Understanding the electrostatic interactions of polymers in aqueous environments is one of the keys for the development of advanced biofunctional materials. To provide answers to fundamental questions on the mechanisms of the charge formation at bio-interfaces as well as to clarify interrelations between charge and structure of polymer materials we develop and apply complementary analytical techniques in combination with tailored models for interfacial charge formation and simulations.
Furthermore, strategies for unravelling the mechanisms of molecular transport in soft materials as well as new diagnostic principles are established.
Advanced electrokinetic methods
Electrokinetic and surface conductivity measurements provide valuable information about the charging and structure of polymers at interfaces. In order to use the versatile options of this approach, we developed the Microslit Electrokinetic Set-up. The instrument was further extended by implementing Reflectometric Interference Spectroscopy for the simultaneous determination of the optical layer thickness of polymer films and ATR-FTIR spectroscopy for assessing secondary structure variations of immobilized biopolymers as influenced by variations of the interfacial electrical charge.
Charging by unsymmetrical water ion adsorption
Charging of solid-liquid interfaces is an ubiquitous phenomenon of particular importance in surface and materials science. On many solid surfaces the charging is caused by ionization of functional groups, e.g., carboxyl or amino groups. However, also for surfaces without ionisable surface groups charging is observed in aqueous environments.
The phenomenon is often attributed to the unsymmetrical adsorption of hydroxide and hydronium ions. Despite of numerous theoretical and experimental studies, very little is known on the interaction of hydroxide and hydronium ions with water-hydrophobic interfaces. To address this question, we systematically perform electrokinetic measurements at various material surfaces.
Charge and structure at soft interfaces
Soft polymer coatings are widely applied in biomaterials science as they allow for tailoring of surface properties and implementation of advanced functional features into traditional materials. The optimization of the coating performance in biomedical and technical applications necessarily requires the measurement, analysis, and understanding of their physico-chemical properties.
We apply streaming current, surface conductivity and swelling measurements in combination with tailored models for the charging and electrokinetics at soft surfaces for a comprehensive characterization of the film charge and structure.
Ion-specific phenomena at bilayer lipid membranes
Cell membranes, the interfacial boundary the between intra- and extracellular space are complex systems and involved in many cell functions such
as signalling, protein sorting or apoptosis. At the MBC we use supported bilayer lipid membranes as model system that allow for a characterization
of cellular membranes in simpler and well defined environments and to study membrane protein functions.
Methods like electrokinetic measurements, fluorescence microscopy, and ATR-FTIR spectroscopy are applied to study the influence of charge
formation on the membrane formation, fluidity, structure, and stability.
Molecular transport in hydrogels
Biohybrid hydrogels consiting of electrically neutral synthetic polymers and highly anionic glycosaminoglycans offer exciting options for
regenerative therapies as they allow for the electrostatic conjugation of various growth factors. We work on the establishment of analytical
methods and models that provide insights into correlations between the molecular transport and the hydrogel composition and structure. These
models are further used to predict the spatially and timely distribution of morphogens in cell culture experiments.
Microchannel flows constitute most part of the transport process in various Lab-On-Chip devices. At the micro- and nanometer size of structures in
these systems, transport processes are significantly affected by interfacial phenomena such as electrokinetic effects and surface roughness.
As the fabrication of chips with fine channels come into realize, people demand detailed understanding how material properties and chip design influence the transport in microchannels. At the MBC we apply analytical and theoretical approaches to better understand electrosurface phenomena in