Particle size of microspheres

Core-shell nanocomposite of Mg(OH)2/PMMA with an average particle size of ca. 500nm where Mg(OH)2 is the core and PMMA is the shell was successfidly prepared by the emulsion polymerization of MMA in the presence of surface modified Mj OH)2. The grapelike ( re-shell microspheres with PMMA nodules could he obtained as stable latex. 

Glass microspheres are widely used because of the strength of the glass and the substantial difference between the elasticities of glass and polymer12 14). Several types of glass microspheres are produced in the Soviet Union in the form of non-cohesive white powders with particle sizes of 10-150 pm and densities of 200 to 400 kg/m3. 

Microspheres based on phenol formaldehyde oligomers (PhFO s) are brown non-cohesive powders with particle sizes of 10—300 pm, apparent densities of 100 to 150 kg/m3, and sinkages of less than 5—10 mass% u,24 26). 

Microsphere Formation. Because the microspheres were fabricated using a batch process, we monitored the viscosity and pH of the catalyst slurry as it aged. Figure 2 shows that the viscosity of the slurry was dependent on both the age of the slurry and the additive type. The reference formula was stable for 3 h, but the CP-alumina and pseudoboehmite formulations thickened or gelled in the same time period. A typical batch starting at pH 3.0 increased to about pH 3.3 before the onset of thickening (about 100 cP). For CP formulations, the onset of thickening may be related to the median particle size of the powder. 

Table IV gives the Attrition Indexes for the commercial and experimental samples. These values are reported for microspheres that were spray dried before the viscosity of the slurry exceeded 100 cP. The data show, again, that sol age and particle size of the CP alumina affect attrition. Sol age also seems to reduce the influence of the CP-2 as a binder. The Reference (4) has an AI of about 3 which is comparable to the index for CP-2(4). The important point here is that the alumina particles can be incorporated into a standard FCC formula to change catalytic activity without a detrimental effect on attrition resistance.

To increase the residence time in the nasal mucosa, a bioadhesive formulation may be one of the most reasonable approaches. In fact, microspheres containing bioadhesive polymers such as starch, albumin, and Sephadex with a particle size of 40-60 pm have been found to be cleared from the nasal cavity much more slowly than solutions. Starch microspheres improved the nasal absorption of insulin, with synergistic effects of some absorption enhancers in sheep. In another paper, dry powder containing starch and Carbopol 974P showed significantly higher bioavailability after nasal administration than the formulation without Carbopol. ° Chitosan, already mentioned above, also has a bioadhesive property and is found to be useful as a potent absorption enhancer for nasal peptide delivery. Other bioadhesive polymer systems,... 

Sanghvi SP, Naim JG. Effect of viscosity and interfacial tension on particle size of cellulose acetate trimellitate microspheres. / Microencapsul 1992 9(2) 215-227. 

Aqueous solutions of proteins such as albumin can be emulsified in an oil and induced to form microspheres, either by crosslinking the protein molecules with glutaraldehyde or other agents or by coagulating the protein by heating. Incorporation of a dmg within the initial protein solution results in dmg-laden microspheres which are biodegradable. The particle size of the microspheres (generally 0.2-300 jum diameter) is determined by the size distribution of the initial emulsion. 

To study the effect of particle size of drug particles and/or carriers for achieving optimal delivery of drug to solid tumors, surfactant-treated fluoresceinated polystyrene spheres containing paclitaxel were administered systemically to tumor-bearing mice. Delivery of the microspheres to solid tumors depended on particle size. Solid tumors took up a 4- to 5-fold greater number of particles with a mean size of 100 nm than of those with a mean size of 200 nm. As... 

FIGURE 2.2 Effect of gelatin Bloom on morphology and particle size of cetyl alcohol cholesterol 2 1 (w/w) lipospheres. Scanning electron microscopy (A) and optical micrographs (B) of microspheres produced with gelatin 200 Bloom grades. Bar corresponds to 76 and 381 pm in panels A and B, respectively. 

FIGURE 2.5 Optical microscopy photographs showing the effect of stirring speed on morphology and particle size of tristearin monostearate 2 1 (w/w) produced at (A) 500 rpm, (B) 750 rpm, and (C) 1000 rpm. Bar corresponds to 650, 650, and 347 pm in panels A, B, and C, respectively. (D) Frequency distribution plot of microspheres produced at 500 rpm (o), 750 rpm (x), and 1000 rpm (0). Data are the mean of three different microsphere batches. Lower panel impellers employed for microsphere production, from left to right a 3-blade rotor with a diameter of 55 mm (taken as reference impeller), a 4-blade helicoidal rotor with a diameter of 50 mm, a 2-blade rotor with a diameter of 50 mm, and finally a double-truncated cone rotor with a diameter of 50 mm. 

The sol-gel process has been developed for the production of spherical oxide fuels with a particle size of up to 1 mm for use in nuclear reactors [B.56]. The following operations are involved in converting the initially aqueous sol of colloidal particles into calcined microspheres ... 

The small particle size of the silica is important not only in enabling the silica to flow to the peripheral region of the porous microsphere but also in forming the hard peripheral oxide-rich shell. Particles of silica 2-3 nm in diameter sinter together to some extent even under the temperature conditions encountered in a conventional spray drying process, whereas particles 10-100 nm do not sinter below 700-1000°C. As a result, attrition resistance of the catalyst, catalyst precursor or catalyst support particle is a function of the particle size and degree of aggreggation of the silica formed by dehydration. 

FI GU RE 22.18 Effect of polymeric solution flow rate on mean particle size of PLGA microspheres produced by EHDA. (From Jafari-Nodoushan, M. et al.. Monitoring the effect of flow rate on size and morphology of microspheres produced by the means of electrospraying method, in International Seminar of Polymer Science and Technology, Tehran, Iran, 2012. With permission. International Seminar on Polymer Science and... 

The particle size of drug cores impacts their release rates. The release of the drug in simulated intestinal fluid was very rapid from microspheres containing large and medium drug crystals, while release was slower and more predictable from microspheres made from micronized drug. ... 

The lowest particle size of microparticles is 1 pm and the largest size is 1 mm. Commercial microparticles have a diameter range of 3 to 800 pm. Microparticles may be formulated as microcapsules or as microspheres that differ in morphology and internal structure. In addition other terms such as beads, microbes are also being used alternatively. 

Surfactant The surfactant, also called tension-active agent, reduces the surface tension of continuous phase, avoids the coalescence and agglomeration of drops, and stabiUzes the emulsion. A suitable surfactant should be able to give microspheres a regular size and a small size distribution, guaranteeing a more predictable and stable drug release. The increase of surfactant concentration reduces the size of microspheres. The addition of surfactant lowers the surface tension of the continuous phase and the diminution of the latter one decreases the particle size. 

In this process, the drng may be dissolved or dispersed in the polymer solution and spray dried. The quality of spray-dried microspheres can be improved by the addition of plasticizers, for example, citric acid, which promote polymer coalescence on the drng particles and hence promote the formation of spherical and smooth-surfaced microspheres. The size of microspheres can be controlled by the rate of spraying, the feed rate of polymer drng solution, nozzle size, and the drying temperature. This method of microencapsulation is particularly less dependent on the solnbility characteristics of the drug and polymer and is simple, reproducible, and easy to scale np. 

Achieving a suitable particle size with better yield is important in precipitation polymerization as many parameters affect its mechanism. We have prepared GA based MIPs by the precipitation polymerization and observed the effect of porogen on particle size and specific molecular recognition properties (Pardeshi et al, 2014], MIP, M-lOO prepared in the porogen acetonitrile and MIP, M-75 prepared in a mixture of acetonitrile-toluene (75 25 v/v), resulted in the formation of microspheres with approximately 4 pm particle size and surface area of 96.73 m g and nanoparticles (0.8-1000 nm] and a surface area of 345.9 m g" respectively. The results have shown that effect of toluene on the particle size of MIPs depends on the type of cross-linker used and its solubility parameter. Matching the solubility parameter of solvent mixture and cross-linkers is important to obtain the desired particle size in MIPs. The MIPs selectively recognized GA in presence of its structural analogues. Pure GA with percent recovery of 75 ( 1.6) and 83.4 ( 2.2) was obtained from the aqueous extract of herb Emblica officinalis by M-lOO and M-75, respectively. 

Although the average particle size of macroaggregated albumin (35 pm) is similar to that of SIR-Spheres (29-35 pm), the size range of MAA particles is broader (10-60 pm) and the shape of the MAA particles may be different from therapeutic microspheres. A clinically relevant impact of these differences in physical properties, however, has not yet been reported. 

---