Dicalcium Phosphate Dihydrate Crystals Research Articles

Effect of Soaking Time on the Compositional and Morphological Changes of DCPD-Coated β-TCP Bioceramic

The aim of this study is to investigate the effect of soaking time on the compositional and morphological changes of dicalcium phosphate dihydrate (DCPD)-coated β-tricalcium phosphate (β-TCP) bioceramic. In this study, an established method from our research group was used to prepare the β-TCP bioceramic pellets and expose them to acidic calcium phosphate solution for 2, 4, 6, and 8 hours to obtain DCPD coated layer on β-TCP pellets through dissolution-precipitation reaction. Characterization methods such as x-ray diffraction analysis (XRD) and scanning electron microscope (SEM) were carried out on the specimen. XRD and SEM analyses indicated that the peak intensity and density of DCPD crystal precipitated on the pellets were increased when increasing the soaking time. Therefore, it was confirmed that the DCPD coated layer formation on the β-TCP pellet surfaces depended on the exposure time to acidic calcium phosphate solution.

Controlled synthesis of dicalcium phosphate dihydrate (DCPD) from metastable solutions: insights into pathogenic calcification

Calcium phosphate (CaP) compounds may occur in the body as abnormal pathogenic phases in addition to their normal occurrence as bones and teeth. Dicalcium phosphate dihydrate (DCPD; CaPO4·2H2O), along with other significant CaP phases, have been observed in pathogenic calcifications such as dental calculi, kidney stones and urinary stones. While other studies have shown that polar amino acids can inhibit the growth of CaPs, these studies have mainly focused on hydroxyapatite (HAp; Ca10(PO4)6(OH)2) formation from highly supersaturated solutions, while their effects on DCPD nucleation and growth from metastable solutions have been less thoroughly explored. By further elucidating the mechanisms of DCPD formation and the influence of amino acids on those mechanisms, insights may be gained into ways that amino acids could be used in treatment and prevention of unwanted calcifications. The current study involved seeded growth of DCPD from metastable solutions at constant pH in the presence of neutral, acidic and phosphorylated amino acid side chains. As a comparison, solutions were also seeded with calcium pyrophosphate (CPP; Ca2P2O7), a known calcium phosphate inhibitor. The results show that polar amino acids inhibit DCPD growth; this likely occurs due to electrostatic interactions between amino acid side groups and charged DCPD surfaces. Phosphoserine had the greatest inhibitory ability of the amino acids tested, with an effect equal to that of CPP. Clustering of DCPD crystals giving rise to a “chrysanthemum-like” morphology was noted with glutamic acid. This study concludes that molecules containing an increased number of polar side groups will enhance the inhibition of DCPD seeded growth from metastable solutions.

Effects of acidic calcium phosphate concentration on setting reaction and tissue response to β-tricalcium phosphate granular cement.

Beta-tricalcium phosphate granular cement (β-TCP GC), consisting of β-TCP granules and an acidic calcium phosphate (Ca-P) solution, shows promise in the reconstruction of bone defects as it sets to form interconnected porous structures, that is, β-TCP granules are bridged with dicalcium phosphate dihydrate (DCPD) crystals. In this study, the effects of acidic Ca-P solution concentration (0-600 mmol/L) on the setting reaction and tissue response to β-TCP GC were investigated. The β-TCP GC set upon mixing with its liquid phase, based on the formation of DCPD crystals, which bridged β-TCP granules to one another. Diametral tensile strength of the set β-TCP GC was relatively the same, at ∼0.6 MPa, when the Ca-P concentration was 20-600 mmol/L. Due to the setting ability, reconstruction of the rat's calvarial bone defect using β-TCP GC with 20, 200, and 600 mmol/L Ca-P solution was much easier compared to that with β-TCP granules without setting ability. Four weeks after the reconstruction, the amount of new bone was the same, ∼17% in both β-TCP GC and β-TCP granules groups. Cellular response to β-TCP granules and β-TCP GC using the 20 mmol/L acidic Ca-P solution was almost the same. However, β-TCP GC using the 200 and 600 mmol/L acidic Ca-P solution showed a more severe inflammatory reaction. It is concluded, therefore, that β-TCP GC, using the 20 mmol/L acidic Ca-P solution, is recommended as this concentration allows surgical techniques to be performed easily and provides good mechanical strength, and the similar cellular response to β-TCP granules. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 108B:22-29, 2020.

Novel two-stage oxidation/crystallization technology for high-purity calcium phosphates recovery from digester supernatant

A novel hybrid technology consisting of oxidation and reactive crystallization was developed for recovery of high-purity CaP from digester supernatant. Initial phosphate concentration in digester supernatant was 10 mmol/L and initial calcium concentration was 0.2 mmol/L. H2O2 (20 ml of 30% ww H2O2/L) in combination with short ultrasound treatment (10 min, P = 50W, A = 94% and C = 70%) was used for the oxidation stage. Effect of pH at oxidation stage and oxidation time on the P-recovery rate and purity of the products was studied by performing the oxidation at 4 different pH values (2.0; 3.9; 7.8 and 10.0) for 24 or 48 h. Oxidation at pH 7.9 showed the best performance in terms of the properties of the crystallized products. Batch crystallization of calcium phosphates was done at the Ca/P ratio 2. Crystallization lasted for 2 h. Nucleation pH was determined and was chosen as operation pH. At the tested conditions, two compounds were recovered: dicalcium phosphate dihydrate (DCPD) and hydroxyapatite (HAp). Addition of DCPD seeds (0.2 g/L) promoted crystallization of pure DCPD. Oxidation at pH 7.9 for 24 h followed by crystallization without seeding resulted in the highest P-recovery (89%) with the production of DCPD as a major product plus minor amounts of HAp.

Calcium phosphates recovery from digester supernatant by fast precipitation and recrystallization

Conditional solubility of dicalcium phosphate dihydrate (DCPD) and hydroxyapatite (HAp) in digester supernatant was determined as a function of pH and was compared to its conditional solubility in distilled water. Conditional solubility of both substances in digester supernatant at pH >5–6 was higher than their conditional solubility in pure water due to the presence of impurities, and this influence is more significant for HAp. Amorphous CaP was precipitated through a fast precipitation process from digester supernatant with initial total phosphate concentration 0.008 mol/L and 0.015 mol/L and Ca/P ratios 2 and 5. The amorphous CaP can be subsequently recrystallized into crystalline CaP. Obtained amorphous products have Ca/P ratio > 1, which allow performing the recrystallization process without further Ca dosing into the system. Batch recrystallization of the amorphous products resulted in crystallization of HAp, DCPD or their mixture depending on the conditions of the process. Maximum achieved P-recovery was 69.5%. The increase of phosphate concentration and the addition of seeding decreased the yield of the process but promoted crystallization of DCPD. The increase of Ca/P ratio had a positive effect on the total P-recovery. Compared with the direct batch crystallization of CaP from digester supernatant, the two-step process with fast precipitation and recrystallization significantly improved the color of the obtained products.

Effect of Mg2+ on acidic calcium phosphate phases grown by electrodeposition

In this work, the effect of Mg2+ ions on the electrodeposition of dicalcium phosphate dihydrate (DCPD), octacalcium phosphate (OCP) and calcium-deficient hydroxyapatite (CDHA) crystals on a commercially pure titanium (cp-Ti) substrate was evaluated. We demonstrated that Mg2+ ions could change the morphology of the coatings by inhibiting the growth rate of the OCP and CDHA crystals and diminishing the crystallite size of DCPD. The inhibition effect on OCP and CDHA was most likely due to a surface adsorption mechanism since no evidence of a doping process was observed using Rietveld refinement and electron diffraction analyses. Conversely, the presence of Mg2+ ions generated a favorable condition for the nucleation of a new Mg2+-rich DCPD crystal population, presenting smaller crystallite sizes.

Fabrication of self-setting β-tricalcium phosphate granular cement.

Bone defect reconstruction would be greatly improved if β-tricalcium phosphate (β-TCP) granules had the ability to self-set without sacrificing their osteoconductivity potential. This study aimed to identify a method to permit β-TCP self-setting whilst maintaining good osteoconductivity. When mixed with acidic calcium phosphate solution, β-TCP granules were found to readily set, forming a fully interconnected porous structure. On mixing, dicalcium phosphate dihydrate crystals formed on the surface of β-TCP granules, bridging the granules and resulting in the setting reaction. The setting time of the β-TCP granular cement (β-TCP GC) was approximately 1 min and its mechanical strength, in terms of diametral tensile strength, was approximately 0.8 MPa. The β-TCP GC and β-TCP granules both showed the same level of osteoconductivity within rat calvaria bone defects. At 2 and 4 weeks post-implantation, new bone formation was comparable between the two β-TCP based bone substitutes. We conclude that β-TCP GC has excellent potential for use as a cement in bone defect reconstruction. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 800-807, 2018.

Effect of citric acid on setting reaction and tissue response to β-TCP granular cement

We recently reported that when an acidic calcium phosphate solution is mixed with β-tricalcium phosphate (β-TCP) granules, the resulting dicalcium phosphate dihydrate (DCPD) crystals form bridges between the β-TCP granules, creating a set interconnected porous structure in approximately 1 min. Although this self-setting β-TCP granular cement (β-TCPGC) is useful for clinical applications, the short setting time is a key drawback for handling. In this study, the setting time of β-TCPGC was adjusted with the addition of citric acid, which is a known inhibiter of DCPD crystal growth. As the concentration of citric acid in the acidic calcium phosphate solution increased, the amount of DCPD formation in the set β-TCPGC decreased, and the crystal morphology of DCPD became elongated. β-TCPGC prepared with various citric acid concentrations were used as grafting material in rat calvarial bone defects to evaluate bone regeneration in vivo. Four weeks after implantation, no inflammatory reaction and approximately 20% new bone formation were observed, regardless of the presence or absence of citric acid in the liquid phase of β-TCPGC. We concluded, therefore, that citric acid might be a useful retarder of β-TCPGC setting times.

Fabrication of interconnected porous calcite by bridging calcite granules with dicalcium phosphate dihydrate and their histological evaluation.

Interconnected porous calcite has attracted attention as an artificial bone replacement material and as a precursor for the fabrication of carbonate apatite, which is also an artificial bone replacement material. In this study, calcite granules were exposed to acidic calcium phosphate solution, and the feasibility of fabricating interconnected porous calcite using this process was evaluated. No setting reaction was observed under the nonloading condition. In contrast, under loading conditions, calcite granules were bridged with dicalcium phosphate dihydrate crystals, and the calcite granules set into interconnected porous calcite foam. When applied 0.4 MPa of loading pressure during sample preparation, compressive strength of the obtained interconnected porous calcite was ∼1.5 MPa. The exposure of the calcite granules to acidic calcium phosphate solution under loading conditions was the key for the setting reaction to occur. This is because calcite granules cannot contact one another under the nonloading condition because of bubble formation on the surfaces of the calcite granules. The interconnected porous calcite revealed excellent tissue response, and new bone was able to penetrate into the porous calcite 2 weeks after implantation. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part A 104A: 652-658, 2016.

Structural changes during the hydrolysis of dicalcium phosphate dihydrate to octacalcium phosphate and hydroxyapatite

Powders prepared through dicalcium phosphate dihydrate (DCPD) hydrolysis to octacalcium phosphate (OCP) and hydroxyapatite (HA) in an aqueous sodium acetate solution have been characterized by X-ray diffraction. The lattice parameters of the synthesized OCP and HA phases have been determined as functions of holding time at synthesis temperatures of 37 and 60°C. The structure of the HA obtained through hydrolysis at 60°C has been refined, and the distortion of the elements of the crystal lattice of this compound has been assessed in terms of Baur indices. A model has been proposed for the heterogeneous nucleation and growth of the OCP phase on DCPD crystals, in which the structure of these compounds is represented as made up of groups similar in structure to Posner regions.

Crystallization of dicalcium phosphate dihydrate with presence of glutamic acid and arginine at 37 °C.

The formations of non-metabolic stones, bones and teeth were seriously related to the morphology, size and surface reactivity of dicalcium phosphate dihydrate (DCPD). Herein, a facile biomimetic mineralization method with presence of glutamic acid and arginine was employed to fabricate DCPD with well-defined morphology and adjustable crystallite size. In reaction solution containing more arginine, crystallization of DCPD occurred with faster rate of nucleation and higher density of stacked layers due to the generation of more OH(-) ions after hydrolysis of arginine at 37 °C. With addition of fluorescein or acetone, the consumption of OH(-) ions or desolvation reaction of Ca(2+) ions was modulated, which resulted in the fabrication of DCPD with adjustable crystallite sizes and densities of stacked layers. In comparison with fluorescein-loading DCPD, dicalcium phosphate anhydrate was prepared with enhanced photoluminescence properties due to the reduction of self-quenching effect and regular arrangement of encapsulated fluorescein molecules. With addition of more acetone, DCPD was prepared with smaller crystallite size via antisolvent crystallization. The simulated process with addition of amino acids under 37 °C would shed light on the dynamic process of biomineralization for calcium phosphate compounds.

Effect of fluorides (KF and NaF) on the growth of dicalcium phosphate dihydrate (DCPD) crystal

Dicalcium phosphate dihydrate (CaHPO 4·2H 2O, DCPD also known as brushite) is the major component of hard tissues like bone, teeth and a medicine for calcium supply. The effect of sodium fluoride and potassium fluoride on the crystallization of DCPD in sodium meta silicate gel has been studied at room temperature under the physiological pH (7.4). Addition of fluorides reduces the crystal size and the number of crystals grown when compared to pure system. Among the two fluorides, the KF suppresses the crystal formation more drastically than that of NaF. In both the cases, the ‘Ca’ content in the DCPD crystals was found to be less when compared to its pure form. The crystal morphology, elemental composition and properties of the grown crystals were analyzed using SEM-EDAX, powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermal analysis (TG-DSC).

Growth and characterization of hydroxyapatite crystals by hydrothermal method

Hydroxyapatite crystals were grown by hydrothermal method using dicalcium phosphate dihydrate crystals as a starting material. The grown crystals were found to be free from carbonate inclusion. Two distinct morphologies were obtained by following two different growth methods. Controlled slow growth process and rapid growth process results in hexagonal and whisker like morphologies.

Preparation and characterization of dicalcium phosphate dihydrate coating on enamel

A coating of 60–80 μm in thickness had been prepared on the surface of enamel by rapid growth of highly crystalline dicalcium phosphate dihydrate crystal (DCPD). The DCPD coating was formed by conversion of calcium-deficient hydroxyapatite (CDHA) in strong acidic conditions. The characterization of the coating was performed using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). No obvious gap between the coating and the enamel was detected by SEM observation, which suggested that the coating adhered well to the enamel. Analysis of FT-IR and XRD revealed that the coating was a good match to DCPD. Moreover, the mean Vicker hardness number (VHN) of the coating was approximately 125, as measured by a microhardness tester.

Influence of an organic and an inorganic additive on the crystallization of dicalcium phosphate dihydrate

Dicalcium phosphate dihydrate (DCPD) was crystallized by single diffusion method under physiological pH, in the presence of cobalt and malic acid. The morphology, composition and microstructure of the grown crystals were analyzed using EDTA titration, UV–Visible, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic absorption spectroscopy (AAS) and scanning electron microscopy (SEM). These analyses showed that the grown crystals were Co 2+-doped DCPD. The temperature has influenced the dopant entry into DCPD crystals, but the dopant content and temperature were having not much influence on the crystal morphology. In pathological crystallization, the size and morphology are very important since they decide the mode of treatment to adopt. The morphological changes arise when the growth assay is doped with cobalt and malic acid. The effect of malic acid on the crystallization was highly specific, adsorbing on certain crystal faces during growth and producing different morphologies. At higher concentration, the morphology showed a feature frequently encountered in biomineralization, the orientational ordering in [0 0 1], leading to elongated crystals.

Influence of iron and temperature on the crystallization of calcium phosphates at the physiological pH

The effect of iron and temperature on the crystallization of dicalcium phosphate dihydrate (CaHPO 4·2H 2O, DCPD) in agarose was studied at various temperatures (27, 37 and 47 °C) at the physiological pH (7.4) by the single diffusion method. The spherulitic crystals of hydroxyapatite with a diameter of about 3 mm were observed in the presence of Fe at temperature of 47 °C. The spherulites consisted of thin, elongated needlelike crystals. Quantification of the iron incorporated in the crystals was carried out by elemental analysis. The crystals were characterized by XRD, FTIR and SEM techniques.

In vitro aging of a calcium phosphate cement.

Cement samples made of beta-tricalcium phoshate (beta-TCP), phosphoric acid (PA) and water mixtures were incubated in several aqueous solutions to determine their stability over time. The effects of the cement composition and the incubating temperature were investigated in more detail. The cement samples contained mostly dicalcium phosphate dihydrate (DCPD) and remnants of beta-TCP crystals. Depending on the initial cement composition, a certain amount of dicalcium phosphate (DCP) crystals were formed. The larger the initial PA concentration, the larger the DCP amount. After setting, the cement composition was stable for at least 16 days up to 60 degrees C. Above that temperature, the DCPD crystals decomposed into DCP crystals. The latter reaction provoked a decrease of the pH of the incubation solution, phenomenon expected for a cement sample containing an excess of PA. As the cement samples contained an excess of beta-TCP, it was postulated that beta-TCP crystals became so covered by DCP or DCPD crystals during setting that the setting reaction was stopped prematurely. The latter phenomenon gave a good explanation for the low pH values measured in the incubation solutions.

Heterogeneous crystallization of dicalcium phosphate dihydrate on titanium surfaces.

The kinetics of nucleation and crystal growth of dicalcium phosphate dihydrate (DCPD, CaHPO4.2H2O) on titanium powders with different grain sizes have been investigated using the constant composition crystal growth method at 37 degrees C and pH = 5.50. Nucleation is independent of titanium powder size while crystal growth rate is strongly size-dependent. A minimum relative supersaturation ratio, sigma(min), required in the system for a detectable crystal growth rate to occur, taking into account the presence of the foreign substrate in the system, was determined. Based on the kinetic data and on the various characterizations by X-ray photoelectron spectroscopy and by scanning electron microscopy, we propose a crystal growth kinetic equation as a function of two parameters: the size of the substrate and the excess of supersaturation (sigma-sigma(min)) which is squared, indicating a spiral growth mechanism.

In Situ Atomic Force Microscopy Study of the Dissolution Kinetics of Dicalcium Phosphate Dihydrate Crystal in a Physiological Solution

The dissolution kinetics of the (010) face of dicalcium phosphate dihydrate crystals in a physiological solution were investigated by in situ atomic force microscopy. Although many etch pits with 0.75 nm high elementary steps were formed, spiral dissolution was hardly ever observed. Step velocity showed strong dependence on the crystallographic orientation and decreased with decrease of the interstep distance. From the ratio of the step kinetic coefficient to the characteristic diffusion rate, it was concluded that the dissolution process under the present conditions was controlled by detachment of molecules at a step front and surface diffusion.

Dissolution kinetics of dicalcium phosphate dihydrate crystal under the physiological condition

Dissolution kinetics of dicalcium phosphate dihydrate crystal under the physiological condition