Spherical Microparticles Research Articles

The effect of medium viscosity and particle volume fraction on ultrasound directed self-assembly of spherical microparticles

Ultrasound directed self-assembly (DSA) allows organizing particles dispersed in a fluid medium into user-specified patterns, driven by the acoustic radiation force associated with a standing ultrasound wave. Accurate control of the spatial organization of the particles in the fluid medium requires accounting for medium viscosity and particle volume fraction. However, existing theories consider an inviscid medium or only determine the effect of viscosity on the magnitude of the acoustic radiation force rather than the locations where particles assemble, which is crucial information to use ultrasound DSA as a fabrication method. We experimentally measure the deviation between locations where spherical microparticles assemble during ultrasound DSA as a function of medium viscosity and particle volume fraction. Additionally, we simulate the experiments using coupled-phase theory and the time-averaged acoustic radiation potential, and we derive best-fit equations that predict the deviation between locations where particles assemble during ultrasound DSA when using viscous and inviscid theory. We show that the deviation between locations where particles assemble in viscous and inviscid media first increases and then decreases with increasing particle volume fraction and medium viscosity, which we explain by means of the sound propagation velocity of the mixture. This work has implications for using ultrasound DSA to fabricate, e.g., engineered polymer composite materials that derive their function from accurately organizing a pattern of particles embedded in the polymer matrix.

Development of vitamin B12 containing pullulan-bovine serum albumin microparticles designed dry powder inhaler: In-vitro and in-vivo study

The poor permeability and low bioavailability of vitamin B12 (vit. B12) through the mucosal lining of lungs are required substitutes. Therefore, the present work aims to develop a dry powder inhaler (DPI) of (Vit.B12) encapsulated into bovine serum albumin (BSA) followed by pullulan coated micro particles (Vit.B12-Pull-BSA) through spray drying. Briefly, pullulan was used as a mucoadhesive agent whereas BSA was used as an encapsulating agent. The obtained Vit.B12-Pull-BSA micro-particles were characterized using different in-vitro spectroscopic techniques, in vitro dissolution, mucoadhesion study, particle size analysis, etc. As a result, the surface morphology of Vit.B12-Pull-BSA micro-particles shows spherical micro-particle with circular surface morphology that can be suitable for pulmonary drug delivery. The PXRD study reveals the conversion of the crystalline nature of vitamin B12 to amorphous nature. Particle size showed 590.1 nm and zeta potential of microparticles was −27.3 mV respectively, which indicates the good stability of particles. The in-vitro assessment of Vit.B12-Pull-BSA microparticles using cascade Impactor revealed that 90.8 ± 1.1% of dry powder formulation was emitted from the device whereas 64.1 ± 6.8% of vitamin B12 loaded particles were reached at a fine stage that suggests preferential delivery of micro-particle. Male Wister rats were utilized for pharmacokinetic analysis through intratracheal administration of Vit.B12-Pull-BSA micro-particles that confirmed the increase in the permeability. Accordingly, it increases the 4.5 folds' relative bioavailability of vitamin B12. In conclusion, the Vit.B12-Pull-BSA micro-particles-based DPI offers improved permeability and bioavailability that can provide the alternative for conventional drug delivery.

Proof-of-concept of a miniature pressure sensor based on coupled optical WGMs excited in a dielectric microsphere

Optical whispering-gallery mode (WGM) resonators retain increased interest as a key element in various high-resolution sensing and spectroscopic devices in modern optoelectronic, optofluidic and Lab-on-chip technologies. As a theoretical proof-of-concept, we present a new miniature pressure sensor based on coupled WGMs optically excited in a dielectric microsphere placed near a flexible reflective membrane which acts as an ambient pressure sensing element. WGMs are excited by free-space coupling of incoming optical radiation to a spherical microparticle. The distinctive feature of proposed sensor is double WGM excitation by forward and backward propagating radiation upon reflection from a membrane that causes WGMs interference in particle volume. Unlike known WGM-sensors, the proposed design utilize not the resonant frequency shift but the changes in optical intensity of resulting field established in the microsphere which carries information about the exact position of pressure-loaded membrane. The sensitivity of the proposed sensor strongly depends on the quality factor of the working resonance, as well as geometrical and mechanical parameters of flexible reflecting membrane. Important advantages of the proposed sensor are its miniature design and the absence of a mechanical contact of pressure-sensitive element with WGM resonator.

Thermo-Reversible Cellulose Micro Phase-Separation in Mixtures of Methyltributylphosphonium Acetate and γ-Valerolactone or DMSO.

We have identified cellulose solvents, comprised of binary mixtures of molecular solvents and ionic liquids that rapidly dissolve cellulose to high concentration and show upper‐critical solution temperature (UCST)‐like thermodynamic behaviour ‐ upon cooling and micro phase‐separation to roughly spherical microparticle particle‐gel mixtures. This is a result of an entropy‐dominant process, controllable by changing temperature, with an overall exothermic regeneration step. However, the initial dissolution of cellulose in this system, from the majority cellulose I allomorph upon increasing temperature, is also exothermic. The mixtures essentially act as ‘thermo‐switchable’ gels. Upon initial dissolution and cooling, micro‐scaled spherical particles are formed, the formation onset and size of which are dependent on the presence of traces of water. Wide‐angle X‐ray scattering (WAXS) and 13C cross‐polarisation magic‐angle spinning (CP‐MAS) NMR spectroscopy have identified that the cellulose micro phase‐separates with no remaining cellulose I allomorph and eventually forms a proportion of the cellulose II allomorph after water washing and drying. The rheological properties of these solutions demonstrate the possibility of a new type of cellulose processing, whereby morphology can be influenced by changing temperature.

Applications of chitosan as a polymer carrier for increasing the drugs’ bioavailability

Oral drug delivery is a dynamic research area, yet associated with multiple issues in its using: enzymatic degradation, hydrolysis, low permeability of intestinal epithelium. The review presents a research papers analysis on the development of targeted drug delivery using a biodegradable polymer chitosan. Chitosan application, singly or in composites, is suitable for various drug delivery systems. Upon oral delivery, chitosan serves as a mucoadhesive polymer with controlled and targeted release. During the last five years, various approaches to the delivery of insulin and other drugs had been reported in literature. The main technological strategy for insulin delivery was its protection against intestinal pH, as well as increasing of permeability via transcellular and/or paracellular pathways. It is observed that application of the biopolymer and its derivatives has a controlled absorption profile. In publications on the drugs delivery, most of the research is focused on development and modification of methods for their producing. According to the presented experimental data, there were obtained particles with well-defined spherical shapes and microparticles capacity of 85-97%. A number of research articles provide data on the chitosan application as a mucoadhesive coating for various nano- or microparticles. It was also noted that application of chitosan microparticles contributed to diminishing adverse side effects.

Microsphere: A Wander around Drug Delivery

Microspheres have free-flowing powder characteristics consisting of synthetic polymers and proteins with a particle size of 1-1000 μm. Microsphere improves bioavailability, stability and targets the drug to a selected site at a predetermined rate. Sorts of microspheres are bioadhesive, floating, radioactive, polymeric, and biodegradable microspheres. Therefore, the array of practices for the groundwork of microspheres offers a chance to regulate drug administration properties and develop the therapeutic efficacy of a given drug. The microsphere is spherical microparticles & is employed where predictable & consistent particle area is vital. The microspheres have the drug located centrally within the particle encased within the unique polymeric membrane. The present review highlights various sorts of microspheres, different methods of preparation, their applications, and various parameters to gauge their efficiency. Microspheres have received much attention not just for prolonged release but also for targeted medicine. A systematic review of one of the most promising drug delivery systems should be easier to read than the medical research articles, as they target a wider audience. The systematic reviews of the microparticles conclude that spherical microspheres & are accustomed to delivering the drug at the target site with specificity if modified and take care of the specified concentration at the location of interest without the untoward effects presented during a consistent therapy to help research and retrieval of health.

Co-encapsulation of vitamin D and rutin in chitosan-zein microparticles

There is a growing interest in co-encapsulating multiple species to harness potential synergy between them, enhance their stability and efficacy in various products. The aim of this work was to co-encapsulate vitamin D3 and rutin inside chitosan-zein microparticles using a simple and easily scalable process for food fortification. This was achieved via anti-solvent precipitation coupled with spray-drying. Free-flowing powders of spherical microparticles with wrinkled surface and particle size < 10 μm were obtained. The encapsulation efficiency was 75% for vitamin D3 and 44% for rutin and this could be attributed to their different molecular size and affinity to the aqueous phase. The physicochemical properties were characterized by X-Ray powder diffraction and Fourier transform infrared spectroscopy. The two crystalline bioactive compounds were present in the microparticles in amorphous form, which would allow for better bioavailability when compared to non-encapsulated crystalline solid. Therefore, the obtained microparticles would be suitable for use as food ingredient for vitamin D3 fortification, with the co-encapsulated rutin acting as stability and activity enhancer.

Deposition of Metal Films on Microparticles Trapped in RF Magnetron Discharge

The technique for a metal film deposition on spherical microparticles in an RF plasma trap is presented. Both the particle confinement and the electrode sputtering are performed by a single RF magnetron discharge. The samples of a coated spheres are obtained and examined. The technique allows confining the particles near to the sputtered region close to the border zone of ballistic bombardment by sputtered atoms.

Investigating the product distribution behaviour of CO2 methanation through thermodynamic optimized experimental approach using micro/nano structured titania catalyst

Catalytic CO2 hydrogenation yields a wide range of products, making products selectivity a major challenge. This study provides a comprehensive investigation on CO2 hydrogenation to CH4 by involving thermodynamic optimized experimental approach. First, thermodynamic analysis was carried out using equilibrium rate constants and Gibbs free and insights on the behaviour and product distribution of CO2 methanation were investigated. A low temperature (150–450 °C), elevated pressure and H2/CO2 feed ratio above 4 are essential for CH4 production. More importantly, as temperature rises, the product formation shifts from CH4 to CO, C2H6 and finally solid carbon. Upon thermodynamic optimization, an experimental approach was conducted using micro/nano structured conductive catalysts. CO2 methanation over Ni-dispersed conductive TiO2 microparticles (MPs)/nanowires (NWs) catalysts involves various complex reactions such as the adsorption, desorption and activation of molecules. An ideal Ni loading of 15 wt%, with GHSV of 6,300 mL g-1h−1 is beneficial for the CH4 production. Furthermore, TiO2 NWs provided a 1.32-fold enhancement in activity and CH4 production comparing to MPs, elucidating the enhancement effect of a one-dimensional (1D) nanowire structure over zero-dimensional (0D) spherical microparticle structure. YCH4, SCH4 and XCO2 over 15% Ni/TiO2 NWs achieved 88.9%, 99.1% and 89.8%, respectively. Despite a good agreement between the thermodynamic and experimental results, there was a slight difference in trend because the theoretical values can be obtained by just considering the feasibility of reactions in terms of ΔG and ln (K). Besides, catalytic experimental runs involves complex reactions through adsorption and desorption, leading to CH4 formation via different pathways. Due to the conductive characteristics and 1D structure of TiO2, the products distribution was close to thermodynamics value and exhibited higher stability that would be beneficial for further investigation in catalytic reactions.

Food nanoparticles from rice vinegar: isolation, characterization, and antioxidant activities

Abundant nanostructures have been constantly found in various foods, like vinegar, tea, coffee, and milk. However, these structures largely remain unexplored and even been eliminated for stability reasons in food industry. Here we report the isolation, characterization, and antioxidant activities of food nanoparticles (NPs) carrying polyphenols from Chinese rice vinegar. Using a gel-chromatography-based isolation protocol, the vinegar was separated into three major fractions. They were identified as spherical NPs (P1), lollipop-like NPs (P2) and spherical microparticles (P3) with average hydrodynamic diameter of 210, 245,1643 nm, separately. The former two fractions accounted for the major parts of dry matter in the vinegar. The P1-NPs fraction was composed of proteins, carbohydrates, and a high number of polyphenols (15 wt%), demonstrated potent antioxidant activity as determined by ABTS and ORAC assays. Moreover, they effectively quenched peroxyl free radicals in peritoneal macrophages and promoted cellular growth. The P2 fraction contained majority of organic acids, esters and mineral elements of the vinegar. It demonstrated the NPs are bioactive units of the rice vinegar, inspiring the development of novel functional nanomaterials with nutraceutical and pharmaceutical applications.

Electrostatic loading and photoredox-based release of molecular cargo from oligoviologen-crosslinked microparticles.

Although on-demand cargo release has been demonstrated in a wide range of microparticle platforms, many existing methods lack specific loading interactions and/or undergo permanent damage to the microparticle to release the cargo. Here, we report a novel method for electrostatically loading negatively charged molecular cargo in oligoviologen-crosslinked microparticles, wherein the cargo can be released upon activation by visible light. A water-in-oil (W/O) emulsion polymerization method was used to fabricate narrowly dispersed microparticles crosslinked by a dicationic viologen-based dimer and a poly(ethylene glycol) diacrylate. A zinc-tetraphenyl porphyrin photocatalyst was also polymerized into the microparticle and used to photochemically reduce the viologen subunits to their monoradical cations through a visible-light-mediated photoredox mechanism with triethanolamine (TEOA) as a sacrificial reductant. The microparticles were characterized by microscopy methods revealing uniform, spherical microparticles 481 ± 20.9 nm in diameter. Negatively charged molecular cargo (methyl orange, MO) was electrostatically loaded into the microparticles through counteranion metathesis. Upon irradiation with blue (450 nm) light, the photo-reduced viologen crosslinker subunits lose positive charges, resulting in release of the anionic MO cargo. Controlled release of the dye, as tracked by absorption spectroscopy, was observed over time, yielding release of up to 40% of the cargo in 48 h and 60% in 120 h in single dynamic dialysis experiment. However, full release of cargo was achieved upon transferring the microparticles to a fresh TEOA solution after the initial 120 h period.

A particulate blood analogue based on artificial viscoelastic blood plasma and RBC-like microparticles at a concentration matching the human haematocrit.

There has been enormous interest in the production of fluids with rheological properties similar to those of real blood over the last few years. Application fields range from biomicrofluidics (microscale) to forensic science (macroscale). The inclusion of flexible microparticles in blood analogue fluids has been demonstrated to be essential in order to reproduce the behaviour of blood flow in these fields. Here, we describe a protocol to produce a whole human blood analogue composed of a proposed plasma analogue and flexible spherical microparticles that mimic the key structural attributes of RBCs (size and mechanical properties), at a concentration matching the human haematocrit (∼42% by volume). Polydimethylsiloxane (PDMS) flexible microparticles were used to mimic RBCs, whose capability to deform is tunable by means of the mixing ratio of the PDMS precursor. Their flow through glass micronozzles allowed us to find the appropriate mixing ratio of PDMS to have approximately the same Young's modulus (E) as that exhibited by real RBCs. Shear and extensional rheology and microrheology techniques were used to match the properties exhibited by human plasma and whole blood at body temperature (37 °C). Finally, we study the flow of our proposed fluid through a microfluidic channel, showing the in vitro reproduction of the multiphase flow effects taking place in the human microcirculatory system, such as the cell-free layer (CFL) and the Fåhræus-Lindqvist effect. A macroscale application in the field of forensic science is also presented, concerning the impact of our blood analogue droplets on a solid surface for bloodstain pattern analysis.

Droplet-Based Microfluidic Preparation of Shape-Variable Alginate Hydrogel Magnetic Micromotors.

This article introduces a facile droplet-based microfluidic method for the preparation of Fe3O4-incorporated alginate hydrogel magnetic micromotors with variable shapes. By using droplet-based microfluidics and water diffusion, monodisperse (quasi-)spherical microparticles of sodium alginate and Fe3O4 (Na-Alg/Fe3O4) are obtained. The diameter varies from 31.9 to 102.7 µm with the initial concentration of Na-Alginate in dispersed fluid ranging from 0.09 to 9 mg/mL. Calcium chloride (CaCl2) is used for gelation, immediately transforming Na-Alg/Fe3O4 microparticles into Ca-Alginate hydrogel microparticles incorporating Fe3O4 nanoparticles, i.e., Ca-Alg/Fe3O4 micromotors. Spherical, droplet-like, and worm-like shapes are yielded depending on the concentration of CaCl2, which is explained by crosslinking and anisotropic swelling during the gelation. The locomotion of Ca-Alg/Fe3O4 micromotors is activated by applying external magnetic fields. Under the rotating magnetic field (5 mT, 1–15 Hz), spherical Ca-Alg/Fe3O4 micromotors exhibit an average advancing velocity up to 158.2 ± 8.6 µm/s, whereas worm-like Ca-Alg/Fe3O4 micromotors could be rotated for potential advancing. Under the magnetic field gradient (3 T/m), droplet-like Ca-Alg/Fe3O4 micromotors are pulled forward with the average velocity of 70.7 ± 2.8 µm/s. This article provides an inspiring and timesaving approach for the preparation of shape-variable hydrogel micromotors without using complex patterns or sophisticated facilities, which holds potential for biomedical applications such as targeted drug delivery.

Fabrication and characterization of osteogenic function of progenitor cell-laden gelatin microcarriers.

Biomaterial-based bone regeneration strategies often include a cellular component to accelerate healing. Modular approaches have the potential for minimally-invasive delivery and the ability to conformally fill complex defects. In this study, spherical gelatin microparticles were fabricated via water-in-oil emulsification and were subsequently crosslinked with genipin. Microparticle diameter depended on impeller geometry, and increased stirring rates consistently produced smaller particles with narrower size distributions. Increasing the concentration of gelatin resulted in larger particles with a broader size distribution. Viscoelastic characterization showed that increased gelatin concentration produced stiffer matrices, though the mechanical properties at lower gelatin concentration were more stable across strain rate. Microparticles of 6.0% wt/vol gelatin were then applied as microcarriers for packed-bed culture of human mesenchymal stromal cells (MSC) at seeding densities of 5.0 × 103 , 2.5 × 104 , or 5.0 × 104 cells/cm2 of surface area, in either control or osteogenic medium. Cell viability was uniformly high (>90%) across seeding densities over 22 days in culture. MSC number stayed approximately constant in the 5.0 × 103 and 2.5 × 104 cells/cm2 samples, while it dropped over time at 5.0 × 104 cells/cm2 . Alkaline phosphatase activity was significantly upregulated in osteogenic conditions relative to controls at day 15, and absolute calcium deposition was strongly induced by days 15 and 22. However, calcium deposition per cell was highest in the lowest cell density, suggesting an inhibitory effect of high cell numbers. These results show that genipin-crosslinked gelatin microcarriers can be reproducibly fabricated and used as microcarriers for progenitor cells, which may have utility in treating large and complex bone defects.

Simplified Synthesis of Spherical Silica Microparticles from Rice Husk

AbstractA facile synthetic method for preparing spherical silica microparticles from rice husks was developed. Spherical silica particles with an overall size of several micrometers were obtained via direct extraction of silicate solution from rice husks, followed by precipitation of silica using nitric acid and a polymer additive. The synthetic process was simplified by omitting the acid leaching and pyrolysis processes of the rice husks. Herein, it was demonstrated that the extraction of silicate under mild conditions, combined with the use of a polyethylene glycol additive during the precipitation step, are crucial for obtaining spherical silica microparticles. Moreover, the porosity of the silica particles could be controlled by adjusting the calcination temperature.

Methods—A Potential–Dependent Thiele Modulus to Quantify the Effectiveness of Porous Electrocatalysts

Electrochemical reactors often employ high surface area electrocatalysts to accelerate volumetric reaction rates and increase productivity. While electrocatalysts can alleviate kinetic overpotentials, diffusional resistances at the pore-scale often prevent full catalyst utilization. The effect of intraparticle diffusion on the overall reaction rate can be quantified through an effectiveness factor expression governed by the Thiele modulus parameter. This analytical approach is integral to the development of catalytic structures for thermochemical processes and has previously been extended to electrochemical processes by accounting for the relationship between reaction kinetics and electrode overpotential. In this paper, we illustrate the method by deriving the expression for the potential-dependent Thiele modulus and using it to quantify the effectiveness factor for porous electrocatalytic structures. Specifically, we demonstrate the application of this mathematical framework to spherical microparticles as a function of applied overpotential across catalyst properties and reactant characteristics. The relative effects of kinetics and mass transport are related to overall reaction rates, revealing markedly lower catalyst utilization at increasing overpotential. Subsequently, we generalize the analysis to different catalyst shapes and provide guidance on the design of porous catalytic materials for use in electrochemical reactors.

Drag-minimizing spore/pollen-mimicking microparticles for enhanced pulmonary drug delivery: CFD and experimental studies

The aim of this work is to build a Computational fluid dynamics (CFD) model to study the flowability of fungal spores and pollen grains to predict their ability to flow to the deep lung in order to relate this to the potentiality of allergies, and predict the possibility of using spores/pollen grains-mimicking microparticles for pulmonary drug delivery. The CFD model was designed using COMSOL Multiphysics to calculate the drag forces exerted on the pollens and spores by the air in the upper and lower lung bronchioles. Experimental verification was conducted by comparing the aerosolization of Aspergillus spores and spherical microparticles, as a control shape, using Next Generation Impactor as a lung-simulation device. The CFD model showed that the drag force exerted on the spores and pollen grains can affect their pathogenicity. In addition, the shapes of some spores (e.g. Alternaria, Drechslera and Aspergillus) or pollens (e.g. Quercus and Eucalyptus) have low drag and can be used for drug delivery to the deep lung. The experimental results coincided with the CFD model and showed that the shape of Aspergillus spores can reach the deep lung with about 1.6-fold higher dose than the spherical shape. The obtained results indicate that shapes of some spores and pollen grains are drag-minimizing allowing them to spread and to be inhaled to the deep lung; so they can be used for the development of dry powder inhaler formulations.

Focusing a vortex laser beam and converting linear to circular polarization

We show that when strongly focusing a linearly polarized optical vortex with the topological charge 2, in the near-focus region, there occurs not only a reverse energy flow (where the projection of the Pointing vector is negative) but the right-handed circular polarization of light as well. Notably, thanks to spin–orbital conversion the on-axis polarization vector handedness is the same as that of the transverse energy flow, i.e. anticlockwise. An absorbing spherical microparticle centered on the optical axis placed in the focus may be expected to rotate anticlockwise around its axis and its center of masses. Theoretical predictions are corroborated by the numerical simulation.

Focusing a Vortex Laser Beam with Polarization Conversion

We show that when strongly focusing a linearly polarized optical vortex with the topological charge 2 (or −2) in the near-focus region, there occurs not only a reverse energy flow (where the projection of the Poynting vector is negative) but the right- (or left-) handed circular polarization of light as well. Notably, thanks to spin–orbital conversion, the on-axis polarization vector handedness is the same as that of the transverse energy flow, i.e., anticlockwise (clockwise). An absorbing spherical microparticle centered on the optical axis placed in the focus may be expected to rotate anticlockwise (clockwise) around its axis and its center of masses. We also show that in the case of sharp focusing of light with linear polarization (without an optical vortex) before and after focus, the light has an even number of local regions with left- and right-handed circular (elliptical) polarizations. Theoretical predictions are corroborated by the numerical simulation.

DEVELOPMENT OF POLYMERIC MICROPARTICLES WITH RADACHLORINE AND ESTIMATION OF THE PROSPECTS OF THEIR USE IN PHOTODYNAMIC THERAPY

Introduction. Nowadays, the development of delivery systems based on micro- and nanoparticles is being actively pursued to increase the selectivity and efficiency of photosensitizers in photodynamic therapy. Such microparticles could increase the effectiveness of the already used chemotherapeutic drugs due to their accumulation in the tumor and help to overcome the drug resistance of tumor cells.The aim of this research was to obtain microparticles based on a biocompatible block copolymer of lactic and glycolic acids with the inclusion of the photosensitizer radachlorin, magnetic nanoparticles, and perfluorodecalin and their subsequent evaluation as therapeutic agents for photodynamic therapy.Materials and methods. Microparticles were obtained using the double emulsion method, described using of electron microscopy. Evaluation of their photodynamic properties was carried out using spectrophotometry and MTTtest on cell culture.Results. Spherical microparticles with a size of less than 1 μm were obtained. The release of the active substance from microparticles occurred gradually over two weeks, and in the case of the presence of magnetic nanoparticles, the concentration of radachlorin remained practically unchanged for a month. Exposure of microparticles to the light of LED is accompanied by the formation ofsinglet oxygen. Electron microscopy indicated intracellular position of microparticlesin tumor cells. The MTT test revealed a significant inhibition of cell viability in the presence of microparticles.Conclusion. The research results allow us to consider the obtained biocompatible polymer microparticles with the inclusion of radachlorin as a depot of radachlorin for local use in photodynamic therapy of tumors.