Dispersed nanospheres

Olesik [5] prepared high-yield low-dispersity nanospheres using self-polymerizing end-capped l,8-dihydroxymethyl-l,3,5,7-octatetrayne by heating to 70°C for 24 hours using 0.04 wt% phenyltrimethyl amine chloride as the surfactant. 

The unique capability of NMR spectroscopy to differentiate by means of molecular mobility makes it a perfect tool to assign chemical constituents to structural elements of a particle dispersion. This is most straightforward in the case of dispersed nanospheres every constituent which is part of the solid matrix will exhibit the slow particle tumbling, while all components of the liquid continuous phase undergo rapid rotational diffusion. 

Micro- or nanosized polymer particles are generally called microspheres (MSs) or nanospheres (NSs), respectively, and have been used for DDS. The term nanoparticle is more general and includes polymer micelles and nanogels, which are described in Sects. 4-6. Although polymer micelles and nanogels have sufficient surface hydrated layers for dispersion or solubilizaton in aqueous media, MSs and NSs are basically spherical particles of hydrophobic polymers without enough hydrated layers. 

Both nanospheres and nanocapsules are prepared from either a polymerization reaction of dispersed monomers or from a solvent dispersion procedure using preformed polymers. In many instances, the latter procedure using preformed polymer is desirable, as potential reactions between drug and monomer are avoided and the potential toxicity of residual monomers, surfactant, and initiator is reduced [37], The final properties of nanoparticles, such as their size, morphology, drug loading, release characteristics, and biodisti-bution, are all influenced by the method of preparation [38],... 

Kreuter and Speiser [77] developed a dispersion polymerization producing adjuvant nanospheres of polymethylmethacrylate) (PMMA). The monomer is dissolved in phosphate buffered saline and initiated by gamma radiation in the presence and absence of influenza virions. These systems showed enhanced adjuvant effect over aluminum hydroxide and prolonged antibody response. PMMA particles could be distinguished by TEM studies and the particle size was reported elsewhere to be 130 nm by photon correlation spectroscopy [75], The particle size could be reduced, producing monodisperse particles by inclusion of protective colloids, such as proteins or casein [40], Poly(methylmethacrylate) nanoparticles are also prepared... 

Figure 6.4 The preparation of nanostructured materials in solution evolves from (a) the classic examples of suspension, dispersion, or emulsion polymerization, to the methods that include the covalent crosslinking of select domains within supramolecular polymer assemblies (b) core crosslinking of polymer micelles (c) shell crosslinking of polymer micelles (SCKs) (d) nanocages from core-eroded SCKs (e) shaved hollow nanospheres from outer shell/core-eroded vesicles.

Polymer/lipid and polymer/protein ratios, spanning a rather wide range, were adopted to highlight their influence on nanosphere sizes and physical stability of the dispersions. 

The slow solvent evaporation technique afforded milky nanosphere dispersions. No effect of the polymer/protein/lipid weight ratios on the dispersion stability was detected, at least in the investigated range. 

Figure 6 SEM micrograph (10,000X) of a centrifuged nanosphere dispersion containing 5%... 

ASpr = 520 to 540 nm), with colloidal dispersions producing a characteristic wine-red color. If the Au nanoparticles are smaller than 5 nm, the LSPR peak is broadened due to surface scattering.14 If the nanospheres are much greater than 40 nm (the approximate mean free path of an electron in Au), the LSPR shifts to longer wavelengths due to retardation effects, and secondary peaks may appear due to multipolar plasmon modes. 

Their hydrophobic/hydrophilic content seems to be just right for applications in cancer and gene therapies. Such nanospheres are prepared by dispersing the methylene chloride solution of the copolymer in water and allowing the solvent to evaporate [38]. By attaching biotin to the free hydroxy groups and complexa-tion with avidin, cell-specific delivery may be attained.NMR studies of such systems [39] revealed that the flexibility and mobility of the thus attached PEG chains is similar to that of the unattached PEG molecules dissolved in water. Re-... 

Nanoparticles Nanoparticles have been among the most widely studied particulate delivery systems over the past three decades. They are defined as submicrometer-sized polymeric colloidal particles ranging from 10 to 1000 nm in which the drug can be dissolved, entrapped, encapsulated, or adsorbed [206]. Depending on the preparation process, nanospheres or nanocapsules can be obtained. Nanospheres have a matrixlike structure where the drug can either be firmly adsorbed at the surface of the particle or be dispersed/dissolved in the matrix. Nanocapsules, on the other hand, consist of a polymer shell and a core, where the drug can either be dissolved in the inner core or be adsorbed onto the surface [207],... 

Drug-loaded nanoparticles were also evaluated for their safety and efficacy. Paclitaxel-encapsulated 6-O-CAPRO-p-CD nanospheres and nanocapsules were evaluated for their physical stability in a one-month period in aqueous dispersion form with repeated particle size and zeta potential measurements and AFM imaging to evaluate recrystallization in aqueous medium. Paclitaxel-loaded amphiphilic CD nanoparticles were found to be physically stable for a period of one month whereas recrystallization occurs within minutes when diluted for intravenous (IV) infusion [85], Finally, paclitaxel-loaded amphiphilic nanoparticles were demonstrated to show similar anticancer efficacy against MCF-7 cells when compared to paclitaxel solution in a cremophor vehicle [85],... 

Polymer nanoparticles including nanospheres and nanocapsules (Fig. 1) can be prepared according to numerous methods that have been developed over the last 30 years. The development of these methods occurred in several steps. Historically, the first nanoparticles proposed as carriers for therapeutic applications were made of gelatin and cross-linked albumin. Then, to avoid the use of proteins that may stimulate the immune system and to limit the toxicity of the cross-linking agents, nanoparticles made from synthetic polymers were developed. At first, the nanoparticles were made by emulsion polymerization of acrylamide and by dispersion polymerization of methylmethacry-late.f These nanoparticles were proposed as adjuvants for vaccines. However, since they were made of non-biodegradable polymers, these nanoparticles were rapidly substituted by particles made of biodegradable... 

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