Assembly of polymeric micelles into hollow microcapsules with extraordinary stability against extreme pH conditions

Hollow microcapsules containing polymeric micelles in their walls were fabricated by alternating assembly of poly(allylamine hydrochloride) (PAH) and poly(styrene- b-acrylic acid) (PS- b-PAA) micelles on MnCO(3) microparticles followed by sacrificing the templates in acid solution. The successful formation of PAH/micelle multilayers on both planar and curved substrates was confirmed by UV-vis spectroscopy, ellipsometry, and xi-potential measurements. The PS- b-PAA micelles retained their structure during the whole assembly process. The as-prepared microcapsules showed extraordinary stability against concentrated HCl (37%) and 0.1 M NaOH solutions. No variation in capsule size or shape was observed in acidic solution, while slight swelling and distortion of the capsules took place in alkaline solution. However, these capsules completely recovered their original size and morphology after being incubated in acidic solution again. The microcapsules, in which large voids exist between the micelle grains on the walls, were totally permeable to fluorescein-tagged dextran with an M(w) of 2000 kDa. Assembly of additional PAH/poly(sodium 4-styrenesulfonate) multilayers could substantially reduce the permeation of the same molecules. These multicompartmental capsules combine polymeric micelles with multilayer polyelectrolyte microcapsules and could possibly be imparted with multifunctions, thus possibly finding diverse applications in the fields of drug delivery, biosensing, and nanobiotechnology.     

Poly(ethyleneimine) microcapsules: glutaraldehyde‐mediated assembly and the influence of molecular weight on their properties

Poly(ethyleneimine) (PEI) microcapsules were prepared via the method of glutaraldehyde (GA)‐mediated covalent layer‐by‐layer (LbL) assembly, which utilized GA to cross‐link the adsorbed PEI layer and to introduce free aldehyde group on the surface for the next PEI adsorption on MnCO₃ microparticles, followed by core removal. Evidenced by ellipsometry, the PEI multilayers grew nearly linearly along with the layer number and their thickness was controlled at the nanometer scale. The hollow structure, morphology, and wall thickness were characterized by scanning electron microscopy (SEM), scanning force microscopy (SFM), and confocal laser scanning microscopy (CLSM), revealing that the capsule structure as well as the cut‐off molecular weight of the capsule wall could be tuned by the molecular weight of PEI. This offers a general and novel pathway to fabricate single component capsules with pre‐designed structure (size, shape, and wall thickness) and properties. Copyright © 2007 John Wiley & Sons, Ltd.     

Sonochemical Synthesis of Magnetic Protein Container for Targeted Delivery

A new targeted delivery system was developed in this paper by depositing magnetic NPs on protein containers which were prepared by sonicating oil in a protein solution. The deposition was conducted by layer‐by‐layer technique and monitored by zeta potential measurement. Such prepared samples can be targeted delivery in an external magnetic field. The hydrophobic dye TPP, as a model of drug, was loaded in the containers by dissolution in the oil phase before sonication. The containers loaded with dye are stable and can sustain the deposition treatment without loss of dye due to the protection of protein nanoshells.

     

Stabilization of Silver Nanoparticles by Polyelectrolytes and Poly(ethylene glycol)

Silver nanoparticles of 23 nm size were formed by chemical reduction of silver nitrate in excess of aqueous sodium borohydride. To examine the aggregation behavior in NaCl solutions, they were coated with poly(diallyldimethylammonium chloride), poly(allylamine hydrochloride) and poly(ethylene glycol) by layer‐by‐layer assembly. Silver nanoparticles coated with PDADMAC of both high and low molecular weight revealed the lowest stability independent of salt concentration. Silver nanoparticles coated with PAH and PEG are stable in 0.1 or 0.01 M NaCl, whereas addition of 0.5 M NaCl destroys the colloidal solution. The destruction of silver agglomerates and the increase of monodispersity in the case of PEG coated silver nanoparticles were observed after heating at 90 °C. In contrast, uncoated silver nanoparticles readily agglomerate and precipitate even after heating at 65 °C.

     

Novel Hollow Polymer Shells by Colloid-Templated Assembly of Polyelectrolytes

Exact control of the film thickness of polyelectrolyte shells (a transmission electron microscopy image is shown) is achieved by colloid-templated consecutive adsorption of polyanions and polycations followed by decomposition of the templating core. Possible areas of application for these shells range from the pharmaceutical, food, cosmetic, and paint industries to catalysis and microcrystallization.     

Sonochemical Synthesis of Highly Luminescent Zinc Oxide Nanoparticles Doped with Magnesium(II)

Mut zur Lücke : Mg/ZnO‐Nanopartikel mit heller, stabiler Photolumineszenz in kolloidalen Dispersionen wie im Festkörper bilden sich durch Dotierung von Mg²⁺‐Ionen in ZnO‐Nanopartikel durch sonochemische Synthese. Ihre Bandlücken und Lumineszenzeigenschaften verändern sich mit der Defektkonzentration in den ZnO‐Nanopartikeln. Diese Konzentration hängt vom molaren Mg/Zn‐Verhältnis ab (siehe Bild).