Research Interests

Research Interests

The research focuses on the understanding of organization and functioning of soft matter nanoscale materials with a special focus on biopolymers.

Polyelectrolyte multilayers are step-wise assembled on colloids or cells employing the electrostatic as well as other types of interaction between the multilayer constituents. As layer constituents various materials can substitute one ore more polyelectrolyte layers. Nanocomposite multilayers with tailored biological, physical and chemical properties can be engineered.

The colloidal core or biological cell can be removed resulting in hollow shells with ultrathin layers. These novel colloidal structures are investigated with respect to their physical, chemical and biological properties. A wide variety of methods is employed to study the thermodynamical, mechanical, electrical and permeability properties of the multilayer composites.

Properties, organization and application of ultrathin polyelectrolyte multilayers on colloids, cells and capsules. Design of Artificial Cells

The encapsulation of various materials with multifunctional layers is an issue with great practical significance in areas, such as drug delivery, sensing and advanced materials.

Of special interest is the fabrication of bio-nanocomposites aiming at artificial nanoscale structures with built-in biological functions. For example, lipid layers can be combined with polyelectrolyte multilayer cushions as replicas of cells.

The hollow shells can be used as nanoreaction cages and templates for precipitation and crystallization. This area of research is closely related to the understanding of biomimetic principles.

Achievements

Ultrathin polyelectrolyte multilayers were stepwise deposited onto a variety of colloidal particles, including biological cells and a number of soluble colloids. The driving force of multilayer assembling is the electrostatic attraction and entropy increase at each step of macroion adsorption.

Microelectrophoresis, single particle light scattering and fluorescence spectroscopy have been applied for controlling the regularity of the multilayer assembly process. Light scattering and fluorescence intensity increased linearily with the number of adsorbed layers. Layer thickness increments of as small as 1 nm can be assessed with single particle light scattering performed on a custom-made device. Fluorescence energy transfer measurements between labelled layer constituents provided an insight into the nanoscale topology of multilayers. Small angle neutron scattering has been applied to directly measure the layer thickness on colloidal particles.

Weakly cross-linked melamine formaldehyde (MF) particles, various organic dye crystals, silica and biological cells are used as templates for the production of hollow polyelectrolyte shells. These novel structures are obtained after removal of the templating core. Hollow polyelectrolyte capsules with diameters ranging from 0.1 to 10 microns and wall thicknesses from few to tens of nanometers, respectively, were obtained. Scanning and transmission electron microscopy, as well as confocal microscopy were employed to characterize the morphology of coated colloids and capsules. Electrorotation was employed to measure the conductance and capacitance of capsules. Scanning force microscopy (SFM) was used to investigate the texture and thickness of the capsule walls. Single capsules were mounted on a SFM cantilever, which was subsequently used for characterizing interaction forces. It was shown that the layer structure can be influenced by annealing at elevated temperatures. Osmotic pressure differences were created between the capsule interior and the bulk. The resulting capsule wall deformation was used to measure the mechanical properties of the ultrathin film. Confocal laser scanning microscopy (CLSM) is a key technique to visualize the capsule morphology as well as the distribution compounds between the interior and the bulk. With CLSM as well as with spectroscopy techniques the permeability properties of the layers were studied. It was shown that the permeability can be tuned by the pH value, by the electrolyte concentration and annealing. This is an important means for controlling encapsulation.

To date a large variety of materials ranging from inorganics and nanoparticles to synthetic and biopolymers have been introduced into the hollow capsules by means of permeability control, controlled precipitation, capsule wall decomposition, and synthesis. Synthesis of polymers was performed by making use of the exclusion properties of the shell wall. Monomers can pass the wall while the synthesized polymer remains confined. Layers with interesting optical properties were obtained when dyes were used as layer materials. By controlling the topology of nucleation it became possible to selectively fill the capsules with solid low molecular weight materials. The intercalation of lipid bilayers into the polyelectrolyte multilayer system was a major step forward to an "artificial cell". These novel colloidal structures may have wide-ranging applications as containers for a large class of materials, as templates for nanocomposites, or as cages for chemical reactions. The polymer capsule wall composition can be tailored to meet various multipurpose requirements.

Tired of so many lines?

Try this! Capsules for Drug Delivery
A presentation by Prof. Dr. Edwin Donath
... or this ... Von supramolekularen Strukturen zu Wirkstoffträgern und künstlichen Zellen
Another presentation by Prof. Dr. Edwin Donath - in deutsch :-)
... or this! Posters
Compilation of recent conference posters
letzte Änderung: 14.06.2017