Characterizing Collapse of Highly Compressed Soft Matter Thin Sheets Using Continuum Mechanics

Current: Anna Gaffney
Alumni: Luka Pocivavsek
Collaborators: Luka Pocivavsek, Nhung Nguyen, Dongxu Liu from SurgBioMech Lab

Lipid monolayers are membranes that self-assemble at the air-water interface and are found biologically in the ears, eyes, and lungs. Studying their responses to mechanical forces and stress can supply information to both the lipid and thin sheet fields. Mechanically, highly compressed lipid monolayers can be represented as elastic sheets. In this sense, at some critical stress, these sheets must undergo instabilities. Some do this through out-of-plane collapse, while others relax in-plane. This in-plane relaxation is experimentally observed with fluorescence microscopy (FM) and is characterized as reorganization of condensed domains within a softer matrix. These different modes of instability are accessible by tuning lipid monolayer softness (via temperature, composition etc), inspiring our search for a generalized material model with similar tunability. The elastic models that are currently used to describe out-of-plane collapse have been unsuccessful in capturing in-plane relaxation. Our lab hypothesizes this is because the matrix is relaxing through strain localization in the form of shear banding. In collaboration with professors Luka Pocivavsek and Nhung Nguyen in the SurgBioMech Lab in UChicago Dept of Surgery, we utilize computational modeling at the continuum mechanics scale, developing a material model that can tune for shear banding. Simulation results from models that incorporate FM-derived condensed domain morphology show that if we trigger shear banding in the matrix around domains, the domains can reorganize and reproduce the experimental in-plane relaxation morphology. With this area of research, we hope to expand understanding of lipid monolayer mechanical response through theoretical frameworks that can be applied to broader research in other thin sheet systems, such as atomic thin sheets and block-copolymers.

Selected bibliography

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Ries, H. E. Stable ridges in a collapsing monolayer. Nature 281, 287–289 (1979). https://doi.org/10.1038/281287a0
Carotenuto, A. R. et al., “Multiscale geometry and mechanics of lipid monolayer collapse” in Current Topics in Membranes, (Elsevier, 2021), pp. 1–45. https://doi.org/10.1016/bs.ctm.2021.08.003
Gaffney, A.D., Liu, D., Samal, D., Cao, K., Carotenuto, A.R., Deseri, L., Fraldi, M., Lee, K.Y.C., Pocivavsek, L., Nguyen, N. Modeling lipid monolayer instability with shear banding as a mechanism for in-plane relaxation, in process