Multifunctional capsules

Selective permeability allows chemical reactions to be performed exclusively in the capsule interior. The in-situ modification of polyelectrolyte capsules by conducting syntheses inside inorganic nanoparticles creates a new class of multifunctional capsules that combines the properties of inorganic nanomaterials. These multifunctional, composite capsules may find applications for the protection, delivery, and storage of biochemical compounds that are unstable in solution or under UV/visible irradiation, where the use of capsules composed solely of polymeric components cannot be envisaged. Clearly, much further research is required in this area, most notably in understanding the mechanism of the chemical reactions that occur in the confined microsized geometric and diffusional limitations of polyelectrolyte multilayers. 

Although they are often categorized as inert, preformulation studies can determine the inhuence of excipients on stability, bioavailability, and processability. Excipients are categorized into groups according to their main function, although some may be multifunctional, and examples of common excipients used in the manufacture of tablets and capsule are detailed in Table 3. 

The first step in all interfacial polymerization processes for encapsulation is to form an emulsion. This is followed by initiation of a polymerization process to form the capsule wall. Most commercial products based on interfacial or in situ polymerization employ water-immiscible liquids. For encapsulation of a water-immiscible oil, an oil-in-water emulsion is first formed. Four processes are schematically illustrated in Figure 5.82. In Figure 5.82(a), reactants in two immiscible phases react at the interface forming the polymer capsule wall. For example, to encapsulate a water-immiscible solvent, multifunctional acid chlorides or isocyanates are dissolved in the solvent and the solution is dispersed in water with the aid of a polymeric emulsifier, e.g., poly(vinyl alcohol). When a polyfunctional water-soluble amine is then added with stirring to the aqueous phase, it diffuses to the solvent-water interfece where it reacts with acid chlorides or isocyanates forming the insoluble polymer capsule wall. Normally some reactants with more than two functional groups are used to minimize a regation due to the formation of sticky walls. 

Most commercial processes use this type of polymerization to produce small uniform capsules in the range of 20-30 micron diameter however, the process can be tuned to produce large microcapsules. The size of these microcapsules and the properties of the wall material/polymer matrix can be altered by using different monomers, utilizing additives, and adjusting reaction conditions. The encapsulation occurs by wall formation around the dispersed core material via the rapid polymerization of monomers at the surface of the droplets or particles. The solution of a multifunctional monomer in the core material is dispersed in an aqueous phase. The polymerization is commenced at the surfaces of the core droplets forming the capsule walls, by adding a reactant to the monomer dispersed in the aqueous phase. 

Landfester, K., A. Musyanovych, and V. Mailander, From polymeric particles to multifunctional nano-capsules for biomedical applications using the miniemulsion process. J. Polym. Sci. A Polym. Chem. 48 (2010) 493-515. 

Motomov, M. Roiter, Y. Tokarev, 1. Minko, S. Stimuli-responsive nanoparticles, nanogels and capsules for integrated multifunctional intelligent systems. Prog. Polym. Sci. 2010,35 (1-2), 174—211. 

For a further development of this method i.e., the preparation of multifunction-alized capsules, a series of multicompartment polymeric capsules were successfully constmcted. For example, Stadler et al. [19] synthesized multicon tartment polymeric capsules with embedded liposomes in the shell via the LbL technique by using poly(styrene sulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) as the polyelectrolytes and 50nm zwitterionic l,2-dioleoyl-i n-glycero-3-phosphochohne (DOPC) liposomes as the cargo. The TEM images (Fig. 6.9) clearly show the encapsulated liposomes in the polymeric shell. 

Empincai C12H22O11 H2O Properties Wh. fine cryst. powd. sol. in water insol. in alcohol m.w. 360.31 Uses Tablet/capsule diluent in pharmaceuticals nutrient, multifunctional ingred. in infant formulas, geriatric, dietetic. 

Despite this lack of fundamental understanding, however, the use of these capsules - and in particular their multifunctional properties - is a rapidly developing field that not only has clear potential but has also gained much interest in industry. 

Figure 5 illustrates the type of encapsulation process, shown in Figure 4a, when the core material is a water-immiscible liquid. Reactant X, a multifunctional acid chloride, isocyanate, or a combination of these reactants, is dissolved in the core material. The resulting mixture is emulsified in an aqueous phase that contains an emulsifier such as partially hydrolyzed poly(vinyl alcohol) or a hgno-suMbnate. Reactant Y, a multifunctional amine or a combination of amines such as ethylenediamine, hexamethylenediamine, or triethylenetetramine, is added to the aqueous phase, thereby initiating interfacial polymerization and formation of a capsule shell. If reactant X is an acid chloride, a base is added to the aqueous phase in order to act as an acid scavenger. 

Metal containing polyynes are multifunctional materials which combine the properties of organic polymers with those of metal centers coordinated to the organic moiety and are able to form nanotemplates, colloidal photonic crystals, multilayer capsules and hollow vesicles [127, 128], An example of a rod-like polymetallayne self-assembly in hollow nanorods has been recently reported [129] the computer simulations of the nanostructure show that the polymer chains are ordered in parallel lines that give rise to a tubular morphology rather unusual for these materials, but promising for sensor devices applications. 

Motornov, M., Roiter,Y., Tokarev, I. and Minko, S. (2010) Stimuli-responsive nano-particles, nanogels and capsules for integrated multifunctional intelligent systems , Progress in Polymer Science, 35,174-211. 

Martin AD, Boulos RA, Hubble LJ, HartUeb KJ, Raston CL (2011) Multifunctional water-soluble molecular capsules based on p-phosphonic acid calix[5]arene. Chem Commun 47 7353-7355... 

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