Polyvinyl microsphere

Microcapsules of PCL and its copolymers may be prepared by aircoating (fluidized bed), mechanical, and, most commonly, solution methods. Typically, the solution method has involved emulsification of the polymer and drug in a two-phase solvent-nonsolvent mixture (e.g., CH2Cl2/water) in the presence of a surfactant such as polyvinyl alcohol. Residual solvent is removed from the tnicrocapsules by evaporation or by extraction (70). Alternatively, the solvent combination can be miscible provided one of the solvents is high-boiling (e.g., mineral spirits) phase separation is then achieved by evaporation of the volatile solvent (71). The products of solution methods should more accurately be called microspheres, for they... 

Fig. 1—Scanning electron micrograph of nifedipine-loaded microspheres (4.7% w/w) prepared using 1 1 of 0.8% polyvinyl alcohol solution, 25 g Eufragit RS RL mixture. (1 1) in 80 ml methylene chloride stirred at 400 rev/min.

Spray dryers rubber chemicals, sulfonates, inorganic phosphates, ceramics, kaolin, coffee, detergents, pharmaceuticals, pigments, inks, lignosulfonate wood waste, melamine and urea formaldehyde resins, polyvinyl chloride, microspheres, skim milk, eggs, starch, yeast, silica gel, urea, salts... 

The effect of NaOH on drug release was examined with microspheres prepared with thioridazine and two biodegradable polymers. The wall-forming polymers were poly(DL-lactide) and poly(L-lactide). Sodium oleate was used as the emulsifier, with the exception of one set of experiments where the emulsions were stabilized with polyvinyl alcohol. 

In order to determine whether the effect of NaOH was specific to the use of sodium oleate as the emulsifier, microspheres were also prepared using polyvinyl alcohol to stabilize the emulsion. Figure 3 indicates that there was only a moderate increase in drug release by the addition of NaOH to the emulsion. 

To recapitulate, thioridazine release from microspheres was enhanced when NaOH was added to the emulsion prior to the solvent evaporation step. This was observed for both poly(DL-lactide) and poly(L-lactide) and also for two emulsifier systems, sodium oleate and polyvinyl alcohol. It should be pointed out that NaOH is added only to the aqueous phase of the emulsion. It is not incorporated into the microspheres by this process. 

Figure 3. Effect of NaOH on thioridazine release from poly(DL-lactide) microspheres. Key (o) no NaOH, 15-85 pm ( ) 0.14 mole NaOH/mole lactic acid, 10-85 pm. Drug loading, 50%. Emulsifier, polyvinyl alcohol.

Nakamura et al. ° studied the adhesion of water-soluble and neutral polymers, hydroxypropyl cellulose (HPC), xanthan gum (XG), tamarind gum (TG), and polyvinyl alcohol (PVA) to nasal mucosa in vitro and in vivo. The polymers, mixed with a dye, were applied as powders to the nasal cavity of rabbits, and the remaining dye residue was determined at 2, 4, and 6 h after nasal instillation with a thin fiberscope. The polymer XG showed the longest residence time of the dye in the cavity, followed by TG, HPC, and PVA in decreasing order. For the mixture XG and XG-PVA (2 8), some residue of dye could still be observed 6h after administration. The order of adhesion of these polymers to agar plates in vitro agreed with that of their mucoadhesion in vivo. Ilium et al. introduced bioadhesive microspheres for nasal delivery of poorly absorbable drugs. Radiolabelled microspheres made from diethylaminoethyl (DEAE)-dextran, starch microspheres, and albumin microspheres were administered to human volunteers and appeared to be cleared significantly slower than solutions or... 

In addition to PEGylation, polyvinyl pyrolidone (PVP) nanoparticles modified with hydrophilic polaxa-mine have been reported to adsorb less protein than the unmodified particles, conventional liposomes, and stealth liposomes.Polystyrene microspheres coated with lecithin and particles coated with Pluronic were also observed to adsorb less protein and demonstrate a prolonged blood circulation time without adversely affecting the safety profile of the drug. 

Thanoo BC, Sunny MC, Jayakrishnan A. Controlled release of oral drugs from crosslinked polyvinyl alcohol microspheres. J Pharm Pharmacol 1993 45 16-20. 

The materials employed for making hollow microspheres include inorganic materials such as glass and silica, and polymeric materials such as epoxy resin, unsaturated polyester resin, silicone resin, phenolics, polyvinyl alcohol, polyvinyl chloride, polyjM-opylene and polystyrene, among others, commercial jx oducts available are glass, silica, phenolics, epoxy resin, silicones, etc. Table 36 shows low-density hollow spheres. Table 37 shows physical properties of glass microspheres, and Table 38 shows comparison of some fillers on the physical properties of resulting foams (10). 

The matrix is considered to be the binder for the microspheres. Typical matrix materials include (a) thermosetting resins such as epoxy resins, unsaturated polyesters, vinyl esters, phenolics, polyurethanes, and silicones (b) thermoplastic resins such as polyethylene, polystyrene, polyvinyl chloride (c) asphalt and (d) gypsiun and cement. 

The raw materials for making hollow microspheres include glass, phenolic resin, epoxy resin, polystyrene, silicone rubber, polyvinyl chloride, polyvinyl alcohol. SOHIO Chemical Co. developed two methods, as shown below. 

Note Experimental parameters were a 55-mm, 3-blade turbine rotor a 1% polyvinyl alcohol solution and a 750-rpm stirring speed. Data represent the average of 3 independent experiments on different microsphere batches standard deviation. 

FIGURE 2.6 Effect of the type of the method of preparation on morphology and particle size of lipospheres. Optical micrographs of microspheres produced by (A) melt dispersion technique and (B) solvent evaporation technique. Lipospheres were constituted of tristearin glyceryl monostearate 2 1 (w/w) and prepared in the presence of 1% polyvinyl alcohol. Bar corresponds to 292 and 162 pm in panels A and B, respectively. (C) Frequency distribution plot of microspheres produced by melt dispersion (A) and solvent evaporation ( ) technique. Data are the mean of three different microsphere batches. 

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