Proposed approach (experimental / theoretical / computational)

Immune cells are highly dynamic, constantly changing shape, migrating, and intermittently interacting with other cells. Major examples include macrophages which need to apply forces to their targets to attach, engulf, break, and digest them [1], and T lymphocytes, which employ mechanical forces to identify pathogenic antigens on the surface of a target cell and to kill it [2]. The spatio-temporal pattern of the applied traction force offers crucial insights into cell behaviour. TFM aims to measure these patterns on engineered substrates with well-defined elastic properties, utilizing deformation information extracted from substrate images [2]. We seek to improve traditional TFM by developing a novel experimental tool to measure feeble forces by-passing current microscopic marker-based detection, that is already mastered in the team [3]. Instead, detection will be based on interaction of polarized light with a deformable anisotropic medium whose distortion in response to cell-applied forces will be optically detected. For that, we plan use deformable polymer-based liquid crystal elastomers, that will be preordered magnetically, and will, like an LCD watch, reveal deformation of the substrate upon changes in orientation, without the need of any extrinsic marker. ML, which is currently being explored for conventional TFM [4], will be used to bypass onerous calculations. The optical strategy of using polarized light also frees up a fluorescence channel for bio-labelling the cells to simultaneously reveal membrane and cytoskeletal structures in real-time. The tasks to be undertaken will be:

• Set-up Force-watch, observe large macrophage generated distortions
• Calibrate and use ML to infer forces from distortions, cross-validate using conventional TFM.
• Optimize to measure feeble forces and apply to both macrophage and T lymphocytes