Microspheres polymer

When active substances are encapsulated in drug delivery systems, their bioavailability and therapeutic index can be improved over an extended period of time. A drug delivery system including polymer microspheres has been developed for injection, implants, transdermal patches, and aerosols (34). 

Polymeric microspheres have a variety of uses in medical and industrial areas since they provide a large surface area, can be easily injected, and do not require removal after completion of drug release. Common methods for the fabrication of microspheres include (34)  

Unfortunately, most methods generate microspheres having a wide size distribution with little or no control over the average diameter (34). However, the control of the sphere size and the size distribution are the ultimate goals of drug delivery. A particular release rate and a desired route of administration typically require a particular sphere size. 

Filters can be used, but the use of filter results in a waste of expensive drug materials. Therefore, several methods that allow better control over particle size and size distribution have been proposed. Each of these methods has drawbacks that prevent the use of microspheres in various applications. 

monomer polymerization techniques are not appropriate for drug encapsulation due to harsh chemical and physical environments that can denaturate drugs. Further, an electrostatically 

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Various novel applications in biotechnology, biomedical engineering, information industry, and microelectronics involve the use of polymeric microspheres with controlled size and surface properties [1-31. Traditionally, the polymer microspheres larger than 100 /urn with a certain size distribution have been produced by the suspension polymerization process, where the monomer droplets are broken into micron-size in the existence of a stabilizer and are subsequently polymerized within a continuous medium by using an oil-soluble initiator. Suspension polymerization is usually preferred for the production of polymeric particles in the size range of 50-1000 /Ltm. But, there is a wide size distribution in the product due to the inherent size distribution of the mechanical homogenization and due to the coalescence problem. The size distribution is measured with the standard deviation or the coefficient of variation (CV) and the suspension polymerization provides polymeric microspheres with CVs varying from 15-30%. 

Self-Organization of Core-Shell Type Polymer Microspheres and Applications to Polymer Alloys... 

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]. 

These core-shell type microspheres have very interesting structural features in that the cores are hardly crosslinked and the shell chains are fixed on the core surface with one end of the shell chains. The other end of the shell chains is free in good solvents for the shell chains. As the result of such a specific structure, the solubilities of the core-shell type polymer microspheres are governed by, not the core, but by the shell sequences, and the core-shell structures do not break even in the dilute solution [9,10]. 

The feature of the core-shell type polymer microspheres that differentiates them the most from the (AB)n type star block copolymers is size. The external diameters of the core-shell type polymer microspheres are generally from about 20-200 nm in the good solvents instead... 

The core-shell type polymer microspheres were synthesized upon the chemical crosslinking of the spherical microdomains in the microphase separated films. The block copolymers were dissolved in 1,1,2-trichloroeth-... 

In three dimensions, Ohta and Kurokawa [32] reported that a BCC arrangement was only slightly more favored than the FCC arrangement. In fact, many BCC structures have been reported for AB type block copolymers and the blends of homopolymer-block copolymer systems [27,33-35]. However, the lattice structure of the core-shell type polymer microspheres was FCC. This FCC formation resulted in the lower viscosity of... 

Position-Selective Arrangement of Nanosize Polymer Microspheres 205... 

Position-Selective Arrangement of Nanosize Polymer Microspheres Onto a PS-b-P4VP Diblock Copolymer Film with Nanoscale Sea-island Microphase Structure... 

Figure 12.1 AFM images of a PS-b-P4VP (301 000 19600) film (a) before and (b) after immersion in methanol for 75 min and the height profiles. S. Machida, H. Nakata, K. Yamada, A. Itaya Position-selective arrangement of nanosized polymer microsphere on diblock copolymer film with sea-island microphase structure.Jpn. /. Appl. Phys. 2006, 45, 4270—4273. Copyright Wiley InterScience. Reproduced with permission.

Edlund, U. and Albertsson, A.-C. Degradable Polymer Microspheres for Controlled Drug Delivery. Vol. 157, pp. 53-98. 

The silica microspheres provide some diversity but not enough for many complex discrimination tasks. To introduce more sensor variety, hollow polymeric microspheres have been fabricated8. The preparation of these hollow microspheres involves coating silica microspheres by living radical polymerization, using the surface as the initiation site. Once the polymer layer forms on the silica microbead surface, the silica core is removed by chemical etching. These hollow spheres can be derivatized with the dye of interest. The main advantage of these polymer microspheres is the variety of monomers that can be employed in their fabrication to produce sensors with many different surface functionalities and polymer compositions. 

To provide for prolonged, site-specific delivery of NGF to the tissue in a convenient manner without affecting the properties of the conduit, biodegradable polymer microspheres of poly(L-lactide)co-glycolide... 

Polymer liquid crystals, 75 107-111 Polymer matrices, 26 761-765 Polymer-matrix composites, 73 502 26 751, 755-756 fabrication of, 26 765 Polymer melts, 75 108-109 27 730-731 chain fluctuations in, 27 714 viscosity of, 20 99 21 712-714 Polymer metal composites, smart, 22 718 Polymer microspheres, 9 73-75 Polymer microstructure, polychloroprene, 79 836-838... 

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