Nanospheres dispersed systems

Emulsions and suspensions are disperse systems that is, a liquid or solid phase is dispersed in an external liquid phase. While emulsions are sometimes formulated from oily drugs or nutrient oils their main function is to provide vehicles for drug delivery in which the drug is dissolved in the oil or water phase. Suspensions, on the other hand, are usually prepared from water-insoluble drugs for delivery orally or by injection, usually intramuscular injection. An increasing number of modern delivery systems are suspensions - of liposomes or of polymer or protein microspheres, nanospheres or dendrimers, hence the need to understand the formulation and stabilization of these systems. Pharmaceutical emulsions and suspensions are in the colloidal state, that is where the particles range from the nanometre size to visible (or coarse) dispersions of several micrometres. 

Structure of the system disperse systems mcrocapsules liposomes polymersomes micro- and nanospheres... 

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... 

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],... 

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... 

Silicone nanospheres with different particle diameters, crosslinking density, and chemical functionalization are accessible by aqueous hydrolysis-condensation sequences of silane and siloxane precursors [1-3] and subsequent isolation. Grafting of functionalized particles with organopolymers [1] or surface modification [2] results in nanosized silicone domains which are readily dispersible in monomeric and polymeric systems. A variety of these versatile, tailor-made products will soon be launched by Wacker on a commercial scale. 

The properties of thermosetting and thermoplastic resin systems are continually improved to meet increasing performance requirements of end users. One way to enhance material properties is to incorporate nano-modifiers, based on elastomeric silicone particles, which are optionally grafted with other (acrylic) polymers to control dispersibility, viscosity, and other parameters. As an example, epoxy resin formulations have been modified with silicone nanospheres to improve low-stress behavior. Table 1 shows the outstanding fracture toughness improvement of silicone coreshell nanospheres, even at very low particle loading levels. 

As in any other system, the phase state of the structural elements of nanoparticle dispersions may change induced by variation of physical parameters. This aspect becomes most interesting if the matrix material is affected, e.g., the bulk stmcture of a nanosphere or the wall material of a nanocapsule membrane. This case has very promising practical applications a nanocapsule or a nanoparticle may be loaded while being in one phase state and subsequently sealed by a phase transition. This possibly allows one to produce prefabricated particle dispersions where the hnal encapsulation step is accomplished by addition of the active ingredient at any given point in time. 

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. 

Most approaches are based on combinations of the drug with a polymer. The latter serves as a carrier system wherein the drug is dispersed or dissolved, or to which it is covalently linked. Cells, microspheres, nanospheres, liposomes, proteins, antibodies, hormones, natural and synthetic... 

Supramolecular spherical assemblies of NPs with photoresponsive adhesion/dispersal behaviour were also obtained in a ternary system hierarchically combining the host-guest interaction of different types of CDs toward porphyrin and azobenzene. The inclusion complexation of an azobenzene modified water soluble porphyrin (1) with phthalo-cyanine-grafted permethyl (3-CDs (2) could be reversibly cross-linked to relatively larger nanospheres with naphthyl bridged bis(a-CD)s (3). The large spheres (12 -3) turned reversibly to small-sized particles (1 2) upon photoisomerization of the azoaromatic group in 1 (Fig. 13). 

Nanoparticles may be defined as submicronic (<1 /Ltm) colloidal systems generally made of synthetic or natural polymers. According to the morphological structure, nanospheres or nanocapsules can be obtained. Nanospheres are matrix systems in which the drug is dispersed throughout the particle or adsorbed onto its surface nanocapsules are vesicular systems in which the drug is confined to a cavity surrounded by a unique polymeric shell (Couvreur et al, 1995). 

Nanodelivery systems can be defined as colloidal particles below lOOOnm size, such as nanospheres, nanocapsules, micelles, liposomes, solid lipid nanoparticles, nanocrystals, etc. The drug can be dissolved, entrapped, encapsulated, or attached to a nanoparticle matrix. Polymeric nanoparticle is a collective term given for any type of polymer nanoparticle (Soppimath et al., 2001). Generally, two main strategies are employed for their preparation the dispersion of preformed polymers and the polymerization of monomers. Depending on the process used for the preparation of nanoparticles, nanospheres (matrix-type), or nanocapsules (reservoir-type) can be obtained (Couvreur, 2013 Fattal et al., 2012 Rao and Geckeler, 2011). 

---