Applications of microspheres

Besides parenteral application of microspheres and nanoparticles for cell selective delivery of drugs, they have more recently been studied for their application in oral delivery of peptides and peptidomimetics [30]. Immunological tolerance induction against beta-lac-toglobulin could be achieved by application of this protein in a poly-lactic-glycolide microsphere formulation [31]. 

Light weight reinforced syntactic plastics are a new application of microspheres, an example being made from an epoxy resin, glass fiber, and carbon or glass microspheres. These materials have also good heat insulation and ablation properties40). 

Fig. 8.1, Safety assessment prior to SIR-Spheres therapy. Scintigraphy with macroaggregated albumin (MAA) acquired after intraarterial administration of MAA during hepatic angiography shows extrahepatic deposition of particles. A therapeutic application of microspheres under the same conditions would have resulted in severe complications...

Wu XS (1995) Preparation, characterization, and drug delivery applications of microspheres based on biodegradable lactic/glycolic acid polymers, hi Wise DL et al (eds) Encyclopedic handbook of biomaterials and bioengineering. Dekker, New York, pp 1151-1200... 

The development of injectable microcapsules for delivery of chemotherapy agents remains an active area of research. The ultimate goal is to achieve targeted delivery of chemotherapy agents to specific sites in the body, ideally by injection of drug-loaded microcapsules that would seek out and destroy diseased cells. Intra-arterial infusion chemotherapy is a direct approach to targeted delivery. The clinical applications of microspheres and microcapsules in embolization and chemotherapy have been assessed (41). 

FDG-PET and FDG-PET-CT can be of benefit in interventional radiological procedures (Fig. 33.10). Compared with CT alone, PET and PET-CT have been found of higher accuracy when assessing the liver for residual disease after radiofrequency ablation (RFA) of liver metastases (Barker et al. 2005). However, a substantial number of false-negative cases caused by very small tumor residuals must be kept in mind. These small tumor residuals, not visible on CT or PET, lead to early tumor recurrence and require a close followup of patients (Veit et al. 2006). Other authors report promising results when following-up patients with liver metastases undergoing therapy with application of microspheres (Lewandowski et al. 2005). 

It is well known that block copolymers and graft copolymers composed of incompatible sequences form the self-assemblies (the microphase separations). These morphologies of the microphase separation are governed by Molau s law [1] in the solid state. Nowadays, not only the three basic morphologies but also novel morphologies, such as ordered bicontinuous double diamond structure, are reported [2-6]. The applications of the microphase separation are also investigated [7-12]. As one of the applications of the microphase separation of AB diblock copolymers, it is possible to synthesize coreshell type polymer microspheres upon crosslinking the spherical microdomains [13-16]. 

Lactide/glycolide polymers have been investigated for delivery of agents in applications outside the pharmaceutical field. For example, the microbiocidal properties of chlorine dioxide disinfectants have been improved by formulating a long-acting chlorine dioxide system based on lactide/glycolide copolymers. Blends of microspheres based on 50 50 and 87 13 copolymers were developed to afford the release of chlorine dioxide over several months (114). 

For many drug delivery applications, the preferred method of delivery of the dosage form is by injection. For controlled release applications, the most frequently used approach to allow this method of administration is to prepare microspheres of the polymer containing the drug to be delivered. Several different techniques have been developed for the preparation of microspheres from polyanhydrides. 

While the major application of albumin microspheres is in the area of chemotherapy, there have been studies reporting the release of such varied compounds as 1-norgestrel (97), insulin (98), and hematoporphyrins (99) from bovine serum albumin, and the antibacterial sulfadiazine from ovalbumin (100). In general, burst phenomena are found for all systems studied. However, the results from the insulin study are worthy of note in that blood glucose levels were depressed for more than 14 days following the administration of insulin-containing BSA microspheres to diabetic rats. The smaller microspheres were absorbed by day 28 and the larger particles by day 56. 

Chen et al. (163) targeted magnetic microspheres containing 5-fluorouracil to the esophagus by application of an external magnet. 

Office supplies and office communication have been revolutionized by the introduction of the 3M product Post-it Notes in 1980. The temporary adhesive of these self-sticking notes actually was initially rejected as a glue by its inventor, 3M chemist Spencer Silver, because of its impermanence. However, 3M researcher Art Fry found a niche for the adhesive—as an adhesive for a temporary bookmark for his choir hymnal. Key to the performance of these removable, repositional adhesive products is the application of the adhesive to the backing of a note sheet via tiny microspheres rather than a continuous film. With an average particle diameter of 25-45 fim, the microsphere adhesives form a discontinuous layer that assists in retaining the ability to re-apply the note to new surfaces. Traditional adhesive tape contains particles of smaller dimension (typically 0.1 to 2.0 pm) that coalesce to form a continuous film that limits removal. ... 

An important demonstrated application of this artificial nose system is the high-speed detection of low levels of explosives and explosive-like vapors. Several sensors, based on Nile Red attached to silica microspheres, show high sensitivity to nitroaromatic compounds (NAC) within a mixture12. Different fluorescence response profiles were observed for several NAC s, such as 1,3,5-trinitrotoluene (TNT) and 1,3-dinitrobenzene (DNB), despite their similar structures. These responses were monitored at low concentrations of the NAC vapors (ca. 5 ppb) and at short vapor exposure... 

Takenaga, M., Application of lipid microspheres for the treatment of cancer, Advanced Drug Delivery Review, 1996, 20, 209-219. 

Rezac, J. P., Properties and Applications of Whispering Gallery Mode Resonances in Fused Silica Microspheres, PhD dissertation, Oklahoma State University, 2002... 

They produced high performance electrets from thin polymer films metallized so as to yield high capacitance. Both electrical and mechanical properties of these transducers have been remarkable examples of how applications of science of solids, including knowledge of electron traps, conduction processes in insulators and the viscoelastic phenomena of semicrystalline polymers, can be combined.(6) Incidentally, similar ideas have been applied to optimization of the properties of particle microphones, through assemblies of perfectly microspherical polymer carbon systems. These have shown what limits of performance... 

Liu J, Zhang Y, Yang T, Ge Y, Zhang S, Chen Z, Gu N (2009) Synthesis, characterization, and application of composite alginate microspheres with magnetic and fluorescent functionalities. J Appl Polym Sci 113 4042 1051... 

Deng Y, Wang C, Shen X, Yang W, Jin L, Gao H, Fu S (2005) Preparation, characterization, and application of multistimuli-responsive microspheres with fluorescence-labeled magnetic cores and thermoresponsive shells. Chem Eur J 11 6006-6013... 

Solid and hollow glass microspheres have been made for many years for a variety of applications. Fabrication techniques involving formation of microspheres were pioneered by Beck7 and later expanded by Howell8 and Marshall9. 

Microspheres made of various polymers biodegradable to nonharm-ful compounds that could be metabolized and/or removed from organisms found many applications in medicine as carriers of drugs or other bioactive compounds [1 ]. Besides chemical composition there are also other properties of microspheres that are of primary importance to their medical applications. In particular, average diameters and diameter distributions illustrated in Table 1 based on data published in [5] are the relationship between the diameters of microspheres and their localization in various cells and tissues of the human body. 

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