Nonstoichiometric Apatite Research Articles

Cheminformatics-Based Design and Synthesis of Hydroxyapatite/Collagen Nanocomposites for Biomedical Applications.

This paper presents a novel cheminformatics approach for the design and synthesis of hydroxyapatite/collagen nanocomposites, which have potential biomedical applications in tissue engineering, drug delivery, and orthopedic and dental implants. The nanocomposites are synthesized by the co-precipitation method with different ratios of hydroxyapatite and collagen. Their mechanical, biological, and degradation properties are analyzed using various experimental and computational techniques. Attenuated total reflection-Fourier-transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction unveil the low crystallinity and nanoscale particle size of hydroxyapatite (22.62 nm) and hydroxyapatite/collagen composites (14.81 nm). These findings are substantiated by scanning electron microscopy with energy-dispersive X-ray spectroscopy, confirming the Ca/P ratio between 1.65 and 1.53 and attesting to the formation of non-stoichiometric apatites in all samples, further validated by molecular simulation. The antimicrobial activity of the nanocomposites is evaluated in vitro against several bacterial and fungal strains, demonstrating their medical potential. Additionally, in silico analyses are performed to predict the absorption, distribution, metabolism, and excretion properties and the bioavailability of the collagen samples. This study paves the way for the development of novel biomaterials using chemoinformatics tools and methods, facilitating the optimization of design and synthesis parameters, as well as the prediction of biological outcomes. Future research directions should encompass the investigation of in vivo biocompatibility and bioactivity of the nanocomposites, while exploring further applications and functionalities of these innovative materials.

Tunable corrosion resistance of rare-earth monosilicate to molten calcia-magnesia-aluminosilicate glass by RE-doping strategy

In this work, CMAS corrosion behavior of hot-pressed (Y1-xYbx)2SiO5 ceramics at 1573 K within 32 h has been investigated. The corrosion products contain non-stoichiometric apatite and garnet, which form according to the dissolution-reprecipitation mechanism. With abundant calcia-magnesia-aluminosilicate, the growth rate of apatite layer increases rapidly with prolonging corrosion time, which results in the rapid corrosion especially after 4 h. Furthermore, the measured thickness of apatite layer in (Y1-xYbx)2SiO5 is much lower than the predicted value based on the optical basicity (OB) theory. This work provides a new insight of solid-solutionizing strategy in the resistance of rare-earth monosilicate to CMAS corrosion.

Mechanism of Calcium Incorporation Inside Sol–Gel Silicate Bioactive Glass and the Advantage of Using Ca(OH)2 over Other Calcium Sources

Calcium is an essential component of osteogenesis and is often required for imparting significant bioactivity to synthetic bone substitutes and, in particular, silicate-based materials. However, the mechanism of calcium incorporation inside sol-gel silicates is poorly understood. In this work, we shed light on the determinant parameters for incorporation of calcium into acid-base-catalyzed sol-gel silicates at ambient temperature: increasing the pH above the isoelectric point of silicic acid and the nature of the calcium counterion in the calcium precursor are found to be the key. Based on our proposed reaction sequence, we were able to compare calcium precursors and select an ideal candidate compound for the synthesis of bioactive glasses (BG) and organic-inorganic hybrids at ambient temperature. Reproducible syntheses and gel times of SiO2-CaO BG were obtained using calcium hydroxide (CH), and we demonstrate its usability in the synthesis of promising BG-polycaprolactone hybrid scaffolds. BG and hybrids prepared with CH were able to form nanocrystalline nonstoichiometric apatite in simulated body fluid. The increased reliability of low-temperature syntheses associated with the use of a stable and inexpensive alkaline-earth precursor are major steps toward the translation of calcium silicate hybrids or other alkaline-earth silicates from bench to clinic.

Apatite Coating of Iron Oxide Nanoparticles by Alternate Addition of Calcium and Phosphate Solutions: A Calcium and Carboxylate (Ca-COO) Complex-Mediated Apatite Deposition

Apatite is a biocompatible material widely used to encapsulate iron-oxide nanoparticles (IONPs) for biomedical applications, such as drug-delivery or fluorescent probe agent. Apatite-coated IONPs are commonly fabricated by initially incubating carboxylate-functionalized IONPs in calcium solution and directly adding phosphate solution to initiate apatite precipitation (direct-addition method). Apatite precipitation took place not only on IONPs surface but also in the bulk solution, resulting in apatite-IONPs mixture instead of coated structure. In this study, robust apatite-coated IONPs structure were aimed by modifying steps in direct-addition method. Initially, carboxylate-functionalized IONPs were incubated in calcium solution, physically separated from the incubating calcium solution by external magnet, and then separately reacted with phosphate solution to induce apatite deposition (alternate-addition method). Fourier-transform infrared (FTIR) analysis showed that a calcium solution at a concentration of 0.8 mol/L was required to initiate the formation of the calcium-carboxylate (Ca-COO) complex. The formation of non-stoichiometric apatite was confirmed for IONPs with Ca-COO complex, as evidenced by X-ray diffraction and FTIR analysis. The alternate-addition method produced apatite coating in the form of flake-like structures, which also exhibited strong adhesion to IONPs surface. In contrast, direct-addition method mainly produced agglomerate of apatite particles that weakly associated with IONPs. Both of apatite-coating methods did not alter the magnetic properties of IONPs. The simple modification of reaction steps in the widely used apatite-coating method was demonstrated to be beneficial in producing robust apatite-coated IONPs structure.

Biowaste-Derived Hydroxyapatite for Effective Removal of Reactive Yellow 4 Dye: Equilibrium, Kinetic, and Thermodynamic Studies

This study examines the application of poultry eggshell (PES) as a source of calcium for the synthesis of hydroxyapatite (HA) via annealation. The synthesized powder (poultry eggshell hydroxyapatite (PESHA)) was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), EDAX, and transmission electron microscopy (TEM) analytical techniques. This powder was used for adsorptive removal of the Reactive Yellow 4 (RY4) dye in a batch process. Results from morphological analysis by SEM and TEM revealed that the microstructure of the apatite is made up of needle–rod-like particles with the length of 15–60 nm, breadth of 4–6 nm, and crystallite size of 86.32 nm. EDAX revealed that HA has Ca/P ratio of 1.63, indicating a nonstoichiometric apatite, whereas XRD analysis presented it as a pure monophasic hydroxyapatite powder. Fourier Transform Infrared (FTIR) spectroscopy indicated that the adsorption is due to the electrostatic interaction between the functional groups of the dye and those on the apatite surface. The maximum adsorption capacity (Qmax) of 127.9 mg g–1 was obtained for the adsorption process, whereas the pseudo-first-order model with R2 > 0.99 best described the adsorption mechanism. Furthermore, the thermodynamic studies revealed that the adsorption process was exothermic and spontaneous in nature with ΔH and ΔS values of 120.79 kJ mol–1 and 0.395 kJ mol–1 K–1, respectively. Thus, hydroxyapatite fabricated from the poultry waste of eggshell can be effectively utilized as an excellent nontoxic and cheap adsorbent for the removal of RY4 dye from aqueous medium.

Crystal Chemical Analysis of Nd9.33Si6O26 and Nd8Sr2Si6O26 Apatite Electrolytes Using Aberration-Corrected Scanning Transmission Electron Microscopy and Impedance Spectroscopy

Lanthanoid silicate apatite solid electrolytes contain one-dimensional channels. These materials display substantial oxygen mobility at temperatures lower than conventional zirconia-based ionic conductors because interstitial oxygen displacements, mediated by Ln cation vacancies, have a lower activation energy. For these nonstoichiometric apatites, crystal structure solutions derived from X-ray and neutron powder diffraction yield the average atomic arrangement, but these techniques also average over local lattice disorders. Large apatite single crystals permit the evaluation of oxygen migration anisotropy using impedance spectroscopy and the correlation of this behavior to atomic scale domain formation or defect cluster aggregation if present. Aberration-corrected scanning transmission electron microscopy, in both high angle annular dark field (HAADF) and bright field (BF) modalities, was applied to characterize the local atomic structure of Nd9.33Si6O26 and Nd8Sr2Si6O26 apatite electrolytes. Quantitativ...

Apatite Formation: Why It May Not Work as Planned, and How to Conclusively Identify Apatite Compounds

Calcium phosphate apatites are inorganic compounds encountered in many different mineralized tissues. Bone mineral, for example, is constituted of nanocrystalline nonstoichiometric apatite, and the production of “analogs” through a variety of methods is frequently reported. In another context, the ability of solid surfaces to favor the nucleation and growth of “bone-like” apatite upon immersion in supersaturated fluids such as SFB is commonly used as one evaluation index of the “bioactivity” of such surfaces. Yet, the compounds or deposits obtained are not always thoroughly characterized, and their apatitic nature is sometimes not firmly assessed by appropriate physicochemical analyses. Of particular importance are the “actual” conditions in which the precipitation takes place. The precipitation of a white solid does not automatically indicate the formation of a “bone-like carbonate apatite layer” as is sometimes too hastily concluded: “all that glitters is not gold.” The identification of an apatite phase should be carefully demonstrated by appropriate characterization, preferably using complementary techniques. This review considers the fundamentals of calcium phosphate apatite characterization discussing several techniques: electron microscopy/EDX, XRD, FTIR/Raman spectroscopies, chemical analyses, and solid state NMR. It also underlines frequent problems that should be kept in mind when making “bone-like apatites.”

Modification of silica surface with nonstoichiometric calcium phosphate and its effects on protein adsorption and osteoblast response

Surface modification of silica particle by calcium phosphate (CaP) film using a heterogeneous precipitation method is reported in this study. Surface potential of silica particle was actively changing at 50min of soaking at 37°C. The surface morphological change observed using field emission scanning electron microscopy (FE-SEM) revealed the highly porous structure of the film and formation pattern was well agreed with that of zeta potential. Fourier transform infrared spectroscopy (FTIR) was used to evaluate the chemical composition of the surface of the CaP film. Chemical composition acquired from energy dispersive X-ray spectroscopy (EDX) illustrated that the CaP films consist of calcium and phosphorus and provided the atomic molar ratio of calcium and phosphorus indicating that the CaP films are non-stoichiometric apatites. The specific surface area of the silica particles was increased by ~2.5-fold when the CaP film was formed on the silica particles. Protein adsorption assays demonstrated that the CaP film had a significant effect on interaction with protein characterized in terms of adsorbed mass and surface charge. The adsorption of model proteins, albumin and lysozyme, was reduced in the presence of CaP film. Lysozyme adsorption appeared to be governed by electrostatic attraction, whereas albumin caused gradual decrease in the negativity of surface potential with increase of lysozyme solution concentration. Cell viability assays using human osteoblast MG63 cells confirmed that the film is cytocompatible. This study strengthened our understanding of interaction between protein and CaP and can be applied to surface modification of bone substitutes in granular shapes for the promotion of bone regeneration.

Correlations among mineral components, progressive calcification process and clinical symptoms of calcific tendonitis

To establish the correlations among the mineral components, progressive calcification process and clinical symptoms of calcific tendonitis. The morphology of the calcified deposits on the shoulders of 28 patients with calcific tendonitis was determined by high-resolution ultrasonography. The calcified deposit from each patient was aspirated and determined by the Fourier transform infrared and Raman microspectroscopies. The curve-fitting program was applied to estimate the chemical component in the calcified deposits of calcific tendonitis. The morphology of calcified deposits for 28 patients was classified into four shapes: arc shape (7 patients), fragmented/punctuate shape (4 patients), nodular shape (13 patients) and cystic shape (4 patients). These classified shapes markedly correlated with the pain levels in patients. The infrared spectra of all the calcified deposits for 28 patients were easily classified into three types in the blind study and corresponded to the formative, resting and resorptive phases in the progressive calcification process of calcific tendonitis. With the progressive calcification, the IR wavenumber at 1018 cm(-1) assigned to poorly crystalline, non-stoichiometric apatite for the formative phase was shifted to 1028 cm(-1) for the resting phase and then to 1031 cm(-1) due to matured crystalline stoichiometric apatite for the resorptive phase. The curve-fitted results revealed that calcified deposits in calcific tendonitis were composed of different quantities of A-type and B-type carbonated apatites in the three phases. A significant difference was found in carbonated apatite content among the three phases (P < 0.001). The different quantities of A-type and B-type carbonated apatites determined by vibrational microspectroscopy in calcified deposits were well correlated with those of the four shapes of morphologic classification, with the three phases in the progressive calcification process and with the clinical symptoms of calcific tendonitis.

Fabrication and biocompatibility of porously bioactive scaffold of nonstoichiometric apatite and poly(ε‐caprolactone) nanocomposite

AbstractBioactive nanocomposite of nonstoichiometric apatite (ns‐AP) and poly(ε‐caprolactone) (PCL) was synthesized and its porous scaffold was fabricated. The results show that the hydrophilicity and cell attachment ratio on the composite surface improved with the increase of ns‐AP content in PCL. The composite scaffolds with 60 wt % ns‐AP content contained open and interconnected pores ranging in size from 200 to 500 μm and exhibit a porosity of around 80%. In addition, proliferation of MG63 cells on the composite scaffolds significantly increased with the increase of ns‐AP content, and the level of alkaline phosphatase (ALP) activity and nitric oxide (NO) production of the cells cultured on the composite scaffold were higher than that of PCL at 7 days, revealing that the composite scaffolds had excellent in vitro biocompatibility and bioactivity. The composite scaffolds were implanted into rabbit mandible defects, the results suggest that the introduction of ns‐AP into PCL enhanced the efficiency of new bone formation, and the ns‐AP/PCL composite exhibited in vivo good biocompatibility and osteogenesis. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Fabrication and biocompatibility of nano non-stoichiometric apatite and poly(ε-caprolactone) composite scaffold by using prototyping controlled process

Nano biocomposite scaffolds of non-stoichiometric apatite (ns-AP) and poly(epsilon-caprolactone) (PCL) were prepared by a prototyping controlled process (PCP). The results show that the composite scaffolds with 40 wt% ns-AP contained open and well interconnected pores with a size of 400-500 mum, and exhibited a maximum porosity of 76%. The ns-AP particles were not completely embedded in PCL matrix while exposed on the composite surface, which might be useful for cell attachment and growth. Proliferation of MG(63) cells was significantly better on the composite scaffolds with porosity of 76% than that those with porosity of 53%, indicating that the scaffolds with high porosity facilitated cell growth, and could promote cell proliferation. The composite scaffolds were implanted into rabbit thighbone defects to investigate the in vivo biocompatibility and osteogenesis. Radiological and histological examination confirmed that the new bony tissue had grown easily into the entire composite scaffold. The results suggest that the well-interconnected pores in the scaffolds might encourage cell proliferation, and migration to stimulate cell functions, thus enhancing bone formation in the scaffolds. This study shows that bioactive and biocompatible ns-AP/PCL composite scaffolds have potential applications in bone tissue engineering.

Preparation and characterization of bioactive calcium silicate and poly(ϵ‐caprolactone) nanocomposite for bone tissue regeneration

A novel biocomposite of nanosized calcium silicate (n-CS) and poly(epsilon-caprolactone) (PCL) was successfully fabricated directly using n-CS slurry, not dried n-CS powder, in a solvent-casting method. The in vitro bioactivity of the composite was evaluated by investigating the apatite-forming ability in simulated body fluid. A proliferation assay with mouse L929 fibroblasts was used to test the in vitro biocompatibility. The composition, hydrophilicity, and mechanical properties were also evaluated. Results suggest that the incorporation of n-CS could significantly improve the hydrophilicity, compressive strength, and elastic modulus of n-CS/PCL composites, with the enhancements mainly dependent on n-CS content. The n-CS/PCL composites exhibit excellent in vitro bioactivity, with surface apatite formation for 40% (w/w) n-CS (C40) exceeding that of 20% (w/w) n-CS (C20) at 7 and 14 days. The Ca/P ratios of apatite formed on C20 and C40 surfaces were 1.58 and 1.61, respectively, indicating nonstoichiometric apatite with defective structure. Composites demonstrated significantly better cell attachment and proliferation than that of PCL alone, with C40 demonstrating the best bioactivity. The apatite layers that formed on the composite surfaces facilitated cell attachment (4 h) and proliferation during the early stages (1 and 4 days). Collectively, these results suggest that the incorporation of n-CS produces biocomposites with enhanced bioactivity and biocompatibility.

Preparation and in vitro bioactivity of poly( d,l-lactide) composite containing hydroxyapatite nanocrystals

The nano-sized hydroxyapatite (n-HA) was incorporated into poly( d,l-Lactide) (PDLLA) to form a bioactive and biodegradable composite for application in hard tissue replacement and regeneration. Thin film of PDLLA composite containing 20 mass% of n-HA fillers was successfully developed through integration of solvent co-blending and hot pressing techniques. firstly, n-HA and PDLLA were chemically synthesized, respectively, then mixed together and homogeneously dispersed in N, N-dimethyl formamide(DMF) solvent, finally, the dried blended hybrid containing PDLLA matrix and n-HA fillers was put into the mould and compacted by hot-pressing machine under 8 MPa pressure at 110 °C for 15 min. In vitro studies were conducted using the simulated body fluid(SBF). Composite specimens were soaked in SBF from 1 day to 21 days prior to surface analysis. Results obtained from scanning electron microscopy(SEM) examination, Energy dispersive X-ray detector(EDX) analysis and X-ray diffraction (XRD) analysis showed that a layer of non-stoichiometric apatite formed within 7 days on HA/PDLLA composite surface after its immersion in SBF, demonstrating moderate in vitro bioactivity of n-HA/PDLLA composite, though a moderate rate of apatite formation in SBF was found on initial stage of immersion periods for n-HA/PDLLA composite, compared to the other biomaterial composite. This type of composite film exhibited certain desirable bioactive characteristics, and they are promising bone candidates to develop novel bioactive composites for biomedical application.

Triclinic apatites

Apatites commonly adopt P6(3)/m hexagonal symmetry. More rarely, monoclinic chemical analogues have been recognized, including the biologically significant hydroxyapatite, Ca(10)(PO(4))(6)(OH)(2), but the driving force towards lower symmetry has not been systematically examined. A combination of diffraction observations and ab initio calculations for Ca(10)(AsO(4))(6)F(2) and Ca(10)(VO(4))(6)F(2) show these materials are triclinic P\bar 1 apatites in which the AsO(4) and VO(4) tetrahedra tilt to relieve stress at the metal and metalloid sites to yield reasonable bond-valence sums. An analysis of the triclinic non-stoichiometric apatites La(10 - x)(GeO(4))(6)O(3 - 1.5x) and Ca(10)(PO(4))(6)(OH)(2 - x)O(x/2) confirms this scheme of tetrahedral rotations, while Cd(10)(PO(4))(6)F(2) and Ca(10)(CrO(4))(6)F(2) are predicted to be isostructural. These distortions are in contrast to the better known P112(1)/b monoclinic dimorphs of chloroapatite and hydroxyapatite, where the impetus for symmetry reduction is ordered anion (OH(-) and Cl(-)) displacements which are necessary to obtain acceptable bond lengths. These results are important for designing apatites with specific structural and crystal-chemical characteristics.

Biomimetic deposition of apatite coating on surface-modified NiTi alloy

TiO 2 coatings were prepared on NiTi alloy by heat treatment in air at 300, 400, 600 and 800 °C. The heat-treated NiTi alloy was subsequently immersed in a simulated body fluid for the biomimetic deposition of the apatite layer onto the surface of TiO 2 coating. The apatite coatings as well as the surface oxide layer on NiTi alloy were characterized using scanning electron microscopy equipped with energy dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. Results showed the samples heat-treated at 600 °C produced a layer of anatase and rutile TiO 2 on the surface of NiTi. No TiO 2 was detected on the surface of NiTi after heat treatment at 300 and 400 °C by X-ray diffraction, while rutile was formed on the surface of the 800 °C heat-treated sample. It was found that the 600 °C heat-treated NiTi induced a layer consisted of microcrystalline carbonate containing hydroxyapatite on its surface most effectively, while 300 and 400 °C heat-treated NiTi did not form apatite. This was due to the presence of anatase and/or rutile in the 600 and 800 °C heat-treated NiTi which could provide atomic arrangements in their crystal structures suitable for the epitaxy of apatite crystals, and anatase had better apatite-forming ability than rutile. XPS and Raman results revealed that this apatite layer was a carbonated and non-stoichiometric apatite with Ca/P ratio of 1.53, which was similar to the human bone. The formation of apatite on 600 °C heat-treated NiTi following immersion in SBF for 3 days indicated that the surface modified NiTi possessed excellent bioactivity.

Formate incorporation in the structure of Ca-deficient apatite: Rietveld structure refinement

Two sets of non-stoichiometric apatites (Ca-deficient apatites) were prepared from calcium phosphate solutions by homogeneous precipitation through the hydrolysis of formamide at 95°C. One set of products contained monetite (CaHPO 4) and apatite, whilst the second, with more formamide, contained only apatite. Rietveld whole pattern fitting structure refinements were undertaken on all samples, and chemical analyses, IR and NMR spectroscopy, on the second set of samples. The Ca/P mol ratio was 1.596. Rietveld analysis gave lattice parameters a=9.4729(20) and c=6.8855(9) Å and showed that Ca 2+ ions were lost exclusively from Ca2 sites, and that the PO 4 tetrahedron volume and P–O bonds were 4.4% and 1.4% smaller, respectively, than in hydroxyapatite (OHAp). Formate, HCO 2 −, was clearly visible in the IR and NMR spectra, but the diffraction studies showed it was not present as a separate crystalline phase. Chemical analysis gave 5.8 wt % formate. We propose that the enlarged a-axis compared with OHAp ( a=9.4243(55) Å) and reduced PO 4 dimensions and P occupancy are, respectively, caused by the partial replacement of OH − and PO 4 3− ions in the structure by HCO 2 − ions. These substitutions would parallel the similar known substitutions of CO 3 2− ions in precipitated carbonate apatites.

Fourier transform infrared microspectroscopic investigation of the maturation of nonstoichiometric apatites in mineralized tissues: a horse dentin study

Fourier transform infrared microspectroscopy (FTIRM) was used to study carbonated apatite/collagen interactions and maturation in horse secondary dentin. Unlike human dentin, this model contains no peritubular material around the odontoblastic processes and is thus quite similar to bone in composition, but not subject to tissue turnover. Crystals close to the mineralization front were very immature, showing high HPO 4 and very low CO 3 levels. Carbonate ions were located essentially in very labile, reactive environments, probably on the crystal surface. Removal of some of the HPO 4 ions from crystals during maturation was linked to an increase in total carbonate content. The CO 3 ions in labile environments decreased, probably after incorporation into more organized regions of the lattice. However, this increase of total carbonate content was associated with greater mineral crystallinity, confirming findings in other studies of synthetic apatite maturation in vitro. The good correlation between these results and those of in vitro experiments suggests that crystal maturation is essentially due to physicochemical processes and that the organic matrix controls only crystal size, multiplication, and/or organization.

Computer Modeling and Description of Nonstoichiometric Apatites Cd5−η/2(VO4)3I1−η and Cd5−η/2(PO4)3Br1−η as Modified Chimney–Ladder Structures with Ladder–Ladder and Chimney–Ladder Coupling

Diffraction patterns from apatite-structure compounds Cd5−η/2(TO4)3X1−η with T=P, V and X=Br, I show sheets of diffuse scattering normal to c* at incommensurate l=q (q=1.63 for Cd–V–I apatite and q=1.78 for Cd–P–Br apatite), because the c repeat of the average unit cell is shorter than two X diameters. The equilibrium X..X spacing along c defines the incommensurate periodicity c/q and stoichiometry (1−η)=q/2. The layers show a honeycomb texture for the Cd–V–I apatite, which is condensed into discrete spots for the Cd–P–Br compound. In both phases, X..X repulsions along 〈100〉 force neighboring rods of X atoms out of phase. In the Cd–P–Br phase, additional 〈210〉 attractions drive incipient formation of a rhombohedral superstructure. Average structure site occupancies and the observation of second-order diffuse layers at both l=2q and l=q+2 imply the existence of strong Cd..X in addition to X..X interactions. A three-dimensional computer model was used to produce finite-temperature structure simulations as a function of X..X interactions along 〈001〉, 〈100〉, and 〈210〉, and X..Cd interactions, from which diffraction patterns were calculated. The experimental patterns were fit and approximate values for the interaction energies obtained (hundreds to thousands of joules per mole). It was apparent that lock-in to commensurability caused by the X..Cd term and the formation of nonprimitive incommensurate modulated structures driven by X..X interactions were mutually antagonistic, and the actual structures are compromises between the two.

Vibration spectroscopy study of hydrolyzed precursors for sintering calcium phosphate bio-ceramics

Diffuse reflectance infrared Fourier transform and Raman spectroscopy is applied to investigate the structure of hydrolyzed CaHPO4 · 2H2O (DCPD) processed to non-stoichiometric apatite to be used as starting material for preparing sintered calcium phosphate materials. The spectra of hydrolyzed DCPD samples, obtained under differing experimental conditions, are analyzed to check how the sintered phase composition correlates with the structure of the hydrolyzed precursor. It is shown that the addition of extra Ca2+ ions in the alkaline solution during the process of hydrolyzing affects strongly the degree of disorder in the structure of the hydrolyzed materials, thus increasing the relative amount of hydroxyapatite in the final sintered product. The addition of F− ions to the synthesis mixture strengthens slightly the P-O bonds in the precursors and increases the content of hydroxyapatite phase in the sintered material. As a result bi-phase ceramics of highest content of hydroxyapatite can be produced using both fluorine additives and calcium compensators in the synthesis suspension.

Solid-State Transformation of a Non-Stoichiometric Calcium Deficient Apatite into the Biphasic Calcium Phosphate

Basing on the results of X-ray diffraction (XRD), FTIR, and analysis of references, a reasonable transformation mechanism of a non-stoichiometric calcium deficient apatite (CDA) into a mixture of stoichiometric hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) has been proposed. The mechanism is based on the directed solid-state ionic diffusion that occurs with relatively high rates at temperatures above 1000 oC in crystal lattice of apatites.