Just as squeezing a tomato in a supermarket reveals its freshness, poking a cyst of cells can reveal the mechanical properties of the cells that make it up. Such indentation tests are perhaps the most direct way of probing material properties across scales and applications. However, biological samples such as cysts of cells respond to force differently than non-living materials, for example, because biological materials are very soft: tissues like the brain are much softer than classical “soft” materials like rubber. Their behavior in these indentation tests should therefore show nonlinear effects. However, the current models don’t include these effects.
Shiheng Zhao and Pierre Haas from the Max Planck Institute for the Physics of Complex Systems (MPIPKS), the Center for Systems Biology Dresden (CSBD), and the Max Planck Institute of Molecular Cell Biology and Genetics (MPI-CBG) have now shown that elastic shells with complex material properties, like cysts of cells, can behave in new and unexpected ways when subjected to force.
The authors used numerical simulations to show that their exact calculations can even predict the behavior of realistic experimental geometries. Shiheng Zhao and Pierre Haas extended their results to shells under pressure, or “pre-stress,” resulting from the contractility of the cell cytoskeleton to predict the scalings of indentation depth with indentation force.
To test their predictions, the researchers analyzed data from cysts that self-assemble from Madin-Darby canine kidney (MDCK) cells, a mammalian cell line widely used in biomedical research. These cysts serve as simple models of the fluid-filled compartments, or lumina, that form during development. In these experimental data, they found their predicted scalings.
Their work provides a theoretical basis for experimental quantification of the mechanical properties of cysts. Further experimental and theoretical work will be needed to understand how these mechanical properties emerge from different cell biological processes.
Original Publication
Shiheng Zhao and Pierre A. Haas: Mechanics of poking a cyst. Phys. Rev. Lett. 134, 228402, 5 June, 2025, doi: https://doi.org/10.1103/PhysRevLett.134.228402