Papers by Keyword: Apatite

Abstract: Lead hydroxyapatite (PbHAP, chemical formula Pb₁₀(PO₄)₆(OH)₂) has been synthesized by ceramic (solid-state reaction) and semi-ceramic (precipitation) methods. The samples were prepared through a solid-state reaction conducted at 830 °C for 60 hours, with the y values ranging from 0.95 to 1.00. We have developed and created the most efficient preparation methods. The well-known technique was used - semi-ceramic (precipitation) deposition of lead and hydroxyapatite. For this purpose, several advanced devices were used to obtain an accurate structural structure of lead hydroxyapatite compounds. It has been observed, as in the case of chemical synthesis, that the elements (lead, phosphorus, and oxygen) appear to be distributed homogeneously within the crystals, regardless of the method of composition, which indicates that the samples are homogeneous. More importantly, the "solid-state reaction" method favored a specific composition range, while the "precipitation" method performed well for other composition ranges. The above methods indicate an ideal method, according to the desired structure, that should be developed for lead hydroxyapatite, depending on its composition. This research aims to establish the first steps in developing a new method for preparing lead hydroxyapatite compounds with the desired properties to improve their purity and crystal structure for potential uses in the future.

Abstract: Apatite nanocomposites with graphene (G) or graphene oxide (GO) nanoflakes, as well as with related carbonaceous materials, present promising applications in hard tissue engineering, biomedicine, or drug delivery. Different methodologies have been explored in the last years to prepare apatite-based nanocomposites. Sitting drop vapour diffusion (SDVD) methodology induces the heterogeneous nucleation of biomimetic apatite on the reinforcement material, improving biological properties of the nanocomposites. In this work SDVD was used to prepare G-apatite and GO-apatite nanocomposites. Prior to the SDVD experiments, G flakes were obtained by sonication-assisted liquid-phase exfoliation (LPE) using L-Alanine (L-Aln) as dispersing biomolecule, while a commercial aqueous Graphene Oxide (GO) dispersion was used for the nucleation essays in presence of the same biomolecules. A parallel set of nucleation experiments was performed in presence of Tb³⁺ ions, to endow the nanocomposites of luminescent properties. Characterization by XRD, FTIR, and TEM demonstrated the heterogeneous nucleation of needle-shaped apatite nanocrystals on the surfaces of G and GO flakes. Fluorescence spectroscopy certified the presence of Tb³⁺ ions in the nanocomposites resulting in luminescent materials which can be used in imaging or theragnostic. Finally, in vitro tests with human mesenchymal stem cells revealed excellent cytocompatibility and cell proliferation in presence of the nanocomposites.

Abstract: Self-assembly and mineralization of type I collagen (Col) with nanocrystalline apatite (nAp), by adding a solution of Ca(OH)₂ to a stirred Col-H₃PO₄ solution by fast dripping, allowed the preparation of Col/nAp fibrils with good crystallographic control of the mineral phase. In this work, in addition, we have cross-linked the mineralized fibers by using different reagents, namely glutaraldehyde (GTA), tannic acid (TA), 1-Ethyl-3-(3-dimethyl aminopropyl)-carbodiimide combined with N-Hydroxysuccinimide (EDC/NHS), and genipin (GP), aimed at producing different types of biopolymeric Col/nAp-based drug delivery scaffolds. In parallel, we have investigated two different methods to impregnate the scaffolds with molecules of the cocrystal diclofenac-metformin (DF-MET). The result, when using TA as a crosslinking reagent, shows the sequence of mineralized fibrils impregnation followed by crosslinking leads to maximum cocrystal molecule loading. The impregnated material is expected to be useful in settings with excessive and prolonged inflammation, since they affect negatively the fracture healing/bone repair processes, especially during the early stages of healing.

Abstract: Strontium (Sr) stimulates osteoblast and inhibits osteoclast activities in-vitro and is used clinically as a treatment for osteoporosis. In this research, the effect of Sr substitution on the apatite formation of sol-gel derived bioactive glass (BG) (55.90SiO₂-1.72P₂O₅ -21.67Na₂O - (20.69-x) CaO -x SrO) (x=0, 5 and 8 mol. %) were investigated. The synthesized Sr doped BG samples were treated in Hank's Balanced Salt Solution (HBSS) for 14 days to study the bioactivity. The achieved samples were evaluated by X-ray powder diffraction (XRD) and Scanning electron microscope (SEM). In XRD, the hydroxyapatite (HA) crystalline peak for 8% Sr-BG is less compared with others. When Sr amount is increased to 8%, the low crystalline peaks of HA were detected although the same soaking duration. FTIR spectra supported the delay precipitation of calcium phosphate (CaP), especially for the specimen containing 8% Sr. After 14 days soaking, SEM images confirmed the bioactivity of the synthesized samples by the formation of apatite on the glass surface.

Abstract: Whether silicate-substituted strontium apatite (SrSiP) stimulates osteogenesis on the surface of implants has been evaluated in the present study. Polyether ether ketone (PEEK) disks were coated with a nanocrystalline SrSiP dispersion using CO₂ laser irradiation. At approximately 300°C, the coating layer of SrSiP was tightly adhered to the surface of PEEK disks. The SrSiP-coated PEEK showed excellent bioactive properties when bone marrow-derived mesenchymal stem cells were cultured on the PEEK disks, when compared to the untreated PEEK disks.

Abstract: Anatase-type titanium dioxide oxide layer was formed on the surface of titanium alloy by chemical oxidation. 0.9 um thick anatase was obtained by soaking in a mixed solution of a certain proportion of hydrogen peroxide and hydrochloric acid and then heat treatment. The surface morphology, phase structures and composition of oxide layers were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). Thickness of titania coating was measured by the ball pit gauge. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) was used to detect the change of Ca ion and P ion concentration in solution. The results showed that anatase layers deposited apatite within 4 days accompanying the decrease of pH when soaked in simulated human body fluid (SBF). Ion exchange between the negative ions and calcium ions in SBF is proposed as the mechanism operative to favor the deposition on apatite.

Abstract: B₂O₃ was doped into the oxide ion conductor La_9.33(SiO₄)₆O₂ according to the formula La_9.33+x/3(SiO₄)_6-x(BO₄)_xO₂ where 0 ≤ x ≤ 2. Samples were prepared by solid state reaction; difficulty was experienced in obtaining fully homogenised products at intermediate x, although they were nominally single-phase by X-ray powder diffraction. A small conductivity enhancement was observed at intermediate B content which further illustrates the important role of La vacancies in optimising the conductivity of La silicates with the apatite structure.

Abstract: Phosphogypsum waste, originating from phosphoric acid production from apatite ores, is well known for its high production rate and possible release of sulphate-rich seepage waters. In addition to negative environmental impacts, phosphogypsum waste heaps are also remarkable secondary sources of Rare Earth Elements (REE); in the phosphoric acid production process a majority of REE, occurring in apatite, are precipitated to the phosphogypsum waste. Therefore, a method treating both sulphate-rich waters and recovering REE from phosphogypsum heaps and seepage waters would offer both economic and environmental benefits. In this ongoing study, seepage waters from a phosphogypsum heap are treated with Sulphate Reducing Bacteria (SRB) and ethanol as a substrate. Sulphate is first reduced to hydrogen sulphide, which then precipitates REE as sulphides. The main challenge, low concentration of REE in seepage waters (e.g. 2.87 μg/l La, 5.13 μg/l Ce, 0.67 μg/l Y and 3.32 μg/l Nd), is overcome by utilizing continuous mode, semi-passive and cost effective column apparatus, requiring no agitation and performing both sulphate reduction and REE recovery in a single reactor. The SRB method results in a sulphate reduction rate of 40-80 % (from app. 1400 mg/l to 276-844 mg/l sulphate in the effluent) and efficient REE recovery from seepage water. The concentrate obtained from the column consists of a mixture of anaerobic sludge and precipitated REE, with respective REE concentrations of 202 mg/kg La, 477 mg/kg Ce, 49 mg/kg Y and 295 mg/kg Nd.

Abstract: A high biocompatibility apatite coated titanium (Ti) could be achieved by biomimetic method. The method is beneficial in surface modification by lowering the processing cost and flexibility. However, the bond between apatite and titanium implant is weak. The structure and composition of apatite formed is different from the apatite in bone. The aim of this research was to investigate the effects of heat and alkali treatment on the physical and chemical properties of Ti6Al4V surfaces and to observe the formation of apatite in Dulbecco’s Phosphate Buffered Saline with CaCl2 and MgCl2 (DPBS) solution on the treated Ti6Al4V for medical implants. Ti discs were surface modified by alkali etching using 5M NaOH at temperature 60°C for 24 hours. A stable mechanical structure of sodium titanate layer formed on alkali-treated is consolidating by heat treated at 500°C and 600 °C. Treated samples were then incubated at 37°C into DPBS solution for 3 days. The morphology structure, phase changes and chemical composition were characterized by using Field Emission Scanning Electron Microscopy (FESEM) and X-Ray Powder Diffraction (XRD). The results shows that apatite coating in globular shape, a group of flakes was found on the samples’ surfaces that had been pre-treated with 5M NaOH at temperature 60°C without thermal treatment and thermal treated at 500°C.

Abstract: La₁₀Si_6-2xBi_2xO_27-x (x = 0.22, 0.46 and 0.72) ceramics have been synthesized by the solid-state reaction method. The calcination temperature of La₁₀Si_6-2xBi_2xO_27-x was 900°C for 4 hours and the sintering temperature was 1500°C for 5 hours with the heating and cooling rates of 10°C per minute. Crystal structures of La₁₀Si_6-2xBi_2xO_27-x have been characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Room temperature XRD patterns of La₁₀Si_6-2xBi_2xO_27-x ceramics doped with Bi³⁺ show hexagonal apatite structure with space group P6₃/m as the primary compound with minor appearance of La₂SiO₅ impurity as the secondary compound. As the bismuth oxide content increased the La₂SiO₅ impurity also increased. La₁₀Si_5.56Bi_0.44O_26.78 has the highest bulk density of 5.2 gcm^-3 and good microstructure compared to La₁₀Si_5.08Bi_0.92O_26.54 and La₁₀Si_4.56Bi_1.44O_26.28.