Collective cell migration

What do we mean by “collective cell migration” ? The scope of this phenomena includes different forms of motion of groups of cells moving together. We focus on eukaryotic cells that belong to a multi-cellular organism. Most cells of a multi-cellular adult organism are rather stationary, but situations of collective migration of cells arise during the normal embryonic development process and the physiological responses during wound healing or immune response. It also plays an important role during pathologies such as cancer metastasis. During these processes cells have to be both motile and have a certain degree of adhesion to one other, so that the collectivity of the migration is maintained.
The theoretical modeling of this phenomenon has explored several approaches, most notably the use of particle-based simulations that include some form of orientational ordering interactions, similar to the descriptions used for flocking and swarming phenomena.
This field presents a challenge both for biologists and for physicists, which are collaborating in order to extend our understanding. We aim to place this scientific inquiry within the larger context of biological physics, where biological phenomena require and inspire new physical concepts and ideas.

See recent overview news article:

Driven by Curvature: Cell shapes and dynamics

Cells in our body have a multitude of shapes, according to their function. The factors that determine the local and global shape of a cell, are numerous, including the internal state of the cell, with respect to the cell cycle and metabolism, and the properties of the extracellular
matrix (ECM). Cells that are round while floating in solution, change their shapes dramatically when in contact with a solid substrate.

Cells also dynamically change their shapes, growing protrusions of various shapes (filopodia, microvilli, stereocilia), and exhibit propagating waves. The driving forces for all of these phenomena arise in the cytoskeleton, which deforms the membrane that envelopes the cell. We have been developing theoretical models which propose that a unifying mechanism behind many of these cellular shapes is the coupling of the cytoskeleton to the membrane via curved (or curvature-sensitive) elements at the membrane. We demonstrate that this general mechanism can give rise to both protrusions (Turing instability) and propagating waves (Wave instability).

It is still an open question what are the possible shapes and dynamics which can be driven by the curvature-based coupling of the membrane and the cytoskeleton. There are many open puzzles regarding cellular shapes, which remain unsolved.

Dynamic phases of molecular motors: pulses, shocks and traffic-jams

Inside cells cargo is carried by molecular motors “walking” processively along one-dimensional tracks (composed of biopolymers of the cytoskeleton). We explore models for interacting motors, to describe some puzzling formations of “pulses” of traffic-jams, and shocks, in these systems.
On a very different length-scale, we explore theoretical modeling of collective carrying of food items by ants to the nest (in collaboration with the experimental group of Ofer Feinerman, Department of Physics, WIS). In these systems, we are in fact trying to figure out how an ant “thinks”, without having access to the underlying neurological processes, but rather utilizing statistical data and modeling.

Collective motion of organisms

Motivated by our studies of the patterns of “active matter”, such as molecular motors and cells, we are interested in developing theoretical models for the motion of groups of organisms. One example is the collective action of ants carrying a load (food item) back to their nest. A round object with ants pulling equally in all directions would not move persistently, so some form of coordination is necessary. Another example includes the swarming behavior of flying midges.

Our methodology is to develop simple models that we then use to calculate the properties of the group and compare to experimental data. We then explore the more general and theoretical aspects of the model, with the aim of shedding light on the space of possible animal behavior.

The work on collective transport by ants got lots of media attention: smiley

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And in:

A popular lecture on collective transport by ants in Hebrew:

A popular lecture on collective transport by ants in English (Colloquium in Ljubljana):


More recently also the midges work got some popular attention smiley:










Active particles and membranes

“Active matter” is a form of matter that has recently generated much attention. It includes cases where particles have self-propulsion which is oriented, or when the active propulsion is random. Even when random, the active noise is distinct from thermal noise, and leads to unique behavior, including new and not-understood phase transitions.
We are interested in specific manifestations of such active systems, as they naturally arise within living cells and organisms, as well as in the general physics of such systems which presents us with numerous open puzzles.

A popular description of our recent work is here:

See also this recent News-and-Views on the active membrane of the RBC: