Preparation and characterization of nanosized silver phosphate loaded hydroxyapatite by single step co-conversion process

The preparation and characterization of silver phosphate nanoparticles loaded hydroxyapatite aiming to enhance the bactericidal performance by a single step co-conversion technique using low temperature phosphorization in the presence of various silver nitrate concentration (AgNO₃, ranging 0.001–0.1 M) was performed. Characterization by using X-ray diffraction, infrared spectroscopy and transmission electron microscopy showed that hydroxyapatite and silver phosphate were the main phases in all converted samples and the microstructure comprised the distribution of spherical-shaped silver phosphate nanoparticles within the cluster of hydroxyapatite nanocrystals. Total silver content (ranging 0.09–5.6%) in the converted samples was found to increase with increasing silver nitrate content. Flexural modulus and strength of converted samples remained unchanged for samples using silver nitrate between 0.001 and 0.01 M, but decreased at greater silver nitrate concentration. Antibacterial activity of two selected samples (0.001 and 0.005 M AgNO₃) against two bacterial strains (Pseudomonas aeruginosa and Staphylococcus aureus) was observed since 100% reduction of viable cells after 24 h contact was detected. Cytotoxic potential by MTT assay of sample using 0.001 M AgNO₃ was only observed at 24 h extraction, but was seen at all extraction periods (24–72 h) for sample using 0.005 M AgNO₃.     

Synthesis of Ag doped calcium phosphate particles and their antibacterial effect as additives in dental glass ionomer cements

Developing dental restorations with enhanced antibacterial properties has been a constant quest for materials scientists. The aim of this study was to synthesize silver doped calcium phosphate particles and use them to improve antibacterial properties of conventional glass ionomer cement. The Ag doped monetite (Ag-DCPA) and hydroxyapatite (Ag-HA) were synthesized by precipitation method and characterized using X-ray diffraction, scanning electron microscope and X-ray fluorescence spectroscopy. The antibacterial properties of the cements aged for 1 day and 7 days were evaluated by direct contact measurement using staphylococcus epidermis Xen 43. Ion concentrations (F^? and Ag⁺) and pH were measured to correlate to the results of the antibacterial study. The compressive strength of the cements was evaluated with a crosshead speed of 1?mm/min. The glass ionomer cements containing silver doped hydroxyapatite or monetite showed improved antibacterial properties. Addition of silver doped hydroxyapatite or monetite did not change the pH and ion release of F^?. Concentration of Ag⁺ was under the detection limit (0.001?mg/L) for all samples. Silver doped hydroxyapatite or monetite had no effect on the compressive strength of glass ionomer cement.     

Sonoelectrochemical deposition of calcium phosphate coatings on carbon materials—effect of electrolyte concentration

Calcium phosphate was deposited on carbon materials using a sonoelectrochemical method in an electrolyte containing calcium and phosphate ions. The effect of electrolyte concentration on sonoelectrochemically deposited calcium phosphate coatings was investigated and the underlying deposition mechanisms were discussed. The morphology, size and composition of the crystalline deposits changed with the electrolyte concentration. A mixture of plate, sphere and needle-like deposits was obtained at Ca(2+) ion concentrations greater than 16 mM, however needle-like hydroxyapatite (HA) was obtained at lower Ca(2+) concentrations. Analysis revealed that the sonoelectrochemical deposition of calcium phosphate consists of two processes-nucleation and crystal growth. The results suggest that the homogeneous nucleation of calcium phosphates in solution, followed by their absorption onto the carbon surface may account for the mechanism of coating observed at higher ionic concentrations. At lower concentrations, heterogeneous nucleation occurs on the surface of the carbon fibres, followed by the development of islands of crystal growth. The lower ionic concentration was shown to favour the generation of hydroxyapatite on carbon-based materials.     

A comparison of the osteoinductive potential of two calcium phosphate ceramics implanted intramuscularly in goats

The osteoinductive potential, or bone induction potency, of two calcium phosphate ceramics was evaluated after intramuscular implantation in goats. The ceramics were comprised of hydroxyapatite (HA) and biphasic calcium phosphate (BCP), the later of which contained a 85/15 mixture of hydroxyapatite and tricalcium phosphate (TCP). Both ceramics had a similar macroporosity of around 55% and a pore distribution between 100 and 800 m. Besides the difference in chemistry, BCP was also microporous and hence had a different surface microstructure. After implantation in the back muscles of four goats for 12 weeks, all 8 BCP samples (7×7×7 mm³) showed the presence of bone formation in the macropores (1±1%), while no bone was found in any of the HA samples. The used BCP can therefore be characterized as an osteoinductive material. Having the ability to induce bone formation in soft tissues, the BCP presented herein may be a useful biomaterial for bone repair when combined with cultured osteogenic cells, growth factors or both.     

Precipitation of octacalcium phosphates on artificial enamel in artificial saliva

The natural saliva samples were collected from 30 Japanese men and women aged between 20 and 30, and the inorganic components in the saliva were analyzed chemically. Artificial saliva (AS) was prepared based on the chemical analysis using chemical reagents. The calcium/phosphate molar ratio of the AS was 0.28 with pH = 7.0. Artificial enamel (AE) was prepared by sintering hydroxyapatite powder at 1,200^∘C. The AE was placed in the AS at 37^∘C. XRD, SEM and EDX investigated precipitation on the AE. The precipitation was always identified as being OCP. As decrease in the pH of the surface of the AE and increase in the concentration of phosphate ions were observed by chemical analysis, it was concluded that the OCP occurs by the pH decrease and phosphate ion concentration increase on the surface of AE.     

Antibacterial and bioactive silver-containing Na2O·CaO·2SiO2 glass prepared by sol–gel method

The antibacterial effect of addition of silver oxide to Na2O x CaO x 2SiO2 glass have been studied. Silver containing and silver free Na2O x CaO x 2SiO2 glasses have been prepared by sol-gel synthesis using tetramethil orthosilicate, sodium ethoxide, calcium nitrate tetrahydrate and silver nitrate as starting materials and methyl ethyl ketone as solvent. The gel was examined by differential thermal analysis, thermo gravimetric analysis, FTIR spectroscopy and X-ray diffraction analysis. Antibacterial and bioactive tests on gel glass powders, obtained after a heat treatment of 2 h at 600 degrees C of the dried gel, were carried out. High antimicrobial effects of samples against Escherichia coli and Streptococcus mutans were found. FTIR measurements and SEM micrographs have ascertained the formation of a hydroxyapatite layer on the surface of samples soaked in a simulated body fluid for different times.     

Preparation of high specific surface area hydroxyapatite for environmental applications

We report the preparation of hydroxyapatite in powdered form by aqueous reaction of calcium nitrate or hydroxide with phosphate ion at room temperature. With a slow maturation step of 48 h avoiding heat, the resulting products show large specific surface areas above 150 m²/g. The specific surface areas also depend on stirring speed with a maximum observed with gentle mixing. Ageing causes a decrease in specific surface area which tends to stabilize near 100 m²/g following a 1 year period. The hydroxyapatite may be spray dried and conserve interesting physical properties for environmental applications.     

Preparation and characterization of fluoride-substituted apatites

Apatites were prepared with three different fluoride concentrations: 0.0 mM (pure hydroxyapatite) 2.5 mM and 5 mM. Reactions were performed in aqueous medium using a reaction between diammonium orthophosphate and calcium nitrate 4-hydrate and ammonium fluoride at temperatures of 3°, 25°, 60° and 90°C. The effects of reaction temperature and fluoride concentration on the crystal morphology, phase purity and crystallinity of the precipitates were observed, using transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and ion chromatography. Transmission electron micrographs revealed that the crystallites precipitated at 3°C were spheroidal, but became increasingly acicular with increasing precipitation temperature. X-ray diffraction results indicated that all the materials produced were phase pure and that the crystallinity of apatites prepared at higher precipitation temperatures was higher than those prepared at lower precipitation temperatures. A significant difference in the a-axis dimension of fluoride-substituted apatites was observed, as compared to hydroxyapatite. FTIR spectroscopy revealed a hydroxyl band at 3568 cm-1, along with a broad peak of adsorbed water in the region of 3568 cm-1 to 2670 cm-1 in the hydroxyapatite and fluoride-substituted apatite powders. Hence by careful selection of the precipitation conditions and fluoride contents, the composition and morphology of fluoride-substituted apatite may be controlled and this has interesting implications for the development of these materials for biomedical implantation.     

Hydroxyapatite pattern formation in PVA gels

Sodium hydroxide solution was allowed to diffuse from the edge of an acidic poly(vinyl alcohol) gel sheet containing dissolved calcium and phosphate ions, and calcium phosphate was observed to precipitate as the pH rose. The precipitation pattern changed depending on the solute concentration near the reaction front; precipitate “walls” were formed in areas in which the calcium phosphate concentration was higher or the sodium hydroxide concentration was lower than the conditions for homogeneous precipitation, and within a very limited concentration combination of calcium phosphate and sodium hydroxide, a regular stripe pattern with a pitch of about 100 μm was formed. The calcium phosphate precipitate obtained was a single phase of hydroxyapatite. It was also found that apatite ceramic sheets with periodic porous structures or with undulate patterns could be manufactured by sintering gels with stripe patterns.     

Setting solution concentration effect on properties of a TTCP/DCPA-derived calcium phosphate cement

The present work was to investigate the effects of concentration of (NH(4))(2)HPO(4) (diammonium hydrogen phosphate) setting solution on properties of a tetracalcium phosphate (TTCP)/dicalcium phosphate anhydrous (DCPA)-derived calcium phosphate cement. Experimental results indicated that working/setting time of the cement paste decreased with increasing (NH(4))(2)HPO(4) concentration of the setting solution. After being immersed in Hanks' solution for 1?day or longer, the XRD intensities of initial TTCP and DCPA phases largely decreased, while apatite phase became dominant. More residual TTCP phase was observed in the 1?day-immersed cement prepared from higher concentration setting solutions. Compressive strength of the cement immersed for 1?day was consistently higher than that immersed for 30?min or 7?days. After being immersed for 1?day, the average CS value reached a maximal value (59?MPa) as (NH(4))(2)HPO(4) concentration was increased to 0.6?M, beyond that the cement strength decreased and maintained in a relatively high range of 47-54?MPa. Cells incubated with conditioned medium of Al(2)O(3) powder and with blank medium exhibited similar average viability values (0.80 and 0.78, respectively). The OD value with extractions of cement decreased with increasing (NH(4))(2)HPO(4) concentration of the setting solution. The average 0.25, 0.5 and 0.6?M-OD values were 0.78, 0.67 and 0.66, respectively. When setting solution concentration was greater than 0.6?M, the OD value sharply declined to 0.47.     

Synthesis and Characterization of Bioceramic Calcium Phosphates by Rapid Combustion Synthesis

Calcium hydroxyapatite(Ca10(PO4)6(OH)2) has been synthesized in short duration by rapid solution combustion by employing different fuels.Calcium nitrate was taken as source of calcium and diammonium hydrogen phosphate served as the source of phosphate ions.Citric acid,tartaric acid,sucrose,glycine and urea were used as the fuels and nitrate ions and nitric acid were used as oxidizers.The influence of fuels on the morphology of the phase formed was studied.Results of the studies by powder X-ray diffraction a...     

Preparation and characterization of thermally stable nanohydroxyapatite

Rod-like hydroxyapatite was synthesized by precipitating calcium nitrate tetrahydrate and ammonium dibase phosphate in the presence of polyacrylic acid followed by hydrothermal treatment. Both polyacrylic acid and the hydrothermal treatment stabilised the hydroxyapatite.     

Composite formation from hydroxyapatite with sodium and potassium salts of polyphosphazene

The low temperature synthesis of composites potentially suitable as bone substitutes which form in vivo, was investigated. The composites were comprised of stoichiometric hydroxyapatite (SHAp) and water-soluble poly phosphazenes. These constituents were selected because of their biocompatibility, and were mixed as powders with a phosphate buffer solution (PBS) to form the composites. The effects of poly[bis(sodium carboxylatophenoxy)phosphazene] (Na-PCPP) or poly[bis(potassium carboxylatophenoxy) phosphazene] (K-PCPP) on stoichiometric hydroxyapatite (SHAp) formation from tetracalcium phosphate and anhydrous dicalcium phosphate were assessed. The kinetics and reaction chemistries of composite formation were followed by isothermal calorimetry, X-ray diffraction, infrared spectroscopy and scanning electron microscopy. In the presence of 1% by weight of polyphosphazenes, composites comprised of SHAp and calcium cross-linked polymer salts were formed. Thus a mechanism for binding between polymer chains was established. Elevated proportions (5 and 10% by weight) of polyphosphazene, however, resulted in the inhibition of SHAp formation. This is attributed to the formation of viscous polymer solution coatings on the calcium phosphate precursors, retarding their reaction, and consequently inhibiting SHAp formation.     

Effects of cooling conditions and chitosan coating on the properties of porous calcium phosphate granules produced from hard clam shells

The main inorganic components of clam shells are calcium carbonate and trace elements of magnesium, strontium, and zinc. Clam shells can be used as a calcium source to synthesize calcium phosphates, and these trace elements promote the growth of bone tissue and improve the performance of bioceramics. In this study, hydroxyapatite (HA) powders were synthesized from clam shells, and porous calcium phosphate granules were prepared through the gas foaming technique. In addition, the effects of a chitosan coating and cooling conditions on the strength of the porous granules were investigated. The results indicated that the samples produced under the furnace cooling condition were biphasic hydroxyapatite/β-tricalcium phosphate granules (HA/β-TCP), whereas the samples produced under the air-cooling condition were triphasic hydroxyapatite/β-tricalcium phosphate/α-tricalcium phosphate granules (HA/β-TCP/α-TCP). The compressive strength of the porous granules prepared through air cooling was 79% higher than that of the granules produced through furnace cooling. The compressive strength of the air-cooled sample after the subsequent application of the chitosan coating further increased by 21%. A degradability test revealed that the weight loss rate of the air-cooled samples was greater than that of the furnace-cooled samples, which was due to the presence of high-solubility α-TCP in the air-cooled samples.     

磷酸钙骨粘合剂的研究

在柠檬酸中添加壳聚糖配成的固化液与磷酸钙骨水泥(CPC)调和制备的骨修复材料具有类似口香糖的胶状特性, 可应用于碎骨粘结, 称之为磷酸钙骨粘合剂(CPCBA)。本研究考察了柠檬酸的含量对抗压强度、固化时间、水化产物和粘结强度的影响, 同时对该体系进行了初步的体外生物学评价。结果显示, 加入柠檬酸可以缩短固化时间并且时间可以通过柠檬酸的含量进行调控, 同时也改善了抗水性能。壳聚糖可以与骨水泥中的钙离子发生螯合作用, 可以增加界面的粘结强度。小鼠原成骨细胞(MC3T3-E1)在其表面粘附良好, 该体系骨水泥有望取代PMMA成为新的骨粘结剂。     

Formation of carbonate apatite on calcium phosphate coatings containing silver ions

The prerequisite for bioactive materials to bond to living bone is the formation of biologically equivalent carbonate apatite on their surfaces in the body. Calcium phosphate ceramic surfaces can be transformed to a biological apatite through a series of surface reactions including dissolution–precipitation and ion exchange. In the present work, apatite coatings with different crystallinity, compositions and crystal sizes, including a well-crystallized hydroxyapatite coating, were synthesized electrochemically and doped with silver ions in silver nitrate solution at room temperature. The formation of a new carbonate apatite on the surface of these coatings was investigated in an acellular simulated body fluid with ion concentrations comparable with those of human blood plasma, using scanning electron microscopy and Fourier transform-infrared spectroscopy. The results show that small quantities of silver ions incorporated into apatite coatings may have a strong stimulatory effect on the formation of carbonate apatite without adversely affecting the chemical stability of these coatings.     

Synthesis and release of trace elements from hollow and porous hydroxyapatite spheres

It is known that organic species regulate fabrication of hierarchical biological forms via solution methods. However, in this study, we observed that the presence of inorganic ions plays an important role in the formation and regulation of biological spherical hydroxyapatite formation. We present a mineralization method to prepare ion-doped hydroxyapatite spheres with a hierarchical structure that is free of organic surfactants and biological additives. Porous and hollow strontium-doped hydroxyapatite spheres were synthesized via controlling the concentration of strontium ions in a calcium and phosphate buffer solution. Similarly, fluoride and silicon-doped hydroxyapatite spheres were synthesized. While spherical particle formation was attainable at low and high temperature for Sr-doped hydroxyapatite, it was only possible at high temperature in the F/Si-doped system. The presence of inorganic ions not only plays an important role in the formation and regulation of biological spherical hydroxyapatite, but also could introduce pharmaceutical effects as a result of trace element release. Such ion release results showed a sustained release with pH responsive behavior, and significantly influenced the hydroxyapatite re-precipitation. These ion-doped hydroxyapatite spheres with hollow and porous structure could have promising applications as bone/tooth materials, drug delivery systems, and chromatography supports.     

Surface analyses of calcite particles reactivity in the presence of phosphoric acid

The reactivity of calcite in phosphoric acid solutions of concentrations between 0 and 0.5 M was monitored during 15 min with complementary in-situ and ex-situ analytical techniques such as Raman and infrared spectroscopies, XRD and SEM analysis. The Raman and infrared spectra show the characteristic carbonate peaks of calcite and phosphate peaks attributed to a new phosphate phase which intensity decreases and increases, respectively with increasing phosphoric acid concentration and reaction time. A similar trend was observed with increasing acid concentration in the XRD analysis of calcite which also revealed that this new phosphate phase is dicalcium phosphate dihydrate or brushite. Fine sheets of calcium phosphate particles were observed by SEM analysis covering the calcite particles at a high phosphoric acid concentration. These changes on the calcite surface were compared to the consumption of protons by the calcite particle suspension with increasing phosphoric acid concentration. The formation and stability of passivating calcium phosphate phases on the calcite surface was evidenced. The obtained results allow to define the contact time and phosphoric acid concentration intervals where the surface of calcite is not passivated by the brushite formed or adsorbed on the mineral surface.     

Surface characterization of hydroxyapatite and related calcium phosphates by XPS and TOF-SIMS

The surfaces of six biologically interesting calcium phosphate (CaP) phases (hydroxyapatite, dibasic calcium phosphate dihydrate, dibasic calcium phosphate, monobasic calcium phosphate, beta-tribasic calcium phosphate, octacalcium phosphate) have been examined by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The intensity of an O(1s) shake-up satellite correlates with the phosphate oxygen content. Together with the Ca/P and O/Ca XPS peak ratios, this feature helps provide identification of the CaP phase(s) present in the surface of unknown samples and establish their mole fractions, as proven with a bone sample. Contributions from carbonate impurities can be quantified using its C(1s) peak at 279.9 eV and subtracted from the O(1s) line shape to aid identification. Principal component analysis (PCA) has been applied successfully to analyze TOF-SIMS spectra of these six CaP phases. Multivariate analysis can help differentiate these CaP phases using the first two PCs, which are dominated by the relative intensities of only a few key ions: PO3-, O-, Ca+, CaOH+, PO2-, and OH-.     

Carbonate-doped hydroxyapatite

A hydroxyapatite slurry was prepared by stirring into water a stoichiometric mixture of tricalcium phosphate and calcium hydroxide until the solid content was 50 wt%. Samples were then prepared by slip casting, drying and firing in vacuum at 1000 to 1300° C for 1 h. The fired samples were crushed and soaked in ordinary mineral water for up to 2 months and examined by differential thermal analysis and thermogravimetry, infrared spectroscopy, X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray analysis, and direct-current plasma emission spectroscopy. One phosphate ion was found to be replaced by carbonate and practically all hydroxide by water, regardless of heat treatment. The infrared spectra showed a close resemblance to that obtained from natural bone.