Poly microsphere

The soapless seeded emulsion copolymerization method was used for producing uniform microspheres prepared by the copolymerization of styrene with polar, functional monomers [115-117]. In this series, polysty-rene-polymethacrylic acid (PS/PMAAc), poly sty rene-polymethylmethacrylate-polymethacrylic acid (PS/ PMMA/PMAAc), polystyrene-polyhydroxyethylmeth-acrylate (PS/PHEMA), and polystyrene-polyacrylic acid (PS/PAAc) uniform copolymer microspheres were synthesized by applying a multistage soapless emulsion polymerization process. The composition and the average size of the uniform copolymer latices prepared by multistage soapless emulsion copolymerization are given in Table 11. 

As previously described, all microspheres discussed in this chapter were synthesized from AB type diblock copolymers. Precursor block copolymers, poly(styrene-b-4-vinyl pyridine) (P[S-b-4VP]) diblock copolymers, were synthesized using the additional anionic polymerization technique [13]. The basic properties of the block copolymers were determined elsewhere [24,25] and are listed... 

As these block copolymers were synthesized using the anionic polymerization technique, their molecular weight distributions were narrow. The microspheres with narrower size distribution are better for well-ordered self-organization. Actually, all block copolymers synthesized for these works formed poly(4-vinyl pyridine) (P4VP) spheres in the PS matrices with narrow size distributions. 

The poly(styrene-b-isoprene) (P(S-b-IP)) and poly(-styrene-b-2-vinyl pyridine) (P(S-b-2VP)) block copolymers with narrow molecular weight distributions for blending with the microspheres were also synthesized using the additional anionic polymerization technique. The number-average molecular weights (Mns) and PS contents are also shown in Table 1. 

PEG/PBT copolymers are also very good matrix materials for the release of growth factors in tissue engineering. Proteins have been delivered from PEG/PBT microspheres with preservation of protein delivery of complete activity. In the case of protein delivery from PLGA and poly(ortho ester) microspheres, the protein activity was significantly reduced. " ... 

Poly(DL-lactide) was used as the excipient in microspheres of CCNU, a nitrosourea, prepared by a solvent evaporation procedure (96,97). PLA-CCNU microspheres 3.0 pm in diameter were injected i.v. and leukemia cell survival was determined by spleen colony assay. A 100-fold decrease in leukemia cell survival was observed with the microspheres in both spleen and liver compared to untreated controls. Promising results were also obtained with Lewis lung carcinoma in mice. These studies showed that 2- to 4-ym microspheres were preferentially targeted to the lungs. 

Lactic acid oligomer microspheres containing aclarubicin have been studied for selective lymphatic delivery. Low (less than 10,000 molecular weight oligomers were used to produce microspheres designed to release drug over a 30-day period (99). Additives have been used to alter the release rate of aclarubicin-loaded poly(lactide) microspheres (100). Mitomycin C was incorporated into poly(lactic... 

Hydrocortisone microspheres (108,109) and films (110) based on poly(lactic acid) have been investigated. A cage implant technique was used to study the performance of monolithic poly (DL-lactide) films loaded with hydrocortisone acetate (110). Films 1.5 x 0.6 cm were inserted into titanium wire-mesh cages 3.5 x 1.0 cm. The cages were implanted in the backs of rats and the inflammatory exudate was sampled periodically. The white cell concentration in the samples was lower than that of controls at all times during the 21-day test. 

The use of polylactides for delivery of insect hormone analogs and other veterinary compounds (115,116) has been studied. Microspheres, pellets, and reservoir devices based on polyglycolide, poly-(DL-Iactide), poly(L-lactide), and various copolymers have been used to deliver methoprene and a number of juvenile hormone analogs. ... 

Lactide/glycoUde polymers have been investigated for delivery of several other macromolecules. Synthetic double-stranded RNA, poly-isosinic acid/polycytidylic acid, a potent inducer of interferon, was formulated in a 53 47 copolymer of DL-lactide-co-glycoUde. The microspheres were evaluated in mice challenged with Right Valley fever virus. More than 16 days protection was afforded versus only 3 days for controls (137). 

Bissery, M. C., Valeriote, F., and Thies, C., Fate and effect of CCNU-loaded microspheres made of poly(D,L) lactide (PLA) or poly B-hydroxybutyrate (PHB) in mice, Proc. Int. Symp. Control. Rel. Bioact. Mater.. 12. 181, 1985. 

Cortisone acetate has been incorporated into several polyanhydrides (15). The rates of release of cortisone acetate from microcapsules of poly(terephthaUc acid), poly(terephthaUc acid-sebacic acid) 50 50, and poly(carboxyphenoxypropane-sebacic acid) 50 50 are shown in Fig. 8. These microcapsules were produced by an interfacial condensation of a diacyl chloride in methylene chloride with the appropriate dicarboxylic acid in water, with or without the crosslinking agent trimesoyl chloride. This process produces irregular microcapsules with a rough surface. The release rates of cortisone acetate from these microcapsules varied correspondingly with the rate of degradation of the respective polyanhydrides. It can be expected that the duration of release of cortisone acetate from solid microspheres, such as those produced by the hot-melt process, would be considerably longer. 

Microencapsulation with PCL using the solvent evaporation method can be experimentally difficult. For example, PCL was the only polymer of five that failed to yield spherically shaped microcapsules using this technique (82). The insecticide Abate has been incorporated into PCL (21% loading) by the solvent separation method in a comparative study, PCL afforded good-quality microspheres although poly (methyl methacrylate) microcapsules were smoother and had fewer defects (83). 

At present there is no reason evident why poly(N-acylhydroxy-proline esters) should not be suitable for the formation of microcapsules or microspheres as well. For microencapsulated drug fonmula-tions the longer degradation times of poly(N-acylhydroxyproline esters) as compared to poly (lactic acid) could again be a distinctive advantage for long-term applications. 

Starch is usually derivatized by the introduction of acrylic groups, prior to polymerization and manufacture into microspheres. Poly(acryl) starch microspheres, as they are referred to, are an example of a semisynthetic polymer system. Their extensive use as... 

The preparation by dispersion polymerization of the microsphere sample employed in this study was previously described [8]. The microsphere sample utilized in this study has a monomodal diameter distribution with mean diameter value d= 3.09 pm and standard deviation dsdev= 0-74 pm. The microsphere surface is covered by a poly(methacrylic acid-co-ethylacrylate) whose percent by weight is 1.1... 

The endopolygalacturonase obtained from a Kluyveromyces marxianus culture broth was purified through the addition of specifically designed core-shell microspheres consisting of an inner polystyrene core and an outer shell constituted by a poly(methacrylic acid-co-ethylacrylate) statistical copolymer. These microspheres were previously found very effective in purifying the pectinlyase within a commercial pectinase sample [15]. 

PD Scholes, AGA Coombes, L Ilium, SS Davis, M Yert, MC Davies. The preparation of sub-200 nm poly (lactide-co-glycolide) microspheres for site-specific drug delivery. J Control Rel 25 145-153, 1993. 

Soppimath, K.S., Kulkarni, A.R. and Aminabhave, M. (2000) Controlled release of antihypertensive drug from the interpenetrating network poly (vinyl alcohol)-guar gum hydrogel microspheres. Journal of Biomaterials Science-Polymer Edition, 11, 27-43. 

Walter, E Dreher, D Kok, M Thiele, L Kiama, S.G., Gehr, P and Merkle, H.P., Hydrophilic poly(dl-lactide-co-glycolide) microspheres for the delivery of DNA to human-derived macrophages and dendritic cells, Journal of Controlled Release, 2001, 76, 149-168. 

Li X, Deng X, Yuan M et al (2000) In vitro degradation and release profiles of poly-DL-lactide-poly(ethylene glycol) microspheres with entrapped proteins. J Appl Polym Sci 78 140-148... 

Liggins RT, Burt HM (2001) Paclitaxel loaded poly(L-lactic acid) microspheres properties of microspheres made with low molecular weight polymers. Int J Pharm 222 19-33... 

Waeckerle-Men Y, Allmen EU, Gander B et al (2006) Encapsulation of proteins and peptides into biodegradable poly(D, L-lactide-co-glycolide) microspheres prolongs and enhances antigen presentation by human dendritic cells. Vaccine 24 1847-1857... 

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