.3 ml/g. After mixing for 1 min, the cement

The progression of the setting reaction of a tetracalcium phosphate (TTCP) –dicalcium phosphate dihydrate (DCPD) rapid setting cement was investigated as a function of time. Compressive strength and extent of conversion to hydroxyapatite (HA) were obtained at different incubation times. The results indicated a rapid development of both strength and HA conversion in the early stages of the reaction, which slowed down after 4 h, presumably as a result of HA formation on the surface of the reactants. This hypothesis was supported by scanning electron microscopy examination of cement fracture surfaces.

The purpose of the present study is to investigate the � -ray effect on the structure and some critical properties, such as working/setting time and compressive strength, of a TTCP/DCPA-based CPC. Experimental results indicate that working/setting time, compressive strength, TTCPHA conversion rate and morphology of the present CPC are all related to the dosage of � -ray sterilization. The best � -ray dosage appears to be 30 kGy which leads to slightly longer setting/working time, the highest TTCP-HA conversion rate and the highest compressive strength. With increasing � -ray dosage, the morphology of CPC changed from sharp-edged petal-like morphology (non-sterilized and 10 kGy) to globular-like morphology (20 and 30 kGy) to dull-edged coralline-like morphology (40 and 80 kGy).

The development of a calcium phosphate cement, comprising tetracalcium phosphate (TTCP) and dicalcium phosphate dihydrate (DCPD), that hardens in 14 min with water as the liquid or 6 min with a 0.25 mol/L sodium phosphate solution as the liquid, without using hydroxyapatite (HA) seeds as setting accelerator, is reported. It was postulated that reduction in porosity would increase cement strength. Thus, the effects of applied pressure during the initial stages of the cement setting reaction on cement strength and porosity were studied. The cement powder comprised an equimolar mixture of TTCP and DCPD (median particle sizes 17 and 1.7 μm, respectively). Compressive strengths (CS) of samples prepared with distilled water were 47.6 ± 2.4 MPa, 50.7 ± 4.2 MPa, and 52.9 ± 4.7 MPa at applied pressures of 5 MPa, 15 MPa, and 25 MPa, respectively. When phosphate solution was used, the CS values obtained were 41.5 ± 2.3 MPa, 37.9 ± 1.7 MPa, and 38.1 ± 2.3 MPa at the same pressure levels. Statistical analysis of the results showed that pressure produced an improvement in CS when water was used as liquid but not when the phosphate solution was used. Compared to previously reported TTCP-DCPD cements, the greater CS values and shorter setting times together with a simplified formulation should make the present TTCP-DCPD cement a useful material as a bone substitute for clinical applications. © 2004 Wiley Periodicals, Inc.

The present study investigates the changes in microstructure and microchemistry (particularly Ca/P ratio) during whisker formation on the surface of TTCP powder in hydrochloric solution. XRD results indicate that the as-fabricated (non-treated) powder has a monolithic TTCP crystal structure. When the powder is treated for 10 min in HCl, a DCPD phase appears on TTCP surface, which increases in intensity with treating time. When treated longer than 4 h, the DCPD intensity decreases. When treated for 24 h, the DCPD phase disappears. TEM results indicate that, when TTCP is treated for 10 min, fine globular-shaped DCPD crystals are observed to precipitate on the surface of TTCP particles. When treated for 1 h, hexagonal Ca-deficient apatite whiskers with an average Ca/P ratio of 1.5 form. With treating time the apatite whiskers continue to grow in size and increase in Ca/P ratio. When treated for 24 h, the length and thickness of the apatite whiskers can reach >500 and >50 nm, respectively, with an average Ca/P ratio of 1.8. The microchemical data indicate that the apatite whiskers grown on the surface of TTCP particles are substantially non-stoichiometric in nature. Compressive strength data indicate that apatite whiskers grown on TTCP surface under a favorable condition can largely improve the properties of the resulting CPC.

Calcium phosphate cements (CPC), based on multicomponent powder mixtures of calcium orthophosphates with medium particle sizes in the region of 1 - 20μm, set isothermally in an aqueous environment to form hydroxyapatite (HA). HA cement reactants include tetracalcium phosphate (TTCP), tricalcium phosphate (TCP), dicalcium phosphate anhydrate (DCPA), dicalcium phosphate dihydrate (DCPD), monocalcium phosphate (MCPA) or octacalcium phosphate (OCP). The aim of this study was to improve the mechanical performance of TTCP / DCPA cement by adding several metal oxides to tetracalcium phosphate during the fabrication process. Cements based on tetracalcium phosphate mixed with silica or titanium oxide showed significant increases in compressive strength, approximately 80 - 100 MPa, whilst no change in the mechanical behavior of CPC was observed if zirconia was added. X-ray diffraction measurement confirmed the setting reaction of doped cements was similar to that of pure CPC. Low crystalline HA was found to be the main constituant of set cement; additional phases, such as calcium titanate or calcium zirconate, were not involved in the reaction. A mechanical reinforcement effect was thought to result from changes in the thermodynamic or kinetic solubilities of doped tetracalcium phosphates, this would lead to slower HA crystal formation and a more cross-linked cement structure.

The structure and phase composition of HAp coatings deposited onto Ti6A14V coupons (50x20x2mm) by atmospheric plasma spraying (APS) were studied by laser-Raman spectroscopy, 31 P-and 1 H-MAS-NMR and 2D- 31 P/ 1 H HETCOR-CP-NMR spectroscopy, and XRD with Rietveld refinement. The samples investigated comprised APS HAp coatings with and without a TiO 2 bond coat as well as coatings incubated for different lengths of time (up to 12 weeks) in simulated body fluid (SBF) under physiological conditions. In APS coatings the presence of a bond coat increased the proportion of well-ordered crystalline HAp at the expense of distorted apatite-like structures such as oxyHAp and oxyapatite, and thermal decomposition products such as tricalcium phosphate (TCP) and tetracalcium phosphate (TTCP), and also decreased the amount of amorphous calcium phosphate (ACP). Incubation in SBF further advanced the proportion of crystalline HAp since the disordered structures, the thermal decomposition products, and ACP exhibit substantially higher solubility.

This work studied transmission electron micros- copy on the setting mechanism of tetracalcium phosphate/ dicalcium phosphate anhydrous (TTCP/DCPA)-based cal- cium phosphate cement. The results suggest the process for early-stage apatite formation as the follows: When TTCP and DCPA powders are mixed in the phosphate-containing solution, the TTCP powder is quickly dissolved because of its higher solubility in the acidic solution. The dissolved calcium and phosphate ions, along with those ions readily in the solution, are then precipitated predominantly on the sur- face of DCPA particles. Few apatite crystals were observed on the surface of TTCP powder. During the later stages of reaction, the extensive growth of apatite crystals/whiskers, with a calcium/phosphorous ratio very close to that of hy- droxyapatite, effectively linked DCPA particles together and also bridged the larger TTCP particles. It is suggested that, when the large TTCP particles are locked in place by the bridging apatite crystals/whiskers, the CPC is set and would not dissolve when immersed in Hanks' solution after 20-40 min of reaction. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 64A: 664-671, 2003

Egg shells have been used as a calcium source for synthesis of tetra calcium phosphate (ETTCP) by solid state reaction method. The cell parameters and cell volume of ETTCP measured by X-ray powder diffraction method were lower than the tetra calcium phosphate prepared using synthetic Ca(CO)3 (pure TTCP) for comparison. The vibration bands of ETTCP were also slightly different from the vibration bands of pure TTCP characterized by Fourier transformed infrared spectroscopy. ETTCP has been tried as a main component in a self setting bone cement to evaluate the advantages of the presence of the biologically relevant ions such as Mg2+, Sr2+, SiO2- 4, F-, K+ and Na+ ions in the cement properties. The setting time of the ETTCP derived cement was ~ 11 min compared to ~ 16 min of the pure TTCP derived cement. The amount of hydroxyapatite formed as the end product was about 12% higher for ETTCP derived cement than pure TTCP derived cement after 28 days of immersion in phosphate buffer solution as confirmed by phase analysis. Elemental analysis also indicates the presence of trace elements in minor concentration in ETTCP derived cement. Although both the cements showed similar compressive strength after 28 days, the initial strength of the ETTCP derived cement was remarkably higher during initial stages of the hardening reaction (24 h–7 days) compared to TTCP derived cement. Cell viability of L6 cells was higher and cell spreading was more for the ETTCP derived cement than pure TTCP derived cement. The present study has demonstrated the advantages of eggshell derived TTCP in bone cement formulations due to the presence of biologically relevant ions. This may help the clinician with brief surgical procedure by using faster setting cement as well as the patient to have quick recovery with a higher initial strength of cement.

Tetracalcium phosphate (TTCP) is the most basic phase among the calcium phosphate bioceramics. TTCP has been used as self setting bone cement and its relatively high surface pH seems to be very beneficial for cell adhesion and bone formation. Various attempts have been made to improve the cement properties for the ease of use during the surgical procedures. The effect of citric acid (CA) on the setting properties, apatite forming ability, strength and biological behavior of TTCP based bone cement has been studied in detail in the present study. The cement formulation containing 15�% CA has been found to have setting time between 9 and 16�min suitable for bone cement. It also showed complete conversion to apatite phase and highest compressive strength after 28�days of immersion in phosphate buffer at physiological conditions. Cell culture studies using rat skeletal muscle cells confirm higher cell viability in the CA containing cements compared to the pure cement without CA content. The results suggest that self-hardening tetracalcium phosphate based bone cement modified with CA holds a promise for its use in orthopaedic and trauma surgery. � 2015, The Indian Institute of Metals - IIM.

The crystallinity of hydroxyapatite (HAp) and the related calcium phosphates for regenerating hard tissues was controlled by the mechanical grinding (MG) method and subsequent heat treatment. The HAp, carbonate-apatite (CO3Ap), fluorapatite (FAp), and α- and β-tricalcium phosphates (α-TCP and β-TCP, respectively) and tetracalcium diphosphate monoxide (TTCP) were used as initial materials. Variations in crystallinity and crystal structure were examined by the X-ray diffraction (XRD) method during MG and the following heat treatment. The crystallinity, based on crystallite size and crystal elastic strain, decreased with grinding time, and the decreasing rate depended on the type of calcium phosphate; crystallographic diffraction peaks disappeared more rapidly in CO3Ap than in FAp. The change in the morphology of powder during MG was influenced by the primary particle size of the first-stage product; α-TCP, β-TCP, and TTCP powders composed of large particles were predominantly shattered into small pieces and then gathered during MG, while the crystal strain in the HAp, CO3Ap, and FAp powders was mainly accumulated without significant refinement of crystallite size. The thermal-recovery process of crystallinity and crystal structure in the milled powders was investigated. The crystallinity of HAp, CO3Ap, and FAp powders recovered depended on annealing temperature. The novel phase of β’-TCP with higher ordering than β-TCP appeared during heat treatment from the amorphous state of α-TCP or β-TCP obtained during MG. The MG and subsequent heat treatment were, finally, concluded to be an effective process for controlling the crystallinity and changing crystal structure in calcium phosphate powders.

This article reports the morphology and mechanical properties of sintered powder injection molded Ti-6Al-4V/HA parts in a simulated physiological environment. Sintered Ti-6Al-4V/HA parts were immersed in a simulated body fluid (SBF) with ion concentrations that were comparable to those of human blood plasma for a total period of 12 weeks. At intervals of 2 weeks, the immersed Ti-6Al-4V/HA parts were analyzed with the use of scanning electron microscopy (SEM), X-ray diffractometry (XRD), and inductively coupled plasma–atomic emission spectroscopy (ICP-AES). Mechanical properties such as flexural strength, flexural modulus, compressive strength, and compressive modulus were also evaluated. Results showed that complete dissolution of the more soluble phases such as tricalcium phosphate (TCP), tetracalcium phosphate (TTCP), and calcium oxide (CaO) were found after 2 weeks of immersion in SBF. ICP analysis showed that high calcium concentration release of around 200 ppm was observed in the SBF solution after 2–4 weeks of immersion, indicating that dissolution has taken place. Next, a gradual decrease in calcium concentration release in the SBF solution was observed after immersion for 4–6 weeks, with increasing amounts of calcium phosphate precipitates being observed on the Ti-6Al-4V/HA surface. Mechanical properties such as strength and modulus were found to deteriorate during 2–4 weeks of immersion, followed by gradual increment as the immersion period increased. This study also showed that parts sintered at 1150 °C exhibited faster dissolution and precipitation rates than parts sintered at 1050 °C in a physiological environment. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res (Appl Biomater) 63: 79–87, 2002; DOI 10.1002/jbm.10082

Commercial hydroxyapatite (HAP) powders were quenched from 1500°C to room temperature and reheated at different temperatures by a program controlled SiC-heated furnace to investigate the reconstruction behavior of quenched HAP powder in air. X-ray diffractometer (XRD) and Fourier-transformed infrared (FTIR) analysis were used to examine changes in crystalline phases and functional groups of quenched HAP powders at different temperatures. Weight changes of the quenched powders during heating were recorded by thermogravimetric analysis (TGA). The XRD results showed that the quenched HAP powder was composed of two crystalline phases of tetracalcium phosphate (TTCP) and α-tricalcium phosphate (αTCP). There was no other calcium phosphate phases to be traced. When quenched HAP powders were reheated, TTCP gradually reconstructed into HAP around 500°C and yield Ca(OH)2. αTCP did not convert to HAP at a temperature lower than 700°C but the transformation of αTCP to βTCP was observed during heating. αTCP reacted with Ca(OH)2, the product of reconstruction of TTCP, to form more HAP at temperatures over 700°C. In addition, the CO32− ion was incorporated into the lattice of the reconstructed HAP around 500°C. The intensity of CO32− ion in FTIR decreased as the temperature increased and totally disappeared around 900°C. Above 1000°C, reconstructed HAP lost OH ions and transformed into oxyhydroapatite.

Development of an apatitic calcium phosphate bone cement is reported. 100 μ Particles of tetracalcium phosphate (TTCP) and dicalcium phosphate dihydrate (DCPD) were mixed in equimolar ratio to form the cement powder. The wetting medium used was distilled water with Na2HPO4 as accelerator to manipulate the setting time. The cement powder, on wetting with the medium, formed a workable putty. The setting times of the putty were measured using a Vicat type apparatus and the compressive strength was determined with a Universal Testing Machine. The nature of the precipitated cement was analyzed through X-ray diffraction (XRD), fourier transform infrared spectrometry (FTIR) and energy dispersive electron microprobe (EDAX). The results showed the phase to be apatitic with a calcium-to-phosphorous ratio close to that of hydroxyapatite. The microstructure analysis using scanning electron microscopy (SEM) showed hydroxyapatite nano-crystallite growth over particulate matrix surface. The structure has an apparent porosity of ∼ 52%. There were no appreciable dimensional or thermal changes during setting. The cement passed the in vitro toxicological screening (cytotoxicity and haemolysis) tests. Optimization of the cement was done by manipulating the accelerator concentration so that the setting time, hardening time and the compressive strength had clinically relevant values.

Polycrystalline tetracalcium phosphate (TTCP), a material of considerable interest for human implantation due to its similarity to hydroxyapatite, was studied by means of Raman and FT-IR spectroscopy. The spectra were interpreted on the basis of group theoretical considerations. In addition, the setting reaction of a calcium phosphate cement (CPC) consisting of an equimolar mixture of TTCP and dicalcium phosphate (DCPA) was investigated by Raman spectroscopy. The band of the totally symmetric phosphate mode v1 of TTCP showed marked factor group splittings. The splitting components arose at coincident wave numbers in the IR and Raman spectra. This observation was in accordance with space group P2(1) (factor group C2(2), Z = 4). The characteristic splitting of v1 allowed the setting reaction of CPC to hydroxyapatite to be followed. According to the Raman spectroscopic results, considerable amounts of TTCP must be present at the sample surface after 24 h of setting in an aqueous environment.

Tetracalcium phosphate (TTCP, Ca4(PO4)2O) was prepared by the calcination of coprecipitated mixture of nanoscale hydroxyapatite (HA, Ca10(PO4)6(OH)2) and calcium carbonate crystal (CaCO3), followed by cooling in the air or furnace. The effect of calcination temperature on crystal structure and phase composition of the coprecipitation mixture was characterized by transmission electron microscope (TEM), thermal analysis-thermogravimetry (DTA-TG), X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), and Raman spectroscopy (RS). The obtained results indicated that the synthesized mixture consisted of nanoscale HA and CaCO3with uniform distribution throughout the composite. TTCP was observed in the air quenching samples when the calcination temperature was above 1185°C. With the increase of the calcination temperature, the amount of the intermediate products in the air quenching samples decreased and cannot be detected when calcination temperature reached 1450°C. Unexpectedly, the mixture of HA and calcium oxide was observed in the furnace cooling samples. Clearly, the calcination temperature and cooling methods are critical for the synthesis of high-purity TTCP. The results indicate that the nanosize of precursors can decrease the calcination temperature, and TTCP can be calcinated by low temperature.

It was found that prolonged high-energy ball-milling of Hilgenstokite (tetracalcium phosphate, TTCP) resulted in a decrease in both particle and crystallite size, leading to a mechanical activation of the compound. This mechanically activated material demonstrated a high reactivity such that, in contrast to highly crystalline TTCP, a setting reaction with water to nanocrystalline hydroxyapatite (HA) and Ca(OH)2 could be achieved at 37°C. However, crystalline TTCP is practically unreactive at physiologic temperatures because of the formation of a thin HA layer on the particle surface preventing further reaction.

The setting time of a calcium phosphate cement consisting of tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA) was reduced from 30 to 5 min by use of a cement liquid that contained a phosphate concentration of 0.25 mol/l or higher. The diametral tensile strength and conversion of the cement ingredients to hydroxyapatite (OHAp) during the first 3 h were also significantly increased by the phosphate. However, the phosphate produced no significant effects on the properties of the 24-h cement samples. Results from additional experiments in a slurry system verified that the high phosphate concentration in the solution accelerated the formation of OHAp in the TTCP + DCPA system, and this reaction could explain the fast-setting properties of the cements.

In order to obtain the properties of the sintered as-dried calcium phosphate with [Ca]/[P] = 1.50, the characteristics of sintered pellets have been investigated using X-ray diffraction (XRD), inductively coupled plasma-mass spectrometry (ICP-MS), Fourier-transform infrared (FT-IR) spectra, Vickers hardness indentation and scanning electron microscopy (SEM). When the pellet samples were sintered between 700 °C and 1200 °C for 4 h, the hydroxyapatite (Ca(10)(PO(4))(6)(OH)(2), HA) still maintained the major phase, accompanied with the rhenanite (NaCaPO(4)) as the secondary phase and β-tricalcium phosphate (β-Ca(3)(PO(4))(2), β-TCP) as the minor phases. In addition, the HA partially transformed to α-tricalcium phosphate (α-Ca(3)(PO(4))(2), α-TCP) and tetracalcium phosphate (Ca(4)(PO4)(2)O, TTCP), when the pellet samples were sintered at 1300 °C and 1400 °C, respectively, for 4 h. The maximum density and Vickers Hardness (HV) of sintered pellet samples were 2.85 g/cm3 (90.18% theoretical density (T.D.)) and 407, which appeared at 1200 °C and 900 °C, respectively.

By using a non-aqueous solution as the mixing liquid, the washout resistance of the calcium deficient apatite biocement (cd-AB) was significantly improved, over that of the conventional method of using cd-AB with water as the liquid phase. In this study, premixed and injectable cd-AB was prepared, which had the advantage of being stable in the syringe and hardens only after being delivered to the defect area. The cd-AB powder with a Ca/P ratio of 1.5 consists of a mixture of tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA). A solution of polylactide (PLA) in N-methyl-2-pyrrolidone (NMP) was used as the liquid phase of the premixed cd-AB. The premixed cd-AB paste injected into an aqueous environment exhibited excellent washout resistance. The premixed cd-AB had longer setting time and lower compressive strength than conventional cd-AB. The hydration products of premixed cd-AB were a mixture of calcium deficient hydroxyapatite (cd-HA) and PLA. In vitro Tris-HCl immersion tests demonstrated that the premixed cd-AB could be degradable. The results revealed that the premixed cd-AB was cytocompatible and had no adverse effects on the attachment and proliferation of MG-63 osteoblast-like cells in vitro. The most distinct advantages of premixed and injectable PLA-modified cd-AB were its excellent washout resistance and in vitro degradability, suggesting that it may be a promising candidate for bone repair.

Hydroxyapatite (HA) has been widely used in clinical field because of its excellent biocompatibility. However, its poor thermal stability limits its application. In present paper, the decomposition characteristics of both nano-sized HA powder prepared by precipitation method and its sinters at the temperature from room temperature to 1500 °C in the air were studied. X-ray diffractometer (XRD), High-temperature Raman spectroscopy, High-temperature differential scanning calorimeter (DSC) and Cell culture work were used to investigate their decomposition characteristics. The results show that HA gradually releases its OH− ions from 1000°C and decomposes into β-tricalcium phosphate (TCP) and tetracalcium phosphate (TTCP) when the heating temperature is higher than 1350°C. β-TCP changes into α-TCP at about 1450 °C, which remains until the sinter cools to the room temperature. The decomposed sinter reconstitutes to HA again under a slow cooling rate and in a specific atmosphere. The osteoblast on the surface of decomposed sinter is less than that on the undecomposed one.

This paper reviews recent studies on self-setting calcium phosphate cements (CPC). Discussions are focused on the cement setting reactions, the products formed, the effects of the products on properties of the cement, and in vivo characteristics of CPC. Although cementation can occur in systems based on several different mixtures, data in the literature at present indicate that mixtures of tetracalcium phosphate and dicalcium phosphate (or dicalcium phosphate dihydrate) may be most desirable because they produce cements that have greater strengths and contain nearly pure hydroxyapatite. The strengths of CPC are considerably lower than ceramic calcium phosphate biomaterial and are also lower than some of the dental cements. On the other hand, the combination of self-setting capability and high biocompatibility makes CPC a unique biomaterial. Near perfect adaptation of the cement to the tissue surfaces in a defect, and an optimum resorption rate followed by new bone formation are some of the distinctive advantages of CPC. In its present state CPC appears to be suitable for a number of applications. Much remains to be done to further improve its properties to meet the requirements for different applications.