Effect of Ca2+ Replacement with Cu2+ Ions in Brushite on the Phase Composition and Crystal Structure

The gradual replacement of Ca2+ with Cu2+ ions in brushite (CaHPO4·2H2O) has been extensively studied and discussed. The approach adopted in this work has not been systematically explored in previous studies. This novel approach may prove beneficial for the production of Ca1−xCuxHPO4·nH2O materials with desired properties suitable for medical applications. Solutions of sodium dihydrogen orthophosphate dihydrate, NaH2PO4·2H2O, calcium nitrate tetrahydrate, Ca(NO3)2·4H2O, copper nitrate trihydrate, Cu(NO3)2·3H2O, ammonium hydroxide solution, and diluted HCl were used for the preparation of these materials. At low Cu/Ca molar ratios (up to 0.25) in the starting solution, biphasic phosphate minerals were formed: brushite and sampleite. When the Cu/Ca molar ratio increases gradually from 0.67 to 1.5, sampleite-like mineral precipitates. Powdered XRD (X-ray diffraction), thermogravimetric (TG) analysis, and SEM (scanning electron microscopy) techniques were employed for the study of the microstructure of the produced materials for different degrees of Ca replacement with Mg. It is found that the Cu/Ca ratio in the starting solution can be adjusted to obtain materials with tailored composition. Thus, a new method of sampleite-like synthesis as a rare mineral is introduced in this study. Both phosphate minerals brushite and sampleite-like minerals are attractive as precursors of bioceramics and biocements. The search for such products that may decrease the possibility of post prosthetic or implant infection can be crucial in preventing devastating post-surgical complications.

Dispersed filler based on synthetic calcium carbonate – requirements for applications quality

The introduction of fillers into various materials improves its technological, physical and mechanical properties, and leads to a decrease in cost. The main areas of application of natural and synthetic calcium carbonate as highly dispersed fillers are: the construction industry, the production of Portland cement, mineral fertilizers, glass, paper, polymer composite materials, paints and varnishes, and rubbers. A promising direction at present is the use of production by-products as fillers, for example, conversion calcium carbonate - a waste product from the production of a complex mineral fertilizer - nitroammophoska. However, its use in the above areas is limited by the content of water-soluble nitrogen-containing impurities, impurities of heavy metals, strontium carbonate, phosphates, etc. The analysis of scientific, technical and patent literature on methods of purification of conversion calcium carbonate has been carried out. These methods are based on the extraction of impurities from the initial product of calcium carbonate production - a melt of calcium nitrate tetrahydrate by precipitation with various reagents, followed by the isolation of an insoluble precipitate (impurities) and processing of the purified melt into calcium carbonate and nitroammofoska. A method is proposed for the extraction of acid-tonic-soluble iron-containing impurities from the initial calcium nitrate melt in order to obtain a cleaner by-product - conversion calcium carbonate, which will expand the scope of its application. An effective method is to dilute the initial calcium nitrate melt with a 60% solution of ammonium nitrate to a calcium content of 12-13%, followed by the isolation of an acid-insoluble precipitate in a vacuum filter, conversion of the purified calcium nitrate solution with ammonium carbonate and separation of the resulting suspension in a drum filter. The described method can reduce the amount of iron-containing impurities by more than 50%.

Green synthesis of Sodium alginate mediated Fluorapatite Nanoparticle via Sol-Gel method

Fluorapatite (FA) can be used as a bioactive substance in the body, especially the teeth implants. The FA nanoparticle was synthesized by adding the fluorine to the structure of HA using sol–gel method and the heat treatment of 700 °C. Being low costs, eco-friendly and safer features are obvious advantages of the green synthesis of FA nanoparticles by using bio stabilizer of sodium alginate. Calcium nitrate tetrahydrate, diammonium phosphate, ammonium fluoride were used as precursors of Ca, P and F respectively with the ratio of 1:67 Ca/P. The presence of crystal structure of HA and FA investigated by the results of XRD which confirmed the substitution of hydroxyl groups with the fluorine in the crystal structure of apatite. FTIR obtained that fluorine was substituted by hydroxyl groups in the structure of fluoridated hydroxyapatite by disappearing the hydroxyl groups at 3600 cm-1 in the FA. TGA investigated the thermal stability of the nanoparticles that showed the discrepancy of weight loss for HA and FA between 600?C to 800?C. By using TEM, average sizes of 35 and 49 nm were determined for HA and FA respectively. FESEM results confirmed the shapes and distribution of particles of HA and FA in that, round like for the former and rode like for the later. The overall performance of utilizing sodium alginate (SA) as a bio-stabilizer is to obtain better precipitate which leads to having better crystallinity and smaller particle size and thermal stability remarkably improved.

Modulated Monoclinic Hydroxyapatite: The Effect of pH in the Microwave Assisted Method

Hydroxyapatite (HAp) is a natural hard tissue constituent widely used for bone and tooth replacement engineering. In the present work, synthetic HAp was obtained from calcium nitrate tetrahydrate (Ca(NO3)2·4H2O) and ammonium phosphate dibasic (NH4)2HPO4 following an optimized microwave assisted hydrothermal method. The effect of pH was evaluated by the addition of ammonium hydroxide (NH4OH). Hence, different characterization techniques were used to determine its influence on the resulted HAp powders’ size, shape, and crystallinity. By Transmission Electron Microscopy (TEM), it was observed that the reaction pH environment modifies the morphology of HAp, and a shape evolution, from sub-hedral particles at pH = 7 to rod-like nanosized HAp at pH = 10, was confirmed. Using the X-ray Diffraction (XRD) technique, the characteristic diffraction peaks of the monoclinic phase were identified. Even if the performed Rietveld analysis indicated the presence of both phases (hexagonal and monoclinic), monoclinic HAp prevails in 95% with an average crystallite size of about 23 nm. The infrared spectra (FTIR) showed absorption bands at 3468 cm−1 and 630 cm−1 associated with OH− of hydroxyapatite, and bands at 584 cm−1, 960 cm−1, and 1090 cm−1 that correspond to the PO43− and CO32− characteristic groups. In summary, this work contributes to obtaining nanosized rod-like monoclinic HAp by a simple and soft method that has not been previously reported.

Gradual Replacement of Ca2+ with Mg2+ Ions in Brushite for the Production of Ca1−xMgxHPO4·nH2O Materials

The present study investigates the gradual replacement of Ca2+ with Mg2+ ions in brushite (CaHPO4·2H2O). To date, this approach has not been systematically explored and may prove beneficial for the production of Ca1−xMgxHPO4·nH2O materials with tailored properties which are suitable for environmental and medical applications. For their production, solutions of sodium dihydrogen orthophosphate dehydrate, NaH2PO4·2H2O, calcium nitrate tetrahydrate, Ca(NO3)2·4H2O, magnesium nitrate hexahydrate, Mg(NO3)2·6H2O and ammonium hydroxide solution, NH4OH, were used. At low Mg/Ca molar ratios (up to 0.25) in the starting solution, partial replacement of Ca with Mg takes place (Mg doping) but no struvite is produced as discrete phase. When the Mg/Ca molar ratio increases gradually to 1.5, in addition to Mg-doped brushite, struvite, NH4MgPO4·6H2O, precipitates. The microstructure of the materials produced for different degrees of Ca replacement with Mg has been analyzed in depth with the use of powdered XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy), thermogravimetric (TG) analysis and SEM (scanning electron microscopy). The results of this study prove that the Mg/Ca ratio in the starting solution can be monitored in such a way that materials with tailored composition are obtained.

Magnetic Hydroxyapatite for Batch Adsorption of Heavy Metals

In this work, magnetic hydroxyapatite or hydroxyapatite-iron (III) oxide (HAp-Fe3O4) composite was used as the adsorbent of heavy metals and the performance was evaluated using the batch test. The presence of heavy metals in the effluent from wastewater discharge can be toxic to many organisms and can even lead to eye burns. Therefore, hydroxyapatite synthesized from the chemical precipitation of calcium nitrate tetrahydrate and diammonium hydrogen phosphate solutions is used to remove heavy metal in aqueous media. Magnetic properties of Fe3O4 can help prevent formation of secondary pollutants caused by the loss of adsorbent. The synthesized HAp-Fe3O4 can remove cadmium, zinc and lead effectively, which is up to 90% removal. Reusability study shows that the adsorbent could retain heavy metal ions even after four cycles. The percentage removal of heavy metals maintains at around 80% after four times of usage. The composite of HAp-Fe3O4 demonstrates good performance and stability which is beneficial for heavy metal removal in the future.

Biofilms of cellulose and hydroxyapatite composites: Alternative synthesis process

A new biofilm of cellulose coated with hydroxyapatite particles have been prepared using a simple, fast and low temperature process based on a microwave-assisted hydrothermal synthesis. The cellulose used as matrix of the biocomposite was extracted from banana stems residues. The hydroxyapatite coating was performed using calcium nitrate tetrahydrate, phosphoric acid, and 1,2-ethylenediamine dispersed in a cellulose/water solution, with posterior microwave-assisted hydrothermal synthesis, for 5 min at 140°C. The chemical, structural, thermal, and morphological properties of the composites were investigated by X-ray diffraction, infrared spectroscopy, thermogravimetry and field emission scanning electron microscopy. Results showed that the methodology was effective to produce high quality composites, with good thermal stability. Cell viability tests indicated that the cellulose/Hap films were not cytotoxic.

Synthesis of Graphene Nanoribbons–Hydroxyapatite Nanocomposite Applicable in Biomedicine and Theranostics

In order to investigate the effect of graphene nanoribbons on the final properties of hydroxyapatite-based nanocomposites, a solvothermal method was used at 180 °C and 5 h for the synthesis of graphene nanoribbons–hydroxyapatite nanopowders by employing hydrogen gas injection. Calcium nitrate tetrahydrate and diammonium hydrogenphosphate were used as calcium and phosphate precursors, respectively. To synthesize the powders, a solvent containing diethylene glycol, anhydrous ethanol, dimethylformamide, and water was used. Graphene oxide nanoribbons were synthesized by chemical unzipping of carbon nanotubes under oxidative conditions. The synthesized powders were consolidated by spark plasma sintering methodat 950 °C and a pressure of 50 MPa. The powders and sintered samples were then evaluated using X-ray diffraction, Raman spectroscopy, high-resolution transmission electron microscopy, Vickers microindentation techniques, and biocompatibility assay. The findings of this study showed that the final powders synthesized by the solvothermal method had calcium to phosphate ratio of about 1.67. By adding a small amount of graphene nanoribbon (0.5%W), elastic modulus and hardness of hydroxyapatite increased dramatically. In biological experiments, the difference of hydroxyapatite effect in comparison with the nanocomposite was not significant. The findings of this study showed that graphene nanoribbons have a positive effect on the properties of hydroxyapatite, and these findings would be useful for the medical and theranostic application of this type of nanocomposites.

Synthesis of plate-like β-tricalcium phosphate nanoparticles and their efficiency in remineralization of incipient enamel caries

The purpose of this study was to synthesize nano-sized β-tricalcium phosphate (nano-TCP) particles and determine its concentration-dependent properties on incipient enamel caries lesions. Nano-TCP was synthesized as a wet chemical through a method using low concentration of precursors and low addition rate of calcium nitrate tetrahydrate as a second phase. Morphology and phase composition of the particles were analyzed by SEM, XRD, and EDXA techniques. Incipient enamel lesions were created in human premolars with an acidic buffer. The teeth were then incubated in aqueous dispersions of nano-TCP as remineralization solutions. Sodium fluoride solution and deionized water were used as positive and negative control groups, respectively. The quality and thickness of the remineralized layer on enamel were investigated using SEM. The data were statistically analyzed by analysis of variance (ANOVA) and post hoc Tukey’s test. The synthesized nano-TCP mostly consisted of porous platelet-like crystals of 50–100 nm thickness and pore diameters of 100–300 nm. SEM observation showed that a homogenous layer was formed on the surface of the enamels remineralized in nano-TCP solutions. The thickness of the mineralized layer was dependent on the incubation time and nano-TCP concentration.

Low temperature synthesis of wollastonite using sol–gel combustion method: In vitro bioactivity evaluation

In this paper, low temperature, economical sol–gel combustion method was adopted to synthesize wollastonite ceramic. Calcium nitrate tetrahydrate and tetraethyl orthosilicate were taken as source for Ca and Si, while citric acid and nitric acid were used as chelating/combustion agents. The yielded powder calcined at 600[Formula: see text]C for 4 h was characterized by FTIR, XRD and SEM techniques. Results showed that the citrate combustion method was the most efficient method to prepare wollastonite at low temperature. Moreover, in vitro bioactivity test performed in simulated body fluid (SBF) showed good bioactivity of synthesized wollastonite ceramics.