- Last Updated on Wednesday, 04 July 2012 09:17
|Huddling in penguin colonies: We study the collective dynamics of penguin movements with image processing technologies adapted from cell migration and particle tracking. During the antarctic winter, emperor penguins have to sustain temperatures down to -50° Celsius combined with strong winds. To conserve energy, they move close together and share their body heat (huddling). Movements inside the huddle are highly coordinated so that every penguin gets to pass the warmest zone in the center of the huddle. We study how these huddles move, and how the penguins move inside the huddle, by taking time lapse images (every 1 sec) from an elevated position, and tracking the head of every single penguin for several hours. (link)|
|Mechanics of 3D-Collagen gels: In collaboration with the rheology group of David. A. Weitz (DEAS, Harvard University) we investigate the mechanical properties of collagen gels on a macroscopic as well as a microscopic level. We measure bulk properties and determine the behavior of deformed collagen gels, i.g. by characterizing the deviations from an affine deformation of a bulk sample under shear (see video of a confocal section of collagen during shear deformation).|
|Morphology of 3-D collagen gels: Cell behavior in 3D collagen gels, such as migration speed, is strongly dependent on the collagen network morphology. By changing the protein concentration, polymerization temperature, pH, and crosslinker concentration, morphological properties such as pore size, fiber thickness, fiber length or branching ratio are changed. We quantify these properties of the collagen network by analyzing 3D confocal image stacks.The image shows a quantification of the gel porosity, which is done by computationally filling the fluid space with spheres of maximum size. This work is done in collaboration with Gerd Schroeder-Turk (Theoretical Physics group, Uni Erlangen) (link)|
|Fourier Transform Traction Microscopy: This technique is used to measure the forces (tractions) that cells exert on their surroundings. These forces that can be calculated from the deformation field of an elastic extracellular matrix (a polyacrylamide gel) in which fluorescent markers are embedded. (link)|
|3-D Traction Microscopy: Under physiologic conditions in the organism, most cells live in a 3-D environment and not on a flat, smooth and hard 2-D plastic or glass surface. Traction forces in 3-D are important, for instance, for the migration of cells (such as cancer cells, or white blood cells) through the connective tissue. To measure forces, we extend ideas from 2-D traction microscopy (see above) to the third dimension. In analogy to 2-D traction microscopy, 3-D tractions can be calculated by measuring the 3-D deformation field of the connective tissue matrix surrounding a cell. The image shows the elastic strain energy stored in the extracellular matrix surrounding an invaded breast carcinoma cell. This work is done in collaboration with James P. Butler (Harvard School of Public Health). (link)|
|Cell behavior in a 3-D extracellular matrix: Cell behavior such as force generation, migratory behavior, cell adhesion, focal adhesion formation, cytoskeletal organization and dynamics of cells in 2-D culture systems has been shown to substantially differ from those observed in a 3-D environment where cells are embedded in a flexible, degradable 3-D extracellular matrix. We use reconstituted collagen fiber networks to study cells in a more physiological 3-D environment.|
|Vinculin in cellular mechanotransduction: Vinculin is a protein responsible for the dynamic coordination and regulation of the focal adhesion complex (FAC) formation and the mechanical properties in cells. We have performed extensive studies in model cell systems in the presence and absence of vinculin and explored the relationship between cell stiffness, contractile forces and mechano-chemical signaling. The image shows vinculin (stained in green) and the actin cytoskeleton (red) of a fibroblast. (Mierke JBC 2010) (Dietz BBRC 2011)|
|Magnetic Tweezers: Magnetic micromanipulation using Magnetic Tweezers is a versatile biophysical technique and has been used for single-molecule unfolding, rheology measurements, and studies of force-regulated processes in living cells. We developed a magnetic tweezers setup for the application of precisely controlled forces up to 100 nN onto 5 micrometer magnetic beads. High precision of the force is achieved by a parametric force calibration method together with a real-time control of the magnetic tweezer position and current. High forces are achieved by bead-magnet distances of only a few micrometers. Applying such high forces can be used to characterize the local viscoelasticity of soft materials in the nonlinear regime, or to study force-regulated processes and mechano-chemical signal transduction in living cells. (link)|
|Nanoscale Particle Tracking: Ligand-coated beads can also serve as fiducial markers of whatever (specific) receptor and cortical or cytoskeletal components they are bound to; the bead motion then reports the remodeling of these components. The movement of the beads (or any other particle visible with phase contrast, modulation contrast or fluorescence microscopy) can then be tracked with nanometer resolution. (link)|
| Models of cell migration: We are developing models that quantitatively describe cell migration as a stochastic process. For this purpose, we apply analytical tools from statistical physics, the theory of nonlinear complex systems and computer simulation methods. According to the multi-scale nature of biological cell migration, we investigate the problem on different levels, ranging from the underlying molecular processes up to the mesoscopic behavior of living cells:
(1) Biochemical reaction networks: Can reaction networks be treated as boolean logic networks, or do intrinsic fluctuations and their modulation by external signals play an active role in biology?
(2) Acto-myosin cytoskeleton: What is the source and function of the universal long-time correlations found in the spatial fluctuations of the cytoskeleton?
(3) Motion of individual cells within complex material: Which strategies do cells apply in order to move through a dense biopolymer network?
(4) Collective cell migration: Do cancer cells cooperate when they invade into new tissue and try to form secondary tumors?
Center for Medical Physics and Technology
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