Polymerization microencapsulated

Polymeric microencapsulates and lipid microencapsulates have extensive potential applications in food, cosmetics and pharmaceutics [1-5]. Microencapsulates can protect and conserve an active component until its release is desired and stimulated. Polymeric microencapsulates consist of a (biocompatible) polymer matrix in which an active component is encapsulated. Most frequently poly(lactic add) (PLA) or poly (lactic-co-glycolic acid) (PLGA) is used as the polymer [6,7], but alternatives have been investigated [8, 9]. Lipid microencapsulates, lipid vesicles and liposomes are composed of a (phospho-)lipid bilayer membrane that encapsulates an aqueous volume, thus mimicking a cell structure. 

Lewis, D. H. and Tice, T. R., Polymeric considerations in the design of microencapsulated contraceptive steroids, in Long-Acting Contraceptive DeUvery Systems (G. I. Zatuchni, ed.). Harper and Row, Philadelphia, 1983, pp. 77-95. 

The second general method, IMPR, for the preparation of polymer supported metal catalysts is much less popular. In spite of this, microencapsulation of palladium in a polyurea matrix, generated by interfacial polymerization of isocyanate oligomers in the presence of palladium acetate [128], proved to be very effective in the production of the EnCat catalysts (Scheme 3). In this case, the formation of the polymer matrix implies only hydrolysis-condensation processes, and is therefore much more compatible with the presence of a transition metal compound. That is why palladium(II) survives the microencapsulation reaction... 

The potential of liposomes in oral drug delivery has been largely disappointing. However, the use of polymer-coated, polymerized, and microencapsulated liposomes have all increased their potential for oral use [63], and it predicted that a greater understanding of their cellular processing will ultimately lead to effective therapies for oral liposomes. 

Interfacial contact area, 10 755-756 Interfacial effects, in CA resists, 15 182 Interfacial energy, 24 157 colloids, 7 281-284 Interfacial forces, in foams, 12 4 Interfacial free energy, 24 119 Interfacial in situ polymerization, in microencapsulation, 16 442 446 Interfacial mass-transfer coefficients,... 

Interfacial polymerization processes, in microencapsulation, 16 445 446 Interfacial tension, 24 134 in polymer blends, 20 323, 333 of fats and oils, 10 822 Interference, as cause of color, 7 326t, 339-340... 

More complex geometries have been developed [40] and the influence of the geometrical structure has been examined. Although straight-through microchannel emulsification has been developed [39,41], the production rates are still low compared to those obtained with standard emulsification methods. However, the very high monodispersity makes this emulsification process very suitable for some specific fechnological applicafions such as polymeric microsphere synfhesis [42,43], microencapsulation [44], sol-gel chemistry, and electro-optical materials. 

Scher HB, Rodson M, Lee KS. Microencapsulation of pesticides by interfacial polymerization utilizing isocyanate or aminoplast chemistry. Pest Sci 1998 54 394-400. 

Figure 4. Microencapsulated Flavobacterium cells. The bead (10 gm diameter) is composed of alginate. Similar beads can be prepared for agar, polyurethane, and other polymeric materials. From Stormo Crawford (1992). Reprinted with permission of the American Society for Microbiology.

A membrane can be generated by polymerization around a few biocatalyst molecules which surround a space of a few hundred micrometers (microencapsulation Figure 5.6, option 5), or it can be of macroscopic dimensions (Figure 5.6, option 6). In the latter case, membrane reactors can be classified according to (i) driving force, (ii) pore structure and (iii) pore size. 

Deasy, P. Polymerization procedures for biodegradable micro- and nanocapsules and particles, in Microencapsulation and Related Drug Processes. Drugs and the Pharmaceutical Sciences, ed. J. Swarbrick, Vol. 20. New York Marcel Dekker, 1984, pp. 219-240. 

Other significant uses of PCBs included heat exchangers and hydraulic fluids. Prior to controls PCBs were also used in adhesives, coatings, plasticizers and inks for microencapsulating dyes for carbonless duplicating paper as extenders in pesticide formulations and catalyst carriers in olefin polymerizations to impart hydrophobicity to materials and surfaces in bactericide formulations (combined with insecticides), and in immersion oil for microscopes. Mixed with chloronaphthalenes, PCBs were also used in wire and cable insulation in the mine and shipbuilding industries (ref. 80, p. 455). 

Saihi, D., Vroman, I., Giraud, S., and Bourbigot, S. 2006. Microencapsulation of ammonium phosphate with a polyurethane shell—Part II Interfacial polymerization technique. React. Funct. Polym. 66 1118-1125. 

Vyas, S. E, Ramchandraiah, S., Jain, C. E, and Jain, S. K. (1992), Polymeric pseudolatices bearing pilocarpine for controlled ocular delivery,/. MicroencapsuL, 9, 347-355. 

Koestler RC (1980) Microencapsulation by Interfadal Polymerization Techniques - Agricultural Applications in Controlled Release Technologies Methods, Theory, and Applications (Ed Kydoneius AF), CRC Press, Florida... 

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. 

A recent innovation in in-situ microencapsulation is the development of acid-triggered release of pesticide from the microcapsules [12]. Diols and aldehydes are reacted to form an acid labile acetal moiety. The acetal is then reacted with isocyanate to create a prepolymer. The prepolymer is a polyisocyanate cmitaining the acid labile moiety and suitable for in-situ shellwall polymerization. The prepolymer is dissolved into a pesticide, emulsified into water, and shellwall formed in-situ. Under alkaline or neutral pH conditions in a container, the insecticide is safely contained in the microcapsules. Acid could be added to the spray tank to rapidly release capsule contents prior to application. Alternate shellwall chemistry for in-situ microencapsulation utilizes etherified urea-formaldehyde prepolymers in the oil phase that are self-condensed with acid catalyst to produce encapsulating aminoplast shellwalls [13]. This process does not have the problem of continuing CO2 evolution. Water-soluble urea-formaldehyde and melamine-formaldehyde prepolymers can be selected to microencapsulate water or aqueous solutions [14]. 

In addition to microelectronic and optical applications, polymers deposited using thermal and plasma assisted CVD are increasingly being used in several biomedical applications as well. For instance, drug particles microencapsulated with parylenes provide effective control release activity. Plasma polymerized tetrafiuoroethylene, parylenes and ethylene/nitrogen mixtures can be used as blood compatible materials. An excellent review of plasma polymers used in biomedical applications can be found in reference 131. 

---