Hydroxyapatite coating on porous polyurethane facilitated by tetraethoxysilane

Biomimetic growth of calcium phosphate compounds on porous polyurethane (PU) treated with tetraethoxysilane (TEOS) and soaked in simulated body fluid (SBF) solution was studied using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), and Fourier transformed infrared spectroscopy–attenuated total reflectance (FTIR–ATR). Polyurethane was treated with TEOS in order to produce silanol groups which stimulated the growth of hydroxyapatite when immersed in SBF solution. Polyurethanes that were not treated with TEOS did not show calcium phosphate growth upon immersion in SBF solution. The Ca and P determined by EDAX and inductively coupled plasma spectroscopy (ICP) analysis revealed that the surface layer was not stoichiometric hydroxyapatite, but carbonated, containing hydroxyapatite with a Ca/P ratio of 1.5–1.6. This was confirmed by FTIR–ATR.     

Effect of Calcium Precursors and pH on the Precipitation of Carbonated Hydroxyapatite

Three types of calcium precursors (nitrate, hydroxide and catbonate) were used in the synthesis of carbonated hydroxyapatite (cHA) using a precipitation method via a chemical reaction with di-ammonium hydrogen phosphate as the phosphate precursor. The precipitation method was chosen over many other methods due to its flexibility to changes in processing parameters to control the phases formed, the particle size, as well as, the morphology of the as-synthesized powders. The focus of the study was on cHA as it is deemed to mimic the composition of the human bone much closer as compared to the stoichiometric hydroxyapatite. When the chemical reaction was completed, the precipitate was dried, ground and characterized by x-ray diffraction (XRD), electron microscopy (both FESEM and TEM) and particle size analysis. Only the nitrate precursor produced a single-phase carbonated hydroxyapatite (cHA), whilst the other two precursors produced a secondary calcite phase or did not react fully. This is due to the low solubility of the calcium hydroxide and the incomplete reaction of the calcium carbonate. An increase in pH has been observed to lead to higher carbonate content in the synthesized cHA and a smaller crystallite size.     

Calcite and apatite coatings on titanium

A new method was used to deposit coatings containing calcium carbonate and calcium phosphates onto titanium. The presence of calcite and hydroxyapatite crystals in specimens as the major phases was proved by X-ray diffraction analysis, IR spectroscopy, elemental analysis, and electron microscopy. The inorganic coatings were revealed to have good adhesion to titanium and be stable in aqueous solutions.     

Composite coatings on titanium

Composite coatings on the surface of metallic titanium containing calcium carbonate, calcium phosphate, chondroitin sulfate and/or gelatin were obtained in a new way. By the methods of XRD, IR spectroscopy, elemental analysis, and electron microscopy the presence in the samples of calcite and hydroxyapatite crystals as the main phase was demonstrated. Inorganic coatings were found to show better adhesion and resistance compared with the coatings containing the corresponding biopolymers.     

Microemulsion method for producing hydroxyapatite

Hydroxyapatite nanoparticles were obtained in the course of reaction in microemulsion system stabilized by surfactant (sodium bis-2-ethylhexylsulfosuccinate). By the methods of X-ray phase analysis, IR spectroscopy, elemental analysis, and electron microscopy the presence of crystals in the samples of hydroxyapatite as the main phase, and detected the formation of additional calcium phosphate compounds was demonstrated.     

Interaction between nanosized crystalline components of a composite based on <Emphasis Type="Italic">Acetobacter xylinum</Emphasis> cellulose and calcium phosphates

A composite consisting of two nanosized biocompatible components, Acetobacter xylinum cellulose and calcium phosphate, is prepared through aggregation in an aqueous suspension. The structures of initial components and composite are investigated by the methods of X-ray and electron diffraction and electron microscopy. The mineral component consists of two crystalline phases, hydroxyapatite and whitlockite (magnesium-containing tricalcium phosphate), which are nanosized platelike crystals. The composite preserves the crystalline structures of initial calcium phosphates and cellulose. In the course of composite formation, hydroxyapatite and whitlockite crystallites are adsorbed on the surfaces of nanofibrillar cellulose ribbons. Whitlockite nanocrystals are predominantly deposited on the surface of cellulose ribbons. The mutual orientation of the surfaces of crystalline structures of cellulose and two types of calcium phosphates, hydroxyapatite and whitlockite, is analyzed by means of computer simulation, and the variants of mutual arrangement of their surfaces during formation of the interfacial boundary are suggested.     

Crystal structure and composition of hydroxyapatite biocomposites prepared at excess of calcium ions

Formation of composites by calcium phosphates with chondroitin sulfate and gelatin obtained at excess content of calcium ion in solution is studied by the methods of X-ray phase analysis, IR spectroscopy and electron microscopy. Inclusion to the crystals of hydroxyapatite as the main phase and the absence of chemical interaction of biopolymers with calcium phosphate is proved and some features of the effect of reagents addition order to the studied system calcium-ammonium hydrogen phosphate-organic component are elucidated.     

类牙釉状丝胶蛋白/羟基磷灰石复合材料的合成及表征

采用化学沉淀法合成了丝胶蛋白(SS)/羟基磷灰石(HAP)复合材料, 并研究了矿化时间对复合材料的影响. X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)、透射电镜(TEM/HRTEM)和扫描电镜(SEM)表征结果表明: 在较短的矿化时间内, 合成的SS/HAP为直径约20 nm的复合颗粒; 随着矿化时间的延长, 这些复合颗粒能够沿轴方向组装并融合成类牙釉结构的较大晶体. 文章讨论了其可能的组装机制.     

Minerals and aligned collagen fibrils in tilapia fish scales: structural analysis using dark-field and energy-filtered transmission electron microscopy and electron tomography

The mineralized structure of aligned collagen fibrils in a tilapia fish scale was investigated using transmission electron microscopy (TEM) techniques after a thin sample was prepared using aqueous techniques. Electron diffraction and electron energy loss spectroscopy data indicated that a mineralized internal layer consisting of aligned collagen fibrils contains hydroxyapatite crystals. Bright-field imaging, dark-field imaging, and energy-filtered TEM showed that the hydroxyapatite was mainly distributed in the hole zones of the aligned collagen fibrils structure, while needle-like materials composed of calcium compounds including hydroxyapatite existed in the mineralized internal layer. Dark-field imaging and three-dimensional observation using electron tomography revealed that hydroxyapatite and needle-like materials were mainly found in the matrix between the collagen fibrils. It was observed that hydroxyapatite and needle-like materials were preferentially distributed on the surface of the hole zones in the aligned collagen fibrils structure and in the matrix between the collagen fibrils in the mineralized internal layer of the scale.     

Influence of Calcium Sources on Microbially Induced Calcium Carbonate Precipitation by Bacillus sp. CR2

Stimulation of microbially induced calcium carbonate precipitation (MICCP) is likely to be influenced by calcium sources. In order to study such influences, we performed MICCP using Bacillus sp. CR2 in nutrient broth containing urea, supplemented with different calcium sources (calcium chloride, calcium oxide, calcium acetate and calcium nitrate). The experiment lasted 7 days, during which bacterial growth, urease activity, calcite production and pH were measured. Our results showed that calcium chloride is the better calcium source for MICCP process, since it provides higher urease activity and more calcite production. The influences of calcium sources on MICCP were further studied using Fourier transform-infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. These analyses confirmed that the precipitate formed was CaCO₃ and composed of predominantly calcite crystals with a little amount of aragonite and vaterite crystals. The maximum yield of calcite precipitation was achievable with calcium chloride followed by calcium nitrate as a calcium source. The results of present study may be applicable to media preparation during efficient MICCP process.     

Regulation of Microstructure of Calcium Carbonate Crystals by Egg White Protein

Crystal growth of calcium carbonate in biological simulation was investigated via egg white protein with different volume fractions,during which calcium carbonate was synthesized by calcium chloride an...     

Effect of inorganic anions on the morphology and structure of magnesium calcite

Calcium carbonate was precipitated from calcium hydroxide and carbonic acid solutions at 25 degrees C, with and without addition of different magnesium (MgSO(4), Mg(NO(3))(2) and MgCl(2)) and sodium salts (Na(2)SO(4), NaNO(3) and NaCl) of identical anions, in order to study the mode of incorporation of magnesium and inorganic anions and their effect on the morphology of calcite crystals over a range of initial reactant concentrations and limited c(i)(Mg(2+))/c(i)(Ca(2+)) molar ratios. The morphology, crystal size distribution, composition, structure, and specific surface area of the precipitated crystals, as well as the mode of cation and anion incorporation into the calcite crystal lattice, were studied by a combination of optical and scanning electron microscopy (SEM), electronic counting, a multiple BET method, thermogravimetry, FT-IR spectroscopy, X-ray diffraction (XRD), and electron paramagnetic resonance (EPR) spectroscopy. In the systems of high initial relative supersaturation, precipitation of an amorphous precursor phase preceded the formation of calcite, whereas in those of lower supersaturation calcite was the first and only polymorphic modification of calcium carbonate that appeared in the system. The magnesium content in calcite increased with the magnesium concentration in solution and was correlated with the type of magnesium salt used. Mg incorporation caused the formation of crystals elongated along the calcite c axis and, in some cases, the appearance of new [011] faces. Polycrystalline aggregates were formed when the c(i)(Mg(2+))/c(i)(Ca(2+)) molar ratios in solution were increased. Addition of sulfate ions, alone, caused formation of spherical calcite polycrystalline aggregates.     

X-ray diffraction and scanning electron microscopy studies of calcium carbonate electrodeposited on a steel surface

Calcium carbonate was deposited on a stainless steel surface with the use of an electrical potential of 10 V. The crystals formed on the surface were examined with X-ray diffraction and with scanning electron microscopy, which revealed that calcite, vaterite and amorphous calcium carbonate was formed. Two different surface active polymers were added to the solution and their effect on the crystal structure was investigated. It was found that the more hydrophilic of the two polymers promoted calcite growth and suppressed vaterite growth. The more hydrophobic polymer completely inhibited vaterite growth. Both polymers decreased the amount of crystals formed on the steel surface, the more hydrophobic polymer being the most effective. The crystal inhibition efficiency was enhanced close to the cloud point of the polymers. The results were compared with the effect of poly(acrylic acid), a commonly used antiscalant. It was found that poly(acrylic acid) was about as efficient as the more hydrophobic polymer in decreasing the amount of calcium carbonate. At higher concentrations of poly(acrylic acid), almost all of the calcium carbonate precipitated in the amorphous form.     

Effect of phosvitin on the nucleation and growth of calcium phosphates in physiological solutions

The promoting effect of phosvitin on the nucleation of hydroxyapatite (HAP) and the inhibitory effect of phosvitin on the transformation from amorphous calcium phosphate (ACP) to HAP were investigated. Atomic force microscopy observations showed that the nucleation of HAP on collagen substrate was greatly enhanced when the phosvitin was bound on the collagen surface. Nucleated crystals were uniformly distributed with a high nucleation rate on the collagen surface in the presence of phosvitin, while, in the absence of phosvitin, crystals nucleated slowly and were observed only at some particular area. Time-resolved static light scattering measurements revealed that the transformation from ACP to HAP was inhibited when free phosvitin was present in the calcium phosphate solutions. The transformation kinetics in the absence of phosvitin, which is a direct reconstruction of the inner ACP structure to HAP, was changed to heterogeneous growth of HAP on ACP with time.     

In situ biomimetic formation of nano‐hydroxyapatite crystals on chitosan microspheres

Chitosan (CS) is a biocompatible, noncytotoxic biomaterial used before as base material for composites. On the other hand, nano‐hydroxyapatite (nHA) is one of the main components of human bones, highly used for biomedical applications. In this work, CS microspheres were produced under a W/O emulsion system. CS microspheres with calcium ions were then exposed to Na₃PO₄ solution. In situ biomimetic nHA crystals were formed on CS microspheres to generate 15.14 ± 3.15‐μm composite microspheres. The microspheres were subsequently seeded with MG63 osteoblasts to observe their cell responses. All microspheres were characterized via scanning electron microscopy (SEM), phase‐contrast photomicroscopy, and X‐ray diffraction (XRD) analysis. The results showed flake‐like shape and islet‐like growth of nHA depositions presented on the surface of the CS microspheres. In vitro tests indicated that the CS/nHA microparticles were not only biocompatible but also enhanced cell adhesion and elongation due to the in situ biomimetic synthesis method.     

Effect of Alizarin Red S on the formation of hydroxyapatite crystals

Hydroxyapatite samples were prepared in systems calcium nitrate-diammonium hydrogen phosphate-ammonium hydroxide-organic component with addition of microamounts of Alizarin Red S. The participation of sulfo and hydroxy groups of the organic compounds in the formation of hydroxyapatite crystals was confirmed by X-ray phase analysis, IR spectroscopy, electron microscopy, and elemental analysis.     

Mechanochemical-hydrothermal synthesis of calcium phosphate powders with coupled magnesium and carbonate substitution

Magnesium- and carbonate-substituted calcium phosphate powders (Mg-, CO₃-CaP) with various crystallinity levels were prepared at room temperature via a heterogeneous reaction between MgCO₃/Ca(OH)₂ powders and an (NH₄)₂HPO₄ solution using the mechanochemical-hydrothermal route. X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis were performed. It was determined that the powders containing both Mg²⁺ and CO₃²⁻ ions were incorporated uniformly into an amorphous calcium phosphate phase while in contrast, the as-prepared powder free of these dopants was crystalline phase-pure, stoichiometric hydroxyapatite. Dynamic light scattering revealed that the average particle size of the room temperature Mg-, CO₃-CaP powders was in the range of 482 nm-700 nm with a specific surface area between 53 and 91 m²/g. Scanning electron microscopy confirmed that the Mg-, CO₃-CaP powders consisted of agglomerates of equiaxed, ≈20-35 nm crystals.     

纳米晶状磷酸钙盐/Al2O3-Ti生物复合材料的制备与结构表征

0引言众所周知,钛及其合金具有优良的机械力学性能,但其生物活性不足。因此,在金属基体上涂敷一层生物活性涂层,结合金属与生物活性材料的各自优势,已成为世界各国学者研究最为活跃的生物复合材料体系之一。该体系可用于临床医学,作为人体硬组织等的修复替换材料。目前,已开发出多种在金属基体上制备生物活性涂层的工艺和方法。如:等离子沉积法[1]、离子束溅射法[2]、激光熔覆法[3]、溶胶鄄凝胶法[4]、电化学沉积与水热处理合成法[5]、电泳沉积[6]、电结晶[7]等多种方法。但现有涂层材料尚存在一些问题:(1)由于替换材料的高硬度而导致其周围硬组织坏死[8];(2)由于疲劳磨损或热膨胀不匹配引起涂层脱落[9];(3)由于异质相导致生物活性降解[10]。因此,研究新的制备工艺,开发新的生物复合材料体系就显得十分重要。考虑到Al2O3具有优异的抗磨损、耐腐蚀等性能,以及较好的生物相容性,常作为临床选用的人造硬组织承载材料[11],故在本研究工作中,我们首次采用阳极氧化与水热处理复合工艺研制酸式磷酸钙/Al2O3鄄Ti生物复合材料体系。该体系不同于由日本Ishizawa等研制的HAp/TiO2鄄Ti复合体系[12]。主要体现在两...     

Synthesis of Nano-hydroxyapatite via Microbial Method and Its Characterization

Nanoparticles of hydroxyapatite were successfully synthesized by microbial method at ambient temperature and pressure, using calcium chloride and specific substrate as reactants. The compositional and morphological properties of products of the syntheses were studied by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The characterization data obtained showed that the phase composition, functional groups, and surface morphology of samples obtained by microbial method were mainly similar to that by chemical precipitation method. The hydroxyapatite powder was shown to be nanometer-grade in size and sphere-like in shape.     

Black crusts and patinas on Pentelic marble from the Parthenon and Erechtheum (Acropolis, Athens): characterization and origin

This study describes an analytical approach for the characterization and origin of the encrustation formed on the surface of monuments from the Acropolis in Athens. The morphology of encrustation was investigated by optical and scanning electronic microscopy. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray fluorescence (EDXRF) and scanning electron microscopy coupled with energy-dispersive X-ray analysis (SEM-EDS) identify and quantify the key elements and compounds associated with the genesis of encrustation. Black crusts (>200 μm thick), consisting of gypsum, calcite and elements such as Si, Al, Fe, Pb, Ti, Zn and Mn, were being formed from interaction between the marble surface and atmospheric pollutants. Orange-brown accretions on the Parthenon, called patinas (∼150 μm thick), comprise calcite, calcium oxalates, low amount of S, and both in the inner and outer parts significant and almost constant amounts of Si, P and Fe; P and Fe identified as hydroxyapatite and hematite, respectively. In the Parthenon patinas, the EDS distribution maps of Si, Fe and P indicate an origin that may be attributed to the residue and transformation of ancient treatments rich in these elements. Patinas from the Erechtheum (∼100 μm thick) resemble plasters consisting of calcite, siliceous sand, hydroxyapatite, calcium oxalates and hematite. EDXRF highlighted the presence of Pb in the patinas from the Erechtheum; FTIR revealed that Pb is in the form of cerussite most probably from the use of attic ochre. The patinas from the Parthenon and Erechtheum, as opposed to black crusts, are associated with the best-preserved surfaces and should remain intact during conservation interventions.