Porous microcapsules

Xie, R. Chu, L.-Y. Chen, W.-M. Zhao, Y. Xiao, X.-C. Wang, S. Preparation of monodispersed porous microcapsule membranes with SPG membrane emulsification and interfacial polymerization. Gaoxiao Huaxue Gongcheng Xuebao (2003), 17(4), 400-405. 

In other words, base-catalyzed microparticle synthesized in W/0 microemulsions results in the formation of relatively large matrix particles of low and even negligible porosity. Thus, in order to obtain porous microcapsules under base-catalyzed conditions, the two-step sol-gel polycondensation process must be employed, in which hydrolysis is first conducted under acidic conditions followed by condensation catalyzed by base. When this approach is adopted, mesoporous microspheres can be synthesized also in basic W/0 emulsions. In contrast, smaller particles synthesized in acid exhibit a strong microporous component (Figure 18.2). 

The pore size and distribution in the porous particles play essential roles in NPS synthesis. For example, only hollow capsules are obtained when MS spheres with only small mesopores (<3 nm) are used as the templates [69]. This suggests that the PE has difficulty infiltrating mesopores in this size range, and is primarily restricted to the surface of the spheres. The density and homogeneity of the pores in the sacrificial particles is also important to prepare intact NPSs. In a separate study, employing CaC03 microparticles with radial channel-like pore structures (surface area 8.8 m2 g 1) as sacrificial templates resulted in PE microcapsules that collapse when dried, which is in stark contrast to the free-standing NPSs described above [64]. 

Enzymes can also be trapped within a nanotubular membrane by capping both faces of the membrane with a thin layer of porous polymer. In effect, arrays of enzyme-filled microcapsules are formed. Small molecules pass through the po-... 

The appearance of the individual microcapsules is shown in Fig. 1. Most individual microcapsules are approximately spherical and show a surface made up of deposited plates of poly(DL-lactic acid) in which the drug is embedded. Many of the larger microcapsules are cemented together by further plates of poly(DL-lactic acid). The effect of compression on these microcapsules is shown in Fig. 2. At a compressive force of 2 kN (Fig. 2(a)) the electron micrograph of the tablet fracture surface shows that the microcapsules, while distorted, remain essentially intact and rounded, with a relatively open porous structure to the tablet as a whole. At 10 kN force (Fig. 2(b)) the microcapsules at the fracture are flattened, cracked and distorted so that the fracture surface shows a far less open, porous aspect. Both of these microcap tablets have a very different appearance from that produced by the simple mixture (Fig. 3), where the individual plates of poly(DL-lactic acid) are mixed with the drug crystals in an open structure from which release would be easily... 

Spray drying. Microencapsulation by spray drying is an ideal method for poorly water-soluble drugs. The drug is dispersed in polymer (coating) solution, and then this dispersion is atomized into an airstream. The air, usually heated, supplies the latent heat of vaporization required to remove the solvent and forms the microencapsulated product. This technique is employed most commonly when microcapsules are intended for oral use because the resulting microspheres are porous in nature, and large batch sizes are required.89... 

The first plot received 500 g.a.i./h of displarlure as NCR gelatin-walled microcapsules containing 2% ai. The formulation, applied as an aqueous suspension, also contained 1 of sticker to aid adhesion of the formulation to foliage. The second plot received 500 g./h. as Herculite Corporation sprayable laminate flakes containing 9.1 ai. The flakes consisted of two layers of vinyl, each 0.08 mm thick on both sides of a central porous layer containing the disparlure the surface area of the flakes was between 7 and 35 mm2 per side. The same sticker as that in the microcapsules was used. The third plot received 330 g.a.i./h as "Conrel" controlled release hollow fibers containing nominally 11.5% ai. a suitable sticker was also incorporated in the formulation. (Note that the use of trade or proprietary names here or elsewhere does not constitute an endorsement by the USDA). 

Liu, R., Ma, G.H., Meng, F.-T., and Su, Z.-G., Preparation of uniform-sized PLA microcapsules by combining Shirasu Porous Glass membrane emulsification technique and multiple emulsion-solvent evaporation method, J. Contrail. Ret, 103, 31, 2005. 

Polymea mictocapsules containing 0,0-3,5,6-trichloro-2-pyridyl phosphorothioate (Dursban) were prepared by reacting a polyisocyanate and a poly amine and the factors affecting the formation of the microcapsule wall examined. The formation of polyurea was confirmed by FTIR spectroscopy, the thermal properties of the microcapsules were investigated by DSC and the morphology of the microcapsules detenninedby scanning electron microscopy. Optimum conditions for the formation of a thin surface l er and a porous matrix were established. 9 lefs. 

Plastic Cl carriers represent an alternative to inhibited pol3mier films used for preservation and packaging of metal ware. They are usually made of polymer porous or fibrous materials or may have microcapsules whose voids are filled by volatile Cl. Plastic Cl carriers like pellets, perforated vessels or fibrous materials are placed inside a tight package to create an inhibited atmosphere that averts corrosion of the packed article. 

The initial burst was further decreased by tiie fact that upon the addition of the hydrophilic additive, the glass transition temperature of the PGLA decreases from 42.5°C to 36.7°C. This allows annealing of the PLGA molecules to take place upon subcutaneous administration (where tire ambient temperature is 37°C). This annealing process causes tire initial porous structures of tire microcapsules to disappear and allows "melted" microcapsules to fuse with each other. A decreased number of surface pores and a decreased surface area to volume ratio serves to limit tire release of insulin from tire annealed microparticles. ... 

Furthermore, porous CPs (e.g., polypyrrole, polyanUine) films have been used as host matrices for polyelectrolyte capsules developed from composite material, which can combine electric conductivity of the polymer with controlled permeability of polyelectrolyte shell to form controllable micro- and nanocontainers. A recent example was reported by D.G. Schchukin and his co-workers [21]. They introduced a novel application of polyelectrolyte microcapsules as microcontainers with a electrochemically reversible flux of redox-active materials into and out of the capsule volume. Incorporation of the capsules inside a polypyrrole (PPy) film resulted in a new composite electrode. This electrode combined the electrocatalytic and conducting properties of the PPy with the storage and release properties of the capsules, and if loaded with electrochemical fuels, this film possessed electrochemically controlled switching between open and closed states of the capsule shell. This approach could also be of practical interest for chemically rechargeable batteries or fuel cells operating on an absolutely new concept. However, in this case, PPy was just utilized as support for the polyelectrolyte microcapsules. 

Capsules were porous on its surface (Figure 19.7a). On the other hand, cross-section of the microcapsules with vanillin showed that microcapsules prepared by using pure water as precipitation bath had macrovoids in their wall. This feature can be observed in Figure 19.7b). Fundamentals of the precipitation technique provide a suitable explanation for this phenomenon, as it has been explained before. When affinity between solvent and nonsolvent is high, as it is the case of DMF and water, a fast demixing of the solution will take place. Fast demixing has been observed to favor the apparition of macrovoids. 

Microsphere reservoirs for controlled release applications in medicine, cosmetics and fragrances are obtained evaporating solvent fi om an oil-in-water emulsion. The microcapsules have diameters of fi om 3 to 300 im. Many polymers are suitable for use in this invention which is based on the knowledge that the inclusion of plasticizer renders porous and spongy structure as opposed to the hollow core and relatively solid surface which results when no plasticizers are used. 

To prepare microcapsules with entrapped protein (or DNA), CaCOa porous spherical microparticles (an inorganic core) with narrow bead-size distribution (mean size of 5 p.m) have been elaborated (Figure 30.5). 

EC microcapsules containing Rosemary oil or limonene were obtained by phase separation method. According to this procedure, EC microcapsules without oil could also be produced. This could be explained due to EC inter cial activity, which stabilizes the formed emulsion. Surfactant-fiee multiple emulsions using EC as a polymeric emulsifier have already been reported by Melzer and collaborators [8]. From the scanning electron micrographs shown in Fig. 1 it is observed that EC microc g)sules had regular spherical sh, the size of microcapsules varied and that the surface was porous. 

The small amount of encapsulated oil is due, probably, to porous structure of EC microcapsules. The oil content is unchanged upon storage at room temperature for 3 months. 

Microcapsules with a narrow size distribution containing oily core material can be prepared by a Shirazu porous glass (SPG) emulsification technique, followed by a suspension polymerization process. The SPG membrane is a special porous glass membrane with very uniform pore size. Guang Hui Ma et al. have reported the preparation of microcapsules containing hexadecane (oil core) using poly(styrene-... 

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