B-type Carbonate Substitution Research Articles

Increased Fluorohydroxyapatite across Dentin after Fluoride Iontophoresis

Due to the multiple factors contributing to dentin demineralization and hypersensitivity among individuals, the effectiveness of the available treatments in the long term remains unclear. A recent study reported a simple strategy to potentially mimic natural remineralization with increased crystallization on the enamel caries using fluoride iontophoresis. Such an effect is also ideal for accomplishing dentin biomineralization and structural strength. This study aimed to investigate structural and compositional characteristics and permeability changes after fluoride iontophoresis with different polarities, cathodal iontophoresis (CIP), anodal iontophoresis (AIP), and the control without iontophoresis for the treatment of etched dentin under simulated pulpal pressure. The 24 premolars were divided into 3 groups: CIP, AIP, and topical application of 5% sodium fluoride (NaF) for 40 s. Relative to before treatment, iontophoresis with both polarities significantly decreased the permeability with a visible increase in occluding tubules containing crystal formation and growth throughout the dentin structure and depth. The CIP not only restored the etched dentin surface into a sound condition but also reinforced the dentin across the structure and depth by the synergistic effects of remineralization, increasing crystal formation and transformation toward the more crystalline structure of fluorohydroxyapatite. Following topical treatment, X-ray diffraction analysis and Raman spectra revealed a significant reduction in the crystal size and crystallinity associated with the raised B-type carbonate substitution into the hydroxyapatite compared with that in the sound dentin. The result was the first to reveal the ideal strategy to rapidly restore the etched dentin surface into a sound condition, including reinforcing the dentin across the structure and depth by the synergistic effects of decreasing permeability, increasing crystal formation, and transformation toward the more crystalline structure of fluorohydroxyapatite using the 5% NaF applied with the DC cathode iontophoresis. The technique is noninvasive and simple and deserves further development for clinical application.

Synthesis and characterization of B-type carbonated hydroxyapatite materials: Effect of carbonate content on mechanical strength and in vitro degradation

The current approach in bone tissue engineering requires resorbable biomaterials that enhance bone formation while maintaining sufficient mechanical stability. In this work, the influence of three levels of B-type carbonate substitution in hydroxyapatite lattice on mechanical strength and degradation rate is analyzed. The inverse aqueous route has been selected as a synthesis method of four powders with carbonate substitution between 4 and 6wt.%. X-ray fluorescence (XRF), (C-S)-Analysis, FT-Infrared, X-ray diffraction, DTA-TG and TEM were used to investigate chemical composition, type of substitution, thermal behaviour, and morphology of the powders. Disc shaped specimens were processed by uniaxial pressing and sintering in argon/CO2 flow. Maximum temperatures of thermal treatment between 750 and 850°C were selected to obtain similar porosity levels for the different compositions. The highest carbonate substituted material (5.3wt.%) presented higher compressive strength and dissolution rate than the other materials showing the beneficial effect of B-type substitution in hydroxyapatite materials for bone repair.

Compositional Analysis of the Dental Biomimetic Hybrid Nanomaterials Based on Bioinspired Nonstoichiometric Hydroxyapatite with Small Deviations in the Carbonate Incorporation.

In our paper, we discuss the results of a comprehensive structural-spectroscopic and microscopic analysis of non-stoichiometric nanocrystalline hydroxyapatite (CHAp) with low carbonate anion content and biomimetic hybrid nanomaterials produced on its basis. It was shown that hydroxyapatite nanocrystals synthesized by chemical precipitation and biogenic calcium source mimic the properties of biogenic apatite and also have a morphological organization of "core-shell" type. The "core" of the CHAp nanocrystal is characterized by an overabundance of calcium Ca/P~1.9. Thus "a shell" with thickness of ~3-5 nm is formed from intermediate apatite-like phases where the most probable are octocalcium phosphate, dicalcium phosphate dihydrate and tricalcium phosphate. The multimode model of the Raman profile of samples CHAp and biomimetic composites for spectral region 900-1100 cm-1 proposed in our work has allowed to allocate precise contribution of B-type carbonate substitution, taking into account the presence on a surface of "core" HAp nanocrystal of various third-party intermediate apatite-like phases. The calibration function constructed on the basis of the described model makes it possible to reliably determine small concentrations of carbonate in the structure of hydroxyapatite with the application of Raman express method of diagnostics. The results of our work can inspire researchers to study the processes of induced biomineralization in mineralized tissues of the human body, using non-destructive methods of control with simultaneous analysis of chemical bonding, as well as determining the role of impurity atoms in the functions exhibited by biotissue.

Nano-carbonated hydroxyapatite precipitation from abalone shell (Haliotis asinina) waste as the bioceramics candidate for bone tissue engineering

In this study, nano-carbonated hydroxyapatite (n-CHAp) was successfully synthesized with abalone shells ( Halioitis asinina) as the calcium source using precipitation methods with aging time variations, namely, 0 (without the aging process), 24, and 48 h. Based on an analysis of X-ray diffraction characterization, the spectrum of the n-CHAp is shown for all sample variations in aging time. The results of the calculation of lattice parameter values confirm that the phase formed is the B-type CHAp phase with the increasing crystallinity degree, crystallite size, particle size, and polydispersity which is confirmed by the presence of the CO32- functional group at 1438 cm−1 and 878 cm−1, that is, the B-type carbonate substitution characteristic. The presence of the carbonate ions identified as smaller during the extension of aging time causes the decreasing value of the Ca/P mole ratio but still has a value greater than the HAp Ca/P value (1.67), which is 1.80–1.72. Based on the transmission electron microscopy analysis, the nanometer-size of B-type CHAp particles was successfully obtained. According to the criteria for nanostructures, crystallographic properties, carbonate content, and chemical processes, B-type CHAp samples based on abalone shells ( Halioitis asinina) are one of the candidates in bioceramics for bone tissue engineering applications.

Carbonate substitution in the mineral component of bone: Discriminating the structural changes, simultaneously imposed by carbonate in A and B sites of apatite

The mineral component of bone and other biological calcifications is primarily a carbonate substituted calcium apatite. Integration of carbonate into two sites, substitution for phosphate (B-type carbonate) and substitution for hydroxide (A-type carbonate), influences the crystal properties which relate to the functional properties of bone. In the present work, a series of AB-type carbonated apatites (AB-CAp) having varying A-type and B-type carbonate weight fractions were prepared and analyzed by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), and carbonate analysis. A detailed characterization of A-site and B-site carbonate assignment in the FTIR ν3 region is proposed. The mass fractions of carbonate in A-site and B-site of AB-CAp correlate differently with crystal axis length and crystallite domain size. In this series of samples reduction in crystal domain size correlates only with A-type carbonate which indicates that carbonate in the A-site is more disruptive to the apatite structure than carbonate in the B-site. High temperature methods were required to produce significant A-type carbonation of apatite, indicating a higher energy barrier for the formation of A-type carbonate than for B-type carbonate. This is consistent with the dominance of B-type carbonate substitution in low temperature synthetic and biological apatites.

The relative stabilities of A- and B-type carbonate substitution in apatites synthesized in aqueous solution

AbstractCarbonated calcium apatites doped with a monovalent cation (Li+, Na+, or K+) or a divalent cation (Mg2+ or Zn2+) were prepared in aqueous solution and analysed by powder X-ray diffraction, inductively coupled plasma atomic emission spectroscopy and infrared spectroscopy. The hypothesis that the location of carbonate in the apatite structure, either in place of hydroxide ions in the c-axis channels (A-type substitution) or in place of phosphate (B-type substitution), is affected by the solution energetics of the cation (specifically its enthalpy of hydration) was strengthened by the observation of larger amounts of Atype carbonate in apatites containing the monovalent cations in aqueous solution. It is shown that cations with low negative enthalpies of hydration favour A-type substitution, whereas cations with higher negative hydration enthalpies, such as divalent cations (Mg2+, Zn2+), favour B-type substitution.

Structural effects on incorporated water in carbonated apatites

Confirmation of structural H2O in apatites using 2H solid state NMR spectroscopy has been followed by the determination of the number of molecules of H2O per unit cell (MPUC) using thermal gravimetric analysis (TGA) in 10 series of carbonated apatites [CMApX; M10(PO4)6X2 = MApX] containing the divalent cations (M) calcium, strontium, barium, and lead, and monovalent anions (X) OH−, F−, and Cl−. For many of the series, the average MPUC ranges from ca. 1.5–2.5 and is independent of the concentration (wt%) of carbonate. For other series, the average MPUC is as low as ca. 0.8 or as high as ca. 4.0. We have found for six of the series, i.e., those in which carbonate predominantly (>90%) substitutes for phosphate that the average MPUC correlates with cation and anion atomic radii, with unit-cell axial lengths, and, especially, with our calculations of the void space available in the c -axis channels. We speculate that the volume of the channels in apatites affects the ability of H2O to occupy channel sites. In most low-temperature apatites of the type M10(PO4)6X2 that have been studied, carbonate prefers to substitute for phosphate (B-type substitution) rather than for monovalent anions in channel sites (A-type substitution), although computer simulations indicate that carbonate is more thermodynamically stable in the channel sites rather than the phosphate sites. In apatites with nearly total B-type carbonate substitution, there is no relationship between the number of molecules of H2O in the channels and the weight percent carbonate in the apatite. This lack of correlation would be expected when there is no competition within the channel between H2O and carbonate occupancy. In apatites with greater channel volumes, however, we infer that increased ease of carbonate incorporation in the channels also increases competition between H2O and carbonate. The originally incorporated amount of H2O is diminished to accommodate the thermodynamically favored carbonate ion substitution in the channels. We further speculate that these scenarios are most easily rationalized by incorporation of H2O early in the formation of nascent crystallites of apatites formed in aqueous solution, with carbonate entering the newly formed channels later and, in some cases, with difficulty.

Sol–gel synthesis and characterization of Sr/Mg, Mg/Zn and Sr/Zn co-doped hydroxyapatites

In the present work, a series of hydroxyapatite (HAp) samples co-doped with Sr/Mg, Mg/Zn, and Sr/Zn were synthesized using sol–gel method. The formation of the HAp phase was found to be in the range of 93.0–97.4%. Compared to the undoped HAp, with increasing amount of the co-dopants, a gradual decrease in the values of the crystallinity percent, lattice parameters and volume of the unit cell decrease were observed. B-type carbonate substitution was detected for all the samples. All the samples had the morphology consisting of the nanoparticles.

Synthesis and structure of carbonated barium and lead fluorapatites: Effect of cation size on A-type carbonate substitution

Substitution of carbonate has long been recognized in both synthetic and natural biologically and geologically precipitated forms of hydroxylapatite. Although the predominant substitution mechanism in all of the calcium members of the apatite group formed below 100 °C is substitution of carbonate for phosphate (B-type), small amounts of A-type substitution of carbonate in the channel sites also occur. The present study focuses on the effect of cation size on the type of substitution of carbonate in members of the apatite group. The barium and lead members offer a larger channel site, which potentially could stabilize A-type substitution. A series of carbonated barium and lead fluorapatites were synthesized in aqueous solution and characterized by powder X-ray diffraction, and infrared and Raman spectroscopy. Carbonate content was determined by combustion analysis. Unit-cell parameters derived from X-ray diffraction showed that, as carbonate content increased, the a -axis length decreased and the c -axis increased slightly for carbonated barium fluorapatites (CBaApF), whereas the lengths of both the a - and c -axes increased for CPbApF. The co-occurrence of two sets of peaks in the ν3 carbonate region of the infrared spectra of lead and barium carbonated apatites are strongly suggestive of both A- and B-type carbonate substitution. This interpretation is supported by Rietveld analysis of X-ray powder diffraction data, which confirms the presence of significant, but not dominant, A-type substituted carbonate ions. The variation in cell parameters as a function of carbonate substitution mode is discussed, and it is shown that B-type carbonate substitution need not be accompanied by a decrease in the a -axis in all apatites. The greater amount of A-type carbonate substitution in barium and lead fluorapatites compared to the their calcium homologs can be attributed to: (1) the less negative enthalpies of hydration of the barium and lead ions relative to that of calcium, and/or (2) the greater amount of space available for the relatively large carbonate ions in the channels defined by these large cations. Thus, the substitution modes can be controlled by either thermodynamic or kinetic considerations.

Crystallinity and compositional changes in carbonated apatites: Evidence from 31P solid-state NMR, Raman, and AFM analysis.

Solid-state (magic-angle spinning) NMR spectroscopy is a useful tool for obtaining structural information on bone organic and mineral components and synthetic model minerals at the atomic-level. Raman and 31P NMR spectral parameters were investigated in a series of synthetic B-type carbonated apatites (CAps). Inverse 31P NMR linewidth and inverse Raman PO43- ν1 bandwidth were both correlated with powder XRD c-axis crystallinity over the 0.3-10.3 wt% CO32- range investigated. Comparison with bone powder crystallinities showed agreement with values predicted by NMR and Raman calibration curves. Carbonate content was divided into two domains by the 31P NMR chemical shift frequency and the Raman phosphate ν1 band position. These parameters remain stable except for an abrupt transition at 6.5 wt% carbonate, a composition which corresponds to an average of one carbonate per unit cell. This near-binary distribution of spectroscopic properties was also found in AFM-measured particle sizes and Ca/P molar ratios by elemental analysis. We propose that this transition differentiates between two charge-balancing ion-loss mechanisms as measured by Ca/P ratios. These results define a criterion for spectroscopic characterization of B-type carbonate substitution in apatitic minerals.

Within subject heterogeneity in tissue-level post-yield mechanical and material properties in human trabecular bone

The ability to determine patient-specific mechanical properties of trabecular bone is needed for a reliable estimation of fracture risks. Tissue mechanics and material composition are important factors that contribute to trabecular bone performance, but only a few studies have investigated the post-yield behaviour of human trabecular bone, and limited knowledge for modelling is available about ultimate properties needed.Aim of this paper was to investigate absolute values and deviation of mechanical and material properties of human trabecular bone at the tissue level, in a healthy and osteoporotic donor. A combination of tensile and bending tests of single trabeculae up to failure, μCT measurement of sample geometry and finite element analysis were incorporated to determine mechanical properties. The samples were analysed with Raman spectroscopy to evaluate the material composition. High within-subject variability was found, for both the healthy and osteoporotic donor. Nevertheless, the two donors could be separated by analysing the ultimate strain and post-yield work, as well as two of the material parameters (B-type carbonate substitution ratio and collagen cross-link ratio). It indicates that tissue level properties seem to be relevant also for macroscopic mechanical behaviour. These findings also suggest that the mechanical variability for the inelastic region at the tissue level may be associated with varying material properties, while until yielding occurs our data does not suggest any connection between the mechanical and the investigated material. Finally, a set of mechanical properties of human bone have been reported that are a relevant reference for computational studies and FE analysis.

Pathological Biominerals: Raman and Infrared Studies of Bioapatite Deposits in Human Heart Valves

We studied pathological bioapatite from patients undergoing valvular replacement due to severe aortic and mitral stenosis. Three different types of mineralized human cardiac valves were analyzed. We used infrared and Raman spectroscopy to infer the presence of the carbonate group and evaluate the carbonate substitution in bioapatite structure. The Raman spectra showed that the pathological bioapatite is a B-type "carbonate-apatite" (CO(3)(2-) for PO(4)(3-)) similar to the major mineralized products derived from normal biomineralization processes occurring in the human body. Fourier transform infrared spectra (FT-IR) confirmed the B-type carbonate substitution (CO(3)(2-) for PO(4)(3-)) and showed evidence for the partial replacement of [OH] by [CO(3)] (A-type substitution). The carbonate content of the samples inferred by the spectroscopic measurements is in good agreement with the range of values estimated for biological apatite. On the contrary, the crystal size of the pathological apatite estimated using the percentage area of the component at 1059 cm(-1) of the infrared spectrum is in the nanometer range and it is significantly smaller than the crystal size of normal mineralized tissues.

Effect of temperature on morphology of triethanolamine-assisted synthesized hydroxyapatite nanoparticles

Hydroxyapatite (HA) nanoparticles have been synthesized using ortho-phosphoric acid as the source of PO43− ions, and calcium chloride, suitably complexed with triethanolamine, as the calcium source. The effect of temperature on the morphology of the product has been investigated. The chemical compositions of the samples have been established through Fourier transform infrared spectroscopy. This study reveals that A-type and B-type carbonate substitution are present in HA samples and the concentration of carbonate ions decrease with rise in temperature. Morphological analyses by TEM studies suggest that the average lengths and widths of the needle-shaped particles size increases with temperature up to 50 °C, while a morphological change of the particles from needle to spherical shape is observed on raising the temperature above 50 °C. This change in morphology has been assigned to the apparent solubility of HA at these temperatures, which has been studied by the determination of thermochemical properties of the reaction system by endpoint conductivity and electrophoretic mobility measurements.

Micro-Raman and FTIR studies of synthetic and natural apatites

B-type synthetic carbonate hydroxyapatite (CHAp), natural carbonate fluorapatite (CFAp) and silicon-substituted hydroxyapatite (SiHAp) have been studied by using micro-Raman and infrared (IR) spectroscopy. It was found that while B-type carbonate substitution predominates in carbonate apatites (CAps), A-type is also detected. B-type carbonate substitution causes a broadening of the v 1 P–O stretching mode that is associated with the atomic disorder and lowering of the local symmetry in CAps from C 6 h 2 to C 3h. An ∼15 cm −1 shift of the v 3c PO 4 stretching IR mode was observed upon decarbonation of the CFAp. Such shift which was confirmed by lattice dynamics calculations points out that the P–O bond lengths on the mirror plane increase when carbonate leaves the apatite structure. The present results support the substitution mechanism proposed on the basis of neutron powder diffraction studies of the same samples whereby carbonate substitutes on the mirror plane of the phosphate tetrahedron. The intensity ratios of the v 2 IR CO 3 and v 1 PO 4 bands in samples of various carbonate contents provide a measure of the degree of carbonation for CAps.

Preparation of bone-like composite coating using a modified simulated body fluid with high Ca and P concentrations

A carbonate hydroxyapatite (HA)–collagen (Col) composite coating on NiTi shape memory alloy (SMA) was synthesized by biomimetic growth in modified simulated body fluid (MSBF), which containing high Ca and P ions concentrations. The morphology of composite coating was uniform and porous. The major phase of coating, identified by Infrared Spectroscopy (IR) and X-ray diffraction (XRD), was HA with B-type carbonate substitution. It was also proved by IR results that the collagen was present in the coating. Transmission Electron Microscopy (TEM) and high resolution TEM analysis showed that the c-axis of HA crystals aligned parallel to the longitudinal direction of the collagen fibrils. The relative orientation maintained in the composite coating may benefit the NiTi SMA to achieve better properties in hard tissue replacement.

Ion incorporation into octacalcium phosphate hydrolyzates

There is considerable evidence indicating that biominerals are formed by precipitation of octacalcium phosphate followed by its hydrolysis. Therefore, the hydrolysis of octacalcium phosphate was studied in aqueous solutions of alkali nitrates/chlorides or carbonates. The hydrolysis was accompanied by incorporation of alkali and carbonate ions into apatitic hydrolysis products. These were characterized by chemical analyses, infrared and X-ray diffraction spectroscopy, and solubility measurements. The extent of hydrolysis in carbonate-free media paralleled the extent of ion incorporation: Li > Na > K. The hydrolyses in corresponding carbonate media produced less crystalline apatitic products with B-type carbonate substitution.