Fractionation of nano- and microparticles in a rotating conoidal coiled column

A method for the continuous-flow fractionation of particles in a transverse centrifugal field in a rotating conoidal coiled (RCC) column has been developed. A model of a planetary centrifuge with a conoidal drum of a special construction has been tested. The effects of the rotation and revolution speed of the conoidal RCC, as well as the direction and pumping rate of the mobile phase on the behavior of particles smaller than 1 μm have been studied. The conditions have been selected and optimized for the retention and elution of spherical particles of the ‘150 nm’, ‘400 nm’, and ‘900 nm’ standard samples of silica gel (Polyscience Inc.). The possibility of using RCC for the analysis and production of monodisperse standard particle samples has been demonstrated. In particular, the ‘900 nm’ particles have been separated from admixtures of small (100–200 nm) particles and nonspherical 1–2 μm particles present in the sample. The separated fractions have been characterized by electron microscopy.     

Magnetic nano- and microparticles in biotechnology

Both synthetic and biologically produced magnetic nano- and microparticles exhibit several types of responses to external magnetic field which have been already employed in various areas of biosciences, biotechnology, medicine, environmental technology, etc. This short review shows selected important biotechnological applications of magnetic particles, and the biological processes leading to biogenic magnetic particles formation. Presented at the 1st Nanomaterials and Nanotechnology Meeting, Nano Ostrava, Ostrava, Czech Republic, 1–4 September 2008.     

Hydrothermal synthesis of metal oxide nano- and microparticles in supercritical water

Hydrothermal syntheses of nano- and microparticles of metal oxides of two types, LiMO _n (LiCoO₂, LiNiO₂, LiZnO₂, and LiCuO₂) and MO _n (Ga₂O₃, CeO₂) were performed under continuous conditions in a tubular reactor with the use of supercritical water. An important role in the synthesis of nanoparticles and the reproducibility of the results was played by the conditions of mixing of supercritical water and precursor solution flows. The morphology and composition of synthesized compounds were studied by scanning electron microscopy and X-ray diffraction. The syntheses of LiCoO₂, LiNiO₂, LiZnO₂, LiCuO₂, Ga₂O₃, and CeO₂ were most successful.     

Pyrolysis in the mesophase: a chemist's approach toward preparing carbon nano- and microparticles

A mild pyrolytic method is proposed for the generation of different carbon micro- and nanoparticles that are either unprecedented or have never been reported under the present experimental conditions. A hexa-alkyl-substituted hexa-peri-hexabenzocoronene serves as a graphite-like starting compound that melts into a discotic liquid crystalline phase prior to heat-induced cross-linking and dehydrogenation. An essential feature of the process is that the liquid crystalline order persists even above 400 degrees C, i.e., during alkyl chain cleavage. The present approach bears a resemblance to carbomesophase formation during graphitization starting from pitch. The pyrolysis products are characterized by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, optical microscopy, selected area electron diffraction (SAED), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM).     

Synthesis of gold nano- and microplates in hexagonal liquid crystals

Single-crystalline gold nano- and microplates with triangular or hexagonal shapes are synthesized by reduction of HAuCl(4) in lyotropic liquid crystal (LLC) mainly made of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers and water after adding a small amount of capping agents, cetyltrimethylammonium bromide (CTAB) or tetrabutylammonium bromide (TBAB). During the growth of such plates, capping agents play the crucial role. It is found that there is an optimal value of CTAB or TBAB concentration for producing microplates. The selective adsorption of CTAB or TBAB on certain crystallographic facets may be the key point of the supposed mechanism. Although LLC does not really act as a template, it provides an ordered structure confining CTAB as well as the nascent metal nuclei, which enhances the oriented attachment of nuclei and thus the consequent growth of single-crystal plates.     

PLA nano- and microparticles for drug delivery: an overview of the methods of preparation

The controlled release of medicaments remains the most convenient way of drug delivery. Therefore, a wide variety of reports can be found in the open literature dealing with drug delivery systems. In particular, the use of nano- and microparticles devices has received special attention during the past two decades. PLA and its copolymers with GA and/or PEG appear as the preferred substrates to fabricate these devices. The methods of fabrication of these particles will be reviewed in this article, describing in detail the experimental variables associated with each one with regard to the influence of them on the performance of the particles as drug carriers. An analysis of the relationship between the method of preparation and the kind of drug to encapsulate is also included. Furthermore, certain issues involved in the addition of other monomeric substrates than lactic acid to the particles formulation as well as novel devices, other than nano- and microparticles, will be discussed in the present work considering the published literature available.     

Proteomic characterization of human platelet-derived microparticles

Microparticles (MPs) are small fragments of apoptotic or activated cells that may contribute to pathological processes in many diseases. Platelet-derived MPs (PMPs) are the most abundant type of MPs in human blood. To characterize the proteins in PMPs we used a shotgun proteomics approach by nanoHPLC separation followed by MS analysis on an LTQ Orbitrap XL. PMPs were produced from isolated platelets stimulated with adenosine diphosphate (ADP). We developed an analytical platform constituted by two different steps: in the first one we used a standard shotgun strategy; in the second one, to improve low-molecular weight, low-abundance-proteins identification, the samples were fractionated using hydrogel nanoparticles, an enrichment system based on a mixed mechanism of dimensional exclusion and colorant affinity. This was chosen to tackle a common issue with shotgun approaches, in which the low-abundance proteins are not detected when surveys are on a broad scale. By means of the entire analytical platform, we identified 603 proteins, 243 of which were not previously identified. A simple and straightforward procedure for the study of PMPs was provided, producing a tool for further understanding their biological and pathological roles, and a baseline for future studies aimed at discovering biomarkers involved in several diseases.     

Comparison of the preparation of PLGA–BSA nano- and microparticles by PVA, poloxamer and PVP

The objective of our study was to prepare nano- and microparticles economically considering some practical parameters such as size and encapsulation efficiency as well as ability of particle recovery. Bovine serum albumin (BSA) model protein was encapsulated by poly(d,l-lactide-co-glycolide) (PLGA) using a multiple water-in-oil-in-water emulsion-solvent evaporation technique. The effect of three surfactants: polyvinyl alcohol, poloxamer, and polyvinyl pyrrolidone, used in the outer water phase, on the properties of particles was investigated. The emulsifier/PLGA mass ratio played an important role in the preparation procedure of the particles. This ratio was found to be approximately 1 for polyvinyl alcohol (PVA) if the aim was to formulate nanoparticles with narrow size distribution (<220 nm), high yield and good encapsulation efficiency (>90%). Although, a ratio of 2:1 was sufficient to produce submicron particles by poloxamer with high yield, more than 70% and 90% encapsulation efficiency required minimum 4 and 10 emulsifier/PLGA mass ratio, respectively. Five times more PVA and 10 times more poloxamer than the PLGA mass were necessary to obtain nanoparticles which were easy to redisperse after centrifugation. Microparticles released more BSA than nanoparticles prepared by PVA, however, the situation was reverse with poloxamer. Microparticles formulated by polyvinyl pyrrolidone (PVP) showed the fastest in vitro release.     

Preparation and characterization of copolymerized aminopropyl/phenylsilsesquioxane microparticles

Poly(aminopropyl/phenyl)silsesquioxane (PAPSQ) microparticles with approximately 350 nm diameter were conveniently synthesized from the hydrolytic co-condensation of γ-aminopropyltriethoxysilane (APS) and phenyltriethoxysilane (PTES) in the presence of ethanol and water (EtOH-H₂O) by using tetramethylammonium hydroxide (TMAOH) catalysts. Hybrid compositions of PAPSQ containing both aminopropyl and phenyl groups were confirmed from FT-IR, ²⁹Si CP-MAS NMR, TGA. XRD patterns indicated that a certain ordered structure existed in PAPSQ molecules. Contents of amino groups of PAPSQ were determined by elemental analysis and back titration. Specific surface areas were evaluated through BET method. PAPSQ offers the potential utility as building blocks for diverse and novel organic/inorganic materials.     

Vapor and liquid equilibria in porous media

The alteration of the vapor–liquid equilibrium (VLE) of volatile organic mixtures by placing porous media at the liquid–vapor interface was studied. Kelvin, assuming ideal behavior of fluids, first introduced the vapor pressure of liquid over a meniscus as a function of its surface tension and the radius of the curvature. A thermodynamic model (SS_mod model) predicting the VLE of non-ideal organic mixtures in porous media was developed as a function of pore sizes. The model was used to predict the VLE of two aqueous alcohol solutions, ethanol–water and propanol–water, and two binary solutions, methanol–isopropanol and ethanol–n-octane. Experiments were conducted using sintered metal and fritted glass plates as porous media, and the results were compared with the model predictions. Using the actual diameter of the porous media, the model prediction showed good agreement with the experimental results.     

Solid-state thermolysis of [MnO]12 containing molecular clusters into novel MnO nano- and microparticles

Novel MnO nano- and microparticles including spherical nanoparticles and various micropolyhedra of pyramid-like, truncated rectangular pyramid-like, cubic, and rhombic dodecahedral particles, were controllably synthesized via solid-state thermolysis of inorganic core containing molecular clusters [Mn₁₂O₁₂(O₂CR)₁₆(H₂O)₄] (R=C₆H₅, CH₃, and C₆H₅OCH₂) in a conventional horizontal tube furnace. Among them, pyramid-like, truncated rectangular pyramid-like, cubic, and rhombic dodecahedral MnO submicroscale particles were reported for the first time. The products were characterized by XRD, XPS, Raman spectrum, SEM, EDX, TEM and HRTEM. During the reaction process, thermolysis temperature, reaction time, and different molecular clusters {Mn12} precursors with different organic ligands as well play important roles in determining the sizes and shapes of the final products. The formed MnO nanospheres from [Mn₁₂O₁₂(O₂CC₆H₅)₁₆(H₂O)₄] at 400 °C for 10 h exhibited weak ferromagnetic behavior at low temperature which may be due to the size-effect of nanomaterials. Furthermore, the possible formation mechanism was also discussed.     

Fractionation of red wine polyphenols by solid-phase extraction and liquid chromatography

A systematic method for separation of aged red wine polyphenols into various distinct fractions using combined techniques of solid-phase extraction and liquid chromatography was proposed. The aged red wine polyphenols were separated into various distinct fractions including phenolic acid fraction, monomer flavanol fraction, oligomer procyanidin fraction, anthocyanin and its pyruvic acid derivative fraction, free or non-colored proanthocyanidin fraction, fraction of direct condensation products between anthocyanins and proanthocyanidins and fraction of other pigmented complexes. The phenolic composition of each fraction was verified by HPLC with diode array detection (HPLC-DAD), thiolysis, vanillin assay, HPLC coupled with electrospray ionization mass spectrometry (HPLC-ESI-MS) and multi-stage MS fragment analysis. For the first time, anthocyanins and their pyruvic derivatives were separated from other phenolic compounds, while free or non-pigmented polymer proanthocyanidins from other pigmented complexes. The fractionation method would be of particular interest in further studying the detailed composition of polymeric polyphenols in red wine.     

Mechanical characterization of soft microparticles prepared by droplet microfluidics

Droplet microfluidics is one of the most promising approaches that allows preparation of microparticles with tailored structure and composition. Various functional microparticles have been developed using microfluidics, where their controlled structure shows high potential for a wide range of applications. Among these, soft polymeric microparticles which exhibit low elastic modulus compared to ceramics and metals are extensively investigated in biomedical applications due to their biocompatibility, high surface-to-volume ratio, as well as soft and deformable nature. As the mechanical properties of soft microparticles play important role in determining how they function in each application, it is essential to adequately characterize them for the optimal design of functional microparticles. In this review, we mainly discuss the mechanical characterization methods of soft microparticles and their elastic property. A brief overview of the droplet microfluidics-assisted fabrication of microparticles is also provided before discussing the mechanical characterization techniques. We then describe the general characterization methods and models employed to determine the elastic properties of microparticles. In addition, we discuss the relationship between the physical parameters (size, composition, and structure) and the elastic properties of the microparticles, followed by the role of elastic properties in various applications including microcarrier, bioink, and self-healing to name a few.     

The characterization of silica microparticles by electrophoretic mobility measurements

Summary Electrophoretic mobility measurements in the pH 2‐10 range are described for several commercial HPLC silica microparticles and a laboratory-produced product. The content of metal impurities for the silicas was also determined by AAS. An acidic/hydrothermal treatment was used to generate a more homogenous surface for some of the silicas. The zero points of charge (zpc) for both a native and a treated silica plus several commercial HPLC silicas were compared. The electrophoretic mobility method may be useful in predicting the utility of certain types of silica supports for chromatographic separations.     

Colloid-induced structure in liquid crystal media

The structural perturbations induced by colloidal particles immersed in a model nematic subjected to an external field are calculated employing integral equation methods. Maps of the density-orientational distribution about a colloidal particle are obtained, and these provide a microscopic picture of the colloid's nematic coat. We focus on colloidal particles that favor homeotropic anchoring, but planar anchoring cases are also considered. The range and structure of the nematic coat is shown to be significantly influenced by the nature of the anchoring, the size of the colloidal particle, the range and strength of the colloid-nematogen interaction, and the external field strength. All of these factors are discussed.