Solvent evaporation method, preparation

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. 

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 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. 

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. 

Poly(alkyl-cyanoacrylates) As poly(alkyl-cyanoacrylates) form strong bonds with polar substrates including the skin and living tissues, they exhibit bioadhesive properties. These polymers are synthesized by free-radical, anionic, or zwitterionic polymerization. As detailed in a recent review, poly(alkyl-cyanoacrylate) nanoparticles are prepared by emulsion polymerization, interfacial polymerization, nanoprecipitation, and emulsion-solvent evaporation methods [102],... 

Lemos-Senna, E., Wouessidjewe, D., Lesieur, S., and Duchene, D. (1998), Preparation of amphiphilic cyclodextrin nanospheres using the emulsion solvent evaporation method, influence of the surfactant on preparation and hydrophobic drug loading, Int. J. Pharm., 170,119-128. 

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. 

Herrmann, J. Bodmeier, R. Somatostatin containing biodegradable microspheres prepared by a modified solvent evaporation method based on W/O/W-multiple emulsions. Int. J. Pharm. 1995, 126 (1-2), 129-138. 

Bodmeier, R. McGinity, J.W. Solvent selection in the preparation of PLA microspheres prepared by the solvent evaporation method. Int. J. Pharm. 1988, 43, 179-186. 

Fig. 3 Scanning electron micrograph of polylactic acid microspheres containing phenolphthalein prepared by the solvent evaporation method. Magnification x4000. (From Ref. . )...

Horoz BB, Kilicarslan M, Yuksel N, et al. Effect of different dispersing agents on the characteristics of Eudragit microspheres prepared by a solvent evaporation method. / Microencapsul 2004 21 191-202. 

Soppimath KS, Kulkarni AR, Aminabhavi TM, Bhaskar C. Cellulose acetate microspheres prepared by o/w emulsification and solvent evaporation method. / Microencapsul 2001 18(6) 811-817. 

Reithmeier investigated the influence of fat/phospholipid ratio to improve drug encapsulation efficiency into microparticles prepared by the solvent evaporation method [37], A cosolvent-solvent evaporation method like the one described above for the preparation of polymer lipospheres [35] was used. Here, somatostatin as a model peptide was dissolved in methanol and added to a solution of the lipid components in hexane [37],... 

This chapter will discuss (a) the production and characterization of LS formed by the melt dispersion technique, by the solvent evaporation method, and by the water/oil/water (w/o/w) double-emulsion method (b) the influence of preparation parameters on liposphere morphology and (c) the encapsulation efficiency and the release characteristics of two lipophilic model drugs, such as retinyl acetate and progesterone, and one hydrophilic drug, sodium cromoglycate (SCG), from the prepared LS. 

Cellulose acetate butyrate is insoluble in water and is available in several viscosity grades depending on their molecular weight. This pol)nner has been used to obtain sustained-release matrices prepared by direct compression technique as well as in obtaining semi-permeable membranes for osmotic pump systems [16]. Cellulose acetate butyrate microparticles (Figure 19.3) for the sustained release of drugs can be obtained by the emulsion-solvent evaporation method [17]. 

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