Microspheres and microcapsules, a survey of manufacturing techniques Part II: Coacervation
TL;DR: A methodological survey of coacervation/phase separation techniques employed for the preparation of microspheres and microcapsules is presented in this article, where basic features of macromolecular co-acervation are discussed, and a classification of different co-cervation procedures (i.e., simple, complex, aqueous and nonaqueous) is provided.
Abstract: A methodological survey of coacervation/phase separation techniques employed for the preparation of microspheres and microcapsules is presented. Basic features of macromolecular coacervation are discussed, and a classification of different coacervation procedures (i.e., simple, complex, aqueous, and nonaqueous) is provided. Microsphere formation and microencapsulation techniques based on coacervation/phase separation of gelatin, gelatin-acacia, and ethylcellulose are described, and those of a wide range of other polysaccharide derivatives and synthetic polymers are tabulated. The dependence of microsphere/microcapsule characteristics on manufacturing parameters and performance evaluation of microspherical/microcapsular products are also discussed.
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TL;DR: The results show that silk I-rich particles possess chemical and physical stability and secondary structure which remained unchanged during post treatments even upon exposure to 100% ethanol or methanol.
420 citations
TL;DR: Particles with liquid cores and solid shells have been prepared by the controlled phase separation of poly(methylmethacrylate) (PMMA) within the droplets of an oil-in-water emulsion, finding that core/shell microcapsules were formed when hexadecane or decane was used as non-solvent and only when polymeric emulsifiers were employed.
346 citations
TL;DR: In this paper, the authors highlight the major reasons behind micro encapsulation, important techniques of microencapsulation and application of micro-encapsulated products in different areas of science and technology.
Abstract: Microencapsulation technology allows a compound to be encapsulated inside a tiny sphere known as microsphere/microcapsule, having an average diameter as small as 1 mm to several hundred micro meters. Many different active materials like drugs, enzymes, vitamins, pesticides, flavours and catalysts have been successfully encapsulated inside microballoons or microcapsules made from a variety of polymeric and non polymeric materials including poly(ethylene glycol)s, poly(methacrylate)s, poly(styrene)s, cellulose, poly(lactide)s, poly(lactide-co-glycolide)s, gelatin and acacia, etc. These microcapsules release their contents at appropriate time by using different release mechanisms, depending on the end use of encapsulated products. This technology has been used in several fields including pharmaceutical, agriculture, food, printing, cosmetic, textile and defence. In defence sector this technology has introduced the concept of self-healing composites as well as chemical decontaminating fabrics. This review paper highlights the major reasons behind microencapsulation, important techniques of microencapsulation and application of microencapsulated products in different areas of science and technology.Defence Science Journal, 2009, 59(1), pp.82-95, DOI:http://dx.doi.org/10.14429/dsj.59.1489
289 citations
TL;DR: A general survey of the manufacturing methods of microspheres and microcapsules based on biodegradable polyesters, including polylactides, polyglycolide, polyhydroxybutyrate, polycaprolactone, polycarbonates and related copolymers is presented in this paper.
282 citations
TL;DR: Small droplets were easier to encapsulate within a coacervate matrix than large ones, which were present in a typical shell/core structure, and the influence of pH on the capsule formation was in accordance with previous results on coacervation of whey proteins and gum arabic.
Abstract: Microencapsulating sunflower oil, lemon and orange oil flavour was investigated using complex coacervation of whey protein/gum arabic (WP/GA) At pH 30-45, WP and GA formed electrostatic complexes that could be successfully used for microencapsulation purposes The formation of a smooth biopolymer shell around the oil droplets was achieved at a specific pH (close to 40) and the payload of oil (ie amount of oil in the capsule) was higher than 80% Small droplets were easier to encapsulate within a coacervate matrix than large ones, which were present in a typical shell/core structure The stability of the emulsion made of oil droplets covered with coacervates was strongly pH-dependent At pH 40, the creaming rate of the emulsion was much higher than at other pH values This phenomenon was investigated by carrying out zeta potential measurements on the mixtures It seemed that, at this specific pH, the zeta potential was close to zero, highlighting the presence of neutral coacervate at the oil/water interface The influence of pH on the capsule formation was in accordance with previous results on coacervation of whey proteins and gum arabic, ie WP/GA coacervates were formed in the same pH window with and without oil and the pH where the encapsulation seemed to be optimum corresponded to the pH at which the coacervate was the most viscous Finally, to illustrate the applicability of these new coacervates, the release of flavoured capsules incorporated within Gouda cheese showed that large capsules gave stronger release and the covalently cross-linked capsules showed the lowest release, probably because of a tough dense biopolymer wall which was difficult to break by chewing
229 citations
Cites methods from "Microspheres and microcapsules, a s..."
...…coacervation—phase separation technology, which has been used as a physicochemical procedure for the preparation of polymeric capsules (Deasy 1984, Arshady 1990, * To whom correspondence should be addressed. e-mail: fanny.weinbreck@nizo.nl j. microencapsulation September, 2004, vol. 21, no. 6,…...
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...…method is known to be strongly influenced by many parameters, such as pH, biopolymer concentration (Cp) and droplet size (Madan et al. 1972, 1974, Nixon and Nouh 1978, Takenaka et al. 1980, Burgess and Carless 1985, Arshady 1990, Burgess 1994, Ijichi et al. 1997, Thimma and Tammishetti 2003)....
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TL;DR: In this paper, simple thermodynamic expressions are used to describe the properties of uncharged binary and ternary polymer solutions, in particular the sedimentation equilibrium of binary systems and the osmotic pressures and "incompatible" phase separations.
Abstract: 1. Simple thermodynamic expressions are used to describe the properties of uncharged binary and ternary polymer solutions, in particular the sedimentation equilibrium of binary systems and the osmotic pressures and ‘incompatible’ phase separations of ternary systems. 2. Sedimentation-equilibrium experiments were performed on four samples of dextran and two of polyethylene glycol. The critical points of the phase diagrams were determined for the mixed solutions of polyethylene glycol–dextran–water and of polyethylene glycol–bovine serum albumin–0·2m-sodium chloride solution. Osmotic pressures were measured on a single-phase mixed solution of a polyethylene glycol and a dextran. By use of the simple thermodynamic expressions consistent values of second virial and interaction coefficients for the materials used were obtained from these experiments. 3. The interpretation of the values of the second virial and interaction coefficients, on the basis of three models of molecular interaction, is discussed.
326 citations
TL;DR: A methodological survey of microsphere formation and microencapsulation techniques based on solvent extraction/evaporation techniques is presented in this article, where the basic features of solvent extraction and solvent evaporation processes, including droplet formation, droplet/particle stabilization, and solvent removal, are outlined.
Abstract: A methodological survey of microsphere formation and microencapsulation techniques based on solvent extraction/evaporation techniques is presented. Thus, basic features of solvent extraction and solvent evaporation processes, including droplet formation, droplet/particle stabilization, and solvent removal, are outlined. Preparation of a wide range of microspherical and microcapsular products based on biodegradable polyesters, polysaccharides, and nonbiodegradable polymers are discussed. Dependence of microcapsule characteristics on manufacturing parameters, as well as performance evaluation of microspherical and microcapsular products, are also briefly covered.
113 citations
TL;DR: A methodological survey of preparation of microspheres and microcapsules by suspension cross-linking is presented in this paper, where the formation of small droplets of a polymer solution (or melt) in an immiscible liquid followed by hardening of these droplets by covalent crosslinking, are discussed.
Abstract: A methodological survey of preparation of microspheres and microcapsules by suspension cross-linking is presented. Thus, basic features of suspension cross-linking, i.e., the formation of small droplets of a polymer solution (or melt) in an immiscible liquid followed by hardening of these droplets by covalent cross-linking, are discussed. Typical microspherical and microcapsular products manufactured by suspension cross-linking of naturally occurring and preformed synthetic polymers, including agarose and cellulose beads, albumin microspheres and microcapsules, polystyrene beads and epoxy resin microcapsules, are described. Manufacturing parameters controlling microsphere/microcapsule characteristics are also briefly outlined.
84 citations