Microspheres characterization

Figure 2.3 IgG levels after administration of drug delivery systems in rats. Controlled-delivery systems for antibody class IgG. The insert figures show the release of antibody from the delivery system during incubation in buffered saline. The panel (a) inset shows release from poly(lactic acid) microspheres these spherical particles were 10-100/rm in diameter. The panel (b) inset shows release from a poly[ethylene-co-(vinyl acetate)] matrix these disk-shaped matrices were 1 cm in diameter and 1 mm thick. In both cases, molecules of IgG were dispersed throughout the solid polymer phase. Although the amount of IgG released during the initial 1-2 days is greater for the matrix, the delivery systems have released comparable amounts after day 5. (a) Comparison of plasma IgG levels after direct injection of IgG (open circles) or subcutaneous injection of the IgG-releasing polymeric microspheres characterized in the inset (filled circles). The delivery system produces sustained IgG concentrations in the blood [3]. (b) Comparison of plasma IgG levels after direct intracranial injection of IgG (open squares) or implantation of an IgG-releasing matrix (filled squares) [4]. The influence of the delivery is less dramatic in this situation, probably because the rate of IgG movement from the brain into the plasma controls the kinetics of the overall process.

Bhoyar P.K., Morani D.O., BiyaniD.M., Umekar M.J., Mahure J.G., and AmgaonkarY.M. Encapsulation of naproxen in lipid-based matrix microspheres Characterization and release kinetics. J Young Pharmacists 3(2) (2011) 105-111. 

A large variety of drug delivery systems are described in the literature, such as liposomes (Torchilin, 2006), micro and nanoparticles (Kumar, 2000), polymeric micelles (Torchilin, 2006), nanocrystals (Muller et al., 2011), among others. Microparticles are usually classified as microcapsules or microspheres (Figure 8). Microspheres are matrix spherical microparticles where the drug may be located on the surface or dissolved into the matrix. Microcapsules are characterized as spherical particles more than Ipm containing a core substance (aqueous or lipid), normally lipid, and are used to deliver poor soluble molecules... 

Extensive studies have been reported with cisplatin in the field of chemoembolization (59,98). Microspheres prepared by a solvent evaporation procedure were characterized in vitro and critical processing parameters in regard to drug release kinetics were identified. 

Dhas NA, Zaban A, Gedanken A (1999) Surface synthesis of zinc sulfide nanoparticles on silica microspheres sonochemical preparation, characterization, and optical properties. Chem Mater 11(3) 806-813... 

Bourlinos, A.B., Karakassides, M.A. and Petridis, D. (2001) Synthesis and characterization of hollow microspheres through a resin template approach. Chemical Communications, 1518-1519. 

Esposito, E., Sebben, S., Cortesi, R., Menegatti, E., and Nastruzzi, C., Preparation and characterization of cationic microspheres for gene delivery, International Journal of Pharmaceutics, 1999, 189, 29—41. 

Lauer SA, Nolan JP (2002) Development and characterization of Ni-NTA-bearing microspheres. Cytometry 48 136-145... 

Fu et al. (2002) report the optimization of a fabrication procedure for microspheres based on the poly( anhydride-co-ether) P(SA-EG). The microspheres are fabricated by solvent removal process that produces a porous structure with densities in the range of 0.344 and 0.077 g cm-3 and sizes that are optimized for delivery to the deep lung by inhalation (Fu et al., 2002). An appropriate in vitro cell culture model for characterization of the particle-epithelia system was also developed (Fiegel et al., 2003). 

Noto, M. Vollmer, F. Keng, D. Teraoka, I. Arnold, S., Nanolayer characterization through wavelength multiplexing of microsphere resonator, Opt. Lett. 2005, 30, 510 512... 

Here n5 and nm are the refractive indices of the microsphere and ambient medium, respectively, and R is the microsphere radius. To determine An and t from this equation, it is sufficient to measure AA for two wavelength, ly1 and A. In Ref. 36, this was done for A[ = 760 nm and A[ = 1,310nm. As the result the authors optically characterized a hydrogel nanolayer with 110-nm thickness and an extremely small excess refractive index of 0.0012, which was formed in situ in an aqueous environment. 

Keij J, Steinkamp J (1998) Flow cytometric characterization and classification of multiple dual-color fluorescent microspheres using fluorescence lifetime. Cytometry 33 318-323... 

Liu J, Zhang Y, Yang T, Ge Y, Zhang S, Chen Z, Gu N (2009) Synthesis, characterization, and application of composite alginate microspheres with magnetic and fluorescent functionalities. J Appl Polym Sci 113 4042 1051... 

Deng Y, Wang C, Shen X, Yang W, Jin L, Gao H, Fu S (2005) Preparation, characterization, and application of multistimuli-responsive microspheres with fluorescence-labeled magnetic cores and thermoresponsive shells. Chem Eur J 11 6006-6013... 

The number average diameter of microspheres obtained after the first step of polymerization was D = 3.97 p,m, and parameter characterizing polydisperity of diameters was D /Dn = 1.09 after the second step D = 5.44 p.m and D /D = 1.13 eventually, after completion of the polymerization after the third monomer addition D = 6.36 p,m and D /Dn = 1.20. Thus, we noticed a substantial increase in the diameter of the microspheres without significant broadening diameter size dispersity. 

Chickering, D.E.lll, Jacob, J.S., and Mathiowitz, E., Bioadhesive microspheres. 2. Characterization and evaluation of bioadhesion involving hard, bioerodible polymers and soft tissue. Reactive Polymers, 25 189-206 (1995). 

This analytical method characterizes the nature of the drug encapsulated in the microspheres. There was no thermal event during the examination of empty microspheres. However, in the case... 

Four methods have been developed for enzyme immobilization (1) physical adsorption onto an inert, insoluble, solid support such as a polymer (2) chemical covalent attachment to an insoluble polymeric support (3) encapsulation within a membranous microsphere such as a liposome and (4) entrapment within a gel matrix. The choice of immobilization method is dependent on several factors, including the enzyme used, the process to be carried out, and the reaction conditions. In this experiment, an enzyme, horseradish peroxidase (donor H202 oxidoreductase EC 1.11.1.7), will be imprisoned within a polyacrylamide gel matrix. This method of entrapment has been chosen because it is rapid, inexpensive, and allows kinetic characterization of the immobilized enzyme. Immobilized peroxidase catalyzes a reaction that has commercial potential and interest, the reductive cleavage of hydrogen peroxide, H202, by an electron donor, AH2 ... 

In a later study by the Schmidt group (27), electron microscopy was used to characterize morphological changes in microspheres (<0.6 cm in diameter) of Pt, Rh, Pd, and Pt-Rh alloy in a number of reaction environments the reactions were ammonia oxidation, ammonia decomposition, and propane oxidation. No other experimental techniques, such as weight-loss measurements, were employed. After prolonged exposure to reaction mixtures of ammonia and air at temperatures less than 727°C, the surfaces of the spheres were reconstructed to favor specific crystal planes. The structure of the facets was found to be a function of the reaction mixture, temperature, and metal (Fig. 13). In the same reaction mixtures, as well as in pure ammonia at higher temperatures... 

Rochira, M., et al. 1996. Novel vaginal delivery systems for calcitonin. II. Preparation and characterization of HYAFF microspheres containing calcitonin. Int J Pharm 144 19. 

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