Redispersible and stable amorphous calcium phosphate nanoparticles functionalized by an organic bisphosphate

Although much effort has been focused on the preparation of stable amorphous calcium phosphate （ACP） nanoparticles in aqueous solution, the redispersibility and long-term stability of ACP nanoparticles in aqueous solution remains an unresolved problem. In this work, stable colloidal ACPs were prepared by using an organic bisphosphonate （BP） as a sterically hindered agent in aqueous solution. The harvested calcium phosphate nanoparticles were characterized by inductively coupled plasma atomic emission spectrometry （ICP-AES）, Fourier transform infrared （FTIR）, X-ray diffraction （XRD）, dynamic light scattering （DLS） and transmission electron microscopy （TEM）. ICP-AES, FTIR and XRD results suggested the particles were ACP. DLS and TEM results indicated that the size of the ACP nanoparticles were in the range of 60 nm with a spherical morphology. The resulting calcium phosphate nanoparticles retained its amorphous nature in aqueous solution for at least 6 months at room temperature due to the stabilizing effect of the organic bisphosphonate. Moreover, the surface of the ACP nanoparticles adsorbed with the organic bisphosphate used showed good redispersibility and high colloid stability both in organic and aqueous solutions.     

Mechanism of solid-state conversion of non-stoichiometric hydroxyapatite to diphase calcium phosphate

Two non-stoichiometric hydroxyapatites (n-HA) with Ca/P molar ratios of 1.50 and 1.58 and one stoichiometric hydroxyapatite (s-HA) with Ca/P = 1.67 were prepared from chemically pure CaHPO₄·2H₂O and KOH. After sintering at 1050 °C for 4 h, n-HA with Ca/P = 1.50 was transformed into -Ca₃(PO₄)₂, n-HA with Ca/P = 1.58 was converted to diphase calcium phosphate (DCP), while s-HA underwent no chemical transformations. The sintered and unsintered samples of hydroxyapatite were studied by IR spectroscopy, chemical analysis, and X-ray diffraction analysis. The crystallite dimensions were calculated, and a model for the DCP structure was proposed. The mechanism of the solid-state n-HA to DCP conversion was proposed on the basis of this model and published values of the volume diffusion coefficients of the OH^–, Ca²⁺, and PO₄ ^3– ions at 1000 °C.     

The mineral phase in the cuticles of two species of Crustacea consists of magnesium calcite, amorphous calcium carbonate, and amorphous calcium phosphate

The cuticules (shells) of the woodlice Porcellio scaber and Armadillidium vulgare were analysed with respect to their content of inorganic material. It was found that the cuticles consist of crystalline magnesium calcite, amorphous calcium carbonate (ACC), and amorphous calcium phosphate (ACP), besides small amounts of water and an organic matrix. It is concluded that the cuticle, which constitutes a mineralized protective organ, is chemically adapted to the biological requirements by this combination of different materials.     

Multifunctional magnetic calcium phosphate nanoparticles for targeted platin delivery

Magnetic mesoporous amorphous calcium phosphate nanoparticles with a size of 62 nm and abundant -COOH groups on the surface have been prepared by a simple method. The particles show excellent aqueous dispersion stability in physiological pH without any deterioration in hydrodynamic size and zetapotential. By virtue of the carboxylate groups on the surface, the platinum pharmacophore cis-diaquadiamine platinum(ii), folic acid and rhodamine isothiocyanate were conjugated on these magnetic calcium phosphate nanoparticles. The cytotoxicity and internalization efficiency of these nanocarriers have been evaluated on folate receptor overexpressed HeLa cells. These drug loaded nanoagents exhibit elevated cytotoxicity and induce apoptosis in HeLa cells.     

Entrapment of organic fluorophores in calcium phosphate nanoparticles with slow release

Two organic fluorophores, fluorescein (F) and rhodamine B (Rd), were entrapped in calcium phosphate nanoparticles. The as-obtained nanoparticles can be used for biological release applications. For this aim, calcium phosphate nanoparticles were synthesized using the precipitation method. Structural analysis of these nanoparticles was performed using XRD, FTIR, and Raman spectroscopy, confirming that the synthesized nanoparticles were hydroxyapatite. TEM and SEM analyses demonstrated that these nanoparticles had a size of 20 nm and a well-defined morphology. F and Rd (about 0.5 wt.%) were entrapped in these nanoparticles and their release, as a function of time, was studied via UV-Vis spectroscopy. The obtained results showed that the release of both fluorophores was progressive over time. The trapping efficiencies of the fluorophores were 67.15% and 90.76% for F and Rd, respectively.     

Continuous preparation of functionalised calcium phosphate nanoparticles with adjustable crystallinity

Calcium phosphate nanoparticles can be prepared in almost uniform size and shape by a continuous precipitation process that also allows their functionalisation by organic molecules (DNA, surfactants).     

Characterization of calcium hydroxyapatite polycrystalline nanoparticles by capillary zone electrophoresis and scanning electron microscopy

A systematic study of factors affecting the parameters of the electrophoretic separation of synthetic nanocrystals of calcium hydroxyapatite is performed. Data of capillary zone electrophoresis and scanning electron microscopy are compared. Optimal conditions for the determination of calcium hydroxyapatite by capillary zone electrophoresis are selected. It is shown that calcium hydroxyapatite nanoparticles are polydisperse; the nanostructures exist in a variety of clusters and floccules with characteristic sizes, which is confirmed by the coinciding data of capillary zone electrophoresis and scanning electron microscopy. A linear dependence of the normalized total area of calcium hydroxyapatite nanoparticles on their concentration in suspension is obtained.     

Light scattering study on the size and structure of calcium phosphate/hydroxyapatite flocs formed in sugar solutions

The formation, flocculation and sedimentation of calcium phosphate particles are among the main physico-chemical reactions that occur during the clarification of cane sugar juice. The mechanisms through which processes occur in juice clarification are still poorly understood. This study (being part of a comprehensive investigation to unravel these mechanisms) reports on the size and structure of calcium phosphate particles and aggregates in water and sugar solutions at 20 degrees C using the small angle laser light scattering technique. The average size of the primary calcium phosphate particles was in the range 10.4+/-1.1 microm to 17.5+/-1.2 microm and the scattering exponents, which describe the structure of the calcium phosphate flocs, varied from 1.97 to 2.76. The flocs formed without flocculant are more compact in water than those formed in sugar solution. The compactness of the flocs was also affected by pH of the solution. This effect has been explained by considering the electrical double layer phenomenon.     

Mediator-template assembly of nanoparticles

The ability to construct size- and shape-controllable architectures using nanoparticles as building blocks is essential for the exploration of nanoparticle-structured properties. This paper reports findings of an investigation of a mediator-template strategy for the size-controllable assembly of nanoparticles. This strategy explores multidentate thioether ligands as molecular mediators and tetraalkylammonium-capped gold nanoparticles (5 nm) as templates toward the preparation of size-controllable and monodispersed spherical assemblies ( approximately 20-300-nm diameters). The combination of the mediation force of the multidentate thioether and the hydrophobic force of the tetraalkylammonium template establishes the interparticle linkage and stability. The morphological properties of the spherical assemblies have been characterized using TEM, AFM, and SAXS techniques. The finding of the soft-hard nature of the nanoparticle assemblies and their interactions with contacting substrates could form the basis of a new strategy for manipulating nanoscale linkages between nanoparticle assemblies, soldering nanoelectronics, and constructing nanosensor devices. The intriguing light scattering and optical absorption properties in response to assembly, disassembly, sizing, and interparticle spacing parameters have been characterized by dynamic light scattering and spectrophotometric measurements. The discovery of the controlled disassembly into individual nanoparticles and the size regulation by a third capping component could form the basis for applications in controlled drug delivery. The fundamental basis for the mediator-template strategy as a versatile assembly technique is further discussed in terms of experimental and theoretical correlations of the morphological and optical properties.     

Peroxo derivatives of hydroxyapatite and calcium hydrophosphate

Hydroxyapatite and calcium hydrophosphate peroxo solvates were synthesized and characterized by IR spectroscopy, powder X-ray diffraction, and TGA to be used as biocompatible and antibacterial medicaments in manufacturing calcium phosphate bioceramics for implantations in orthopedics and dentistry. A wide range of hydrogen peroxide percentages in stable mixtures of mCa₅(PO₄)₃(OH) + nCaHPO₄ · H₂O₂ · H₂O (ranging from 0.5 to 18%) allows composites to be prepared with a tailored active oxygen content.     

Bio-approach synthesis of nanosilver impregnation on calcium hydroxyapatite by biological activated ammonia from urinary waste

A novel biological approach is attempted to convert the human urinary waste into a well-designed bionanomaterial. In the present study, biological activated ammonia gas (NH_3(g)) mediated synthesis of hydroxyapatite material (B-HAp) and then impregnation of silver nanoparticles (AgNPs) on the B-HAp material surface was performed by photoreduction method and was followed by an evaluation of its antibacterial activity and 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. X-ray diffraction spectroscopy (XRD) and Field emission-scanning electron microscopy (FE-SEM) were engaged to analyze the synthesized materials. Analytical studies revealed the morphology of the crystalline B-HAp synthesized by biologically activated NH_3(g) as spherical shaped with AgNPs impregnated on over it. Atomic Absorption Spectrometers (AAS) estimated 2–7 ppm of Ag⁺ ion were released from the 100 ppm of Ag concentration was impregnated with B-HAp material (B-HAp-Ag-10). It was also found to be an excellent performance of antibacterial activity against Pseudomonas sp, E.coli and S. aureus. The cell- material interaction study of the thus synthesised B-HAp-Ag-10 was found to exhibit a minimal cytotoxicity level when incorporated in MG63 osteosarcoma cell lines, thus confirming the prospective biological application of our material in the biomedical field.     

Sodium and carbonate distribution in substituted calcium hydroxyapatite

Hydroxyapatites containing sodium and carbonate are prepared according to a double decomposition method. Two samples have been investigated by IR absorption spectroscopy and X-ray powder pattern fitting methods. Results confirm that both compounds pertain to the apatite family crystallising in a hexagonal system, space group P6₃/m. The cell parameters of the lower carbonate content apatite are a=9.3892(4) and c=6.9019(3) Å, while those of the higher one are a=9.3249(1) and c=6.9213(1) Å. Occupancy factors show that sodium is localised mainly in a 6h cationic site. Furthermore, carbonate ions occupy phosphate sites leading to a B-type carbonate apatite. These simultaneous substitutions affect the OH⁻ position in the channel, as well as the metaloxygen interatomic distances. The substitution mechanism can be described using two of the six known elementary mechanisms.     

Isolation of calcium phosphate crystals from complex biological fluids using bisphosphonate-modified superparamagnetic beads

The surface of superparamagnetic magnetic beads was modified with bisphosphonates to selectively capture calcium phosphate crystals from complex biological fluids (i.e. synovial fluid).     

Directed assembly of gold nanoparticles

As a complement to common “top–down” lithography techniques, “bottom–up” assembly techniques are emerging as promising tools to build nanoscale structures in a predictable way. Gold nanoparticles that are stable and relatively easy to synthesize are important building blocks in many such structures due to their useful optical and electronic properties. Programmed assembly of gold nanoparticles in one, two, and three dimensions is therefore of large interest. This review focuses on the progress from the last three years in the field of directed gold nanoparticle and nanorod assembly using, for example, DNA or specific chemical interactions as template.     

DNA-controlled assembly of soft nanoparticles

Immobilization of DNA (encoding) on solid nanoparticles requires surface chemistry, which is well established for gold surfaces but often tedious and not generally applicable for many other inorganic surface materials. While substantial effort has been devoted to expanding surface chemistry techniques for solid nanoparticles, considerably less attention has been given to the development of noncovalent attachment of DNA to soft nanoparticles, like liposomes. Here we report a DNA-controlled assembly of liposomes in solution and on solid supported membranes, this process displays remarkably sharp thermal transitions from an assembled to a disassembled state, allowing application of DNA-controlled liposome assembly for the detection of polynucleotides (e.g., DNA) with single mismatch discrimination power. The method is based on a single DNA strand (contains two lipid membrane anchors), which is able to noncovalently attach to a liposome surface. This design enables detection of biological polynucleotide targets as the complementary strand can be unmodified DNA and RNA strands.     

Structural characterization and thermal behaviour of biological hydroxyapatite

Thermal study and structural characterization of biological hydroxyapatite (HA) samples were done as well as their comparison with commercial and synthetic samples in this study. The X-ray micro analyser shows that all three samples of human teeth (HT1–HT3) contain two types of HA structures with different crystallite sizes, unlike sample of bovine thigh-bone (BTB). The bone sample was composed only of one HA phase with varied porosity. The molar Ca/P ratio in biological samples was lower compared to theoretical ratio for pure HA; moreover, in the case of teeth, Ca/P ratio varyies between the centre and the periphery of the cross-sectional samples. Thermogravimetry of the biological samples showed mass decreases—three regions for the bone and four regions for the teeth. In comparison, commercial HA has only two-step weight loss and synthetic HA three-step weight loss. After the calcination up to 1280 °C all the samples of teeth transformed into whitlockite, β-(Ca,Mg)₃(PO₄)₂ (98 wt%) and 2 wt% HA. Besides, HT3 contained further trace amount of hilgenstockite (HIL, Ca₄P₂O₉). The sample BTB partly transited from natural HA into HIL (6 wt%) and lime, CaO (14 wt%). X-ray powder diffraction (XRD) proved occurrence of HIL (9 wt%) beside stability part HA (91 wt%) in the commercial HA after thermal treatment but the synthetic HA composed from Ca₃(PO₄)₂ (74 wt%) and HA (26 wt%).