The stronger the adhesion strength, the longer it takes for a cell to detach from the substrate. With an atomic force microscope (AFM) an external force can be applied to the adherent cell, thereby driving the cell to the detached state. The strength of cell adhesion can be quantified experimentally by measuring the average detachment time of an adherent cell to a stiff substrate. Beyond this point the thermodynamic phase transition becomes rate-limiting, whereas the fully associated and fully dissociated states are thereupon reached by typical density fluctuations At the dynamical critical point (center) the barrier to the fully associated or dissociated state, respectively, is smallest, resulting in the fastest attachment/detachment rate.
The latter corresponds to a coexistence of dense and dilute macroscopic domains of associated bonds. If the rigidity is greater than the thermodynamic critical membrane rigidity the landscape has a single well, whereas is has two minima when the rigidity is smaller than the thermodynamic critical membrane rigidity.
#Magnetic building blocks free#
Bellow the dynamical critical membrane rigidity the transition to a fully associated/dissociated state (and hence the left-/right-most free energy barrier) is always rate-limiting, whereas the detailed shape of the free energy landscape depends on membrane rigidity. The central column depicts the corresponding free energy landscapes along the fraction of dissociated bonds with the two end-points reflecting the fully associated (green circle) and fully dissociated (red circle) states.
From top to bottom: a stiff membrane (above the thermodynamic critical membrane rigidity) dynamical critical membrane rigidity a floppy membrane (below the dynamical critical membrane rigidity).
#Magnetic building blocks Patch#
Outer columns: A patch of a cell membrane with 16 adhesion bonds which are all associated (left) or dissociated (right). A new critical point in magnetism: the dynamical critical pointĭetachment and attachment times, and the dynamical critical point. The membrane rigidity at which CAMs start to cluster or show ’collective behavior’ is called the ’critical membrane rigidity’, which relates directly to the Curie (or critical) temperature in ferromagnetism. The coupling decreases with increasing membrane rigidity: CAMs are non-interacting when embedded in very stiff membranes, and strongly interacting in floppier membranes (or cells). This contributes to the so-called ‘avidity’ – N CAMs may collectively display a much stronger/weaker binding than N separate CAMs in solution. The wiggling motion of the cell membrane as a result of thermal fluctuations gives rise to an interaction between nearby CAMs – CAMs tend to associate (dissociate) more easily if nearby CAMs are also associated (dissociated). CAMs can be either one of two states: associated or dissociated. © Kristian Blom & Aljaž Godec / Max Planck Institute for Biophysical ChemistryĬell adhesion in turn arises through the association of cellular adhesion molecules (CAMs) which are attached to the cell membrane, or the cytoskeleton. The temperature at which such spontaneous magnetization occurs is called the Curie or critical temperature. On the contrary, at small enough temperatures coupling dominates over entropy, resulting in clusters of spins aligned in the same direction, and thus a nonzero magnetic dipole. At high temperatures the interaction has a weak effect (entropy dominates), and therefore on average half of the spins point up and the other half down, resulting in a vanishing net magnetic dipole. Spins interact with their direct neighbors via a coupling strength J, which favors the spins to align. Each atom inside ferromagnetic material carries a magnetic dipole, here called a ’spin’, that can point in one of two directions: up or down.
This phenomenon can be explained by the Ising model, which was originally developed by the German Wilhelm Lenz in 1920. (Physical Review X, September 27, 2021) From ferromagnetism to cell adhesionįerromagnetism is the process through which certain materials spontaneously become magnetic when the temperature is lowered.
Kristian Blom and Aljaž Godec at the Max Planck Institute for Biophysical Chemistry have now exploited this model to understand, through exact calculations, how the avidity of adhesion receptors and the strength of cellular adhesion can be regulated by mechanics. The last twenty years of experiments and theory have shown that cell adhesion may be accurately described by a model originally developed to describe ferromagnetism: the Ising model. For multicellular organisms like ourselves, cell adhesion plays a crucial role in our immune response, in wound healing and cancer development, and it prevents us from degrading into a pool of individual cells. Cells, the fundamental building blocks of all living organisms, stick to other cells via a process called cell adhesion.
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