Microwave-assisted synthesis and characterization of cellulose-carbonated hydroxyapatite nanocomposites in NaOH-urea aqueous solution

We report the microwave-assisted synthesis of the cellulose-carbonated hydroxyapatite (CHA) nanocomposites with CHA nanostructures dispersed in the cellulose matrix by using the cellulose solution, CaCl₂, and NaH₂PO₄. The cellulose solution was previously prepared by the dissolution of microcrystalline cellulose in NaOH-urea aqueous solution. The influences of the heating time and cellulose concentration on the products were also investigated. The X-ray powder diffraction (XRD) and Fourier transform infrared spectrometry (FT-IR) results indicated that the obtained products were the cellulose-CHA nanocomposites. The scanning electron microscopy (SEM) micrographs showed the CHA nanostructures were dispersed in the cellulose matrix. The thermal stability of the cellulose-CHA nanocomposites in air was investigated using thermogravimetric analysis (TGA) and differential thermal analysis (DTA). This method is simple, fast, low-cost and suitable for large-scale production of cellulose-based nanocomposites.     

Preparation of hollow hydroxyapatite microspheres

The preparation of hollow hydroxyapatite (HA) microspheres as potential drug-delivery vehicles was investigated. A lithium-calcium-borate (10Li₂O-15CaO-75B₂O₃) (mol%) glass, made by fusing the components at 1100°C for 1 h, was ground to a powder and passed through a flame at ∼1400°C to spheroidize the particles. The resulting glass microspheres (106–125 μm in diameter) were reacted in 0.25 M K₂HPO₄ solution for 5 days at 37°C and pH 10–12, resulting in the formation of porous, hollow microspheres of a calcium phosphate (Ca-P) material with external diameters similar to those of the original glass particles. Heat treatment at 600°C for 4 h partially converted the Ca-P material to HA, as confirmed by X-ray diffraction, and also increased the strength of the hollow microspheres.     

Dissolution behavior of hollow hydroxyapatite microspheres immersed in deionized water

Hollow hydroxyapatite (HA) microspheres were fabricated by plasma spraying method. These microspheres were immersed in deionized water for different periods of time to investigate their dissolution behavior with the starting HA powders as contrast. The results showed that although having a relatively lower crystallinity, the dissolution rate of the HA microspheres is somewhat lower than that of HA powders, which was due to the very dense surface layer of the microspheres. Moreover, open pores were seen on the surface of hollow microspheres after immersion. These results suggest that there might be a novel application in drug delivery for the hollow HA microspheres.     

Controlled preparation of hollow zinc oxide microspheres from aqueous solution using hexamethylenetetramine and cysteine

Zinc oxide particles were synthesized by precipitation from an aqueous solution of zinc nitrate tetrahydrate, R-(+)-cysteine and hexamethylenetetramine (HMTA, urotropine). Hollow microspheres of ZnO-cysteine hybrid material with a diameter of ca. 1 μm and a wall thickness ca. 50 nm were obtained. After heating up to 850 °C pure ZnO microspheres of roughly the same size were formed. The particles were characterized by XRD, SEM, FT-IR and TGA.     

Sol-emulsion-gel synthesis of hollow mullite microspheres

Hollow mullite microspheres were obtained from emulsified diphasic sols by an ion extraction method. The surfactant concentration and viscosity of the sols were found to affect the characteristics of the derived microspheres. The gel and calcined microspheres were investigated by using thermogravimetry analysis (TGA), differential thermal analysis (DTA), Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), optical and scanning electron microscopy (SEM) and particle size analysis. TGA indicated the removal of most of the volatiles, i.e. 30.77 wt% up to about 500°C. Crystallization of the Si-Al spinel at 900°–970°C in gel microspheres was confirmed by DTA and XRD. XRD results also showed the formation of orthorhombic mullite at 1200°C. FTIR indicated the sequence of transformations taking place during heat-treatment of gel microspheres at different temperatures. The optical and scanning electron microscopy confirmed the spherical morphology of the gel and calcined particles. Formation of hollow microspheres with a single cavity was identified by SEM. The particle size distribution of the mullite microspheres calcined at 1300°C/1h exhibited a size range of 6–100 m with an average particle size (d ₅₀) of 22.5 m.     

Hydrothermal synthesis of SnO2 hollow microspheres

SnO₂ hollow microspheres have been synthesized by a hydrothermal method. X-ray powder diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) were used to characterize such hollow microspheres. SEM image shows that SnO₂ microspheres with diameters of 0.5–1 μm are composed of SnO₂ nanoparticles with about 15 nm in diameter. Some broken microspheres indicate the hollow spherical structure. XRD shows that SnO₂ hollow microspheres have tetragonal structure.     

Template-free hydrothermal synthesis of hollow hematite microspheres

Hollow hematite (α-Fe₂O₃) microspheres with an average diameter of 3-4 μm and a shell thickness of approximate 150 nm was synthesized by a simple hydrothermal route using FeCl₃·6H₂O solution and acetic acid without using any templates. The hollow microspheres were composed of α-Fe₂O₃ nanoparticles with the diameter range from 20 to 40 nm. The effects of reaction parameters such as reaction time, temperature, concentration of FeCl₃·6H₂O solution, and initial pH on the morphology of the final products were investigated. A possible formation mechanism of hollow α-Fe₂O₃ microspheres was also proposed, where the acetic acid played a role of etching in the formation of hollow structure.     

Preparation and characterization of hollow hydroxyapatite microspheres by spray drying method

Hollow hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) microspheres were prepared using a simple spray drying method. The incorporation of ammonium bicarbonate could produce carbon dioxide and ammonia gas bubbles during the spraying, and thus created a hollow inner structure in the resultant microspheres. The hollow microspheres prepared using different amounts of ammonium bicarbonate were also characterized. These microspheres were composed of nanoparticles with an average crystallite size of 15 nm. A high surface area (80 m²/g) and porosity of the microspheres could be achieved when the concentration of ammonium bicarbonate was about 5 wt.%. Fourier transform infrared results showed that CO₃^2? was incorporated into the HA microspheres. These hollow microspheres have many potential uses such as injectable drug-delivery carriers.     

Factors influencing the deposition of hydroxyapatite coating onto hollow glass microspheres

Hydroxyapatite (HA) and HA coated microcarriers for cell culture and delivery have attracted more attention recently, owing to the rapid progress in the field of tissue engineering. In this research, a dense and uniform HA coating with the thickness of about 2 μm was successfully deposited on hollow glass microspheres (HGM) by biomimetic process. The influences of SBF concentration, immersion time, solid/liquid ratio and activation of HGM on the deposition rate and coating characteristics were discussed. X-ray diffraction (XRD) and Fourier transform infrared spectrum (FTIR) analyses revealed that the deposited HA is poorly crystalline. The thickness of HA coating showed almost no increase after immersion in 1.5SBF for more than 15 days with the solid/liquid ratio of 1:150. At the same time, SBF concentration, solid/liquid ratio and activation treatment played vital roles in the formation of HA coating on HGM. This poorly crystallized HA coated HGM could have potential use as microcarrier for cell culture.     

Environmentally friendly aqueous solution synthesis of hierarchical CaWO4 microspheres at room temperature

An environmentally friendly route for the synthesis of hierarchical CaWO4 microspheres with novel morphology at room temperature has been successfully developed. CaCl2 and Na2WO4 were used as reaction regents, and distilled water was used as an environmentally friendly solvent. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence spectroscopy. This green wet-chemical route provides a simple, one-step, low-cost approach for the large-scale synthesis of hierarchical CaWO4 microspheres with relatively uniform diameters of 3-6 microm. The hierarchical microspheres are built up with numerous nanorods with an average diameter of 50 nm, which are radially oriented to the microsphere center. SEM observations of different intermediates indicate the possible growth process, in which the hierarchical structure growth is from nuclei through kayak-like, rod-like, peanut-like, dumbbell-like, and peach-like structures to final microspheres, via "self-assembled preferential end growth" of kayak-like particles in aqueous solution. The hierarchical CaWO4 microspheres exhibit a strong, broad blue emission peak of 412 nm.     

Evaluation of BSA protein release from hollow hydroxyapatite microspheres into PEG hydrogel

Implants that simultaneously function as an osteoconductive matrix and as a device for local drug or growth factor delivery could provide an attractive system for bone regeneration. In our previous work, we prepared hollow hydroxyapatite (abbreviated HA) microspheres with a high surface area and mesoporous shell wall and studied the release of a model protein, bovine serum albumin (BSA), from the microspheres into phosphate-buffered saline (PBS). The present work is an extension of our previous work to study the release of BSA from similar HA microspheres into a biocompatible hydrogel, poly(ethylene glycol) (PEG). BSA-loaded HA microspheres were placed in a PEG solution which was rapidly gelled using ultraviolet radiation. The BSA release rate into the PEG hydrogel, measured using a spectrophotometric method, was slower than into PBS, and it was dependent on the initial BSA loading and on the microstructure of the microsphere shell wall. A total of 35–40% of the BSA initially loaded into the microspheres was released into PEG over ~ 14 days. The results indicate that these hollow HA microspheres have promising potential as an osteoconductive device for local drug or growth factor delivery in bone regeneration and in the treatment of bone diseases.     

以碳酸钙为模板制备空心羟基磷灰石微球及其表征

以碳酸钙为模板和钙源,与磷酸氢二铵通过水热反应,制备出尺寸均匀、形态规则的空心羟基磷灰石微球。采用X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)、扫描电镜(SEM)、透射电镜(TEM)测试制备的样品,结果显示,制备的空心羟基磷灰石微球具有与碳酸钙微球模板相似的形貌,空心,尺寸均匀且形貌规则。并通过改变水热反应时间探索了羟基磷灰石微球的形成机理。此羟基磷灰石空心微球在生物医学领域具有较大的应用前景。     

Template-free synthesis of NiO hollow microspheres covered with nanoflakes

α-Ni(OH)₂ hollow microspheres precursors were synthesized without any template through a solvothermal method. Hydrolyzing NiCl₂ in alkaline solution, the Ni(OH)₂ hollow microspheres covered with a disordered covering of perpendicular nanoflakes were prepared. Subsequently, the similar microstructured NiO hollow microspheres with BET area around 222.8 m²/g and specific pore volume around 0.5 cm³/g were obtained by calcining the above precursor at 250–300 °C with a slow heating rate (about 1 K/min). The effects of the surfactant and the calcining temperature on the morphology and the mesostructure of the NiO hollow microspheres were also discussed.     

Fabrication and dissolution behavior of hollow hydroxyapatite microspheres intended for controlled drug release

Hollow hydroxyapatite (HA) microspheres were fabricated by a simple spray drying method in this study. Moreover, the dissolution behavior of these hollow HA microspheres after immersion in simulated body fluid (SBF) was also studied. The results indicated that the dissolution of the HA microspheres in SBF is not homogeneous in a layer-by-layer fashion but was preferential at different locations of the particle surface. Generically, dissolution preferentially occurs on the location with looser structure and high porosity of the microspheres. The degradable HA microspheres are expected to have potential applications in bone local drug delivery systems.     

一种中空二氧化硅微球掺杂改性的聚氨酯水性分散体乳液的研究

采用化学方法制备了一种中空二氧化硅微球掺杂改性的聚氨酯水性分散体乳液,并采用扫描电镜、投射电镜、热失重、紫外-可见光吸收和涂膜力学性能等测试手段对该中空二氧化硅微球掺杂聚氨酯分散体及其涂膜的微观结构、热、光和力学等性能进行研究.实验结果表明,该乳液具有良好的室温贮存稳定性能,中空二氧化硅微球与水性聚氨酯分散体具有良好的相容性和协同增强效应.中空二氧化硅微球的掺杂改性不仅能够提高聚氨酯涂膜的耐热性能,显著提高水性聚氨酯涂膜的硬度和耐水性,同时该掺杂聚氨酯涂膜还具有优异的抗紫外光能力.     

Microwave-assisted hydrothermal synthesis of ZnO rod-assembled microspheres and their photocatalytic performances

ZnO rod-assembled microspheres were successfully fabricated by using the microwave-assisted hydrothermal method in the existence of the poly ethylene glycol (PEG) with the molecular weight of 2000. The structure and morphology of as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive spectrometer (EDS), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The experimental results exhibit that the as-prepared ZnO microspheres with a diameter about 1.5–2.0 μm were composed of many rods with the diameter of 300 nm and the length of 1 μm, respectively. Photoluminescene measurement shows a broad visible emission band centered at around 500–560 nm. The improved catalytic activity may be attributed to structural difference, including morphology, surface orientation and surface defects. Furthermore, the possible growth and photodegradation mechanism of the as-prepared sample is also briefly discussed.     

中空层状羟基磷灰石微球对溶菌酶的吸附与缓释研究

利用锂钙硼玻璃在磷酸盐溶液中的原位转化反应制备表面多孔且具有中空层状结构的羟基磷灰石(HA)微球,以溶菌酶为蛋白的药物模型,研究了中空层状结构的羟基磷灰石微球对溶菌酶的吸附及缓释特性,结果显示,中空微球对不同浓度的溶菌酶溶液,具有不同的吸附机理,当溶菌酶溶液的浓度低于0.8mg/mL时,溶菌酶的吸附主要发生在微球的外表面,符合Langmuir模型,释放速率较快,48h内基本释放完全;当溶菌酶溶液的浓度高于0.8mg/mL时,溶菌酶扩散进入微球内部及球壁的微孔中,使得吸附量显著增加,满足Henry吸附模型,溶菌酶的释放周期明显增加,可持续释放800h,微球对蛋白具有很好的缓释效果。     

Arsenate removal from aqueous solution by cellulose-carbonated hydroxyapatite nanocomposites

Microwave-assisted synthesis of the cellulose-carbonated hydroxyapatite nanocomposites (CCHA) with CHA nanostructures dispersed in the cellulose matrix was carried out by using cellulose solution, CaCl(2), and NaH(2)PO(4). The cellulose solution was previously prepared by the dissolution of microcrystalline cellulose in NaOH-urea aqueous solution. Study was carried out to evaluate the feasibility of synthetic CCHA for As(V) removal from aqueous solution. Batch experiments were performed to investigate effects of various experimental parameters such as contact time (5 min - 8h), initial As(V) concentration (1-50mg/L), temperature (25, 35 and 45°C), pH (2-10) and the presence of competing anions on As(V) adsorption on the synthetic CCHA. Kinetic data reveal that the uptake rate of As(V) was rapid at the beginning and equilibrium was achieved within 1h. The adsorption process was well described by pseudo-first-order kinetics model. The adsorption data better fitted Langmuir isotherm. The maximum adsorption capacity calculated from Langmuir isotherm model was up to 12.72 mg/g. Thermodynamic study indicates an endothermic nature of adsorption and a spontaneous and favorable process. The optimum pH for As(V) removal was broad, ranging from 4 to 8. The As(V) adsorption was impeded by the presence of SiO(3)(2-), followed by PO(4)(3-) and NO(3)(-). The adsorption process appeared to be controlled by the chemical process.