Soft Condensed Matter Group
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Supported Membranes and Artificial Micro-Niches

Supported membranes are versatile biomimetic interfaces. We study the structure and dynamics of supported membranes on various solid supports in collaboration with the group of Bert Nickel. The control of fluidity, spacing and lateral organisation is a current research challenge.

Dynamic patterns in a supported lipid bilayer driven by standing surface acoustic waves

dynamicpatternsIn the past decades supported lipid bilayers (SLBs) have been an important tool in order to study the physical properties of biological membranes and cells. So far, controlled manipulation of SLBs is very limited. Here we present a new technology to create lateral patterns in lipid membranes controllable in both space and time. Surface acoustic waves (SAWs) are used to generate lateral standing waves on a piezoelectric substrate which create local ‘‘traps’’ in the lipid bilayer and lead to a lateral modulation in lipid concentration and membrane density. We demonstrate that pattern formation is reversible and does not affect the integrity of the lipid bilayer as shown by extracting the diffusion constant of fluid membranes. The described method could possibly be used to design switchable interfaces for the lateral transport and organization of membrane bound macromolecules to create dynamic bioarrays and control biofilm formation.

Transport, Separation, and Accumulation of Proteins on Supported Lipid Bilayers

transportseperationTransport, separation, and accumulation of proteins in their natural environment are central goals in protein biotechnology. Miniaturized assays of supported lipid bilayers (SLBs) have been proposed as promising candidates to realize such technology on a chip, but a modular system for the controlled transport of membrane proteins does not exist. We demonstrate that standing surface acoustic waves drive the in-plane redistribution of proteins on planar SLBs over macroscopic distances (3.5 mm). Accumulation of proteins in periodic patterns of about 10-fold protein concentration difference is accomplished and shown to relax into the homogeneous state by diffusion. Different proteins separate in individual fractions from a homogeneous distribution and are transported and accumulated into clusters using beats. The modular planar setup has the potential of integrating other lab-on-a-chip tools, for monitoring the membrane-protein integrity or adding microfluidic features for blood screening or DNA analysis.

Alignment and Deformation of Lipid Bilayer Domains in Vesicles Adhering to Microstructured Substrates

alignmentanddeformation

In heterogeneous lipid membranes, the lateral organization is coupled to local curvature as the membrane bending energies depend on composition. We investigate phase separated vesicles of ternary lipid composition in contact with structured surfaces, where the distinct elastic properties of the Lo (liquid ordered) and Ld (liquid disordered) phases come into play. We show that fused silica substrates with microstructured grooves induce sorting, alignment and deformation of Lo domains in adhering vesicles. The same phenomenon is observed on flat, chemically modified substrates with alternating stripes of roug

h and smooth regions. In both cases it is the Lo phase which accumulates over the smooth substrate and membrane spanned groove regions respectively. Deformation of Lo domains occurs when domain diameters grow beyond the width of the microstructured stripes. Domain alignment was also observed in binary membranes featuring gel and fluid phase coexistence showing the generic character of domain sorting on microstructured surfaces.

DNA-stretching

dnastretch

In the case of substrates with etched channels, we observe DNA stretching at the groove edges: The concave edges form attractive line potentials that bind the diffusing molecules after some time, thus polymer confinement to 1D.
The reason for the DNA stretching results from the geometry: Finally, molecules in a concave edge have closer contact with the positive charges within the membrane and are therefore bound tighter. Convex edges would have a contrary effect. The effect is strong enough to stretch DNA molecules to 95% of their contour length which could make applications like gene mapping possible.

 

 

Conformational dynamics of DNA electrophoresis on cationic membranes

conformational

The conformational dynamics of DNA molecules undergoing electrophoresis on a fluid substrate-supported cationic lipid bilayer is investigated using fluorescence microscopy. At low electrophoretic velocities, drift of 2-D random coils is observed. In contrast, at velocities larger than 0.3 mm/s, the DNA molecules stretch out and assume branched configurations. The cross-over scenario is explained by the observation that cationic lipids segregate underneath the adsorbed DNA and confine the DNA to its counter charge imprint on time scales shorter than the relaxation time of the imprint. The concept of a tube-like confinement of the DNA is corroborated by the observed 1/N size dependence of the electrophoretic mobility in analogy to the biased reptation model in gels. The role of membrane defects and possible applications of membrane-based electrophoresis in microfluidic devices are discussed.

Literature:

  • Martin Hennig, Manuel Wolff, Jürgen Neumann, Matthias Schneider, Joachim Rädler
    DNA Manipulation on Supported Lipid Bilayers by Surface Acoustic Waves
    in preparation, 2011
  • Jürgen Neumann, Martin Hennig, Achim Wixforth, Stefan Manus, Joachim Rädler, Matthias Schneider
    Transport, Separation and Accumulation of Proteins on Supported Lipid Bilayers (cache)
    Nano Letters, DOI: 10.1021/nl100993r, 10, 2903-2908, 2010
    Press: LMU (cache), NIM (cache)
  • Tobias Stögbauer, Martin Hennig, Joachim Rädler
    Substrate induced phase separation in giant unilamellar vesicles
    Biophysical Reviews and Letters, Vol. 5, No. 3, 1-9, 2010
  • Martin Hennig, Jürgen Neumann, Achim Wixforth, Joachim O. Rädler and Matthias F. Schneider
    Dynamic patterns in a supported lipid bilayer driven by surface acoustic waves (cache)
    Lab on a Chip, 9, 3050-3053 DOI:10.1039/B907157A, (2009)
  • Valentin Kahl, Martin Hennig, Berenike Maier and Joachim O. Rädler:
    Conformational Dynamics of DNA-Electrophoresis on Cationic Membranes (cache)
    Electrophoresis, Vol. 8, 30, 1276-1281 (2009)
  • M. Hochrein, J. Leierseder, L. Golubovic and J.O. Rädler:
    "DNA Molecules on Periodically Micro-structured Lipid Membranes: Localization and Coil Stretching"
    Physical Review E, (2007)
  • M.B. Hochrein, J.A. Leierseder, L. Golubovic and J.O. Rädler:
    "DNA Localisation and Stretching on Periodically Microstructured Lipid Membranes"
    Phys. Rev. Lett. 96(3), 2006
  • Berenike Maier and Joachim Rädler:
    "DNA on Fluid Membranes: A Model Polymer in Two Dimensions"
    Macromolecules 33, 2000
  • Berenike Maier and Joachim Rädler:
    "Conformation and Self-Diffusion of Single DNA Molecules Confined to Two Dimensions"
    Phys. Rev. Lett. 82, 1999

Funded by SFB563 A4 and NIM Area G