Emulsions microencapsulation

The GA is a heterogeneous material having both hydrophilic and hydrophobic affinities. GA physicochemical responses can be handled depending on the balance of hydrophilic and hydrophobic interactions. GA functional properties are closely related to its structure, which determines, for example, solubility, viscosity, degree of interaction with water and oil in an emulsion, microencapsulation ability, among others. 

Liquid-to-liquid emulsification is a critical step in the multiple emulsion microencapsulation process (W/OAV or O/W/O). It was found that the size of these droplets decreases with increasing homogenization intensity and duration. The emulsion droplet size depends, as expected, on viscosity, total volume size, and the volume ratio of the continuous phase to the dispersed phase in the rotor/stator design being investigated. All these physical parameters influence the structure of the microspheres obtained by this technique. 

GA is mainly used for fat microencapsulation because it produces stable emulsions in the case of most oils in a wide pH range, and it has the ability to form films (Kenyon, 1995). Barbosa et al., 2005 studied the photostability of the microencapsulated carotenoid bixin in different edible polysaccharide. They found out that microencapsulated bixin in GA was three to four times more stable than the one microencapsulated with maltodextrin, and about ten-fold than in homogeneous solvents. 

The steroid-loaded formulations are prepared by a patented solvent evaporation process (45,46). Basically, the wall-forming polymer and the steix>id are added to a volatile, water-immiscible solvent. The dispersion or solution is added to an aqueous solution to form an oil-in-water emulsion. The volatile solvent is then removed to afford solid microparticles. The microparticles are usually subd vided with sieves to isolate fractions of the desired diameters. It is i nper-ative that a reliable and reproducible microencapsulation procedure be used to fabricate long-acting formulations. 

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)... 

K Heinzelmann, K Franke. Using freezing and drying techniques of emulsions for the microencapsulation of fish oil to improve oxidation stability. Colloids Surfaces B Biointerfaces 12(3—6) 223—229, 1999. 

N Garti, A Aserin. Pharmaceutical emulsions double emulsions and microemulsions. In S Benita, ed. Microencapsulation-Methods and Industrial Applications. New York Marcel Dekker, 1996, pp 411-534. 

Chen, H Wu, J.-C. and Chen, H.-Y. (1995) Preparation of ethylcellulose microcapsules containing theophylline by using emulsion non-solvent addition method. Journal of Microencapsulation, 12, 137-147. 

Water-hydrogen chloride-inorganic compound systems, 13 817-818 Water-immiscible core materials, in microencapsulation, 16 442, 443 Water injection molding, 19 789 Water-in-oil (W/O) emulsions, 11 551, 24 155... 

Giunchedi P, Gavini E, Bonacucina G, Palmieri GF. Tabletted polylactide microspheres prepared by a w/o emulsion-spray drying method. J Microencapsul 2000 17(6) 711-720. 

Sznitowska, M., et al. 2001. In vivo evaluation of submicron emulsions with pilocarpine The effect of pH and chemical form of the drug. J Microencapsul 18 173. 

Microbial biomethylation, antimony, 12, 644 Microbial dealkylation, examples, 12, 610 Microbial demethylation, examples, 12, 610 Micro-emulsion techniques, for molecular precursor transformations, 12, 46 Microencapsulation... 

Microencapsulation can be used to provide a temporary barrier between a chemical species and its surrounding environment see also Section 14.3). This permits controlled (slow) release of the active agents following application. Depending on the product and the situation, an active ingredient such as a pesticide may need to be released slowly at low concentration, or slowly at high concentrations. Such controlled release can both reduce the number of crop applications that are required and also help prevent over use and subsequent run-off. The barrier can be provided by a polymer film, in the case of suspensions [867], or a liquid membrane, in the case of single or multiple emulsions [865], Microemulsions have also been used [234,865],... 

Li JK, Wang N, Wu XS (1998) Gelatin nanoencapsulation of protein/peptide drugs using an emulsifier-free emulsion method. J Microencapsul 15(2) 163-172... 

Reis, C. P, Neufeld, R. J., Vile la, S., Ribeiro, A. J., and Veiga, F. (2006), Review and current status of emulsion/dispersion technology using an internal gelation process for the design of alginate particles, /. Microencapsul., 23(3), 245-257. 

Hogan SA, O Riordan, E.D., and O Sullivan, M. (2003). Microencapsulation and oxidative stability of spray-dried fish oil emulsions. J. Microencapsulation 20,675-688. 

Two types of microencapsulation are known in the art based upon the shellwall forming chemistry. These are interfacial polymerization and in-situ polymerization. Encapsulating plastic shellwalls are synthesized at the 0/W (Oil-in-Water) interface of a pesticide emulsion by reacting oil-soluble monomers dissolved in the pesticide with water-soluble monomers added to the emulsion. This process is referred to as interfacial polymerization. 

Aqueous solutions can also by microencapsulated in high concentration [6]. To prepare the reverse phase W/0 (Water-in-Oil) emulsions care must be taken to select monomers that will remain in the dispersed water droplets during the emulsion stage. If the monomers diffuse from suspended droplets into the continuous phase polymerization will happen throughout the emulsion and not at the interface as intended. No microcapsules will be formed. This problem has been addressed utilizing carboxy-functional polymers to associate with amine functional reactive monomers dissolved into the water droplets [7]. Shellwalls are formed at the W/0 interface by addition of the oil-soluble monomers to the continuous oil phase. Without the carboxy-functional protective polymers amine monomers would have partitioned out of dispersed water droplets and into the oil phase. Microcapsules would not have been produced. 

In an alternate process organic pesticide was microencapsulated in aminoplast shellwalls starting with the urea-formaldehyde or melamine-formaldehyde prepolymers dissolved in the aqueous phase [16]. Growing polymer chains wrap around the pesticide emulsion... 

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