Membrane elasticity

[Lucie Plazen]

Hi developpers!

Cell are known to have elastic membrane which depend on their function, by the mean of surface tension... Nevertheless, in Morpheus, cell membrane length/area (depending on the dimensionality of the simulation) is written as a constant and isn't subject to fluctuations: the strength of this contraint in the hamiltonien can be adjusted (but I haven't yet figured out a way to switch it nicely: my cells breaks into pieces when this constraint doesn't receive enough weight, or have an almost constant membrane length when the weight is increased. No divergence from the objective length can happen at this point..)

Also, one might want to see an increase in the area/length of the membrane for the cell to be able to generate protrusions, small protrusions going quite far from the center of mass. I have found that when I increase the objective length the cpm here will often lead to a "spiky" membrane to increase its length instead of generating real protrusion, and had the feeling that allowing the cell to have an elastic membrane could change the result.. is it something that you've already worked on? Would you have advices here?

Thanks!

[Эрвин Визард]

Hello!
1) In Morpheus, cell membranes are subject to fluctuations. And intensivity of this fluctuations depends from temperature.
2) You can organize actin-based motion of cells using Protrusion hamiltonian (Textor 2015), you can find this module in CellTypes.

3) Also you can use qualitatively-like ConnectivityConstrainsts so that cells do not fall apart into fragments or more quantitative hamiltonian-based SurfaceConstraints. To make last constraints stronger try to increase corresponding lambda.

пятница, 26 ноября 2021 г. в 20:52:14 UTC+3, luciep...@gmail.com:

[Lucie Plazen]

Hi! Thanks for your answers and your time.

1) The energy difference caused by an elastic deformation is proportional to the square of the elongation, as it is written in the Hamiltonian, but I still have the feeling that some movement of the membranes are impossible to get because of the constant value of the surface constraint strength... Temperature allows membrane to locally move even if the energy is increased, it doesn't help to explore a very far configuration without resulting in a non-sense cell.

2) With the Protrusion tool, I'm able to get small protrusions but nothing like what we can see on real cells where very long outgrowths of the cell go away from its center. I guess it has to go with the fact that the Hamiltonian is a local way in energy minimization...

3) I've always been using the <Connectivity /> for ConnectivityConstrainsts, but still, my cells sometimes break into piece when I decrease too much the SurfaceConstraints strength (done when I try to allow more elasticity in the membrane) 

If anyone has any idea on how to solve this issue, it would be great

[francois el-daher]

Hi,

I face a similar limtation when trying to reproduce realistic protrusions of macrophages. 

I am even wondering if using a CPM is the right approach, but I give it more thoughts recently and I could generate slightly better protrusion using obstacles that add a constraint on the membrane. It might seem unnatural at first sight, but in the end, it might well be the reason why cells in interaction with ECM, other cells or tissue structure don't show blebs but fine and elongated protrusions.

I will explore that further.

What do you think?