Quantifying Cell Traction Forces at the Individual Fiber Scale in 3D: A Novel Approach Based on Deformable Photopolymerized Fiber Arrays

The forces exerted by cells upon the fibers of the extracellular matrix play a decisive role in cell motility in development and disease. How the local physical properties of the matrix (such as density, stiffness, orientation) affect cellular forces remains poorly understood. Existing approaches to measure cell 3D traction forces within fibrous substrates lack control over the local properties and rely on continuum approaches, not suited for measuring forces at the scale of individual fibers. A novel approach is proposed here to fabricate multilayer arrays of deformable fibers with defined geometrical and mechanical properties using two-photon polymerization. The fibers are characterized using Atomic Force Microscopy and span a wide range of sizes and mechanical properties. This approach is combined with a new reference-free method for measuring traction forces in 3D, which relies on automated segmentation of the fibers coupled with finite element modeling. The force measurement pipeline is applied to study forces exerted by adherent cells, endothelial cells, fibroblasts or macrophages, and reveals how these forces are influenced by fiber density and stiffness. Additionally, coupling to fast volumetric imaging with lattice light-sheet microscopy enables the measurement of the low-intensity and short-lived tractions exerted by amoeboid cells, such as dendritic cells.