Influence of Particle Characteristics

Particle size. Particles greater than 7 pm are larger than blood capillaries ( 6 pm) and become entrapped in the capillary beds of the lungs (which may have fatal effects). The majority of particles that pass the lung capillary bed accumulate in the elements of the RES (spleen, liver and bone marrow). The degree of splenic uptake increases with particle size. Removal of particles 200 nm is due to a non-phagocytic process (physical filtration) in the spleen and phagocytosis (by Kupffer cells) by the liver. Particles 200 nm decreases splenic uptake and the particles are cleared by the liver and bone marrow. Colloidal particles not cleared by the RES can potentially exit the blood circulation via the sinusoidal fenestration of the liver and bone marrow. 

Surface charge. Surfeice charges only influence the particle-protein or particle-macrophage interactions at very short distances. The surface charge may ciffect the surface hydrophobicity which can affect protein adsorption. 

Surface hydrophobicity. Serum components adsorb on the surface of colloidal particles via their hydrophobic sites. An increase in surface hydrophobicity increases opsonization. To reduce opsonization, a predomincmtly hydrophilic surface is required. This led to the conclusion that adsorption of poly(ethylene glycol (PEG) type block copolymers on the surface of the particles should reduce the opsonization process. This will be discussed in the next section. 

KupfFer cells) by the liver. Particles 200 nm decrease splenic uptake and the particles are cleared by the liver and bone marrow. Colloidal particles not cleared by the RES can potentially exit the blood circulation via the sinusoidal fenestration of the liver and bone marrow. 

---

Guerrero, N.R.V., Taylor, M.G., Wider, E.A. and Simkiss, K. (2003) Influence of particle characteristics and organic matter content on the bioavailability and bioaccumulation of pyrene by clams, Environmental Pollution 121 (1), 115-122. 

DPMs may be used to understand the influence of particle characteristics on bubble formation, cluster formation and so on. These models may provide information regarding bubble size, cluster size, heat and mass transfer from such clusters to... 

M. Leva, Variables in Fixed-Bed Systems. Influence of Particle Characteristics on the Voidage,... 

CFD models, liquid and gas distribution and distributor design, influence of particle characteristics, nonisothermal effects, scaling effects, better understanding andy insights into flow patterns... 

The influence of particle characteristics on bulk powder properties... 

J.L. Anthony and C. Marone. Influence of particle characteristics on granular friction. Journal of Geophysical Research Solid Earth, 110(B8), 2005. 

The characteristics of a powder that determine its apparent density are rather complex, but some general statements with respect to powder variables and their effect on the density of the loose powder can be made. (/) The smaller the particles, the greater the specific surface area of the powder. This increases the friction between the particles and lowers the apparent density but enhances the rate of sintering. (2) Powders having very irregular-shaped particles are usually characterized by a lower apparent density than more regular or spherical ones. This is shown in Table 4 for three different types of copper powders having identical particle size distribution but different particle shape. These data illustrate the decisive influence of particle shape on apparent density. (J) In any mixture of coarse and fine powder particles, an optimum mixture results in maximum apparent density. This optimum mixture is reached when the fine particles fill the voids between the coarse particles. 

INFLUENCE OF PARTICLE SIZE DISTRIBUTION ON KINETIC CHARACTERISTICS... 

Litka, T., and Glicksman, L. R., The Influence of Particle Mechanical Properties on Bubble Characteristics and Solid Mixing in Fluidized Beds, Powder Technol., 42 231 (1985)... 

Davies, N. A., Taylor, M. G. and Simkiss, K. (1997). The influence of particle surface characteristics on pollutant metal uptake by cells, Environ. Poll., 96, 179-184. 

The most important characteristics of the final formulation to be compacted are particle size and particle size distribution, density and/or porosity, powder flow, cohesiveness, and lubrication. Particle size, particle size distribution, and density and porosity of the formula will not be addressed here because they are the result of other operations in the scale-up sequence, such as granulation and milling. They should be evaluated as part of those specific operations. It should be noted, however, that the influence of particle size on powder flow and, therefore, on uniform die fill is very important to the compaction operation, but is not a result of it. The one consideration to keep in mind during scale-up is the speed of the press, which will directly affect the time available for the die filling to occur. This is an important parameter to observe carefully. 

The physical characteristics of final dosage forms such as texture (porosity and surface area) and particle size distribution can affect the dissolution rate, and therefore the bioavailability of the product. It is common to see an increase in particle size when scaling up, therefore to anticipate the in vitro release profiles for a Spray Dried Drug Product (SDDP) manufactured at a larger scale, we have evaluated the influence of particle size and texture on dissolution in the case of a laboratory scale SDDP. 

DPMs can also be used to understand the influence of particle properties on fluidization behavior. It has been demonstrated that ideal particles with restitution coefficient of unity and zero coefficient of friction, lead to entirely different fluidization behavior than that observed with non-ideal particles. Simulation results of gas-solid flow in a riser reactor reported by Hoomans (2000) for ideal and nonideal particles are shown in Fig. 12.8. The well-known core-annulus flow structure can be observed only in the simulation with non-ideal particles. These comments are also applicable to simulations of bubbling beds. With ideal collision parameters, bubbling was not observed, contrary to the experimental evidence. Simulations with soft-sphere models with ideal particles also indicate that no bubbling is observed for fluidization of ideal particles (Hoomans, 2000). Apart from the particle characteristics, particle size distribution may also affect simulation results. For example, results of bubble formation simulations of Hoomans (2000) indicate that accounting... 

Table 1. Influence of particle size on some important characteristics of materials ... 

As the particle size of solids decreases, many characteristics of individual units change. Particle behavior in bulk masses also changes. Tab. 5.9 illustrates the influence of particle size, listing some important examples. In this context it is immaterial how size is defined the table considers the relative decrease of a linear particle dimension which is randomly called particle size . The upper part of Tab. 5.9 presents... 

Fig. 10.16 shows some fictional pressure/densification plots of high-pressure agglomeration, which illustrate the above and some additional characteristics of this technology, particularly the influence of particle size and distribution on degassing during and spring-back after compaction. It was assumed that all materials reach a final density of 90% (residual porosity 10%) at maximum pressing force. 

A certain specificity in biodistribution may be achieved passively by control of the physicochemical properties of the injected carrier system, such as particle size and dose, together with surface charge and surface characteristics. An infiu-ence of emulsion properties as well as the particle structure on the elimination rates from plasma and drug distribution in animals has been described after intravenous administration of emulsions containing coenzyme QIO as shown in Fig. 2 (9). The possible influence of particle structures on the pharmacokinetics of incorporated drugs and the bioacceptibility of the carrier can be deduced. 

The Influence of Particles on the Field Resonant chambers for particle manipulation (including microfluidic chambers) are designed to provide specific acoustic characteristics. However, the chambers must work when filled with a fluid-particle mix which will have acoustic characteristics that differ from the particle-free fluid. Many applications will need to work over a range of particle concentrations that will modify the acoustic field. In cases where the particles are very different acoustically from the fluid medium, agglomerations can cause localized breakdown of... 

The entry model of Maxwells et al. was derived from and/or supported by data on the influence of particle surface characteristics (charge, size) on the entry rate coefficient [312]. It was assumed that the aqueous radicals became surface active when the degree of polymerization reached 2-3. This was based on thermodynamic considerations of the entering species. 

As part of a study aimed at the rational development of immunoassays, the influence of surface characteristics on the interaction of F(ab )2 fragments obtained by peptic digest of rabbit polyclonal IgG has been investigated [12]. The latex particles differed in their hydrophilic character and in the nature and density of their surface ionic groups. The most important force governing the adsorption of the protein onto the surface was shown to be hydrophobic interactions, although in low ionic strength buffers electrostatic interactions were also found to play a part. On anionic latices, maximum F values were obtained at pH... 

As the performance of the composite is profoxmdly dominated by the micromechanical deformation process, its knowledge and control are critical for the improvement of composite properties. The effect of particle characteristics and interfacial adhesion on the micromechanical deformation processes in PP-wood composites was investigated by Renner et al. [7]. They proposed a failure map as well as the practical results and considered the influence of matrix characteristics on deformation and failure in PP-natural fiber composites in other research [24]. Hietala et al. [78] studied the effect of chemical pre-treatment and moisture content of wood chips on the wood particle aspect ratio during the processing and mechanical properties of WPCs. The use of pretreated wood chips enhanced the flexural properties of the wood chip-PP composites. Moreover, the use of undried wood chips compared to dried one can improve and reduce the flexural strength and flexural modulus, respectively. On the other hand, they concluded that the use of pretreated and undried wood chips lead to the highest aspect ratio after compounding. The effect of composition and the incorporation... 

---