Physical encapsulation

Delivery of physically encapsulated small molecules at targeted sites by dendrimers has been superbly envisioned in a recent report by McGrath and Junge [95]. Second generation Frechet type dendrons linked to a central azo-benzene-derivative (32, Fig. 15) underwent reversible cis/trans isomerization of... 

Initial efforts gave rise to well-characterized dendritic macromolecules, but applications remained limited because of the lack of specific functionalities. An exponential increase of publication volume observed for about 15 years testified the growing interest for dendrimers and has led to versatile and powerful iterative methodologies for systematically and expeditiously accessing complex dendritic structures. The perfect control of tridimensional parameters (size, shape, geometry) and the covalent introduction of functionalities in the core, the branches, or the high number extremities, or by physical encapsulation in the microenvironment created by cavities confer such desired properties as solubility, and hydrophilic/hydrophobic balance. Thus, creativity has allowed these structures to become integrated with nearly all contemporary scientific disciplines. 

In the preceding section, we reviewed the non-covalent dynamic encapsulation of guest probe molecules within dendrimer interiors. The second case, Scheme 2, involves the physical encapsulation of guest molecules wherein, guest molecules are locked inside dendritic containers (so-called dendritic boxes). This concept was originally proposed by Tomalia et al and referred to as unimolecular encapsulation [2]. More recent and well characterized examples have now been demonstrated by Meijer and co-workers [11-15]. 

The CHEMFIX process is defined as a chemical fixation/stabilization technology. This proprietary process, patented by Chemfix Technologies, Inc. (CTI), stabilizes mobile constituents of concern within a waste by chemical reactions and physical encapsulation. (<>)... 

Solidification The physical encapsulation of contaminants in clays, cement, or other solid binders so that they may undergo safe disposal in the environment (such as landfilling). In contrast, stabilization refers to the immobilization of contaminants through the formation of chemical bonds between the contaminants and the binders. Solidification and stabilization simultaneously occur in waste treatment and are commonly called solidification/stabilization. 

Solidification/stabilization Refers to reducing the mobility of a contaminant in soils, other solids, or even liquid wastes by mixing them with Portland cement, lime, cement kiln dust, clays, slags, polymers, water treatment sludges, iron-rich gypsum, fly ash, and/or other binders. The process decreases the mobility of contaminants through physical encapsulation (solidification) and chemical bonding between the contaminants and the binders (stabilization). 

The sol-gel procedure enables encapsulation of enzymes in optically transparent, porous silicate matrices, under mild room-temperature conditions. The small pores prevent microbial degradation and, due to the biomolecule size, they will not diffuse out of the polymer network. The physical encapsulation avoids self-aggregation effects as well as protein unfolding and denaturalization. At the same time, the catalytic activity is maintained as the enzymes are able to react with small substrates that can transfer across or within the support, assuring continuous transformations [75]. 

RoyA (1992) Solidification/stabilization of hazardous waste evidence of physical encapsulation. Environ Sci Technol 26 1349-1353... 

Macroencapsulation is used for large objects such as concrete debris that is contaminated, or structural steel that has fixed contamination. The chemical stabilization and microencapsulation work together to immobilize chemical constituents, while the macroencapsulation is used to physically encapsulate large objects. For this reason, we will discuss chemical stabilization and microencapsulation together and address macroencapsulation in a separate section in this chapter. 

By the second approach, the enzyme is immobilized in a redox polymer assembly (Figure 39B). Electron-transfer quenching of the photosensitizer by the polymer matrix generates an electron pool for the activation of the enzyme. Photoreduction of nitrate to nitrite was accomplished by the physical encapsulation of NitraR in a redox-functionalized 4,4 -bipyridinium acrylamide copolymer [234]. In this photosystem, Ru(bpy)3 + was used as a photosensitizer and EDTA as a sacrificial electron donor. Oxidation of the excited photosensitizer results in electron transfer to the redox polymer, and the redox sites on the polymer mediate further electron transfer to the enzyme redox center, where the biocatalyzed transformation occurs. The rate constant for the MET from the redox polymer functionalities to the enzyme active site is — (9 + 3) x 10 s. Similarly, the enzyme glutathione reductase was electrically wired by interacting the enzyme with a redox polymer composed of polylysine modified with A-methyl-A -carboxyalkyl-4,4 -bipyridinium. The photosensitized reduction of oxidized glutathione (GSSG) (Eq. 21) ... 

Photoreduction of nitrate to nitrite, Eq. (52), was accomplished by physical encapsulation of nitrate reductase, NitraR, in a redox functional-... 

Non-covalent drug encapsulation In this method, the drug is physically encapsulated in a dendrimeric structure by virtue of a micellar structure. Although it is relatively easy to produce a drug delivery systan with this approach, the drug release is often uncontrolled. ... 

The various cabinet systems described above were all of rigid construction. Experience shows that rigid cabinets offer many advantages they are robust, can support heavy items of equipment and peripherals such as pass boxes and interface panels. However, it is practical to consider the use of plastic film isolator technology as an alternative approach to providing physical encapsulation. ... 

The application of containment principles developed for the safe culture and process of pathogenic micro-organisms can be seen to be appropriate to modern process biotechnology. Physical encapsulation of fermenters is a... 

The encapsulation of the drug (guest) in the interior of the dendrimers was achieved through physical encapsulation, hydrophobic or hydrogen interaction and so on. Non-covalent interaction, besides the complexation in the dendrimer interior, includes the electrostatic interaction with the surface periphery of the dendrimer. Dendrimers have available surface group modifications, which are used as platforms to facilitate the complexation of drug molecules. ... 

Fig. 7 Methods for physical encapsulation of drugs in polymeric micelles A dialysis method, and B O/W emulsion method...

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