Encapsulation methods

Apart from the passive encapsulation methods, different active entrapment techniques are described in the literature. Nichols and Deamer (1976) prepared liposomes with a pH gradient across the membrane (acidic interior with respect to the external buffer). These liposomes efficiently incorporated several catecholamines added to the external buffer. The same technique has been used to concentrate doxorubicin (DXR) in pH gradient liposomes (Mayer et al., 1986b). 

Abstract. This section is an introduction into materials that can be used as Phase Change Materials (PCM) for heat and cold storage and their basic properties. At the beginning, the basic thermodynamics of the use of PCM and general physical and technical requirements on perspective materials are presented. Following that, the most important classes of materials that have been investigated and typical examples of materials to be used as PCM are discussed. These materials usually do not fulfill all requirements. Therefore, solution strategies and ways to improve certain material properties have been developed. The section closes with an up to date market review of commercial PCM, PCM composites and encapsulation methods. 

Common to all encapsulation methods is the provision for the passage of reagents and products through or past the walls of the compartment. In zeolites and mesoporous materials, this is enabled by their open porous structure. It is not surprising, then, that porous silica has been used as a material for encapsulation processes, which has already been seen in LbL methods [43], Moreover, ship-in-a-bottle approaches have been well documented, whereby the encapsulation of individual molecules, molecular clusters, and small metal particles is achieved within zeolites [67]. There is a wealth of literature on the immobilization of catalysts on silica or other inorganic materials [68-72], but this is beyond the scope of this chapter. However, these methods potentially provide another method to avoid a situation where one catalyst interferes with another, or to allow the use of a catalyst in a system limited by the reaction conditions. For example, the increased stability of a catalyst may allow a reaction to run at a desired higher temperature, or allow for the use of an otherwise insoluble catalyst [73]. 

Dave, B.C., Dunn, B., Valentine, J.S. and Zink, J.I. (1994) Sol-gel encapsulation methods for biosensors. Analytical Chemistry, 66, 1120A-1127A. 

PMBV and PVA can spontaneously form a hydrogel without using any crosslinkers. Even in cell culture conditions, the gelation can be confirmed. Therefore, it was possible to encapsulate cells in the PMBV/PVA hydrogel. The encapsulation method is illustrated in Fig. 6. 

Cell encapsulation method using PMBV/PVA hydrogel... 

B.C. Dave, B. Dunn, J.S. Valentine, and J.I. Zink, Sol-gel encapsulation methods for biosensors. Anal. Chem. 66, 1120A-1126A (1994). 

Domb, A.J., L. Bergelson, S. Amselem, Lipospheres for Controlled Delivery of Substances, in Micro encapsulation, Methods and Industrial Applications, Marcel Dekker, 1996, 377. 

We chose to organize the discussion of catalyst encapsulation by separating examples into catalyst type as opposed to encapsulation method. As previously, we do not intend to present a comprehensive treatment of the literature and discuss only examples we consider particularly illustrative. 

Development of new encapsulation methods is time- and effort-consuming, requiring a multidisciplinary approach. In contrast with foods, materials used for fragrance encapsulation are not subject to the extensive legislation that applies to food approval. This makes the use of new materials as matrix materials easier. Some new developments with potential for the near future are discussed next. 

Besides new technologies also new materials are being found. Several (patent) overviews of the art of the encapsulation of various materials, such as flavours and fragrances, can be found in the literature [44, 45]. This section highlights some typical more recent new patented carrier materials used for improvement of fragrance performance in detergents using encapsulation methods. 

Each method was generally developed to solve a particular problem encountered by a product development or formulation chemist. The relationships among problems, capabilities, and encapsulation methods are shown. The overview concludes with a list of reasons for encapsulation, such as prevention of oxidation, conversion of liquids to solids and detackification. 

There are a wide variety of encapsulating agents available on the market. Modified food starches, maltodextrins, gums, proteins, corn syrups and sugars are popular choices (4-7). The selection of an encapsulating agent depends upon the chemical composition of the flavor, the encapsulation method, the desired properties of the final microcapsule and its end uses. Other considerations include cost and availability. 

Although alginate encapsulation or entrapment of oil soluble flavors is quite different from traditional encapsulation methods, it could serve as a valuable tool for liquid systems where a protective effect, delayed release, or combination texture/flavor effect is needed. 

The success of freeze drying as an encapsulation method depends on the following critical factors ... 

Peng, H.S., Wu, C.F., Jiang, Y.F. et al. 2007a. Highly luminescent Eu3+ chelate nanoparticles prepared by a reprecipitation-encapsulation method. Langmuir 23(4) 1591-1595. 

By developing encapsulation methods, scientists and engineers mimic nature to obtain innovative structures to isolate, protect, release and functionalize active ingredients.1 However nature is not so easy to mimic, and what humans have developed are still inferior to what biological cells offer. 

Entrapping I Encapsulation Methods Enzymes can be immobilized by physical entrapment without involving any chemical bonding. This route is somewhat more laborious but yields an enzyme that is least altered by the immobilization. 

When using the encapsulation method the enzyme is enclosed in a scmipcrmeablc membrane. Particles of 1 -... 

In terms of oral delivery, under normal conditions, only negligible amounts of proteins are absorbed intact through the gastrointestinal (GI) tract [70,71]. Ingested proteins are naturally fragmented into amino acids and short peptides by various enzymes present in the gut [72]. These proteolytic enzymes are found both in the lumen and in the mucosal epithelium therefore, although proteins can be protected from the luminal enzymes by common encapsulated methods, they are still susceptible to degradation at the absorption site by various mucosal enzymes located in the intestinal walls. 

The best way to immobilize an enzyme while affecting its structure as little as possible is to encapsulate it Out of all the different encapsulation methods the most prominent and widely used is the sol gel technique [5, 7, 62). Sol gels are highly porous silica materials that are readily prepared and modified (Scheme 2.5). The sol gel obtained is a chemically inert glass that be formed into any desired shape and can be designed to be thermally and mechanically very stable. Most importantly the synthesis proceeds under condihons that are relatively benign for many enzymes. In the first step a tetra-aUcoxysilane such as tetramethoxylsilane (TMOS) is hydrolysed by acid catalysis. Hydrolysis is followed by condensation and the sol is formed, which is a mixture of partially hydrolyzed and partially... 

Diallylamine hydrochloride plus crosslinker Crosslinked polyfethyl acrylate) Encapsulation method 2.10 239)... 

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