Calcium-deficient Apatite Research Articles

Microstructural Observation of Calcium-Deficient Single Crystal Apatite Fibers and Phase Changes during Heating

Three types of calcium-deficient apatite fibers (Ca-def AF) were synthesized by a homogeneous precipitation method using starting solution with Ca/P ratios of 1.00, 1.50 and 1.67, and then the resulting fibers were characterized by XRD, FT-IR and SEM. Especially, the microstructure including strain and defect of individual Ca-def AF was examined by transmission electron microscopy (TEM). All the resulting Ca-def AFs had a single phase of apatite, and contained carbonate ions. These fibers were of single crystal, and highly strained. However, when Ca-def AFs were heated to higher than 800 °C, they changed to HAp and TCP biphases. The content of the carbonate group in the Ca-def AFs decreased with heating temperature.

Influence of Association Type of Bisphosphonates with Calcium-Deficient Apatite on Drug Release

Influence of Association Type of Bisphosphonates with Calcium-Deficient Apatite on Drug Release

Mineralization of radiation-crosslinked polyvinyl alcohol/polyvinyl pyrrolidone hydrogels

A study of the calcification of the polyvinyl alcohol/polyvinyl pyrrolidone (PVA/PVP) hydrogels during their exposure to a calcium chloride solution or a simulated body fluid has been carried out. On the basis of the experiments, using a two-compartment permeation cell, the diffusion of calcium ions and their subsequent deposition in the hydrogels were elucidated. Steady-batch experiments were also performed to further elaborate the deposition pattern and the types of calcium deposits. It was demonstrated that Fick's second law of diffusion can describe the diffusion of calcium ions through PVA/PVP hydrogels at 310 K. The diffusion coefficient was determined to be (4.4+/-0.1)x10(-10) m2/s and the partition coefficient for the hydrogels was 0.06. Formation of calcium deposits was noticed taking place both on the surface and inside the hydrogels. The deposits formed on the surface have flake morphology, while the deposits inside the hydrogels are more like globular aggregates. Both types of deposits have been characterized as being comprised calcium and hydroxyl ion deficient apatites with chloride ions the most likely substituting species at the hydroxyl sites.

Synthesis of hydroxyapatite nanoparticles using an emulsion liquid membrane system

Hydroxyapatite (HAp) has been synthesized by various methods, such as co-precipitation, sol–gel, and microemulsion. However, particle size, particle size distribution and cost were drawbacks of those techniques. In this study, HAp nanoparticles were prepared by means of emulsion liquid membrane system (ELM) or water-in-oil-in-water system (W/O/W). The aim of the work was to evaluate the preparation of HAp nanoparticles using ELM consisting of Span 20 and Tween 80 as a mixture of biodegradable surfactant and caproic acid as an extractant. The effect of Ca/P ratio, reaction temperature, and calcination temperature on the characteristics of synthesized particles was investigated. The synthesized HAp particles were amorphous calcium deficient apatites. Ca/P molar ratio of the synthesized particle (Ca/P p) increased with increasing initial Ca/P molar ratio (Ca/P i) and reach maximum at Ca/P p of 1.65. We found significant amount of β-TCP in the particles prepared with high initial Ca/P i molar ratio of 2.00 at which the undesired reactions at high Ca 2+ concentration occurred. Increasing of reaction and calcinations temperature resulted in the reduction of surface area. After thermal treatment at temperatures ranged from 450 to 750 °C, the specific surface area reduced from 227 to 58 m 2/g. At temperature of 750 °C, we found that the morphology of microsized particles instead of nanosized ones.

Effect of sodium addition on the preparation of hydroxyapatites and biphasic ceramics

HAP and biphasic ceramics of two different HAP and β-TCP proportions with substituted sodium were prepared through an aqueous precipitation method. The prepared powders were characterized by XRD, thermal analysis, FT-IR and elemental analysis. Sodium was found to incorporate into the apatite structure without showing any significant change in the phase behaviour of the resultant apatites. The substitution of sodium in the calcium deficient apatites tends to form a biphasic mixture of HAP and β-TCP, while the effect of calcination beyond 700 °C and the resultant mixtures were dependent on the initial Ca/P ratios of the precursors. The calculated lattice parameter values for sodium substituted apatites have shown a marginal increase in c-axis values thereby leading to the enlargement of the hexagonal cell volume with respect to the pure HAP prepared under the same experimental conditions. Powders obtained from the present results were stable up to 1200 °C.

Synthesis and thermal stability of potassium substituted hydroxyapatites and hydroxyapatite/β-tricalciumphosphate mixtures

Hydroxyapatite (HAP) and biphasic ceramics of two different HAP and β-tricalcium phosphate (β-TCP) proportions with substituted potassium were prepared through the aqueous precipitation method. The prepared powders were characterized using XRD, FT-IR and elemental analysis. The results have shown that potassium added during the synthesis was found present in the apatite structure even after calcination at 1300 °C without showing any significant change in the phase behaviour of resultant apatites. The substitution of potassium in the calcium deficient apatites was accompanied by the formation of biphasic mixture of HAP and β-TCP ceramics, upon calcination beyond 700 °C and the resultant mixtures were dependent on the initial Ca/P ratios of the precursors. The calculated cell constant values for potassium substituted apatites have shown contraction in a-axis and irregular changes in the c-axis relative to those of pure HAP prepared under the same experimental conditions.

Development of a degradable cement of calcium phosphate and calcium sulfate composite for bone reconstruction

A new type of composite bone cement was prepared and investigated by adding calcium sulfate (CS) to calcium phosphate cement (CPC). This composite cement can be handled as a paste and easily shaped into any contour, which can set within 5–20 min, the setting time largely depending on the liquid–solid (L/S) ratio; adding CS to CPC had little effect on the setting time of the composite cements. No obvious temperature increase and pH change were observed during setting and immersion in simulated body fluid (SBF). The compressive strength of the cement decreased with an increase in the content of CS. The degradation rate of the composite cements increased with time when the CS content was more than 20 wt%. Calcium deficient apatite could form on the surface of the composite cement because the release of calcium into SBF from the dissolution of CS and the apatite of the cement induced the new apatite formation; increasing the content of CS in the composite could improve the bioactivity of the composite cements. The results suggested that composite cement has a reasonable setting time, excellent degradability and suitable mechanical strength and bioactivity, which shows promising prospects for development as a clinical cement.

Synthesis and mechanical behaviour of chlorapatite and chlorapatite/β-TCP composites

Chlorine substituted hydroxyapatite (HAP) and biphasic mixtures (HAP + β-TCP) were prepared through an aqueous precipitation method. Characterization studies using XRD, thermograms, elemental analysis and FT-IR spectra have confirmed the incorporation of added chlorine into the apatite structure forming a solid solution. Substitution of chlorine in the calcium deficient apatites tends to form biphasic mixtures of HAP and β-TCP and the proportions in the formed mixtures were dependent on the deficiency of calcium in the precursors used. The thermal stability of the chlorine substituted apatites was evident up to 1200 °C from the present results. The cell parameters for chlorine substituted apatite powders tend to follow significant expansion with respect to those of stoichiometric HAP, being always smaller than those of the stoichiometric chlorapatite sample. The mechanical properties of the solid solution of chlorapatites have shown promising features when compared to the pure stoichiometric chlorapatite sample.

Calcium‐deficient apatite synthesized by ammonia hydrolysis of dicalcium phosphate dihydrate: Influence of temperature, time, and pressure

In this work, calcium-deficient apatites (CDA) were synthesized by ammonia hydrolysis reaction of dicalcium phosphate dihydrate (DCPD; CaHPO4 x 2 H2O) to obtain biphasic calcium phosphates (BCP) without any extraionic substitution. The influence of three parameters was studied: temperature of the reaction (70 and 100 degrees C), time of the reaction (4 and 18 h), and the pressure (open and closed system). Experiments were made according to a factorial design method (FDM) allowing optimization of the number of samples as well as statistical analysis of results. Moreover, the influence of temperature (until 200 degrees C) was investigated. The crystal size of CDA was determined according to the Scherrer's formula and from Rietveld refinements taking the CDA anisotropy into account. The last method seems to be a reliable method to determine crystallite sizes of CDA, since crystallite sizes of CDA along <00l> and <hk0> directions were accessible. The results describe the hydroxyapatite % (HA%) in BCP by a first-order polynomial equation in the experimental area studied and the HA content was found to increase by raising time and temperature of the reaction. Moreover, the type of reaction system (open/closed vessel) appeared to have little influence on HA%.

Properties of Calcium Phosphate Powder Prepared from Phosphoryl Oligosaccharides of Calcium

The phosphoryl oligosaccharides of calcium (POC), extracted from potato starch, are composed of phosphorus oligosaccharides and calcium ions. Ultrafine calcium phosphate particles, whose main phase was hydroxyapatite (Ca10(PO4)6(OH)2: HAp), could be prepared through the hydrothermal treatment of POC solution at a temperature between 110 and 130°C; X-ray diffraction indicated the crystallinity of HAp in the resulting powder to be poor and similar to that of living bone. The present HAp powder was regarded to be calcium deficient carbonate apatite with the OH- group being partly substituted by a carbonate (CO3 2-) group. The solubility of the resulting powder in dilute hydrochloric acid was higher compared to that of commercially available HAp, suggesting excellent bioabsorbability for the present powder.

Inherent Luminescence of Annealed Biomimetic Apatites

Biomimetic apatite coatings are widely used in orthopaedic applications to provide bioinert material surfaces with bioactive behaviour by means of initiating bone growth at the implant surface. In this study we manufactured biomimetic calcium phosphate coatings consisting of a calcium deficient carbonated apatite by immersing activated titanium platelets into simulated body fluid (SBF). The development of the crystal phases was monitored by X-ray diffractometry (XRD) in addition to Fourier-transform infrared (FT-IR) spectroscopy. After annealing in air up to 600 °C luminescence of the biomimetically derived apatite was observed. The photo-induced emission spectra were recorded in the range from 400-750 nm at excitation wavelengths ranging 238 to 450 nm. A blue (437 nm) and a green (556 nm) emission were found between 200 to 600 °C visually appearing white. The results are discussed in terms of chemical and crystallographic changes in the biomimetic calcium phosphate layer during heat treatment.

Aqueous precipitation method for the formation of Mg-stabilized β-tricalcium phosphate: An X-ray diffraction study

The preparation of magnesium (Mg)-stabilized β-tricalcium phosphate [β-TCP, β-Ca 3(PO 4) 2] was carried out by an aqueous precipitation method and the characterization was performed by powder X-ray diffraction. The transformation of calcium-deficient apatite (def-apatite) into β-TCP occurred in the range of 600–700 °C in the case of Mg substitution, whereas in the absence of Mg the transformation took place at higher temperatures (700–800 °C). The thermal stability of Mg-stabilized β-TCP powders was observed until 1400 °C resulting in higher density values when compared to that of pure β-TCP, which indicated thermal stability only till 1100 °C and comparably lower density values. Addition of Mg to the precursors Ca/P molar ratio = 1.5 resulted in the formation of small amounts of hydroxyapatite [HAP, Ca 10(PO 4) 6(OH) 2]. The calculated values for lattice parameters confirm the stabilization role played by Mg.

Novel phosphate–phosphonate hybrid nanomaterials applied to biology

A new process for preparing oligonucleotide arrays is described that uses surface grafting chemistry which is fundamentally different from the electrostatic adsorption and organic covalent binding methods normally employed. Solid supports are modified with a mixed organic/inorganic zirconium phosphonate monolayer film providing a stable, well-defined interface. Oligonucleotide probes terminated with phosphate are spotted directly to the zirconated surface forming a covalent linkage. Specific binding of terminal phosphate groups with minimal binding of the internal phosphate diesters has been demonstrated. On the other hand, the reaction of a bisphosphonate bone resorption inhibitor (Zoledronate) with calcium deficient apatites (CDAs) was studied as a potential route to local drug delivery systems active against bone resorption disorders. A simple mathematical model of the Zoledronate/CDA interaction was designed that correctly described the adsorption of Zoledronate onto CDAs. The resulting Zoledronate-loaded materials were found to release the drug in different phosphate-containing media, with a satisfactory agreement between experimental data and the values predicted from the model.

Synthesis and characterization of magnesium substituted biphasic mixtures of controlled hydroxyapatite/ β-tricalcium phosphate ratios

The present paper investigates the preparation of magnesium (Mg) substituted biphasic mixtures of different hydroxyapatite (HAP)/ β-tricalcium phosphate ( β-TCP) ratios through aqueous precipitation method. The concentrations of added magnesium (Mg) were varied with the calcium in order to obtain constant (Ca+Mg)/P ratios of 1.67 ranging from 1.62+0.05, 1.58+0.09 and 1.54+0.13, respectively. The as prepared powders were calcined at different temperatures to study the phase behaviour and thermal stability. The powders were characterized by the following analytical techniques: TG–DTA, X-ray diffraction and FT-IR. The results have shown that substitution of Mg in the calcium-deficient apatites resulted in the formation of biphasic mixtures of different HAP/ β-TCP ratios after heating above 700 °C. The ratios of the formation of phase mixtures were dependent on the calcium deficiency in the apatites with the higher deficiency having the strongest impact on the increased formation of β-TCP and the substituted Mg was found to stabilize the β-TCP phase.

In Situ Formation and Characterization of Flourine-Substituted Biphasic Calcium Phosphate Ceramics of Varied F-HAP/β-TCP Ratios

Fluorine substitution on the calcium-deficient apatites resulted in the formation of fluorine-substituted biphasic ceramics of different F-HAP and β-TCP ratios upon calcination at 1200 °C. The higher degree of calcium deficiency in the apatites have made a stronger impact on the increased formation of β-TCP in the biphasic mixtures.

Mechanochemical–hydrothermal synthesis and characterization of fluoridated hydroxyapatite

Fluoridated hydroxyapatite (FHAp) was successfully synthesized from the starting materials of CaCO 3, CaHPO 4·2H 2O, and CaF 2 via a mechanochemical–hydrothermal route. X-ray diffraction, infrared spectroscopy, surface area measurements, and scanning electron microscopy identified the resultant powders as FHAp nanocrystals with the specific surface areas of up to 114.72 m 2/g. The mechanism study revealed that under such mechanochemical–hydrothermal conditions the formation reactions of FHAp were completed in two stages. The starting materials firstly reacted into a poorly crystallized calcium-deficient apatite and the complete incorporation of fluoride ions into apatite occurred in the second stage.

Studies on calcium deficient apatites structure by means of MAS-NMR spectroscopy

The development of synthetic apatites that replicate the features and properties of the contained in natural tissues will help to diminish the misfit between artificial implants and natural hostesses but the structure of these compounds is still under discussion. The variability in Ca/P ratio of calcium deficient apatites has been explained through different models: surface adsorption, lattice substitution and intercrystalline mixtures of hydroxyapatite and octacalcium phosphate. This work investigates which of the models mentioned suits better in a range of samples. Hydroxyapatites obtained by precipitation, by hydrolysis of dicalcium phosphate and calcined samples with Ca/P ratio between 1.50 and 1.77 and specific surface area between 7 and 108 m2/g have been analysed. OCP and surface adsorption models suit better for great SSA particles and low Ca/P ratio while for smaller SSA particles the lattice substitution model is more accurate. SSA also plays the main role when the capacity to absorb substances is studied though their chemistry can not be explained solely in terms of surface reactivity.

Apatite Layer with Serum Protein as a Suitable Scaffold for Growth of Osteoblast-Like Cell

Autograft, allograft, and biomaterials had been developed for bone regeneration. In recent year, a tissue engineering technique has been paid much attention for next generation implant. A problem of bone tissue engineering to be solved is a development of the substrate that is suitable for cell adhesion, proliferation, and differentiation. A biomimic scaffold for tissue culture was proposed, and then a cell response on the scaffold was estimated. The scaffold composed by a calcium deficient apatite with an adsorbed serum protein was formed on a ceramic hydroxyapatite (HAp) and surface-modified titanium by a soaking in cell-culture medium supplemented with fetal bovine serum. Excellent results on cell proliferation and cell adhesion were obtained only on osteoblast-like cells (MC3T3-E1). An actin filament in narrow filopodium of the spindle-shaped MC3T3-E1 cells on the ceramic HAp had a regular course. On the other hand, ends of the actin filament of the widely spread cells on the apatite layer with serum protein were scattering. It was suggested that the scattering of the actin end showed an existence of fibronectin, and then tight adhesion would be obtained by the many focal adhesion. Accordingly, the effectiveness of the biomimic scaffold containing serum protein on cell growth was confirmed.

Electrochemically Deposited Calcium Phosphate Coating on Titanium Alloy Substrates

Plasma-sprayed HA coating combines the strength of the metal and the bioactivity of the HA. However, this method has several disadvantages. Alternatives to the plasma-spray method such as electrochemical deposition (ECD) and biomimetic or precipitation methods are being explored. The purpose of this study was to develop an ECD method for coating Ti alloy substrate with different calcium phosphates (octacalcium phosphate, calcium deficient apatite, carbonatesubstituted apatite, fluoride-substituted apatite). Pairs of Ti6Al4V plates that have been mechanically polished, ultrasonically cleaned, acid etched, rinsed and dried were used as anodes and cathodes. ECD was carried out using programmed pulse time electric fields. Results showed that uniform coating with only the desired calcium phosphate can be obtained using metastable calcium phosphate solutions at different pH and temperature conditions and different electrolyte concentrations. Coating thickness varied with the duration of coating deposition. Crystal size varied with other ECD conditions (e.g., pulse time, current density). This method can be used to obtain uniform coating of the desired calcium phosphate composition at low temperatures (25 to 80oC) on substrates of any type of geometry.

Manipulation of nanoneedle and nanosphere apatite/poly(acrylic acid) nanocomposites

Colloidal apatitic nanosphere of 2-5 nm in diameter was synthesized in the presence of poly(acrylic acid), PAA. PAA, which has long been recognized as an inhibitor in the synthesis of hydroxyapatite, is used as a structure-directing agent for the synthesis of calcium-deficient apatite (CDHA) in this study. Experimental observation suggests a critical amount of the low-molecular-weight PAA, above which morphological evolution of CDHA nanoparticles from needle to sphere was observed. This reveals that the PAA acts as an inhibitor for the growth of CDHA crystals. Further incorporation of PAA of high molecular weight formed a highly optically transparent nanocomposite, even with the nanospherical apatite loading up to 35 wt %, suggesting no agglomeration. This was further justified through transmission electron microscopy (TEM), where the CDHA nanospheres were uniformly distributed in the PAA-CDHA nanocomposites. No interfacial crevices were visually observed, indicating a highly compatible interface between the inorganic CDHA and organic PAA phase.