Encapsulation, magnetite nanoparticles

The crosslinking of starch at the droplet interface in inverse miniemulsion leads to the formation of hydrogels. The formulation process for the preparation of crosslinked starch capsules in inverse miniemulsion is schematically shown in Fig. 10. The influence of different parameters such as the amount of starch, surfactant P(E/B-fe-EO), and crosslinker (2,4-toluene diisocyanate, TDI) on the capsule size and stability of the system were studied. The obtained capsules were in a size range of 320-920 nm. Higher amounts of starch and surfactant result in a smaller capsule size. The TEM images of crosslinked starch capsules prepared with different amount of crosslinker (TDI) are presented in Fig. 11. The nanocapsules can be employed as nanocontainers for the encapsulation of dsDNA molecules with different lengths [114] and for the encapsulation of magnetite nanoparticles. 

Ramtrez LP, Landfester K (2003) Magnetic polystyrene nanoparticles with a high magnetite content obtained by miniemulsion processes. Macromol Chem Phys 204 22-31 Landfester K, Ramirez LP (2003) Encapsulated magnetite particles for biomedical application. J Phys Condens Matter 15 S1345-S1361... 

A further proof for the complete encapsulation and protection of magnetite nanoparticles by a polymeric shell was delivered by Zheng et al. [181], who treated magnetite/PS particles with 1M HCl solution and found no evidence for dissolved iron in the solution. 

Ramfrez et al. encapsulated double-layer (oleic acid and SDS) surfactant-coated magnetite into polystyrene particles by miniemulsion polymerization [171]. In the three-step process, oleic-acid-coated magnetite and oleic acid/SDS double-coated magnetite were prepared in the first and second step, respectively. The third step consists of the preparation of a miniemulsion by stirring 1 h for pre-emulsification, followed by ultrasonication for 2 min using St as monomer with hexadecane and SDS in water. The encapsulation of magnetite was accomplished by cosonication of an St miniemulsion and SDS-stabilized magnetite nanoparticles. The polymerization was initiated by KPS at 80°C. 

Zhang J. L., Srivastava R. S, and. Misra R D. K (2007). Core-Shell Magnetite Nanoparticles Surface Encapsulated with Smart Stimuli-Responsive Polymer Synthesis, Characterization, and LCST of Viable Drug-Targeting Delivery System, Langmuir, Volume 23, Issue 11, pp 6342-6351. 

A) Elaboration of PLLA-based superparamagnetic nanoparticles Characterization, magnetic behavior study and in vitro relaxivity evaluation Abstract. Oleic acid-coated magnetite has been encapsulated in biocompatible magnetic nanoparticles (MNP) by a simple emulsion evaporation method. 

The encapsulation of magnetite particles into polystyrene particles was efficiently achieved by a miniemulsion process using oleoyl sarcosine acid [ 109] or the more efficient oleic acid as first surfactant system to handle the interface magnetite/styrene, and SDS to stabilize the interface styrene/water, thus creating a polymer-coated ferrofluid (Fig. 15b). Since the magnetite particles were very small (ca. 10 nm), each polymer particle was able to incorporate many inorganic nanoparticles. A content of 20 wt% could be incorporated in this way. 

PMAA- or citrate-coated magnetite [160] or citrate-coated maghemite [162] nanoparticles could successftiUy be encapsulated in a crosslinked polyacrylamide matrix using an inverse miniemulsion process. Here an inert hydrocarbon (cyclohexane or dodecane) was used as continuous phase and SpanSO as stabilizer. 

Other inorganic nanoparticles have been encapsulated with miniemulsion polymerization, and a hydrophobilizing agent was used to render the particles hydrophobic prior to minianulsification. For example, calcium carbonate was pretreated with stearic acid prior to being dispersed into the monomer phase. Alumina and magnetite were pretreated with oleic acid, laponite was pretreated with a cetyltrimethylammonium bromide, and silica was pretreated with cetyltrimethyl-ammonium chloride" or methacryloxy(propyl)trimethoxysilane. ... 

Xu et al. used the same process to encapsulate PMAA-coated magnetite in silica [157]. By adding TEDS to a miniemulsion of magnetite-PMAA/water dispersed in SpanSO/cyclohexane, siUca/magnetite hybrid nanoparticles could be generated. About 19 wt% of magnetite could be incorporated in the silica matrix. 

Magnetite coated with sodium l,2-bis(2-ethylhexoxycarbonyl)ethanesulfonate (AOT) was directly dispersed in styrene, but led to an inhomogeneous distribution of magnetite in the hybrid system [161, 162]. Pure PS nanoparticles, as well as polymeric particles partially covered with magnetite, could be distinguished by TEM analysis. Although this can be regarded as a hybrid system, the actual encapsulation in polymer seems to be uncertain from the presented results. 

---