Encapsulation forming polymers

Fig. 30 Types of nanocarriers for drug delivery, (a) Polymeric nanoparticles polymeric nanoparticles in which drugs are conjugated to or encapsulated in polymers, (b) Polymeric micelles amphiphilic block copolymers that form nanosized core-shell structures in aqueous solution. The hydrophobic core region serves as a reservoir for hydrophobic drugs, whereas hydrophilic shell region stabilizes the hydrophobic core and renders the polymer water-soluble.

Preparation of iron oxide magnetic nanoparticles and their encapsulation with polymers in W/0, i.e. inverse microemulsion polymerization, was also applied by O Connor et al. [167]. Inverse microemulsion polymerization was used to prepare submicron hydrophilic magnetic latex containing 5-23 wt% iron oxide. AM and crosslinker MBA were added to an aqueous suspension of previously synthesized iron oxide nanoparticles (6 wt%) this aqueous phase was dispersed in a aerosol OT (sodium l,4-bis(2-ethylhexoxy)-l,4-dioxobutane-2-sulfonate) (AOT)-toluene solution to form a W/O microemulsion, followed by polymerization with AIBN or V-50 as initiator. The particle size (80-180nm)was controlled by tuning the concentration of the water-soluble crosslinker agent as well as the amount of surfactant with respect to water [168]. 

McLean, E., Donaldson, E. M., Mayer, I., Teskeredzic, E., Teskeredzic, Z., Pitt, C., and Souza, LM., 1994, Evaluation of a sustained-release polymer encapsulated form of recombinant porcine somatotropin upon long-term growth performance of Coho salmon, Oncorhynchns kisutch, Aquaculturel22 359- i6i. 

The fifth type of enzyme immobilization is encapsulation in an already formed polymer. An example of this is to utilize alcoholic solutions to swell the micellar pockets of hydrophobically modified Nafion and then to add enzyme and dehydrate the polymer. This encapsulates the enzyme within the polymer and provides a structural entrapment without covalent binding. This technique can tailor the polymer to provide added stabilization to the enzyme, but these polymers typically retard transport of the substrate/product in and out of the film. 

In slurry polymerization, the polymer precipitates from the solution partly or totally and this certainly limits the macromer mobility. Forming polymer encapsulates the active center and the polymerization occurs in the polymer phase [127], this is even more so the case with supported (immobilized) catalysts. 

Multi-component PCM fibers can be prepared using a PCM as the core and other polymer materials as the sheath. The PCMs are often micro-encapsulated and blended with other fiber-forming polymers prior to spirming, using the melt spinning or wet spirming process. 

Figure 4c also describes the spontaneous polymerisation ofpara- s.yX en.e diradicals on the surface of soHd particles dispersed in a gas phase that contains this reactive monomer (16) (see XylylenePOLYMERS). The poly -xylylene) polymer produced forms a continuous capsule sheU that is highly impermeable to transport of many penetrants including water. This is an expensive encapsulation process, but it has produced capsules with impressive barrier properties. This process is a Type B encapsulation process, but is included here for the sake of completeness. 

Spray Drying. Spray-dry encapsulation processes (Fig. 7) consist of spraying an intimate mixture of core and shell material into a heated chamber where rapid desolvation occurs to thereby produce microcapsules (24,25). The first step in such processes is to form a concentrated solution of the carrier or shell material in the solvent from which spray drying is to be done. Any water- or solvent-soluble film-forming shell material can, in principle, be used. Water-soluble polymers such as gum arable, modified starch, and hydrolyzed gelatin are used most often. Solutions of these shell materials at 50 wt % soHds have sufficiently low viscosities that they stiU can be atomized without difficulty. It is not unusual to blend gum arable and modified starch with maltodextrins, sucrose, or sorbitol. 

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