Projected Area Equivalent Diameter Research Articles

Effect of the formulation on mucoadhesive spray-dried microparticles containing iron for food fortification

Food fortification through iron encapsulated spray-dried microparticles can alleviate the iron deficiency. Here, we analyze the impact of the ratio between the wall and the bulk material, the amount of solids, the type of wall material, and the type of iron compound on the properties of spray dried powder. Optimal formulations contain equal weight percentages of iron compound, bulk material, and wall material. In this case, spray-dried microparticles show an average projected area equivalent diameter of 4.3 μm with a bioavailability of 60%. Moreover, the encapsulation of iron gluconate reduces the toxicity of Caco-2 and Hep-G2 at any quantities of iron below 12 mg/ml. We verified that most mucoadhesive microparticles include dextran or hydroxyl-methylcellulose; the detachment force between microparticles with a shell made of hydroxyl-methylcellulose and the human intestine is 1.6 N. Moreover, the encapsulation of iron gluconate via spray drying increases Caco-2 iron absorption by 38% compared to non-encapsulated material. An opposite response was observed using iron fumarate, where the absorption was reduced by 31% when the iron compound was encapsulated. • Encapsulation is aeffective with 1:1:1 of HP-MC, maltodextrin, iron gluconate. • HP-MC shows the highest muco-adhesivity with intestine and stomach walls. • Encapsulation of iron gluconate doubles the cell viability with Caco-2. • Dextran in the formulation produces 100% of the release rate after only 20 min.

Spray freeze drying for protein encapsulation: Impact of the formulation to morphology and stability

Proteins, the building blocks of life, are increasingly being used as therapeutics for treating several diseases. Yet, there are challenges in the delivery of highly labile materials like proteins, which is often circumvented with the help of encapsulation for targeted delivery and enhanced stability. Spray drying technology has recently been employed for encapsulation due to its’ low cost and scale-up capabilities, yet the high temperatures of drying air makes the technology unsuitable for proteins. More recently, spray freeze drying has evolved as an emerging technology that combines spray drying with freeze drying by using low temperatures, and is thus suitable for maintaining the stability of proteins. This study investigates the correlation between formulation parameters and the properties of protein encapsulated microparticles prepared by spray freeze drying. Morphology was investigated using microscopic methods, and protein stability was examined using infrared and mass spectrometry. By using bovine serum albumin, we verify that increasing the total weight to 15 mg/ml results in microencapsulates with a projected area equivalent diameter of 100 µm larger. We demonstrate that some types of amino acids are essential for shell formation; however, glutamine generates an increase in dimer areas in mass spectra of 5.5. D-Mannitol is the suggested carrier for high encapsulation efficiency (above 90 %). The formulation containing polyvinylpyrrolidone, mannitol, and leucine (at 6, 9, and 2 mg/ml, respectively) produced the lowest reduction in the stability of a few types of proteins; deconvoluted infrared peaks show a difference of less than 2% compared to the free protein. Understanding the spray freeze drying phenomenon for protein encapsulation would allow the control over morphological and chemical properties of microparticles containing active proteins.

Characterizing soot in TEM images using a convolutional neural network

Soot is an important material with impacts that depend on particle morphology. Transmission electron microscopy (TEM) represents one of the most direct routes to qualitatively assess particle characteristics. However, producing quantitative information requires robust image processing tools, which is complicated by the low image contrast and complex aggregated morphologies characteristic of soot. The current work presents a new convolutional neural network explicitly trained to characterize soot, using pre-classified images of particles from a natural gas engine; a laboratory gas flare; and a marine engine. The results are compared against other existing classifiers before considering the effect that the classifiers have on automated primary particle size methods. Estimates of the overall uncertainties between fully automated approaches of aggregate characterization range from 25% in dp,100 to 85% in DTEM. A consistent correlation is observed between projected-area equivalent diameter and primary particle size across all of the techniques.

A multivariate approach applied to quality on particle engineering of spray-dried mannitol

Box-Benhken design was applied to engineer spray dried mannitol particles. Particles were characterized by optical microscopy to determine size, size distribution, shape and morphology comparing to a reference material commercially available. Two shape factors calculated with the results of image analysis, circularity and projected area equivalent diameter (Heywood diameter), as well as span value for size distribution, were chosen as responses for analyses of variance. Outlet temperature was shown to be the most important factor to control during the process in order to produce particles with high value of circularity. Particle size represented as Heywood diameter was affected by ethanol while particle size distribution was affected by concentration of mannitol solution. Desirability function was applied to determine the best process parameters and to predict the responses, which were confirmed experimentally. Morphology was evaluated with scanning electron microscopy and confirmed results of ANOVA for circularity, showing that regulars and spherical particles were produced at low temperature. FTIR and DRX were used to demonstrate that particles did not modify polymorph after the spray drying keeping the same β-form of the raw mannitol.

Radial-profile and divergence measurements of combustion-generated soot focused by an aerodynamic-lens system

We used light-scattering techniques to measure the angular divergence of a soot-particle beam produced by an aerodynamic-lens system in common use. Soot was generated in an atmospheric coflow ethylene diffusion flame and focused using this aerodynamic-lens system. The width of the beam generated was probed every ∼32μm over a range of more than 100mm downstream of the exit nozzle by imaging laser light scattered from the particle beam onto an intensified CCD camera. We collected transmission electron microscopy (TEM) grids downstream of the exit nozzle and analysed the images to size the particles focused in the beam. Our measurements yield a divergence angle in the range of 2.24–2.59mrad corresponding to a solid angle of 1.59–2.11×10−5sr for a soot lognormal size distribution with an average projected area equivalent diameter of 88nm and median of 73nm. We characterized three similar aerodynamic-lens systems. Our results demonstrate that the radial profile of the particle beam has more Gaussian character near the exit of the aerodynamic-lens system and is almost purely Lorentzian in character further downstream of the lens-system exit.

Structural properties of silver nanoparticle agglomerates based on transmission electron microscopy: relationship to particle mobility analysis

In this work, the structural properties of silver nanoparticle agglomerates generated using condensation and evaporation method in an electric tube furnace followed by a coagulation process are analyzed using Transmission Electron Microscopy (TEM). Agglomerates with mobility diameters of 80, 120, and 150 nm are sampled using the electrostatic method and then imaged by TEM. The primary particle diameter of silver agglomerates was 13.8 nm with a standard deviation of 2.5 nm. We obtained the relationship between the projected area equivalent diameter (d pa) and the mobility diameter (d m), i.e., d pa = 0.92 ± 0.03 d m for particles from 80 to 150 nm. We obtained fractal dimensions of silver agglomerates using three different methods: (1) D f = 1.84 ± 0.03, 1.75 ± 0.06, and 1.74 ± 0.03 for d m = 80, 120, and 150 nm, respectively from projected TEM images using a box counting algorithm; (2) fractal dimension (D fL) = 1.47 based on maximum projected length from projected TEM images using an empirical equation proposed by Koylu et al. (1995) Combust Flame 100:621–633; and (3) mass fractal-like dimension (D fm) = 1.71 theoretically derived from the mobility analysis proposed by Lall and Friedlander (2006) J Aerosol Sci 37:260–271. We also compared the number of primary particles in agglomerate and found that the number of primary particles obtained from the projected surface area using an empirical equation proposed by Koylu et al. (1995) Combust Flame 100:621–633 is larger than that from using the relationship, d pa = 0.92 ± 0.03 d m or from using the mobility analysis.

Influence of Diesel Engine Combustion Parameters on Primary Soot Particle Diameter

Effects of engine operating parameters and fuel composition on both primary soot particle diameter and particle number size distribution in the exhaust of a direct-injected heavy-duty diesel engine were studied in detail. An electrostatic sampler was developed to deposit particles directly on transmission electron microscopy (TEM) grids. Using TEM, the projected area equivalent diameter of primary soot particles was determined. A scanning mobility particle sizer (SMPS) was used for the measurement of the particle number size distribution. Variations in the main engine operating parameters (fuel injection system, air management, and fuel properties) were made to investigate soot formation and oxidation processes. Primary soot particle diameters determined by TEM measurements ranged from 17.5 to 32.5 nm for the diesel fuel and from 24.1 to 27.2 nm for the water-diesel emulsion fuel depending on the engine settings. For constant fuel energy flow rate, the primary particle size from the water-diesel emulsion fuel was slightly larger than that from the diesel fuel. A reduction in primary soot particle diameter was registered when increasing the fuel injection pressure (IP) or advancing the start of injection (SOI). Larger primary soot particle diameters were measured while the engine was operating with exhaust gas recirculation (EGR). Heat release rate analysis of the combustion process revealed that the primary soot particle diameter decreased when the maximum flame temperature increased for the diesel fuel.

Structural Properties of Diesel Exhaust Particles Measured by Transmission Electron Microscopy (TEM): Relationships to Particle Mass and Mobility

Structural properties of diesel particles preclassified by particle mobility and mass are measured using transmission electron microscopy (TEM). These measurements enable us to determine the dynamic shape factor and inherent material density of diesel particles. We also compare fractal dimensions obtained independently using two different approaches. We show that the projected area equivalent diameter of mobility-classified diesel particles nearly equals the mobility diameter in the size range reported here (50 to 220 nm). Evidence for doubly charged particles and possible “fragments” are observed for DMA-classified particles on TEM substrates. The fractal dimension was obtained using two independent approaches. Images obtained by TEM were analyzed to determine the maximum length and the number of primary particles. The fractal dimension obtained from these measurements, D fL, was 1.75. The fractal dimension obtained from the mass-mobility relationship, D fm was 2.35. We found that these values are in reasonable agreement after accounting for the relationship between the projected area diameter and maximum length. The size-dependent dynamic shape factor and inherent material density of diesel particles are obtained from independent measurements of mobility (DMA), mass (APM), and volume (TEM). We found that the dynamic shape factor increased from 1.11 to 2.21, and that the inherent material density increased from 1.27 to 1.78 g/cm3 as particle mobility size increased from 50 to 220 nm. The increase in dynamic shape factor with size occurs because large particles are more irregular than smaller ones. The increase in density occurs because the ratio of elemental carbon to condensed organics increases with increasing size.

Kinetics and visualization of soot oxidation using transmission electron microscopy

Visualization of the oxidation of individual soot particles using transmission electron microscopy (TEM) was performed and quantitative oxidation rates were determined. Soot particles were sampled from an ethylene diffusion flame burner and collected on a TEM grid. Individual particles were then tracked by creating maps of TEM images at different magnifications, and images were compared before and after the oxidation process in a separate furnace at low temperatures (<800 K). Mono-area soot particles were sampled on TEM grids using a differential mobility analyzer (DMA) and a low-pressure impactor. It was found that the mobility equivalent diameter determined by the DMA is equivalent to the projected area equivalent diameter determined by the TEM for particles below 150 nm. Groups of mono-area particles were visualized before and after the oxidation process and oxidation rates were determined from the change in projected area equivalent diameter by image-processing a series of TEM images. For these low temperatures (<800 K), an activation energy of 148 kJ/mol was found for the oxidation of soot particles. The overall oxidation rate was found to be significantly higher than in prior studies, and some possible reasons for the discrepancy discussed.

Optical properties of dense and porous spheroids consisting of primary silica nanoparticles

The light scattering by granular and macroporous silica spheroids consisting of nanometer-sized primary particles was systematically investigated using a laser particle counter coupled with a pulse height analyzer. The shape- and porosity-controlled spheroids as model particles were prepared using spray drying method by changing the particle size of colloidal suspension. The effect of shape and porosity of dense and porous spheroidal particles on electrical mobility was also studied using a differential mobility analyzer and an electron microscope. The electrical mobility equivalent diameter of particles classified by the differential mobility analyzer was estimated by measuring Feret diameter and the projected area equivalent diameter from the SEM micrographs. The electrical mobility diameter of the spheroids was in good agreement with the projected area equivalent diameter regardless of the primary particle size and porosity. The measured partial scattering cross section of dense and porous silica particles with same mobility diameter showed significant differences. As the primary particle size of granules and the porosity of porous particles increased at parity of electrical mobility diameter, the scattering intensity decreased. The effective refractive indices of dense and porous particles were computed by best fitting of the scattering intensity measurements. The porosities of dense and porous spheroids were calculated using the effective refractive indices as obtained by the effective medium theory. The porosities were also measured by a comparison of particle size before and after annealing at 1700°C. By comparing these porosities, the effective refractive indices of the spheroidal particles were confirmed.

Passive Sampler Used for Simultaneous Measurement of Breathing Zone Size Distribution, Inhalable Dust Concentration and Other Size Fractions Involving Large Particles

The particle size-dependent sampling velocity of the passive dust sampler developed by Vinzents (1996) is investigated under field conditions. Microscopical determination of the projected area equivalent diameter is used to quantify particles deposited on the sampler foils. Parameters for a semi-empirical model for particle deposition velocities on upward and forward facing foils are fitted to the data and it is shown that deposition mechanisms other than gravitational settling on the upward facing foil can be neglected. For calculation of airborne mass concentration no information on particle density is needed and only the ratio between the dynamic and volume shape factors needs to be known. Given the sampling velocity, the airborne mass per diameter interval is calculated from samples obtained in the wood industry, from which inhalable dust concentrations are calculated. The results are in line with parallel samples obtained with an inhalable dust sampler. A 'total' dust sampling characteristic can be fitted which reproduces measured 'total' dust with a closed face monitor. The results of this study demonstrate the validity of the passive dust sampling principle in environments involving even large (>100 microm) particles and the potential to predict the concentration of several size fractions.