Publications
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Articles in scientific journals
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Books
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Theses
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1. Articles in scientific journals
![](grafiken/33flexoelectric_icon.png) | Flexoelectric fluid membrane vesicles in spherical confinement
Niloufar Abtahi, Lila Bouzar, Nadia Saidi-Amroun, Martin Michael Müller |
The morphology of spherically confined flexoelectric fluid membrane vesicles in an ex-
ternal uniform electric field is studied numerically. Due to the deformations induced by
the confinement, the membrane becomes polarized resulting in an interaction with the
external field. The equilibrium shapes of the vesicle without electric field can be clas-
sified in a geometrical phase diagram as a function of scaled area and reduced volume
[1, 2]. When the area of the membrane is only slightly larger than the area of the con-
fining sphere, a single axisymmetric invagination appears. A non-vanishing electric field
induces an additional elongation of the confined vesicle which is either perpendicular or
parallel depending on the sign of the electric field parameter. Higher values of the surface
area or the electric field parameter can reduce the symmetry of the system leading to
more complex folding. We present the resulting shapes and show that transition lines
are shifted in the presence of an electric field. The obtained folding patterns could be of
interest for biophysical and technological applications alike.
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EPL, 131(1): 18001, 2020. See also arXiv:2006.04475.
![](grafiken/32tangentdev_icon.png) | Isometric bending requires local constraints on free edges
Jemal Guven, Martin Michael Müller, Pablo Vázquez-Montejo |
While the shape equations describing the equilibrium of an unstretchable thin sheet that is free
to bend are known, the boundary conditions that supplement these equations on free edges have remained elusive.
Intuitively, unstretchability is captured by a constraint on the metric within the bulk. Naïvely one would then
guess that this constraint is enough to ensure that the deformations determining the boundary conditions on these
edges respect the isometry constraint. If matters were this simple, unfortunately, it would imply unbalanced torques
(as well as forces) along the edge unless manifestly unphysical constraints are met by the boundary geometry. In this
article, we identify the source of the problem: not only the local arc-length but also the geodesic curvature need to
be constrained explicitly on all free edges. We derive the boundary conditions which follow. In contrast to conventional
wisdom, there is no need to introduce boundary layers. This framework is applied to isolated conical defects, both
with deficit as well, but more briefly, as surplus angles. Using these boundary conditions, we show that the lateral
tension within a circular cone of fixed radius is equal but opposite to the radial compression, and independent of
the deficit angle itself. We proceed to examine the effect of an oblique outer edge on this cone perturbatively
demonstrating that both the correction to the geometry as well as the stress distribution in the cone kicks in at
second order in the eccentricity of the edge.
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Math. Mech. Solids, 24: 4051, 2019. See also arXiv:1904.05855.
![](grafiken/31squeelixsimulations_icon.jpg) | Helical Superstructure of Intermediate Filaments
Lila Bouzar, Martin Michael Müller, René Messina, Bernd Nöding, Sarah Köster, Hervé Mohrbach, Igor M. Kulić |
Abstract
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Phys. Rev. Lett., 122: 098101, 2019. See also arXiv:1803.04691.
![](grafiken/30vesicleflow_icon.png) | Vesicle dynamics in confined steady and harmonically modulated Poiseuille flows
Zakaria Boujja, Chaouqi Misbah, Hamid Ez-Zahraouy, Abdelilah Benyoussef, Thomas John, Christian Wagner, Martin Michael Müller |
Abstract
Phys. Rev. E, 98: 043111, 2018. See also arXiv:1810.04500.
![](grafiken/29confinementtorusadhesion_icon.png) | Confining a fluid membrane vesicle of toroidal topology in an adhesive hard sphere
Lila Bouzar, Ferhat Menas, Martin Michael Müller |
Abstract
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IOP Conf. Series: MSE, 186: 012021, 2017.
![](grafiken/28squeelix_icon.png) | Squeezed helical elastica
Lila Bouzar, Martin Michael Müller, Pierre Gosselin, Igor M. Kulić, Hervé Mohrbach |
We theoretically study the conformations of a helical semi-flexible filament
confined to a two-dimensional surface. This squeezed helix exhibits a variety of unexpected shapes
resembling circles, waves or spirals depending on the material parameters. We explore the conformation
space in detail and show that the shapes can be understood as the mutual elastic interaction of
conformational quasi-particles. Our theoretical results are potentially useful to
determine the material parameters of such helical filaments in an experimental setting.
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Eur. Phys. J. E, 39: 114, 2016. See also arXiv:1606.03611.
![](grafiken/27dynamin_icon.png) | How bio-filaments twist membranes
Julien Fierling, Albert Johner, Igor M. Kulić, Hervé Mohrbach, Martin Michael Müller |
Abstract
Soft Matter, 12: 5747, 2016.
![](grafiken/26confinementtorus_icon.png) | Toroidal membrane vesicles in spherical confinement
Lila Bouzar, Ferhat Menas, Martin Michael Müller |
Abstract
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Phys. Rev. E, 92: 032721, 2015. See also arXiv:1509.00765.
![](grafiken/25sleeve_icon.png) | Non-linear buckling and symmetry breaking of a soft elastic sheet sliding on a cylindrical substrate
Norbert Stoop, Martin Michael Müller |
Abstract
Read more
Int. J. Non-Linear Mech., 75: 115, 2015. See also arXiv:1503.05030.
![](grafiken/24dynamin_icon.jpg) | Crunching Biofilament Rings
Julien Fierling, Martin Michael Müller, Hervé Mohrbach, Albert Johner, Igor M. Kulić |
We discuss a curious example for the collective mechanical behavior of coupled non-linear monomer units entrapped in a circular filament. Within a simple model we elucidate how multistability of monomer units and exponentially large degeneracy of the filament's ground state emerge as a collective feature of the closed filament. Surprisingly, increasing the monomer frustration, i.e., the bending prestrain within the circular filament, leads to a conformational softening of the system. The phenomenon, that we term polymorphic crunching, is discussed and applied to a possible scenario for membrane tube deformation by switchable dynamin or FtsZ filaments. We find an important role of cooperative inter-unit interaction for efficient ring induced membrane fission.
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Europhys. Lett., 107(6): 68002, 2014. See also arXiv:1408.6787.
![](grafiken/23microtubules_icon.png) | Confotronic dynamics of tubular filaments
Osman Kahraman, Hervé Mohrbach, Martin Michael Müller, Igor M. Kulić |
Tubular lattices are ubiquitous in nature and technology. Microtubules and nanotubes of all
kinds act as important pillars of biological cells and the man-made nano-world. We show that
when prestress is introduced in such structures, localized conformational quasiparticles emerge and
govern the collective shape dynamics of the lattice. When coupled via cooperative interactions these
quasiparticles form larger-scale quasipolymer superstructures exhibiting collective dynamic modes
and giving rise to a hallmark behavior radically different from semiflexible beams.
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Soft Matter, 10(16): pp. 2836-2847, 2014. See also arXiv:1312.3106.
![](grafiken/22rotation_icon.png) | Whirling skirts and rotating cones
Jemal Guven, J. A. Hanna, Martin Michael Müller |
Steady, dihedrally symmetric patterns with sharp peaks may be observed on a spinning skirt, lagging behind the material flow of the fabric. These qualitative features are captured with a minimal model of traveling waves on an inextensible, flexible, generalized-conical sheet rotating about a fixed axis. Conservation laws are used to reduce the dynamics to a quadrature describing a particle in a three-parameter family of potentials. One parameter is associated with the stress in the sheet, aNoether is the current associated with rotational invariance, and the third is a Rossby number which indicates the relative strength of Coriolis forces. Solutions are quantized by enforcing a topology appropriate to a skirt and a particular choice of dihedral symmetry. A perturbative analysis of nearly axisymmetric cones shows that Coriolis effects are essential in establishing skirt-like solutions. Fully non-linear solutions with three-fold symmetry are presented which bear a suggestive resemblance to the observed patterns.
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New J. Phys., 15: 113055, 2013. See also arXiv:1306.2619.
![](grafiken/21cubicmembranes_icon.png) | Myotubularin and PtdIns3P remodel the sarcoplasmic reticulum in muscle in vivo
Leonela Amoasii, Karim Hnia, Gaëtan Chicanne, Andreas Brech, Belinda Simone Cowling, Martin Michael Müller, Yannick Schwab, Pascale Koebel, Arnaud Ferry, Bernard Payrastre, Jocelyn Laporte |
Abstract
J. Cell Sci., 126(8): 1806, 2013.
![](grafiken/20epole_icon.png) | Dipoles in thin sheets
Jemal Guven, J. A. Hanna, Osman Kahraman, Martin Michael Müller |
A flat elastic sheet may contain pointlike conical singularities that carry a metrical "charge" of Gaussian curvature. Adding such elementary defects to a sheet allows one to make many shapes, in a manner broadly
analogous to the familiar multipole construction in electrostatics. However, here the underlying field theory is non-linear,
and superposition of intrinsic defects is non-trivial as it must respect the immersion of the resulting surface in three
dimensions. We consider a "charge-neutral" dipole composed of two conical singularities of opposite sign.
Unlike the relatively simple electrostatic case, here there are two distinct stable minima and an infinity of unstable equilibria.
We determine the shapes of the minima and evaluate their energies in the thin-sheet regime where bending dominates
over stretching. Our predictions are in surprisingly good agreement with experiments on paper sheets.
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Eur. Phys. J. E, 36: 106, 2013. See also arXiv:1212.3262.
![](grafiken/19confinement_icon.png) | Fluid membrane vesicles in confinement
Osman Kahraman, Norbert Stoop, Martin Michael Müller |
Abstract
Read more
New J. Phys., 14: 095021, 2012.
![](grafiken/18flowermorpho_icon.png) | Petal shapes of sympetaleous flowers: the interplay between growth, geometry and elasticity
Martine Ben Amar, Martin Michael Müller, Miguel Trejo |
The growth of a thin elastic sheet imposes constraints on its geometry such as its Gaussian curvature KG.
In this paper, we construct the shapes of sympetalous bell-shaped flowers with a constant Gaussian curvature. Minimizing the bending energies
of both the petal and the veins, we are able to predict quantitatively the global shape of these flowers. We discuss two toy problems
where the Gaussian curvature is either negative or positive. In the former case the axisymmetric pseudosphere turns out to mimic the correct
shape before edge curling; in the latter case, singularities of the mathematical surface coincide with strong veins. Using a variational
minimization of the elastic energy, we find that the optimal number for the veins is either four, five or six, a number which is deceptively
close to the statistics on real flowers in nature.
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New J. Phys., 14: 085014, 2012. Also featured in the Highlights of 2012.
![](grafiken/17confinement_icon.png) | Morphogenesis of membrane invaginations in spherical confinement
Osman Kahraman, Norbert Stoop, Martin Michael Müller |
Abstract
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Europhys. Lett., 97(6): 68008, 2012. See also arXiv:1201.2518.
![](grafiken/16econeunstab_icon.jpg) | Conical instabilities on paper
Jemal Guven, Martin Michael Müller, Pablo Vázquez-Montejo |
Abstract
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J. Phys. A: Math. Theor., 45(1): 015203, 2012. See also arXiv:1107.5008.
![](grafiken/15casimir_icon.png) | Interface-mediated interactions: Entropic forces of curved membranes
Pierre Gosselin, Hervé Mohrbach, Martin Michael Müller |
Abstract
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Phys. Rev. E, 83(5): 051921, 2011. See also arXiv:1011.1221.
![](grafiken/14econetouch_icon.jpg) | Self-Contact and Instabilities in the Anisotropic Growth of Elastic Membranes
Norbert Stoop, Falk K. Wittel, Martine Ben Amar, Martin Michael Müller, Hans J. Herrmann |
Abstract
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Phys. Rev. Lett., 105(6): 068101, 2010. See also arXiv:1007.1871.
![](grafiken/13cellmodel_icon.png) | Cell Model Approach to Membrane Mediated Protein Interactions
Martin Michael Müller, Markus Deserno |
Abstract
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Prog. Theor. Phys. Suppl., 184: pp. 351-363, 2010.
![](grafiken/12pseudo_icon.jpg) | Hamiltonian formulation of surfaces with constant Gaussian curvature
Miguel Trejo, Martine Ben Amar, Martin Michael Müller |
Abstract
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J. Phys. A: Math. Theor., 42(42): 425204, 2009.
![](grafiken/11indentstretch_icon.jpg) | Local Membrane Mechanics of Pore-Spanning Bilayers
Ingo Mey, Milena Stephan, Eva K. Schmitt, Martin Michael Müller, Martine Ben Amar, Claudia Steinem, Andreas Janshoff |
Abstract
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J. Am. Chem. Soc., 131(20): pp. 7031-7039, 2009.
![](grafiken/10substrate_icon.jpg) | Elasticity Mapping of Pore-Suspending Native Cell Membranes
Bärbel Lorenz, Ingo Mey, Siegfried Steltenkamp, Tamir Fine, Christina Rommel, Martin Michael Müller, Alexander Maiwald, Joachim Wegener, Claudia Steinem, Andreas Janshoff |
The mechanics of cellular membranes is governed by a non-equilibrium composite framework
consisting of the semiflexible filamentous cytoskeleton and extracellular matrix proteins linked to
the lipid bilayer. While elasticity information of plasma membranes has mainly been obtained from
whole cell analysis, techniques that allow to address local mechanical properties of cell
membranes are desirable to learn how their lipid and protein composition is reflected in the elastic
behavior on local length scales. Here, we introduce an approach based on basolateral
membranes of polar epithelial Madin-Darby canine kidney (MDCK) II cells, prepared on a highly ordered porous substrate that
allows elastic mapping on a submicrometer length scale. A strong correlation between the
density of actin filaments and the measured membrane elasticity is found. Spatially resolved indentation experiments carried out with atomic force and fluorescence microscope permit to relate the supramolecular structure to the elasticity of cellular membranes. It is shown that the elastic response of the pore-spanning cell membranes is governed by the local bending modules rather than the lateral tension.
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Small, 5(7): pp. 832-838, 2009.
![](grafiken/09econe_icon.png) | Conical Defects in Growing Sheets
Martin Michael Müller, Martine Ben Amar, Jemal Guven |
A growing or shrinking disc will adopt a conical shape, its intrinsic geometry characterized by a surplus angle φe at the apex. If growth is slow, the cone will find its equilibrium. Whereas this is trivial if φe≤0, the disc can fold into one of a discrete infinite number of states if φe is positive. We construct these states in the regime where bending dominates, determine their energies and how stress is distributed in them. For each state a critical value of φe is identified beyond which the cone touches itself. Before this occurs, all states are stable; the ground state has twofold symmetry.
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Phys. Rev. Lett., 101(15): 156104, 2008. See also arXiv:0807.1814.
![](grafiken/08drape_icon.png) | How paper folds: bending with local constraints
Jemal Guven, Martin Michael Müller |
A variational framework is introduced to describe how a surface bends when it is subject to local constraints on its geometry. This framework is applied to describe the patterns of a folded sheet of paper. The unstretchability of paper implies a constraint on the surface metric; bending is penalized by an energy quadratic in mean curvature. The local Lagrange multipliers enforcing the constraint are identified with a conserved tangential stress that couples to the extrinsic curvature of the sheet. The framework is illustrated by examining the deformation of a flat sheet into a generalized cone.
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J. Phys. A: Math. Theor., 41(5): 055203, 2008. See also arXiv:0712.0978.
![](grafiken/07vesad_icon.jpg) | Contact lines for fluid surface adhesion
Markus Deserno, Martin Michael Müller, Jemal Guven |
Abstract
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Phys. Rev. E, 76(1): 011605, 2007. See also cond-mat/0703019. Also featured in the Virtual Journal of Biological Physics Research.
![](grafiken/06Eulerelastica_icon.png) | Balancing torques in membrane-mediated interactions: Exact results and
numerical illustrations
Martin Michael Müller, Markus Deserno, Jemal Guven |
Abstract
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Phys. Rev. E, 76(1): 011921, 2007. See also cond-mat/0702340. Also featured in the Virtual Journal of Biological Physics Research.
![](grafiken/05curvemedcover_icon.jpg) | Aggregation and vesiculation of membrane proteins by curvature-mediated
interactions
Benedict J. Reynwar, Gregoria Illya, Vagelis A. Harmandaris, Martin Michael Müller, Kurt Kremer, Markus Deserno |
Membrane remodelling plays an important role in cellular tasks such as endocytosis, vesiculation and protein sorting, and in the biogenesis of organelles such as the endoplasmic reticulum or the Golgi apparatus. It is well established that the remodelling process is aided by specialized proteins that can sense as well as create membrane curvature, and trigger tubulation when added to synthetic liposomes. Because the energy needed for such large-scale changes in membrane geometry significantly exceeds the binding energy between individual proteins and between protein and membrane, cooperative action is essential. It has recently been suggested that curvature-mediated attractive interactions could aid cooperation and complement the effects of specific binding events on membrane remodelling. But it is difficult to experimentally isolate curvature-mediated interactions from direct attractions between proteins. Moreover, approximate theories predict repulsion between isotropically curving proteins. Here we use coarse-grained membrane simulations to show that curvature-inducing model proteins adsorbed on lipid bilayer membranes can experience attractive interactions that arise purely as a result of membrane curvature. We find that once a minimal local bending is realized, the effect robustly drives protein cluster formation and subsequent transformation into vesicles with radii that correlate with the local curvature imprint. Owing to its universal nature, curvature-mediated attraction can operate even between proteins lacking any specific interactions, such as newly synthesized and still immature membrane proteins in the endoplasmic reticulum.
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Nature 447(7143): pp. 461-464, 2007.
![](grafiken/04tip_icon.jpg) | How to determine local elastic properties of lipid bilayer membranes
from atomic-force-microscope measurements: A theoretical analysis
Davood Norouzi, Martin Michael Müller, Markus Deserno |
Abstract
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Phys. Rev. E, 74(6): 061914, 2006. See also cond-mat/0602662. Also featured in the Virtual Journal of Biological Physics Research.
![](grafiken/03DODAB_icon.png) | Mechanical Properties of Pore-Spanning Lipid Bilayers Probed by Atomic Force Microscopy
Siegfried Steltenkamp, Martin Michael Müller, Markus Deserno, Christian Hennesthal, Claudia Steinem, Andreas Janshoff |
Abstract
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Biophys. J., 91(1): pp. 217-226, 2006.
![](grafiken/02multibody_icon.gif) | Interface mediated interactions between particles -- a geometrical approach
Martin Michael Müller, Markus Deserno, Jemal Guven |
Abstract
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Phys. Rev. E, 72(6): 061407, 2005. See also cond-mat/0506019. Also featured in the Virtual Journal of Biological Physics Research.
![](grafiken/01surfacemed_icon.jpg) | Geometry of surface-mediated interactions
Martin Michael Müller, Markus Deserno, Jemal Guven |
Abstract
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Europhys. Lett., 69(3): pp. 482-488, 2005. See also cond-mat/0409043.
2. Books
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New Trends in the Physics and Mechanics of Biological Systems
Lecture Notes of the Les Houches Summer School, vol. 92 (Oxford University Press, 2011),
edited by Martine Ben Amar, Alain Goriely, Martin Michael Müller and Leticia Cugliandolo.
Chapter 9:
The physics of the cell membrane
Martin Michael Müller and Martine Ben Amar.
3. Theses
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Theoretical examinations of interface mediated interactions between colloidal particles,
diploma thesis (2004).
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Theoretical studies of fluid membrane mechanics, dissertation (2007).
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Symmetry breaking in bioelasticity, habilitation thesis (2015).
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