Prof. Sam Safran

Lecture: Physical theories of cell mechanic

Affiliation: Department of Materials and Interfaces,
the Weizmann Institute,
Rehovot, Israel
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Lecture: Physical theories of cell mechanics

Cell contractility at either the coarse-grained level of an entire cell or at the sub-cellular level of individual acto-myosin fibers, can be understood using the concept of elastic force dipoles. These dipoles interact via their mutual deformations of the surrounding elastic medium which can be either the extra-cellular matrix (in the case of cells modeled as dipoles) or the internal, cellular cytoskeleton (in the case of acto-myosin fibers within the cell). The theory of these elastically mediated interactions combined with the unique "living" nature of cells (implying that the activity of these dipoles is non-equilibrium and energy consuming) allows us to understand the organization and order of acto-myosin fibers within the cytoskeleton of a single cell or among contractile cells in systems of non-motile and adherent cells. We present the general theory of elastic interactions in the context of acto-myosin activity with examples that demonstrate its utility in understanding experiments on cytoskeletal alignment in stem cells that differentiate into muscle cells, the structure and beating of cardiomyocytes, very long-ranged cell-cell interactions in fibrous elastic matrices, and elastically controlled diffusion of biomolecules that trigger development in embryos.

Short biography

Safran received his Ph.D. in Physics from MIT, followed by a postdoctoral position at Bell Laboratories. From 1980-1990 he served as a Senior Staff member in the Complex Fluids Physics group of Exxon Research and Engineering in New Jersey. Prof. Safran joined the faculty of the Weizmann Institute of Science in 1990 as a Professor in the Department of Materials and Interfaces.  He has served as Dean of the Graduate School and as Vice President of the Weizmann Institute. His current research interests in the theory of soft and biological matter focus on cellular response to mechanical stress and domain (“raft”) formation in charged and multicomponent membranes.  The latter extends his earlier work on surfactant membranes that unified their mesocale structures, phase behavior and dynamics. Recent honors include the de Gennes Lecture Award of the European Physical Journal and the Beller Lectureship of the American Physical Society.  He is the author of a graduate level text on the physics of surfaces, interfaces and membranes, translated into Japanese and Chinese.