Composites based on Gluconacetobacter xylinus bacterial cellulose and calcium phosphates and their dielectric properties

Dielectric properties a Gluconacetobacter xylinus bacterial cellulose and its composites with calcium phosphates were studied and used to analyze structural changes in a matrix polymer upon its mechanical treatment and introduction of a mineral fi ller. It was found that, when composites are formed, the ratio between amorphous and crystalline regions is disturbed in the cellulose matrix.     

Formation of calcium phosphates in gelatin with a novel diffusion system

The present paper demonstrated a novel and simple diffusion system to precipitate calcium phosphates in gelatin gel. In this system, a gelatin cup was specially used as the membrane separating reservoirs of calcium and phosphate ions. Relative to the conventional diffusion system, the novel one in our experiment decreased the time required for the deposition from 5-7 days to 20 h and increased the amount of the precipitated mineral phases significantly. The influence of pH values and concentrations of calcium and phosphate solutions buffered with Tris-HCl and NaOH, respectively, was investigated. The results showed that precipitation of the mineral phase at low pH values (7 for calcium and 11 for phosphate) and concentrations (200 mM for calcium and 15 mM for phosphate) resulted in the formation of plate-like octacalcium phosphate (OCP) crystals. With increasing the pH values of calcium and phosphate solutions to 8 and 12, respectively, spherical amorphous calcium phosphate (ACP) particles were obtained uniquely. Furthermore, flower-like hydroxyapatite (HAP) aggregates composed of many nano-sized needles were formed from the solutions with high pH values (8 for calcium and 12 for phosphate) and concentrations (500 mM for calcium and 37.5 mM for phosphate). The novel diffusion system is proposed to play an important role in both studying the process of biological mineralization and synthesizing calcium phosphates in different forms.     

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.     

Nanoscale Confinement Controls the Crystallization of Calcium Phosphate: Relevance to Bone Formation

A key feature of biomineralization processes is that they take place within confined volumes, in which the local environment can have significant effects on mineral formation. Herein, we investigate the influence of confinement on the formation mechanism and structure of calcium phosphate (CaP). This is of particular relevance to the formation of dentine and bone, structures of which are based on highly mineralized collagen fibrils. CaP was precipitated within 25–300 nm diameter, cylindrical pores of track etched and anodised alumina membranes under physiological conditions, in which this system enables systematic study of the effects of the pore size in the absence of a structural match between the matrix and the growing crystals. Our results show that the main products were polycrystalline hydroxapatite (HAP) rods, together with some single crystal octacalcium phosphate (OCP) rods. Notably, we demonstrate that these were generated though an intermediate amorphous calcium phosphate (ACP) phase, and that ACP is significantly stabilised in confinement. This effect may have significance to the mineralization of bone, which can occur through a transient ACP phase. We also show that orientation of the HAP comparable, or even superior to that seen in bone can be achieved through confinement effects alone. Although this simple experimental system cannot be considered, a direct mimic of the in vivo formation of ultrathin HAP platelets within collagen fibrils, our results show that the effects of physical confinement should not be neglected when considering the mechanisms of formation of structures, such as bones and teeth.     

Silver as a test element for Zeeman furnace AAS

Silver was studied as a candidate element to test the stability of graphite furnace performance. Several problems were found, but when these were controlled the instrumental performance was quite stable and reproducible. When the Ag line at 328.1 nm was used with a matrix containing phosphate and a metal, a small spectral interference was produced when Zeeman background correction was used. The interference appeared to result from Zeeman splitting of PO bands that overlapped the 328.1-nm line from the source. Since phosphate had been recommended as a matrix modifier for Ag, this could be a serious problem. Both Pd and Cu are shown to be preferable to phosphate as a matrix modifier for Ag, especially with Zeeman corrected instruments.     

Raman spectroscopic of osteoporosis model in mouse tibia in vivo

In this work, we correlate Raman spectroscopy in vivo which is performed in healthy bone tibia, 3-month-old mice with osteoporotic bone, within two groups: OVX (ovariectomized) and sham (lumbar access, no ovariectomy group control). Laser beam was applied directly in a punch of skin in the distal medial part of tibia. To access bone quality, we calculate mineral/matrix ratio, relative lipid and proteoglycan content as well as the crystallinity using normalized spectrum within the integrated area method. The variables obtained for bone quality were statistically verify by ANOVA and tested for normality, where differences were considered to be significant for P < 0.05. In osteoporotic bone (OVX) we found a decreasing ratio between mineral to matrix and relative proteoglycan content, followed by a relative increasing lipid content when comparing with healthy bone (Sham) with statistical significance. The crystallinity showed higher value for OVX group but without statistical significance. Our Confocal Raman Spectroscopy provides a well-controlled environment to differentiate osteoporotic bone from healthy bone by decreasing calcium and glycosaminoglycans and increasing the amount of lipids in the cortical tibia of the mouse in vivo.     

Mineralization of Phosphorylated Fish Skin Collagen/Mangosteen Scaffolds as Potential Materials for Bone Tissue Regeneration

In this study, a potential hard tissue substitute was mimicked using collagen/mangosteen porous scaffolds. Collagen was extracted from Tilapia fish skin and mangosteen from the waste peel of the respective fruit. Sodium trimetaphosphate was used for the phosphorylation of these scaffolds to improve the nucleation sites for the mineralization process. Phosphate groups were incorporated in the collagen structure as confirmed by their attenuated total reflection Fourier transform infrared (ATR-FTIR) bands. The phosphorylation and mangosteen addition increased the thermal stability of the collagen triple helix structure, as demonstrated by differential scanning calorimetry (DSC) and thermogravimetry (TGA) characterizations. Mineralization was successfully achieved, and the presence of calcium phosphate was visualized by scanning electron microscopy (SEM). Nevertheless, the porous structure was maintained, which is an essential characteristic for the desired application. The deposited mineral was amorphous calcium phosphate, as confirmed by energy dispersive X-ray spectroscopy (EDX) results.     

空心纳米磷酸钙载药体系的制备与表征

非离子表面活性剂Tween 80和PEG 6000在水溶液中以一定的比例混合可形成稳定的类磷脂囊泡结构,这些囊泡可以作为模板来合成磷酸钙纳米空球颗粒。所制备的磷酸钙材料的结构和形貌通过TEM,SEM,FTIR,XRD进行了表征,是尺寸为100～150 nm左右的无定形磷酸钙空心颗粒。磷酸钙具有良好的生物相容性,因此这些具有空心结构特征的磷酸钙可发展为理想的载药体系。我们以牛血清蛋白(BSA)为模型体系研究了材料的载药和释放性能,发现所获得的空心纳米磷酸钙不仅具有良好的蛋白质负载量而且还具有优异的可释放性,明显优于传统的羟基磷灰石体系。     

骨及生物材料中的纳米磷酸钙

纳米磷酸钙在自然界骨组织的形成过程中起到了关键作用。尽管骨的类型有所不同,但在其初级结构中的无机成分都是纳米磷酸钙。纳米磷酸钙结构能够给予骨良好的机械性能和生物学活性。在生物体中,无机纳米磷酸钙在有机基质的调控下能定向自组装成特定的生物矿物。体外细胞实验显示小尺寸纳米羟基磷灰石更能促进骨髓基质干细胞的增殖,而同尺寸的结晶型纳米磷酸钙则比无定形磷酸钙更能利于干细胞分化。鉴于纳米磷酸钙具有很好的生物相容性和骨诱导性,可以发展成为理想的生物材料常用于骨组织工程和生物医学。     

Separate K-line contributions to fluorescence enhancement in electron probe microanalysis

The behaviour of the fluorescence enhancement correction factor in electron probe microanalysis, as a function of incident electron energy and take-off angle, is assessed for different binary samples in a wide range of compositions. Monte Carlo simulations are employed to validate Reed's correction algorithm [S.J.B. Reed, Characteristic fluorescence corrections in electron-probe microanalysis, Br. J. Appl. Phys. 16 (1965) 913-926], by means of estimating the primary excited radiation volume and the volume corresponding to secondary fluorescence generation. Then, Reed's expression for the fluorescence enhancement has been modified to account for Kα and Kβ line contributions separately. It is clearly shown that in certain cases the assignment of all fluorescent contribution to the Kα lines may be inadequate, particularly when trace element analysis imposes an accurate determination of elemental concentrations.     

骨及生物材料中的纳米磷酸钙

纳米磷酸钙在自然界骨组织的形成过程中起到了关键作用。尽管骨的类型有所不同,但在其初级结构中的无机成分都是纳米磷酸钙。纳米磷酸钙结构能够给予骨良好的机械性能和生物学活性。在生物体中,无机纳米磷酸钙在有机基质的调控下能定向自组装成特定的生物矿物。体外细胞实验显示小尺寸纳米羟基磷灰石更能促进骨髓基质干细胞的增殖,而同尺寸的结晶型纳米磷酸钙则比无定形磷酸钙更能利于干细胞分化。鉴于纳米磷酸钙具有很好的生物相容性和骨诱导性,可以发展成为理想的生物材料常用于骨组织工程和生物医学。     

Chemical stability of ZnO nanostructures in simulated physiological environments and its application in determining polar directions

The in vitro chemical stability and etching of ZnO nanostructures in simulated physiological solution (SPS) were studied using electron microscopy. Calcium hydrogen phosphate thin layers were observed to be uniformly deposited on the surfaces of ZnO nanomaterials in SPS. Electron diffraction and high-resolution transmission electron microscopy revealed that the calcium hydrogen phosphate layers were amorphous and had excellent interfacial contact with the nanocrystals. ZnO nanostructures fabricated by thermal evaporation were found to survive much longer in SPS than those fabricated using a hydrothermal solution method. The shapes of the voids formed in the ZnO nanostructures by the etching in SPS can be used to deduce the polar directions of ZnO nanostructures.     

Kinetic Aspect of Thermal Decomposition of Natural Phosphate and its Kerogen. Influence of heating rate and mineral matter

The natural phosphate and its demineralization products from Moroccan deposit were pyrolysed in a thermogravimetric analyser (TG) to examine the influence of the heating rate and mineral matter on their thermal decomposition. The heating rates investigated in the TG were 5–100°C min⁻¹ to final temperature of 1200°C. The integral method was used in the analysis of the TG to determine the kinetic parameters. It has been found that for the natural phosphate and corresponding kerogen analysed in the TG, the increase of the heating rate shifts the maximum rate loss to higher temperature. A first order reaction was found to be adequate for pyrolysis in the range 150–600°C which was attributed to kerogen decomposition. In addition, the results indicate that the removal of mineral matter affected the kinetic parameters found for kerogen in the natural phosphate. This revised version was published online in August 2006 with corrections to the Cover Date.     

Intercalation of n-alkyltrimethylammonium ions into layered calcium octyl phosphates thermally treated in vacuo

Layered calcium octyl phosphate (CH3(CH2)7OPO3Ca.1.6H2O: CaOP), which is composed of a multilayer alternating bilayer of octyl phosphates and a dicalcium phosphate dihydrate (DCPD)-like phase, was thermally treated in vacuo and the intercalation of n-alkyltrimethylammonium ions into the materials was examined. The octyl groups in the layer were eliminated by outgassing above 250 degrees C to give the amorphous calcium phosphates. Further, the specific surface area was steeply increased and mesopores with a diameter of ca. 2.0 nm were formed. IR results indicated that the surface P-OH groups were generated by outgassing at 250 degrees C. When the CaOP outgassed at 250 degrees C was treated with n-alkyltrimethylammonium ion solutions (carbon number of alkyl group, n=14-18), three XRD peaks reappeared below 2theta=15 degrees and the d-spacing ratio of these peaks was 1:1/2:1/3. These facts indicate that the n-alkyltrimethylammonium ions were intercalated into the amorphous calcium phosphate phases.     

Use of polyamino acid analogs of biomineral proteins in dispersion of inorganic particulates important to water treatment

Synthetic polyamino acids (peptides) based on the structure and activity of matrix proteins isolated from oyster shell and other biomineral structures have been identified for use in the prevention of mineral scaling. Matrix proteins are polyanionic and are thought to act as regulators of crystallization during the development of skeletal and other mineral structures. These proteins and their synthetic analogs also contain hydrophobic regions that may enhance their surface-active properties. The dispersion activity of a variety of polyamino acids that are matrix protein analogs has been evaluated in bench-top tests using inorganic mineral particles.

Dispersion activities were measured using particles of iron oxide, kaolin, calcium carbonate, and calcium phosphate (hydroxyapatite). The activity was measured by increases in the spectrophotometric absorbance of test particle suspensions in the presence of dispersants. The increases in absorbance were due to turbidity resulting from the production of smaller particle sizes or slower rates of settling. The results suggest that biopolymers composed of polyanionic polyamino acids may be effective as dispersants. Polyamino acids containing a hydrophobic or phosphorylated domain attached to a polyaspartate backbone demonstrate enhanced activity over polyaspartate. These polyamino acids display comparable activity to commercially available hydrocarbon-based polymeric dispersants.

An economical process for the manufacture of polyamino acids by thermal polycondensation is under development. Clearly, non-toxic and biodegradable polyamino acids present a desirable alternative to toxic non-biodegradable polymers in a number of applications such as detergents and cooling tower additives.     

Mineralization mechanism of calcium phosphates under three kinds of Langmuir monolayers

Three kinds of Langmuir monolayers formed by dipalmitoylphosphatidylcholine (DPPC), arachidic acid (AA), and octadecylamine (ODA) were used as templates to study the initial stage of nucleation and crystallization of calcium phosphates. It was demonstrated that the combination of calcium ions (or phosphates) to the monolayer/subphase interface is a prerequisite for subsequent nucleation. It was found that calcium phosphate dihydrate (DPCD) formed at 25.0 degrees C for 12 h has a biphasic structure containing both amorphous and crystalline phases. These results showed that calcium phosphates were formed through a multistage assembly process, during which an initial amorphous phase DPCD was followed by a phase transformation into a crystalline phase and then the most stable hydroxyapatite (HAp). This provided new insights into the template-biomineral interaction and a mechanism for biomineralization.     

Background overcorrection problems for lead in the presence of phosphate with various metals in Zeeman graphite furnace atomic absorption spectrometry

Phosphate in various chemical forms has been widely used as a chemical modifier for the determination of Pb by graphite furnace AAS. When Pb was determined in bone digestate, with NH₄H₂PO₄ modifier and a transversely-heated furnace and a longitudinal Zeeman background correction system, low recoveries of Pb were found. This was found to be caused by a background overcorrection problem associated with the matrix of phosphate plus Ca and/or Mg. The overcorrection problem caused erroneously low Pb concentrations to be predicted when using aqueous Pb standards for calibration. The overcorrection problem was not reproduced with a transverse Zeeman correction system. While the magnitude and shape of the background signal changed with different phosphate compounds, the important features remained constant. We suggest that the background overcorrection problem was caused by molecular absorption of PO formed during atomization in the presence of any of several metals, most specifically the alkaline earth elements, since the PO molecular absorption bands appear to be subject to Zeeman-effect splitting.     

基质中加入少量盐类改善MALDI-TOF MS的谱图信噪比

自20世纪80年代发明基质辅助激光解吸电离(Matrix assisted laser desorption ionization,MALDI)质谱以来,该技术已在生物分子分析方面得到了广泛应用．作为一种离子化方法,MALDI具有灵敏度高,对样品要求低,能耐高浓度盐和缓冲剂等优点．测定过程中使用合适的基质不仅能提高测试灵敏度和分辨率,还能扩增测试样品的种类。     

The determination of chromium, copper and nickel in groundwater using axial plasma inductively coupled plasma atomic emission spectrometry and proportional correction matrix effect reduction

The performance of a proportional correction matrix effect reduction procedure was investigated for an axially viewed inductively coupled plasma. It was shown that the proportional correction factor (ratio of analyte matrix effect and internal standard matrix effect) was sufficiently stable over the investigated matrix element concentration ranges (0–2000 mg/L of Na and 0–400 mg/L of Ca) for the procedure to be successful. Proportional correction results in the best correction for matrix effects compared to the classical 1?:?1 intensity ratio correction procedure or the approach without any correction, as was shown in recovery experiments using analyte spiked groundwater samples. Matrix effects as high as 18% without correction were reduced to less than 4% applying proportional correction.     

Amorphous calcium barium monophosphate and its dehydration in air at room temperature

The change in the state of chemical bonds during dehydration of amorphous calcium barium monophosphate was studied. The monophosphate was obtained by precipitation from an aqueous phosphate solution under the action of a binary solution containing simultaneously calcium and barium chlorides in the atomic ratio Ba/Ca ～0.2.