Synthesis of a new potassium-substituted lead fluorapatite and its structural characterization

Prismatic crystals of partially potassium substituted lead fluorapatite Pb5.09Ca3.78K1.13(PO4)6F0.87 were grown through a solid-state reaction. The structural study conducted by single-crystal X-ray diffraction revealed that the compound crystallizes in the hexagonal P63/m space group, with unit cell parameters a = b = 9.7190(5) Å, c = 7.1700(6) Å and V = 587.37(7) Å3(Z = 1), as well as final values amounting to R and wR of 0.0309 and 0.0546, respectively. The structural refinement demonstrated that Pb occupies both the (6h) and (4f) structural sites of hexagonal fluorapatite, K occupies the (6h) site, and Ca is placed on the (4f) site. Powder X-ray diffraction study indicated the absence of additional phases or impurities. Chemical analysis using atomic absorption spectrometry and energy-dispersive X-ray spectroscopy confirmed the expected chemical formula. The electrical conductivity measured over a wide temperature range was found to be governed by the ion mobility mechanism in the tunnel along the c axis (probably attributed to the fluorine ion located there). We, therefore, could infer from the analysis of the complex impedance spectra that the electrical conductivity of our apatite depends essentially on the temperature and frequency, which produces a relaxation phenomenon and semiconductor-like behavior. Moreover, the strong absorption in the UV-Visible region was substantiated through studies of the optical properties of the developed sample. Fluorescence spectra exhibited emissions in the orange regions when excited at 375 nm. The findings of the phenomena resulting from the emission and conduction of the apatite in question suggest its potential for application in various technological fields such as photovoltaic cells, optoelectronics, photonics, LED applications, catalysis and batteries.

Novel Remineralizing and Antibiofilm Low-Shrinkage-Stress Nanocomposites to Inhibit Salivary Biofilms and Protect Tooth Structures

Recurrent caries remain a persistent concern, often linked to microleakage and a lack of bioactivity in contemporary dental composites. Our study aims to address this issue by developing a low-shrinkage-stress nanocomposite with antibiofilm and remineralization capabilities, thus countering the progression of recurrent caries. In the present study, we formulated low-shrinkage-stress nanocomposites by combining triethylene glycol divinylbenzyl ether and urethane dimethacrylate, incorporating dimethylaminododecyl methacrylate (DMADDM), along with nanoparticles of calcium fluoride (nCaF2) and nanoparticles of amorphous calcium phosphate (NACP). The biofilm viability, biofilm metabolic activity, lactic acid production, and ion release were evaluated. The novel formulations containing 3% DMADDM exhibited a potent antibiofilm activity, exhibiting a 4-log reduction in the human salivary biofilm CFUs compared to controls (p < 0.001). Additionally, significant reductions were observed in biofilm biomass and lactic acid (p < 0.05). By integrating both 10% NACP and 10% nCaF2 into one formulation, efficient ion release was achieved, yielding concentrations of 3.02 ± 0.21 mmol/L for Ca, 0.5 ± 0.05 mmol/L for P, and 0.37 ± 0.01 mmol/L for F ions. The innovative mixture of DMADDM, NACP, and nCaF2 displayed strong antibiofilm effects on salivary biofilm while concomitantly releasing a significant amount of remineralizing ions. This nanocomposite is a promising dental material with antibiofilm and remineralization capacities, with the potential to reduce polymerization-related microleakage and recurrent caries.

Hydroxyapatite and Fluorapatite in Conservative Dentistry and Oral Implantology-A Review

Calcium phosphate, due to its similarity to the inorganic fraction of mineralized tissues, has played a key role in many areas of medicine, in particular, regenerative medicine and orthopedics. It has also found application in conservative dentistry and dental surgery, in particular, as components of toothpaste and mouth rinse, coatings of dental implants, cements, and bone substitute materials for the restoration of cavities in maxillofacial surgery. In dental applications, the most important role is played by hydroxyapatite and fluorapatite, i.e., calcium phosphates characterized by the highest chemical stability and very low solubility. This paper presents the role of both apatites in dentistry and a review of recent achievements in the field of the application of these materials.

Lead bioaccumulation in Opuntia ficus-indica following foliar or root exposure to lead-bearing apatite

The contamination of edible leafy vegetables by atmospheric heavy metal-bearing particles is a major issue in environmental toxicology. In this study, the uptake of lead by cladodes of Opuntia ficus-indica (Ofi), traditionally used in Mexican cuisine and in livestock fodder, is investigated after a 4-months exposure of either cladodes or roots to synthetic Pb-fluorapatite particles. Atomic Absorption Spectroscopy (AAS) for the quantitative analysis of Pb levels, Scanning Electron Microscopy coupled with Energy Dispersive X-Ray Spectroscopy (SEM-EDX) for the examination of the cladode surface and fate of particles, and Micro-X-ray fluorescence (μXRF) measurements for elemental mapping of Pb in cladodes, were used. The results evidence that foliar contamination may be a major pathway for the transfer of Pb within Ofi cladodes. The stomata, areoles, and cuticle of cladode surface, play an obvious role in the retention and the incorporation of lead-bearing apatite, thus revealing the hazard of eating contaminated cladodes. The possibility of using series of successive cladodes for biomonitoring the atmospheric pollution in arid and semi-arid regions is also rapidly discussed.

Impedance spectroscopy and mechanical response of porous nanophase hydroxyapatite-barium titanate composite

The present study aims to develop the porous nanophase hydroxyapatite (HA)-barium titanate (BT) composite with reasonable mechanical and electrical properties as an electrically-active prosthetic orthopedic implant alternate. The porous samples (densification ~40-70%) with varying amounts of BT (0, 25, 35 and 100 vol.%) in HA were synthesized using optimal spark plasma sintering conditions, which revealed the thermochemical stability between both the phases. The reasonably good combination of functional properties such as compressive [(236.00 ± 44.90)MPa] and flexural [(56.18 ± 5.82) MPa] strengths, AC conductivity [7.62 × 10(-9)(ohm-cm)(-1) at 10 kHz] and relative permittivity [15.20 at 10 kHz] have been achieved with nanostructured HA-25 vol.% BT composite as far as significant sample porosity (~30%) is concerned. Detailed impedance spectroscopic analysis was performed to reveal the electrical microstructure of developed porous samples. The resistance and capacitance values (at 500 °C) of grain (RG, CG) and grain boundary (RGB, CGB) for the porous HA-25 vol.% BT composite are (1.3 × 10(7) ohm, 3.1 × 10(-11)F) and (1.6 × 10(7) ohm, 5.9 × 10(-10)F), respectively. Almost similar value of activation energy (~1-1.5 eV) for grain and grain boundary has been observed for all the samples. The mechanism of conduction is found to be same for porous monolithic HA as well as composite samples. Relaxation spectroscopic analyses suggest that both the localized as well as long range charge carrier translocations are responsible for conduction in these samples. The degree of polarization of porous samples has been assessed by measuring thermally stimulated depolarization current of the poled samples. The depolarization current is observed to depend on the heating rate. The maximum current density, measured for HA-25 vol.% BT sample at a heating rate of 1 °C/min is 2.7 nA/cm(2). Formation of oxygen vacancies due to the reduced atmosphere sintering contribute to the space charge polarization, which is obtained as the dominant polarization mechanism in the developed porous samples. Overall, such integrated functional responses do establish spark plasma sintered porous HA-BaTiO3 nanocomposite as potential alternative for electroactive prosthetic orthopedic implants.

Room temperature gas sensing properties of tubular hydroxyapatite

Tubular hydroxyapatite was synthesized and showed high response, selectivity, good reproducibility and short response and recovery time to ammonia.

Enhanced polarization of hydroxyapatite using the design concept of functionally graded materials with sodium potassium niobate

The present work aims to enhance the electrical activities of hydroxyapatite (HA) without affecting its bioactivity through the development of functionally graded materials (FGM) using biocompatible sodium potassium niobate (NKN) piezoelectrics as an intermediary layer.

Adsorption of phenol from an aqueous solution by selected apatite adsorbents: kinetic process and impact of the surface properties

Batch adsorption experiments were conducted to investigate the removal of phenol from wastewater by addition of three apatites (porous hydroxyapatite (PHAp) and crystalline hydroxyl- (HAp) and fluoroapatite (FAp)). The best performances were obtained with porous hydroxyapatite PHAp, which presented higher adsorption capacities (experimental: 8.2mgg(-1); calculated 9.2mgg(-1)) than HAp and FAp (3-4mgg(-1)). Different models of adsorption were used to describe the kinetics data, to calculate corresponding rate constants and to predict the theoretical capacities of apatite surfaces for phenol adsorption. A mechanism of phenol adsorption associating chemisorption and physisorption processes is presented allowing the discussion of the variations in adsorption behavior between these materials in terms of specific surface area and chemical composition. These data suggest that apatites are promising materials for phenol sorption.

Electrical characterization of hydroxyapatite-based bioceramics

This paper studies the AC conductivity and permittivity of hydroxyapatite (HA)-based ceramics from 0.1 Hz-1 MHz at temperatures from room temperature to 1000 degrees C. HA-based ceramics were prepared either as dense ceramics or in porous form with interconnected porosity and were sintered in either air or water vapour. Samples were thermally cycled to examine the influence of water desorption on AC conductivity and permittivity. Surface-bound water was thought to contribute to conductivity for both dense and porous materials at temperatures below 200 degrees C. At temperatures below 700 degrees C the permittivity and AC conductivity of HA was also influenced by the degree of dehydration and thermal history. At higher temperatures (700-1000 degrees C), bulk ionic conduction was dominant and activation energies were of the order of approximately 2 eV, indicating that hydroxyl ions are responsible for conductivity.

Periodic ab initio study of structural and vibrational features of hexagonal hydroxyapatite Ca10(PO4)6(OH)2

Structural and vibrational features of hexagonal hydroxyapatite HA [Ca(10)(PO(4))(6)(OH)(2), space group P6(3)] are computed ab initio within a periodic approach using the CRYSTAL03 program and the B3LYP hybrid functional with a Gaussian-type basis set of polarized double zeta quality. Experimental lattice parameters and internal coordinates have been fully optimized and the final structure characterized by means of its band structure, density of states and Mulliken analysis. The full B3LYP harmonic vibrational spectrum of HA at Gamma point has also been computed and compares well with the available experimental IR and Raman data. Nevertheless, the presence of one negative frequency in the computed spectrum shows that, within the hexagonal symmetry imposed by the P6(3) group, the structure is a saddle point. This is at variance with the monoclinic structure (under P2(1)/b space group), which has been computed, with the same approach, to be a minimum of 17 kJ mol(-1) (per unit cell) more stable than the corresponding hexagonal HA structure.