Solvent-evaporation methods

Eudragit RS microspheres containing chitosan hydrochloride were prepared by the solvent evaporation method using an acetone/liquid paraffin solvent system, and their properties were compared with Eudragit RS microspheres without chitosan. The content of pipemidic acid, an antibacterial, increased in larger microspheres as a consequence of cumulation of undissolved pipemidic acid particles in larger droplets. Pipemidic acid release was faster from microspheres with chitosan [212]. 

In vitro release profiles on phase II and phase III clinical supplies prepared more than 2 years apart are shown in Fig. 2. SeveT al thousand doses were prepared for the phase III trial initiated in 1988. Figure 3 shows the reproducibility of six individual batches of microspheres produced by the solvent evaporation method. Other studies have been reported with similar processes (47). 

Spenlehauer, G., Vert, M., Benoit, J. P., Chabot, F., and Veillard, M., Biodegradable cisplatin microspheres prepared by the solvent evaporation method Morphology and release characteristics, J. Control. Rel., 7, 217, 1988. 

Microencapsulation with PCL using the solvent evaporation method can be experimentally difficult. For example, PCL was the only polymer of five that failed to yield spherically shaped microcapsules using this technique (82). The insecticide Abate has been incorporated into PCL (21% loading) by the solvent separation method in a comparative study, PCL afforded good-quality microspheres although poly (methyl methacrylate) microcapsules were smoother and had fewer defects (83). 

Chloropromazine (8—34 wt% loading) has been microencapsulated in PCL-cellulose propionate blends by the emulsion solvent evaporation method (61). Phase separation for some ratios of the two polymers was detectable by SEM. The release rate from microcapsules in the size range of 180-250 pm in vitro (Fig. 11) was directly proportional to the PCL content of the blend, the half-life (50% drug release)... 

Yuksel N, Turkoglu M, Baykara T. Modelling of the solvent evaporation method for the preparation of controlled release acrylic microspheres using neural networks. J Microencapsulation 2000 17 541-51. 

J Herrmann, R Bodmeier. Biodegradable somatostatin acetate containing microspheres prepared by various aqueous and non-aqueous solvent evaporation method. Eur J Pharm Biopharm 45(l) 75-82, 1998. 

The solvent evaporation method resulted in the production of LS characterized by a smaller size (20 pm mean diameter) but poor mechanical properties in respect to particles with the same composition that were obtained by the melt dispersion technique (170 pm mean diameter). The use of a combination of lipids and a methacrylic polymer (Eudragit RSI00) overcame this problem, resulting in the production of spherical particles with a narrower size distribution and good mechanical properties [53,56],... 

The solvent evaporation method is especially useful for polymers that can be cast onto the surface of the salt plate. Casting involves dissolving the polymer in an appropriate solvent at an elevated temperature and evaporating the solvent on the salt plate by heating the salt plate on a hot plate or under a heat lamp. 

The number average diameter of microspheres obtained from polymers synthesized, by emulsification of polymer solutions followed by solvent extraction and/or solvent evaporation methods, can be controlled by choosing the appropriate conditions at which particles are produced. However, by this method particles with 15 p,m and with D D > 1.9 are produced. Spray drying did not provide poly(L-Lc) particles with regular spherical shape. Direct synthesis of poly(L-Lc) microspheres by ring-opening polymerization with stepwise monomer addition can be used as a method of choice for the production of microspheres with diameters controlled to ca. 6 p.m and with diameter polydispersity parameter < 1.20. 

The purely siliceous MCM-41 and Ti-containing MCM-41 were synthesized by the solvent evaporation method. The chiral salens were immobilized step by step on the siliceous MCM-41 by the new grafting method using 3-aminopropyltrimethoxysilane and 2,6-diformyl-4-tert-butylphenol. The enantioselective diols could be synthesized directly from olefins using the hybrid catalysts of chiral salen complexes and Ti-MCM-41. 

Fig. 1 shows the X-ray diffraction patterns of Ti-MCM-41. These samples w ere obtained by the solvent evaporation method in the acidic condition using C ,TMABr and C TMACI... 

Fig.3. TEM images of Ti-MCM-41 obtained by the solvent evaporation method. (A) C22TMACl/Ethanol solvent (B) C22TMACl/methanol solvent...

Fig. 4 shows the IR spectra of various Ti-mesoporous materials obtained by the solvent evaporation method. These samples were synthesized using a C22TMaC1 surfactant and methanol solvent. The IR spectra of Ti containing MCM-41 exhibited an absorption band near 970 cm"1, which was also found for the purely siliceous MCM-41 samples in the Fig. 4. 

The incorporation of a cationic azobenzene derivative, p-( a> -dimethyl-ethanolammonioethoxyj-azobenzene bromide, into nanoporous silica films and the photochemical reactions of the adsorbed dye were investigated. The nanoporous silica films were prepared from tetramethoxysilane and octadecyltrimethyl-ammonium chloride by the rapid solvent evaporation method which we have reported previously. The adsorption of the cationic azo dye was conducted by casting an ethanol solution of the dye onto the nanoporous silica films. Upon UV light irradiation, trans-azobenzene isomerized photochemically to the c/s-form and photochemically formed c/ s-form turned back to the frans-form upon visible light irradiation. The nanoporous silica films were proved to be an excellent reaction media to immobilize organic photocromic species. 

Sethia, S. and E. Squillante. 2002. Physicochemical characterization of solid dispersions of car-bamazepine formulated by supercritical carbon dioxide and conventional solvent evaporation method. 

Figures 9.1-9.3 illustrate these interconnected relationships.13 Figure 9.1 defines some of the terms used in this chapter. Small molecules are species with molecular weights below about 1,000. They are volatile at temperatures below say 200 100 °C. Clusters are oligomers derived from covalently linked small molecules. They have a lower volatility than small molecules and, if large enough, can be shaped by melting or by solvent evaporation methods. Linear polymers can be simple chain structures or may consist of rings linked together. In either case they are usually non-volatile and easily fabricated. Cross-linked systems can be produced from polymers or from clusters. The final ceramic may be amorphous or crystalline.

In an effort to develop an effective bioadhesive system for buccal administration, insulin was encapsulated into polyacrylamide nanoparticles by the emulsion solvent evaporation method [98]. Though nanoparticle formation ensures even distribution of the drug, pelleting of the nanoparticles was performed to obtain three-dimensional structural conformity. In addition, it was hypothetized that the pelletized particles will remain adhered to the mucosa, leading to good absorption. While studying bioadhesion and drug release profiles, it was found that the... 

In one study, a solvent evaporation method was used to produce cocrystals of nicotinamide with ibuprofen (2-(4-isobutylphenyl)propanoic acid) [53]. The properties of the cocrystal could be studied in the solid state, but the synthon proved to be too weak to survive in fluid solutions. Nevertheless, the solubility of ibuprofen was enhanced by 62 times when the nicotinamide concentration was 13.3 mg/ml, suggesting that the... 

Evaporation. As a liquid droplet is formed of a volatile solvent and a polymer, evaporation of the solvent will lead to polymer beads entrapping the active ingredients. Spray drying consists of spraying a (aqueous) polymer solution and droplet drying. Emulsification of polymer volatile organic solvent in water followed by solvent removal is called the solvent evaporation method. 

The most widely used emulsion solvent evaporation method for preparation of nanoparticles using PLGA requires surfactants to stabilize the dispersed particle [23]. This method often has a problem that the surfactant remains at the surface of the particles and is then difficult to remove when PVA is used as surfactant. Other surfactants such as the span series or tween series, PEO, etc. are also used... 

In the other procedure, Rojas et al. [215] optimized the encapsulation of BLG within PLGA microparticles prepared by the multiple emulsion solvent evaporation method. The role of the pH of the external phase and the introduction of the surfactant tween 20, in the modulation of the entrapment and release of BLG from microparticles were studied. Better encapsulation of BLG was noticed on decreasing the pH of the external phase. Addition of tween 20 increased the encapsulation efficiency of BLG and considerably reduced the burst release effect. 

In addition, tween 20 reduced the number of aqueous channels between the internal aqueous droplets as well as those communicating with the external medium. The inventors claimed that these results constitute a step ahead in the improvement of an existing technology in controlling protein encapsulation and delivery from microspheres prepared by the multiple solvent evaporation method [215]. 

FIGURE 4 Schematic of microspheres prepared by emulsification/solvent evaporation method. 

Youan, B. B. C., Gillard, J., and Rollmann,B. (1999),Protein-loaded poly(e-caprolactone) microparticles. III. Entrapment of superoxide dismutase by the (water-in-oil)-in water solvent evaporation method, STP Pharma Sci., 9,175-181. 

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