H. Möhwald

Metallosupramolecular thin polyelectrolyte films.

Molecular recognition and electrostatic interaction of oppositely charged polyelectrolytes are combined in the fabrication of ultrathin metallosupramolecular multilayers [shown schematically in the picture, PEI=polyethyleneimine, PSS=poly(styrene sulfonate)]. The layers between the PSS layers are composed of an iron(II) bis(terpyridine) coordination polymer.

New Method for Fabrication of Loaded Micro-and Nanocontainers: Emulsion Encapsulation by Polyelectrolyte Layer-by-Layer Deposition on the Liquid Core

A novel approach to the emulsion encapsulation was developed by combining the advantages of direct encapsulation of a liquid colloidal core with the accuracy and multifunctionality of layer-by-layer polyelectrolyte deposition. Experimental data obtained for the model oil-in-water emulsion confirm unambiguously the alternating PE assembly in the capsule shell as well as the maintenance of the liquid colloidal core. Two different mechanisms of capsule destruction upon interaction with the solid substrate were observed and qualitatively explained. The proposed method can be easily generalized to the preparation of oil-filled capsules in various oil/water/polyelectrolyte systems important in the field of pharmacy, medicine, and food industry.

Biological cells as templates for hollow microcapsules.

Microcapsules in the micrometer size range with walls of nanometer thickness are of both scientific and technological interest, since they can be employed as micro- and nano-containers. Liposomes represent one example, yet their general use is hampered due to limited stability and a low permeability for polar molecules. Microcapsules formed from polyelectrolytes offer some improvement, since they are permeable to small polar molecules and resistant to chemical and physical influences. Both types of closed films are, however, limited by their spherical shape which precludes producing capsules with anisotropic properties. Biological cells possess a wide variety of shapes and sizes, and, thus, using them as templates would allow the production of capsules with a wide range of morphologies. In the present study, human red blood cells (RBC) as well as Escherichia coli bacteria were used; these cells were fixed by glutardialdehyde prior to layer-by-layer (LbL) adsorption of polyelectrolytes. The growth of the layers was verified by electrophoresis and flow cytometry, with morphology investigated by atomic force and electron microscopy; the dissolution process of the biological template was followed by confocal laser scanning microscopy. The resulting microcapsules are exact copies of the biological template, exhibit elastic properties, and have permeabilities which can be controlled by experimental parameters; this method for microcapsule fabrication, thus, offers an important new approach for this area of biotechnology.Microcapsules in the micrometer size range with walls of nanometer thickness are of both scientific and technological interest, since they can be employed as micro- and nano-containers. Liposomes represent one example, yet their general use is hampered due to limited stability and a low permeability for polar molecules. Microcapsules formed from polyelectrolytes offer some improvement, since they are permeable to small polar molecules and resistant to chemical and physical influences. Both types of closed films are, however, limited by their spherical shape which precludes producing capsules with anisotropic properties. Biological cells possess a wide variety of shapes and sizes, and, thus, using them as templates would allow the production of capsules with a wide range of morphologies. In the present study, human red blood cells (RBC) as well as Escherichia coli bacteria were used; these cells were fixed by glutardialdehyde prior to layer-by-layer (LbL) adsorption of polyelectrolytes. The growth of the layers was verified by electrophoresis and flow cytometry, with morphology investigated by atomic force and electron microscopy; the dissolution process of the biological template was followed by confocal laser scanning microscopy. The resulting microcapsules are exact copies of the biological template, exhibit elastic properties, and have permeabilities which can be controlled by experimental parameters; this method for microcapsule fabrication, thus, offers an important new approach for this area of biotechnology.

Assembly of polyelectrolyte multilayer films by consecutively alternating adsorption of polynucleotides and polycations

Abstract Multilayers films of nucleic acids (DNA, polyuridylic and polyadenylic acids) and polycations (polyallylamine, polyethylenimine, polylysine and polyarginine) were fabricated by consecutive adsorption of anionic and cationic polyelectrolytes. The film growth process was controlled by X-ray reflectivity and UV spectroscopy. The penetration of DNA-specific dye was examined for DNA-polyallylamine self-assembled films.

Microencapsulation by means of step-wise adsorption of polyelectrolytes.

Step-wise adsorption of polyelectrolytes is used for the fabrication of microand nanocapsules with determined size, capsule wall composition and thickness. The capsule walls made of polyelectrolyte multilayers exclude high molecular weight compounds. Assembling of lipid layers onto these polyelectrolyte capsules prevents the permeation of small dyes. Encapsulation of magnetite nanoparticles is demonstrated and the features of these novel capsules are discussed.Step-wise adsorption of polyelectrolytes is used for the fabrication of micro- and nanocapsules with determined size, capsule wall composition and thickness. The capsule walls made of polyelectrolyte multilayers exclude high molecular weight compounds. Assembling of lipid layers onto these polyelectrolyte capsules prevents the permeation of small dyes. Encapsulation of magnetite nanoparticles is demonstrated and the features of these novel capsules are discussed.

Layer-by-layer arrangement by protein-protein interaction of sulfite oxidase and cytochrome c catalyzing oxidation of sulfite

Layer-by-layer self-assembly of sulfite oxidase and cytochrome c was carried out without additional polymeric polyelectrolytes. The arrangement shows a linear increase in the immobilized protein mass after each deposition cycle. The modified electrodes demonstrate electrocatalytic activity for sulfite oxidation generating catalytic current with a linear increase with the number of layers. This effect shows that, in the protein assembly without a polyelectrolyte, electron transfer occurs, thus supporting the concept for direct interprotein electron exchange.

Competitive Adsorption from Mixed Hen Egg-White Lysozyme/Surfactant Solutions at the Air-Water Interface Studied by Tensiometry, Ellipsometry, and Surface Dilational Rheology

The competitive adsorption at the air-water interface from mixed adsorption layers of hen egg-white lysozyme with a non-ionic surfactant (C10DMPO) was studied and compared to the mixture with an ionic surfactant (SDS) using bubble and drop shape analysis tensiometry, ellipsometry, and surface dilational rheology. The set of equilibrium and kinetic data of the mixed solutions is described by a thermodynamic model developed recently. The theoretical description of the mixed system is based on the model parameters for the individual components.

Polyelectrolyte multilayer capsules templated on biological cells: core oxidation influences layer chemistry.

Abstract Polyelectrolyte multilayer capsules have been fabricated in aqueous media by step-wise assembling of sodium polystyrene sulfonate (PSS) and polyallylamine hydrochloride (PAH) on human red blood cells and melamine formaldehyde resin particles as templates, followed by removal of these templates by two different procedures. The melamine formaldehyde core can be dissolved in pH 1.1. The removal of the cell cores was achieved by an oxidation with sodium hypochlorite solution (pH 12). The effect of these treatments on the chemical composition of the capsules and of a randomly formed polyelectrolyte complex was studied. The melamin resin templated capsules have basically the same composition as the untreated complex revealing no chemical changes induced by the acid. But about 20% of the total hollow capsules mass can be attributed to a rest of melamin resin. The treatment with NaOCl solution changed the chemical composition of the capsules drastically. The amino groups of polyallylamine were oxidized to nitriles, nitroso-, nitro-, azo- and carbonyl groups. Positive charges disappeared. Covalent bonds were formed which crosslink the polymer chains. Simultaneously, the amount of PSS is strongly reduced to 10% of the original value. The stability of the capsules can be understood as a result of crosslinking and hydrophobic interactions. The cell templated capsules are monodisperse, being replicas in size and shape of the template but their chemical composition is different compared with the initial polyelectrolyte multilayer film. The altered chemical properties are responsible for new physical and mechanical properties such as higher elasticity, high chemical stability, as well as selective adsorption and permeation for charged ions.

Specific adsorption of PLA2 at monolayers

Specific phospholipase A2 (PLA2) adsorption studies were performed on monolayers of d-dipalmitoyl-phosphatidylcholine (d-DPPC) and of an ether-ester d-1-O-hexadecyl-2-stearoyl-phosphatidylcholine (d-HSPC). In order to separate interfacial recognition from subsequent lipid cleavage, PLA2-resistant d-enantiomers were utilized for the investigations. Snake venom (N. naja naja and Crotalos atrox) PLA2, which hydrolyzes the sn-2 ester bond of l-phospholipids, was used. Fluorescence microscopy, film-balance pressure–area isotherms, and grazing incidence X-ray diffraction (GIXD) experiments were carried out. Fluorescence microscopy studies show that the enzyme accumulates preferentially at the liquid-expanded/condensed interface. At low surface pressure enzyme penetration into the monolayer is observed, whereas at high pressures the area per molecule is reduced upon specific adsorption. Monolayer structure, as determined by GIXD, is greatly affected by adsorption of PLA2. The tilt angle of the aliphatic chains of the monolayer becomes drastically reduced due to an enzyme-induced increase of the lipid packing efficiency. The unspecific adsorption of serum albumin to a d-DPPC monolayer does not change the monolayer structure. The structural changes, caused by PLA2 adsorption on d-enantiomer monolayers, are related to the chemical structure of the lipid molecules. Therefore, a relation between structure change and hydrolysis efficiency of PLA2 on the respective l-enantiomer monolayers can be assumed.

Resealing of polyelectrolyte capsules after core removal

Communication: Poly(styrene sulfonate) and poly(allylamine hychloriocide) layers have been adsorbed supplementarily on polyelectrolyte capsules. The permeability of the original capsules consisting of four layer pairs was of the order of 10 -5 m/s for fluorescein. They were also permeable for macromolecules. Polyelectrolyte layers adsorbed afterwards reduced the permeability by three orders of magnitude for small molecules. These findings are interreted at a resealing of pores, induced by the osmotic stress during fabrication.