Selective laser sintering of porous tissue engineering scaffolds from poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide)/carbonated hydroxyapatite nanocomposite microspheres

This study focuses on the use of bio-nanocomposite microspheres, consisting of carbonated hydroxyapatite (CHAp) nanospheres within a poly(L: -lactide) (PLLA) matrix, to produce tissue engineering (TE) scaffolds using a modified selective laser sintering (SLS) machine. PLLA microspheres and PLLA/CHAp nanocomposite microspheres were prepared by emulsion techniques. The resultant microspheres had a size range of 5-30 mum, suitable for the SLS process. Microstructural analyses revealed that the CHAp nanospheres were embedded throughout the PLLA microsphere, forming a nanocomposite structure. A custom-made miniature sintering platform was installed in a commercial Sinterstation((R)) 2000 SLS machine. This platform allowed the use of small quantities of biomaterials for TE scaffold production. The effects of laser power; scan spacing and part bed temperature were investigated and optimized. Finally, porous scaffolds were successfully fabricated from the PLLA microspheres and PLLA/CHAp nanocomposite microspheres. In particular, the PLLA/CHAp nanocomposite microspheres appeared to be promising for porous bone TE scaffold production using the SLS technique.     

Synthesis and characterization of Fe-Co binary ferrospinel nanospheres via one-step nonaqueous solution pathway

Fe-Co binary ferrospinel (CoFe₂O₄) nanospheres were synthesized by a facile nonaqueous solution route. X-ray diffraction (XRD) and electron diffraction (ED) showed that the obtained nanospheres had the cubic spinel structure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that the samples consisted of abundant uniform CoFe₂O₄ nanospheres with the particle size in the range of 35-40 nm. The magnetic properties of the sample were measured by using a vibrating sample magnetometer (VSM) at room temperature, which showed that the nanospheres exhibited a typical ferromagnetic behavior.     

Effect of nanosilica addition on the physicomechanical properties,pore morphology,and phase transformation of freeze cast hydroxyapatite scaffolds

Freeze casting technique is a simple and effective method for the fabrication of porous ceramic structures. The objective of this work is to study the production and characterization of hydroxyapatite/nanosilica (HA/nSiO₂) scaffolds fabricated through this method. In the experimental procedure, the solidified samples were prepared by slurries containing different concentration of HA and nSiO₂ followed by sintering procedure at 1200 and 1350 °C. The phase composition, microstructure, and compressive strength of the scaffolds were characterized by X-ray diffraction, scanning electron microscopy, and mechanical strength test. It was found that the porosity of the scaffolds was in the range of 30–86.5 % and the value of compressive strengths lied between 0.16 and 71.96 MPa which were influenced by nSiO₂ content, cooling rate, and sintering temperature. With respect to porosity, pore size, and compressive strength, the scaffolds with 5 % nSiO₂, the cooling rate of 1 °C/min and the sintering temperature of 1350 °C showed preferable results for bone tissue engineering applications.     

Resorbable, porous glass scaffolds by a salt sintering process

Resorbable, porous glass scaffolds for tissue engineering were prepared by sintering borate glass with salt (sodium chloride). Subsequently, the sodium chloride was dissolved in water resulting in a highly porous material. By modifying the process parameters including salt particle size, salt volume percentage, sintering temperature and sintering time, sintered matrix structures were optimized. Analysis of the structure data indicates that the 50 vol% glass—50 vol% salt with particle sizes from 250–315 μm sintered at a temperature of 520°C for 10 min resulted in an optimum structure with 76.5% porosity and 29.3 N/cm² compressive strength. The process of HAP formation on the scaffolds in 0.25 M K₂HPO₄ solutions with pH 9.0 at 37°C was evaluated. The structural changes were analyzed by X-ray diffraction and scanning electron microscopy. An amorphous phosphate was formed on the surface of the scaffolds within 1d and crystalline hydroxyapatite (HA) within 10d.     

Structural characterization of zinc-substituted hydroxyapatite prepared by hydrothermal method

Zinc-substituted hydroxyapatite (Zn-HA) powders were prepared by hydrothermal method using Ca(NO₃)₂, (NH₄)₃PO₄ and Zn(NO₃)₂ as reagents. X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM) were used to characterize the crystalline phase, microstructure, chemical composition, morphology and thermal stability of Zn-HA. The results show that the substitution content of zinc (Zn) in Zn-HA powders prepared in NaOH solution is higher than that prepared in NH₃ solution, and is lower than that of the corresponding amount of starting materials. The substitution of the Zn ion for calcium ion causes a lower crystallinity of Zn-HA and changes the lattice parameters of Zn-HA, since the ionic radius is smaller in Zn²⁺ (0.074 nm) than in Ca²⁺ (0.099 nm). Furthermore, the substitution of the Zn ions restrains the growth of Zn-HA crystal and decreases the thermal stability of Zn-HA. Zn-HA powder prepared in NH₃ solution starts to decompose at 800 °C when the Zn fraction increases to 15 mol%, while that prepared in NaOH solution start to decompose at 5 mol% Zn. The substitution content of Zn significantly influences the thermal stability, microstructure and morphology of Zn-HA.     

Spray drying process to synthesize multiple fullerene-like MoS2 particles

Multiple inorganic fullerene-like (IF) molybdenum disulfide hollow spheres were synthesized through spray drying method. The molybdenum trisulfide precursor, which was prepared by the mixed solution of ammonium molybdate ((NH₄)₂MoO₄) and ammonium disulfide ((NH₄)₂S) with a spray drying method, was desulfurized at 850 °C in a mixture of hydrogen and argon, and subsequently multiple fullerene-like molybdenum disulfide hollow spheres were obtained. The samples were identified and characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM), and the mechanism of formation is also discussed based on the experimental result. The spray drying process would be an effective method to synthesize large-scale of inorganic fullerene-like materials.     

Simple synthesis of MoS2 inorganic fullerene-like nanomaterials from MoS2 amorphous nanoparticles

The amorphous MoS₂ nanoparticles have been synthesized by a simple oxidation–reduction reaction in an aqueous solution. A series of products with different morphologies, such as MoS₂ nanospheres, inorganic fullerene-like nanospheres, nanorods and Mo bended rods, can be obtained by annealing the amorphous MoS₂ nanoparticles under N₂ atmosphere under 400–1200 °C. These products have been characterized by X-ray diffraction, field emission scanning electronic microscopy, transmission electron microscopy and high-resolution transmission electron microscopy in detail. The possible transformation mechanism for the structure has been discussed based on the experimental results. In addition, the optical properties of IF-MoS₂ have also been performed by UV–vis absorption spectroscopy.     

Synthesis of hollow calcium carbonate particles by the bubble templating method

Hollow calcium carbonate (CaCO₃) is a potential component in many industrial fields such as plastics, rubbers, papermaking, and drug delivery. This paper described a novel approach to synthesize hollow CaCO₃ particles by using bubble as template via passing CO₂ bubbles into calcium chloride (CaCl₂) solution in the presence of ammonia (NH₃) at 27 °C. The CO₂ bubble is not only the reactive material, but also the template of hollow particles. The newly-formed primary particles attach to bubbles and form a solid shell. After filtering and drying the hollow CaCO₃ particles were obtained. Physical characteristics of the precipitate were evaluated using scanning electron microscopy (SEM) and X-ray diffraction (XRD).     

Calcium phosphate/block copolymer hybrid porous nanospheres: Preparation and application in drug delivery

Calcium phosphate (CaP)/block copolymer hybrid porous nanospheres were synthesized by a simple solution method using CaCl₂ and (NH₄)₂HPO₄ in the presence of a block copolymer at room temperature. X-ray diffraction showed that the sample consisted of amorphous calcium phosphate (ACP). The BET specific surface area and the pore size distribution of the CaP/PLLA-mPEG hybrid porous nanospheres were also characterized. The as-prepared CaP/PLLA-mPEG hybrid porous nanospheres were explored as drug carriers, and showed a high ibuprofen loading capacity and in vitro prolonged drug release behavior in a simulated body fluid. These CaP/block copolymer hybrid porous nanospheres exhibit a great potential for application in drug delivery.     

Vapor phase growth of GaN crystals with different morphologies and orientations on graphite and sapphire substrates

GaN crystals were grown on graphite and sapphire substrates at 990–1050 °C by reaction of Ga₂O with flowing NH₃. Ga₂O gas was produced at a constant rate (1.3 wt% min⁻¹) by reaction of Ga₂O₃ with carbon at 1000–1060 °C. The effect of NH₃ concentration (3–100 vol%) and the nature of the substrate on the morphology and orientation of the GaN crystals were determined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and selected area electron diffraction. It was found that sheet and plate-like crystals grew at different orientations to the substrate with different NH₃ concentrations and substrates.     

Synthesis and properties of calcium hydroxyapatite/silk fibroin organomineral composites

The coprecipitation of calcium hydroxyapatite (HA) (Ca₁₀(PO₄)₆(OH)₃) and silk fibroin (SF) from an aqueous solution in the Ca(NO₃)₂–(NH₄)₂HPO₄–NH₃–H₂O–SF system has been used to synthesize HA/SF organomineral composites based on nanocrystalline HA, containing 2, 5, and 10 wt % SF. The synthesis products were characterized by X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, scanning electron microscopy, and electron spectroscopy for chemical analysis.     

Self-assembly into temperature dependent micro-/nano-aggregates of 5,10,15,20-tetrakis(4-carboxyl phenyl)-porphyrin

Various nanostructures of 5,10,15,20-tetrakis(4-carboxyl phenyl)-porphyrin (H₂TCPP) can be easily synthesized by a surfactant-assisted self-assembly (SAS) method at different temperatures. When the DMF solution of porphyrin monomer was injected into cetyltimethylammonium bromide (CTAB) aqueous solution by a syringe, diverse H₂TCPP nanostructures dependent on the different temperatures, including hollow nanospheres, solid nanospheres and nanospheres with holes, were successfully obtained. As a result, the suitable concentration of the CTAB aqueous solution used to form nanostructues of porphyrin ranges from 0.15 to 0.2 mM. The various morphologies of porphyrin nanostructures were characterized by transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). UV–vis adsorption spectra showed that the micro-/nano-aggregate properties of porphyrin transformed from H-aggretates to J-aggregates during the process of self-assembly of porphyrin at different temperatures. Fluorescence spectra revealed a greater fluorescence quenching of various micro-/nano-aggregatess of porphyrin formed at different temperatures in aqueous solution, compared to the DMF solution of porphyrin monomer.     

Preparation and magnetic properties of hollow ferrite microspheres by a gas-phase diffusion method in an ionic liquid/H2O mixed solution

In this work, hollow ferrite microspheres were prepared using a gas-phase diffusion method with cobalt nitrate and ferric nitrate as metal salt sources, an ionic liquid 1-butyl-3-methylimidazolium-tetrafluoroborate and water-mixed solvent as medium and ammonium carbonate as precipitant. Their structures and magnetization were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, thermogravimetry, infrared spectroscopy, and vibrating sample magnetometer. The effects of reaction time, reaction temperature, precipitant loading, and mole ratio of Co to Fe n(Co/Fe) on the structures and magnetization of the microspheres were studied. The results showed that ferrite hollow microspheres with uniform morphology and high-magnetic performance were obtained at 60–80 °C for 12–16 h, while the (NH₄)₂CO₃ loading was 0.15 g/ml, n(Co/Fe) was 0.5:1, and calcination temperature was 550 °C. The obtained products consisted of CoFe₂O₄ phase accompanied by ferric oxide phase, with an average particle size about 1 μm and magnetization intensity about 10 emu/g.     

Hydrothermal synthesis of lead dioxide/multiwall carbon nanotube nanocomposite and its application in removal of some organic water pollutants

Lead dioxide/multiwall carbon nanotube (PbO₂/MWCNT) nanocomposite was synthesized by hydrothermal formation of lead dioxide on functionalized MWCNT. PbO₂ nanoparticles were formed from 0.015 M Pb(OH) ₃ ^? (75 ml) solution in the presence of polyvinyl pyrrolidone (0.1 g). The solution was mixed with ammonium persulfate (NH₄)₂S₂O₈ as oxidizing agent and transferred to 100 ml Teflon-lined stainless steel autoclave heating it to 60 °C for 3 h. To prepare nanocomposite, PbO₂ formation was carried out in the presence of ultrasonically dispersed MWCNT. A black-brown product was formed in reaction vessel. The product was collected and then dried in an oven at 70 °C for 24 h. The morphology and composition of precipitate were investigated by X-ray power diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy and transmission electron microscopy (TEM). The results of XRD and TEM show globular α-PbO₂ nanoparticles immobilize on the surface of the MWCNTs. Also, TGA results demonstrated the presence of CNT in nanocomposite. The prepared PbO₂/MWCNT nanocomposite is used to construct the solid-phase cartridge. The performance of solid phase in the removal of pesticides from drinking water is determined by gas chromatography–mass spectroscopy (GC–MS) analysis. The average adsorption depends on concentration of spiked pollutants and their relative standard deviations were between 1.4 and 11 %.     

Synthesis of doubly functional nanowhiskers from a colloid solution including a V–Ti complex precursor

In this study, we synthesized vanadium (V) nanoparticles precursor (NH₄)₅[(VO)₆(CO₃)₄(OH)₉]·10H₂O a two-phase system of toluene and water. Colloid solution including titanium(IV) isopropoxide and polyvinylpyrrolidone (PVP) was subsequently deposited onto the nanoparticles to form urchin-like structures in a toluene solution as the vanadium–titanium (V–Ti) complex precursor. Calcining the urchin-like precursor at 700 °C generated nanowhiskers of the Ti/V oxide complex after annealing process. These nanowhiskers were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron microscopy (XPS). Films of the Ti/V oxide nanowhisker structure exhibited good visible transparency and a large change in transmittance at near-infrared (NIR) wavelengths before and after the metal–insulator phase transition. For a 44-nm-thick single-layer nanowhisker thin film, the transmittances at 700 nm in the metallic (M) and semiconductive (S) states were 75 and 72.2 %, respectively; the NIR switching efficiency (ΔT ₂₀₀₀) increased from 17 to 21.3 % at 2000 nm under UV light irradiation. In addition, the nanowhisker thin film of the Ti/V oxide complex significantly enhanced the photodecomposition of methylene blue under UV irradiation, relative to that of the unmodified TiO₂. The dual functions of this material—thermochromicity and photocatalytic behavior—suggest that it might have interesting applications in energy-saving smart windows.     

Thick LPE layers of InAs1−x Sb x for 3–5 μm optoelectronic applications

A calculation of the In–As–Sb phase diagram in the low-temperature range 300–450 °C has been made. Liquid phase epitaxy was performed to grow InAs_1?x Sb _x layers on InAs substrates at temperatures as low as 300 °C. High-quality layers were grown on InAs with x up to 0.26. Scanning electron microscopy (SEM) X-ray microprobe compositional analysis was performed and Raman scattering proved the layer homogeneity and crystal perfection. Pd/Ge/Au ohmic contacts (OC) to InAsSb LPE solid solutions with a low Sb content, doped with group IV elements (Sn and Si) were thermally evaporated. The incorporation of Ge and the redistribution of Si and Sn on the groups III and V vacancies after annealing at T_ann=250–400 °C governs the contact behavior. The C–V characteristics and photosensitivity of the p-InAs/n-InAsSb heterostructures confirmed their device applicability in the 3–5 μm spectral range. The OC deposited on surfaces pre-treated with (NH₄)₂S solid solution exhibited improved ohmic behavior.     

Preparation of high strength macroporous hydroxyapatite scaffold

Hydroxyapatite (HAp) powder was prepared from CaNO₃·4H₂O and (NH₄)₂HPO₄ by wet-chemical method and has phase stable up to 1250 °C. High strength macroporous HAp–naphthalene (HN) and HAp–naphthalene–benzene (HNB) scaffolds were fabricated by adapting sintering method. The resulting HAp scaffolds have porosity about 60 vol.% with compressive strength of ~ 11 MPa and average pore diameter in the range of ~ 125 μm. The incorporation of benzene in HN scaffold reduces the strength whereas enhanced both the porosity and pore size distribution. XRD, FTIR, SEM and mercury porosimeter techniques were used to study the phase purity, morphology, pore size and pore size distribution of scaffold. The study compared the effect of concentration of naphthalene on strength, porosity and pore size distribution on both HN and HNB scaffold. In-vitro bioactivity studies on HN and HNB scaffolds show the nucleation of spherical carbonated apatite particles on the surface in SBF solution.     

Characteristics and optical properties of Cd1−xMnxS nanorods prepared through hydrothermal route

CdS semiconductor nanorods doped with different contents of manganese have been successfully prepared by the hydrothermal reaction of CdCl₂ · 2.5H₂O and MnCl₂ · 5H₂O with (NH₄)₂S in aqueous solution at 180 °C. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that these samples are almost total rod-like with approximately identical diameter around 20 nm and the maximal length up to 300 nm. Novel optical properties have been observed via UV–Visual absorption spectra and photoluminescence (PL) spectra. The absorption shoulder and the two luminescence emission peaks have shifted in different way as the mole ratio of manganese in the nanorods varies. A possible PL mechanism is suggested to explain this spectroscopy behavior.     

Preparation of (NH4)Zr2(PO4)3 and HZr2(PO4)3

(NH₄)Zr₂(PO₄)₃ has been prepared, hydrothermally, from α-zirconium phosphate in three different ways; (1) from amine intercalates at 300°C, (2) from mixtures of ZrOCl₂·8H₂O in excess (NH₄)H₂PO₄ and (3) reaction of NH₄Cl with Zr(NaPO₄)₂. Ammonium dizirconium triphosphate is rhombohedral with a = 8.676(1) and $\text{c}\text{= 24.288(5)}\text{A}\text{?}$. It decomposed on heating to HZr₂(PO₄)₃. Below 600°C a complex, as yet unindexed, X-ray pattern was obtained. A very similar X-ray pattern was obtained by washing LiTi_0.1Zr_1.9(PO₄)₃ with 0.3N HCl. Heating this phase or NH₄Zr₂(PO₄)₃, above 600°C resulted in the appearance of a rhombohedral phase of HZr₂(PO₄)₃ with cell dimensions a = 8.803(5) and $\text{c}\text{= 23.23(1)}\text{A}\text{?}$. The protons were not completely removed until about 1150°C. Decomposition of (NH₄)Zr₂(PO₄)₃ at 450°C yielded an acidic gas whereas at 700°C NH₃ was evolved. A possible explanation for this behavior is presented.     

An analysis of the ammonium chloride route to anhydrous rare-earth metal chlorides

The ammonium chloride route to anhydrous rare-earth metal trichlorides, RECl₃, is a two-step procedure consisting in, firstly, the (dry or wet) synthesis of a complex chloride, (NH₄)₃ RECl₆ (t≈ 220°C) and, secondly, its decomposition either directly (small RE, t≈ 425°C) or via the intermediates (NH₄)₂ RECl₅ (large RE, t≈ 385°C) and NH₄RE₂Cl₇ (medium-size RE), respectively.