Polymer microparticles

O Hagan DT, Jeffery H, Davis SS (1994) The preparation and characterization ofpoly (lactide-co-glycolide) microparticles III. Microparticle/polymer degradation rates and the in vitro release of a model protein. Int J Pharm 103 37-45... 

Another example of a delivery system based on microbubbles and ultrasound is the delivery of circulating microparticles (polymer latex beads) or fluorescent red blood cells outside of the capillaries into the surrounding tissues by the action of ultrasound on the co-injected Optison microbubbles [79]. Interestingly, polymer beads and red blood cells could be detected tens of micrometers away from the capillaries where the bubble destruction took place. This may imply that during rapid destruction of a microbubble in a very strong ultrasound field, adjacent microsphere beads in the bloodstream can be propelled deep into the surrounding tissues. 

S.-W. Phang and N. Kuramoto, Morphology studies of doped polyaniline micro/nanocompo-sites containing Ti02 nanoparticles and Fe304 microparticles, Polym. Compos., 30,970 975 (2009). 

Staudinger polymerized divinylbenzene under ultradilute conditions and predicted the formation of microparticle polymers [2]. The obtained solution had extremely low viscosity. Bobalek et al. [8] and Solomon and Hopwood [9] stopped the reaction immediately preceding the macroscopic gelation to synthesize microgels. When they synthesized an alkyd resin at... 

Starch is a polysaccharide found in many plant species. Com and potatoes are two common sources of industrial starch. The composition of starch varies somewhat in terms of the amount of branching of the polymer chains (11). Its principal use as a flocculant is in the Bayer process for extracting aluminum from bauxite ore. The digestion of bauxite in sodium hydroxide solution produces a suspension of finely divided iron minerals and siUcates, called red mud, in a highly alkaline Hquor. Starch is used to settle the red mud so that relatively pure alumina can be produced from the clarified Hquor. It has been largely replaced by acryHc acid and acrylamide-based (11,12) polymers, although a number of plants stiH add some starch in addition to synthetic polymers to reduce the level of residual suspended soHds in the Hquor. Starch [9005-25-8] can be modified with various reagents to produce semisynthetic polymers. The principal one of these is cationic starch, which is used as a retention aid in paper production as a component of a dual system (13,14) or a microparticle system (15). 

As mentioned earlier, the contact-mechanics-based experimental studies of interfacial adhesion primarily include (1) direct measurements of surface and interfacial energies of polymers and self-assembled monolayers (2) quantitative studies on the role of interfacial coupling agents in the adhesion of elastomers (3) adhesion of microparticles on surfaces and (4) adhesion of viscoelastic polymer particles. In these studies, a variety of experimental tools have been employed by different researchers. Each one of these tools offers certain advantages over the others. These experimental studies are reviewed in Section 4. 

Polymers are suspended as microparticles in the latex and interactions between these microparticles are prevented by the presence of adsorbed suspending agent and soap molecules. Blending results in a random suspension of dissimilar particles in the mixture of latexes, each unaffected by the other. Rate of flocculation depends entirely on the stabilizer and not on the polymer characteristics as such. Coagulated mass contains an intimate mixture of the polymers. Acrylonitrile butadiene styrene (ABS) polymers [23-25] may be prepared by this method. 

Polymeric microparticles have been studied and developed for several years. Their contribution in the pharmacy field is of utmost importance in order to improve the efficiency of oral delivery of drugs. As drug carriers, polymer-based microparticles may avoid the early degradation of active molecules in undesirable sites of the gastrointestinal tract, mask unpleasant taste of drugs, reduce doses and side effects and improve bioavailability. Also, they allow the production of site-specific drug targeting, which consists of a suitable approach for the delivery of active molecules into desired tissues or cells in order to increase their efficiency. 

The aim of this chapter is to summarize some of the research findings on xylan, a natural polymer extracted from corn cobs, which presents a promising application in the development of colon-specific drug carriers. Physicochemical characterization of the polymer regarding particle size and morphology, composition, rheology, thermal behavior, and crystallinity will be provided. Additionally, research data on its extraction and the development of microparticles based on xylan and prepared by different methods will also be presented and discussed. 

Xylan-based micro- and nanoparticles have been produced by simple coacervation (Garcia et al., 2001). In the study, sodium hydroxide and chloride acid or acetic acid were used as solvent and non-solvent, respectively. Also, xylan and surfactant concentrations and the molar ratio between sodium hydroxide and chloride acid were observed as parameters for the formation of micro- and nanoparticles by the simple coacervation technique (Garcia et al., 2001). Different xylan concentrations allowed the formation of micro- and nanoparticles. More precisely, microparticles were found for higher concentrations of xylan while nanopartides were produced for lower concentrations of the polymer solution. When the molar ratio between sodium hydroxide and chloride acid was greater than 1 1, the partides settled more rapidly at pH=7.0. Regarding the surfactant variations, an optimal concentration was found however, at higher ones a supernatant layer was observed after 30 days (Garda et al., 2001). 

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). 

Thus, spray-dried xylan/ESlOO microparticles were produced at different polymer weight ratios dissolved in alkaline and neutral solutions, separately. More precisely, xylan and ESIOO were dissolved in 1 1 and 1 3 weight ratios in 0.6 N NaOH and phosphate buffer (pH 7.4). Then, the suspensions were spray-diied at the feed rate of 1.2 mL/min (inlet temperature of 120°C) using a Biichi Model 191 laboratory spray-dryer with a 0.7 mm nozzle, separately. Cross-linked xylan microcapsules were also coated by ESIOO after spraydrying at the same conditions. 

It was observed that this technique was able to produce microparticles with a mean diameter of approximately 10.17 + 3.02 pm in a reasonable to satisfactory yield depending on the formulation. This value was observed to be higher for the polymer weight ratio of 1 3 (87.00 + 4.25 %), which indicates that ESIOO improves the final result of the spray-drying process. According to the SEM analysis, the polymeric microparticles were shown to be quite similar in shape. Regardless of the formulation, they appeared to be mostly concave and asymmetric (Figure 12). 

Fig. 12. SEM images of 5-ASA-loaded spray-dried xylan and ESIOO microparticles in different polymer weight ratios (Unpublished data).

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. 

Won, J., Inaba, T., Masuhara, H., Fujiwara, H., Sasaki, K, Miyawaki, S. and Sato, S. (1999) Photofhermal fixation of laser-trapped polymer microparticles on polymer substrates. Appl. Phys. Lett., 75, 1506-1508. 

CR Robert, PA Buri, NA Peppas. Effect of degree of crosslinking of water transport in polymer microparticles. J Appl Polym Sci 30 301-307, 1985. 

BD Barr-Howell, NA Peppas. Structural analysis of poly(2-hydroxyethyl methacrylate) microparticles. Eur Polym J 23 591-596, 1987. 

Morales, M.E., Ruiz, M.A., Oliva, I., Oliva, M. and Gallardo, V. (2007) Chemical characterization with XP S of the surface of polymer microparticles loaded with morphine. International Journal of Pharmaceutics, 333, 162—166. 

Recently, the LbL technique has been extended from conventional nonporous substrates to macroporous substrates, such as 3DOM materials [58,59], macroporous membranes [60-63], and porous calcium carbonate microparticles [64,65], to prepare porous PE-based materials. LbL-assembly of polyelectrolytes can also be performed on the surface of MS particles preloaded with enzymes [66,67] or small molecule drugs [68], and, under appropriate solution conditions, within the pores of MS particles to generate polymer-based nanoporous spheres following removal of the silica template [69]. 

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