Elastic shell theory–based AFM quantification of mechanical properties in adherent animal cells

Emi Kurnia Sari^1*, Yuka Tsuri^1,2, Naomi Tanga^1,3, Yoichiroh Hosokawa^1,2,3

¹Division of Material Science, Nara Institute of Science and Technology, Nara, Japan
²Medilux Research Center, Nara Institute of Science and Technology, Nara, Japan
³Center for Digital Green-innovation, Nara Institute of Science and Technology, Nara, Japan

* Presenter:Emi Kurnia Sari, email:kurniasariemi@gmail.com

Cells, the smallest unit of living organisms, can grow and change their morphology by complexly altering their mechanical properties such as stiffness (elasticity), internal pressure and membrane tension, thereby controlling physiological function. We previously proposed a new method to measure these factors for plant cells using an atomic force microscopy (AFM). In this analysis, the cell wall is treated as a “shell” enclosing the cell to apply elastic shell theory (EST). The AFM measurements provide topographic images and force-indentation curves to jointly infer the elastic modulus (E) and internal pressure (P) based on EST. Here, we applied this approach to adherent animal cells using NIH3T3 fibroblasts. The cells in culture were probed on an AFM using a spherical-tip cantilever. The force-indentation curves showed out-of-plane deformation proportional to the point force on the NIH3T3 cells in the large indentation region, suggesting the application of EST. Using cell curvature and apparent stiffness (the slope of the force-indentation curve), EST fitting yielded E = 15.09 ± 4.44 MPa and P =11.95 ± 3.17 kPa. These parameters capture the in-plane elasticity of the cortical shell and the intracellular pressure; together with cytoplasmic viscoelasticity, they stabilize the cell shape under load. This finding demonstrates that EST can be applied to certain adherent animal cells to separately estimate cortical elasticity and internal pressure, which is expected to provide mechanistic insights into the physiological behavior of animal cells.

Keywords: animal cell, cell mechanics, atomic force microscopy, nanoindentation