Emulsion microparticles

Adjuvants can be classified into two main groups based on their mechanism of action. The first group are particulate materials that act as vaccine delivery systems and target associated antigens into APC. These include emulsions, microparticles, iscoms, and liposomes. The second group are immunostimula-tory and are derived mainly from pathogens. These include lipopolysaccharide... 

Shchnkina, E. M. and Shchukin, D. G. (2012). Layer-by-layer coated emulsion microparticles as storage and delivery tool. Current Opinion in Colloid Interface Science, 17,281-289. 

Shchukina, E.M., Shchukin, D.G. Layer-by-layer coated emulsion microparticles as sUnage and delivery tool. Curr. Opin. Colloid Interface Sci. 17, 281-289 (2012)... 

Chitosan microparticles were prepared with tripolyphosphate by ionic cross-hnking, starting from chitosan acetate 1% and oil as an emulsion in the presence of the surfactant Tween-80 2% the o/w 1 10 emulsion was introduced into tripolyphosphate solution by a spray gun. The microparticles were then washed their sizes were in the 500-710 jim range. As the pH of tripolyphosphate solution decreased and the molecular weight of chitosan increased, the microparticles had a more spherical shape and smoother surface [98]. 

In the first step of the interfacial cross-linking polymerization, the polymer is dissolved into the solvent, which is the internal phase of the emulsion, and another phase with a nonsolvent to the polymer is produced then the aqueous phase is poured to the organic phase to produce the emulsion. Afterwards, a solution containing the cross-linking agent is added to the emulsion to form a rigid structure of the microparticles (Couvreur et al., 2002 Rao Geckeler, 2011). 

The steroid-loaded formulations are prepared by a patented solvent evaporation process (45,46). Basically, the wall-forming polymer and the steix>id are added to a volatile, water-immiscible solvent. The dispersion or solution is added to an aqueous solution to form an oil-in-water emulsion. The volatile solvent is then removed to afford solid microparticles. The microparticles are usually subd vided with sieves to isolate fractions of the desired diameters. It is i nper-ative that a reliable and reproducible microencapsulation procedure be used to fabricate long-acting formulations. 

Another application of microparticle technology is the production of polymeric microspheres, which are usually produced by emulsion polymerization techniques. But a variety of polymer colloids can be made by aerosol techniques (Partch et al, 1983 Nakamura et al, 1984 Partch et al, 1985). One advantage of the aerosol route is that larger sizes can be attained... 

Ohagan, D. et al. (1997). Recent advances in vaccine adjuvants — the development of Mf59 emulsion and polymeric microparticles. Mol. Med. Today 3(2), 69-75. 

Fig. 14. Targeting of microparticles (e.g., bubbles and emulsion droplets) destined for molecular imaging and drug delivery Schematic simultaneous binding to a microparticle of a targeting device (antigen-specific ligands), of stealth-providing elements (e.g., PEG strands), and of drugs and markers (e.g., a Gd + chelate for MRI contrast enhancement).

Following route A (Fig. 1), Yan Xiao et al. reported the chemoenzymatic synthesis of poly(8-caprolactone) (PCL) and chiral poly(4-methyl-8-caprolactone) (PMCL) microparticles [5]. The telechelic polymer diol precursors were obtained by enzymatic polymerization of the corresponding monomers in the presence of hexanediol. Enzymatic kinetic resolution polymerization directly yielded the (R)-and (S )-enriched chiral polymers. After acrylation using acryloylchloride, the chiral and nonchiral particles were obtained by crosslinking in an oil-in-water emulsion photopolymerization. Preliminary degradation experiments showed that the stereoselectivity of CALB is retained in the degradation of the chiral microparticles (Fig. 2). 

Fig. 2 Synthesis of acrylated chiral PMCL left) and microparticles (right) obtained from acry-lated polymers by oil-in-water emulsion photopolymerization [5]...

Figure 16.2 Preparation of starch acetate microparticles by water-in-oil-in-water double emulsion technique.

A very recent development is encapsulation of actives in colloidosomes [16, 41]. The method is analogous to liposome entrapment. Selectively permeable capsules are formed by surface-tension-driven deposition of solid colloidal particles onto the surface of an inner phase or active ingredient in a water-in-oil or an oil-in-water emulsion composed of colloidal particles. Initially synthetic polymer microparticles were used but more recently a natural alternative has been described based on small starch particles. After spray-drying, redispersible emulsions can be formed. 

Prolonged hypoglycemic effect of insulin was reported after using poly(butyl cyanoacrylate) microparticles with a mean diameter of 254.7 nm (Zhang et al. 2001). Insulin-loaded poly(butyl cyanoacrylate) microparticles were prepared by emulsion polymerization in the presence of insulin. Insulin-loaded microparticles were administered intratracheally to normal rats. The duration of glucose levels below 80% of baseline was maintained for a longer period when insulin was administered in... 

The water-in-oil-in-water (w/o/w) emulsion method (Figure 11.4) is the predominant method used for encapsulation of biomacromolecules in these microparticles. Protein solution forms the internal water phase of the w/o/w emulsion. Loading efficiency of the microparticles has not been optimal using water or buffer as an internal phase, so water is sometimes substituted with polymeric liquids, such as low molecular weight polyethylene glycol. The primary emulsion is then added to a secondary liquid phase, forming the secondary emulsion. The solvent for the... 

Chitosan is a polymer produced from hydrolysis of natural chitin. Chitosan is not readily soluble in aqueous solutions, but can be solubilized and is thus considered with other water soluble polymers. In the hydrophobic form, chitosan has been treated in a similar manner to other hydrophobic polymers with microparticles produced by emulsion and phase separation techniques. Microparticles can be taken up by the gastrointestinal lining in a manner similar to that discussed for other hydrophobic microparticles. 

Layer-by-layer electrostatic deposition of biopolymers at interface of emulsion droplets Polyelectrolyte capsules microparticles with novel functionality and triggered release multiple layers around oil droplets exhibiting improved stability towards environmental stresses (temperature, ionic strength, pH, freezing, dehydration) McClements, 2005, 2006 Sanguansri and Augustin, 2006... 

O Hagan DT, Ott GS, Van Nest G. Recent advances in vaccine adjuvants the development of MF59 emulsion and polymeric microparticles. Mol Med Today 1997 3 69-75. 

Meng FT, Ma GH, Qiu W, Su ZG. W/O/W double emulsion technique using ethyl acetate as organic solvent effects of its diffusion rate on the characteristics of microparticles. J Control Release 2003 91(3) 407-416. 

In another approach, a fluorescent conjugated polymer was used as the material for the preparation of a chemosensor to detect 2,4,6-trinitrotoluene (TNT) and its related nitroaromatic compounds. To this end, microparticles, made of three-dimensionally cross-linked poly(l,4-phenylene vinylene) (PPV) via emulsion polymerization, were synthesized [61]. This material was chosen due to its high fluorescence intensity and sensitivity to changes in its microenvironment. The chemosensor was exposed to vapour containing different amounts of TNT and quenching of the polymer luminescence at 560 nm was observed after excitation at 430 nm. The dependence of the fluorescence signal in response to the analyte was described by a modified Stem-Volmer equation that assumes the existence of two different cavity types. The authors proposed the modified Stem-Volmer equation as follows ... 

Different architectures, such as block copolymers, crosslinked microparticles, hyperbranched polymers and dendrimers, have emerged (Fig. 7.11). Crosslinked microparticles ( microgels ) can be described as polymer particles with sizes in the submicrometer range and with particular characteristics, such as permanent shape, surface area, and solubility. The use of dispersion/emulsion aqueous or nonaqueous copolymerizations of formulations containing adequate concentrations of multifunctional monomers is the most practical and controllable way of manufacturing micro-gel-based systems (Funke et al., 1998). The sizes of CMP prepared in this way vary between 50 and 300 nm. Functional groups are either distributed in the whole CMP or are grafted onto the surface (core-shell, CS particles). 

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