Stable Hollow Spheres Research Articles

Factors influencing the properties and the stability of spray-dried Sennae fructus extracts

Objective: The objective of this study was to characterize the properties of aqueous Sennae fructus extracts prepared by spray-drying at varying process conditions.Significance: From an industrial point of view it is essential to develop a formulation which has a constant quality over the whole period of its specified shelf-life.Method: Sennae fructus extracts were spray-dried with different atomizing gas pressures, pump feed rates, and inlet temperatures. The extracts were analyzed for their physical properties and stored at accelerated conditions. Sennoside degradation was monitored by HPLC analysis.Results: An increase of the atomizing gas pressure had the most pronounced influence on the decrease of moisture content and particle size. An increase of the inlet temperature led to a decrease of moisture content and particle density, as well as an increase of smooth particle amount. An increase in the pump feed rate, increased the moisture content and resulted in stable hollow spheres. The different conditions also led to smooth or wrinkled particle surfaces, and to golfball, donut, and shard particle shapes. The chemical stability of the sennosides differed from each other after storage. Stability-reducing factors were the moisture content of the samples and their hygroscopicities, as well as different particle morphologies. These factors were influenced by the inlet temperature of the spray-drying process. High inlet temperatures led to a positive influence on dryness and particle morphology and therefore on the stability of the sennosides.Conclusions: Variation of the process conditions affected the resulting particle properties and their storage stability of Sennae fructus extract.

Self-templating synthesis of hollow spheres of zeolite ZSM-5 from spray-dried aluminosilicate precursor

Synthesis of hollow spheres consisting of ZSM-5 zeolite crystals, prepared by a cost- and time-saving self-templating process, requires neither a hard/soft template for sphere formation nor tetraalkylammonium compound as a zeolite structure-directing agent. A preshaped aluminosilicate precursor, obtained by spray drying of a mixture of colloidal solution of silicic acid and aluminum butoxide, plays the role of a shape-directing agent for the formation of spheres, and is used as a source of silica and alumina for zeolite growth. The zeolite structure is directed using ZSM-5 seeds. This method yielded highly stable hollow spheres with diameters of 15–25 μm, consisting of inter-grown ZSM-5 crystals (Si/Al 14) with a size of 0.5–2.0 μm.

Stabilizing Alginate Confinement and Polymer Coating of CO-Releasing Molecules Supported on Iron Oxide Nanoparticles To Trigger the CO Release by Magnetic Heating.

Maghemite (Fe2O3) iron oxide nanoparticles (IONPs) were synthesized, modified with covalent surface-bound CO-releasing molecules of a tri(carbonyl)-chlorido-phenylalaninato-ruthenium(II) complex (CORM), and coated with a dextran polymer. The time- and temperature-dependent CO release from this CORM-3 analogue was followed by a myoglobin assay. A new measurement method for the myoglobin assay was developed, based on confining "water-soluble" polymer-coated Dextran500k@CORM@IONP particles in hollow spheres of nontoxic and easily prepared calcium alginate. Dropping a mixture of Dextran500k@CORM@IONP and sodium alginate into a CaCl2 solution leads to stable hollow spheres of Ca(2+) cross-linked alginate which contain the Dextran500k@CORM@IONP particles. This "alginate-method" (i) protects CORM-3 analogues from rapid CO-displacement reactions with a protein, (ii) enables a spatial separation of the CORM from its surrounding myoglobin assay with the alginate acting as a CO-permeable membrane, and (iii) allows the use of substances with high absorptivity (such as iron oxide nanoparticles) in the myoglobin assay without interference in the optical path of the UV cell. Embedding the CORM@IONP nanoparticles in the alginate vessel represents a compartmentation of the reactive component and allows for close contact with, yet facile separation from, the surrounding myoglobin assay. The half-life of the CO release from Dextran500k@CORM@IONP particles surrounded by alginate was determined to be 890 ± 70 min at 20 °C. An acceleration of the CO release occurs at higher temperature with a half-life of 172 ± 27 min at 37 °C and 45 ± 7 min at 50 °C. The CO release can be triggered in an alternating current magnetic field (31.7 kA m(-1), 247 kHz, 39.9 mT) through local magnetic heating of the susceptible iron oxide nanoparticles. With magnetic heating at 20 °C in the bulk solution, the half-life of CO release from Dextran500k@CORM@IONP particles decreased to 155 ± 18 min without a noticeable temperature increase in the dispersion. At 37 and 50 °C, the half-life for the CO release triggered by local magnetic heating was 65 ± 5 min and 30 ± 3 min, respectively. Thus, at a physiological temperature of 37 °C, magnetic heating accelerates the CO release of the IONP-bound CORM by a factor of ∼ 2.6. The activation energy for CO release from a CORM-3 analogue was determined to be EA = 78 kJ/mol.

Microemulsion template synthesis of copper sulfide hollow spheres at room temperature

CuS hollow spheres have been synthesized through a facile microemulsion template route at room temperature using copper naphthenate as metal precursor and thioacetamide as the source of S 2−. In our method, the metal precursor and sulfur source dissolved in two different phases; the reaction only occurs at oil/water interface. Thus, hollow spheres can be fabricated more easily. The CuS hollow spheres prepared at room temperature are loose aggregates which are composed of small primary nanoparticles. To form stable hollow spheres it is a key to ensure the growth of nanoparticles at initial stage of reaction by a high interfacial reaction rate. So the reaction conditions that can control interfacial reaction rate are important factors for forming hollow spheres.

Stable luminescent films and hollow spheres comprising CdTe nanoparticles

CdTe nanoparticles (CdTe-NPs) capped by 3-mercaptopropionic acid weresynthesized and used to self-assemble (SA) with poly(allylamine hydrochloride)(PAH) layer-by-layer via electrostatic interaction to form luminescentmultilayer films. Composite particles were prepared with polymer orSiO2 beads as the core and PAH/CdTe-NP SA films as the shell. The composite particleswere dissolved out of the core with tetrahydrofuran (THF) or HF to preparehollow spheres, then treated with 1-ethyl-3-(3-dimethyl-aminopropyl)-carbodiimidehydrochloride (EDC) in aqueous solution to form stable hollow spheres with a crosslinkedPAH/CdTe-NP shell. Both the crosslinked films and the hollow spheres with ahigh luminescence are very stable in aqueous solutions at a wide range of pH.

Synthesis of stable hollow spheres of Si/Al composite oxide with controlled pore size in the shell wall

Stable hollow spheres of Si/Al composite oxide were synthesized by sol–gel process in o/w/o (oil/water/oil) microemulsion with PEG as the additive. The images of optical microscope and scanning electron microscope (SEM) showed that the spheres were consisted of hollow structure with the uniform sphere size of about 10 μm and shell thickness of about 3 μm. Furthermore, from transmission electron microscope (TEM), we clearly observed many worm-like pores in the shell of spheres. It was interesting to first find that the pore sizes in the shell of spheres can be controlled by the chain length of PEG. The hollow spheres also exhibited good thermal stability and they could maintain the complete structure even after calcination under 650 °C for 8 h.

Synthesis of stable hollow spheres of Si/Al composite oxide with controlled pore size in the shell wall

Stable hollow spheres of Si/Al composite oxide were synthesized by sol–gel process in o/w/o (oil/water/oil) microemulsion with PEG as the additive. The images of optical microscope and scanning electron microscope (SEM) showed that the spheres were consisted of hollow structure with the uniform sphere size of about 10 μm and shell thickness of about 3 μm. Furthermore, from transmission electron microscope (TEM), we clearly observed many worm-like pores in the shell of spheres. It was interesting to first find that the pore sizes in the shell of spheres can be controlled by the chain length of PEG. The hollow spheres also exhibited good thermal stability and they could maintain the complete structure even after calcination under 650 °C for 8 h.

On stable spherical configurations of artificial protocells

The stability of protocells is discussed in terms of macroscopic energies. It is shown that bulk and surface energy contributions alone cannot lead to stable protocells. If electrostatic energy, due to transmembrane voltage, is taken into account, stable hollow spheres are proved to exist. For several reasons, however, this result should not be regarded as an ultimate explanation.

The stability of proteinoid microspheres

Proteinoid microspheres are stable hollow spheres of diameter of the order of 5 μm. Their stability is discussed in terms of macroscopic energies. it is shown that bulk and surface energy contributions alone cannot lead to stable microspheres. If electrostatic energy, due to transmembrane voltage, is taken into account, stable hollow spheres are proved to exist. For several reasons, however, this result should not be regarded as the ultimate explanation of microsphere stability.