Nanosphere porous

Scaffold-mediated gene delivery. Plasmid DNA condensed with cationic polymers can be encapsulated into various types of 3D polymeric scaffold systems (micro/nanospheres, porous sponges, or hydrogels) for sustained gene delivery. Source Reprinted and adapted from Reyes etal., 2013, copyright 2013, with permission from Elsevier B.V.)... 

As an example of composite core/shell submicron particles, we made colloidal spheres with a polystyrene core and a silica shell. The polar vapors preferentially affect the silica shell of the composite nanospheres by sorbing into the mesoscale pores of the shell surface. This vapor sorption follows two mechanisms physical adsorption and capillary condensation of condensable vapors17. Similar vapor adsorption mechanisms have been observed in porous silicon20 and colloidal crystal films fabricated from silica submicron particles32, however, with lack of selectivity in vapor response. The nonpolar vapors preferentially affect the properties of the polystyrene core. Sorption of vapors of good solvents for a glassy polymer leads to the increase in polymer free volume and polymer plasticization32. 

Zhou J, Li Z, Liu G. Diblock copolymer nanospheres with porous cores. Mactomolecules 2002 35 3690-3696. 

To what extent can the example of a solid exoskeleton be replicated in the laboratory Going against most contemporary examples of flexible artificial cells, Muller and Rehder published an example of a complex molybdenum oxide that spontaneously forms discrete nanospheres [23], The hollow spheres were porous and allowed lithium cations to pass through the exoskeleton. While this a perhaps an extreme example of what may be considered an artificial cell, the authors assert that the presence of ion selective channels through the encapsulating oxide is directly analogous to natural ion channels in organic cells. 

Fig. 15.13. Schematic depiction of generation of porous nanospheres with increased host uptake capacity.

The practical applicability of such a system is quite clear nanospheres or nanoparticles may be produced by the emulsion-diffusion method and stored in the gel state of the particle framework. At any later point of time, an active ingredient may be added to the dispersion which easily diffuses into or through the porous gel matrix. By a simple freezing step, the particles are sealed and the active ingredient is trapped inside the spheres or capsules. The whole process is easily monitored by solid-state NMR which, in this case, could hardly be replaced by any other analytical approach. 

RESS is useful for materials that are soluble in CO2. Unfortunately, CO2, with no dipole moment and very low polarizability, is a very weak solvent and dissolves very few polymers. Cosolvents such as methanol or acetone can be mixed with SCFs to increase the solvating power of SCFs during RESS. In drug delivery applications, RESS has been used to prepare polymeric films, microparticles, nanospheres, liposomes, and porous foams (Figure 1). A... 

Nanospheres 100 Blends. [Exsymol] Porous polymeric particles blended with various ingredients provides con-... 

As to their structure, micro- and nanospheres can be of two types i) micelles formed from copolymers and ii) porous spheres in micrometer size or in the colloid size range. 

Morphology control is indispensable in many of the advanced applications envisioned for functional mesoporous materials (54, 267). Permselective membranes, micro-spheres, or monoliths are important for sorption, separation, and chromatography purposes. Porous thin films or fibrous structures are relevant for electronics, optics, low fe-dielectrics, and sensing applications. Colloidal particles or nanospheres are preferred for biomedical systems to be used in drug delivery or magnetic resonance imaging (MRl) with contrast agents. 

The potential of zeolites and porous solids as high capacity carriers for drug molecules has also been recognised. Whereas zeolites may have applications for the controlled release of small molecules of medicinal importance, such as nitric oxide, mesoporous silica nanospheres that are sub-micron in particle size, with pore sizes of 2 10 nm, may be used for the targeted in situ delivery of larger drug molecules. 

Water-soluble therapeutic proteins and peptides can be delivered using porous nanospheres or nanocapsules formed by a double emulsion solvent evaporation procedure. A concern with the delivery of proteins by nanoparticles is the loss of protein activity before its release. Desai et al. showed about 30% of tetanus toxoid activity was lost due after encapsulation and release from nanoparticles (Desai et al. 1996). Protein may be inactivated due to denaturation based on exposure to organic solvents and adsorption onto the oil-water interface during fabrication (van de Weert et al. 2000 Lu et al. 2000). A strategy for reducing adsorption of the therapeutic protein is the incorporation of human or bovine semm albumin in the aqueous phase, which restricts the access of the therapeutic protein to the phase interface (Kim and Park 1999). Another proposed cause of protein inactivation is decreased local pH experienced by the encapsulated protein due to acidic degradation byproducts. This can be addressed by including an alkaline buffer into the aqueous phase (Zhu et al. 2000). 

Figure 2.11 SEM image of carbon nanospheres (left-above] and after (left-below] calcination of nanofibers prepared with carbon nanospheres, and XRD patterns of TiOj nanofibers (right] (a] and porous TiOj nanofibers (b]. Reprinted from Ref. 62, Copyright 2012 Shanhu Liu et al.

Zeng Q, Wu D, Zou C, Xu F, Fu R, Li Z, Liang Y, Su D (2010) Template-free fabrication of hierarchical porous carbon based on intra-Zinter-sphere crosslinking of monodisperse sty-rene-divinylbenzene copolymer nanospheres. Chem Commun 46 5927-5929... 

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