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Cells are known to continuously remodel their local extracellular matrix (ECM) and in a reciprocal way, they can also respond to mechanical and biochemical properties of their fibrous environment. In this study, we measured how stiffness around dermal fibroblasts (DFs) and human fibrosarcoma HT1080 cells differs with concentration of rat tail type 1 collagen (T1C) and type of ECM. Peri-cellular stiffness was probed in four directions using multi-axes optical tweezers active microrheology (AMR). First, we found that neither cell type significantly altered local stiffness landscape at different concentrations of T1C. Next, rat tail T1C, bovine skin T1C and fibrin cell-free hydrogels were polymerized at concentrations formulated to match median stiffness value. Each of these hydrogels exhibited distinct fiber architecture. Stiffness landscape and fibronectin secretion, but not nuclear/cytoplasmic YAP ratio differed with ECM type. Further, cell response to Y27632 or BB94 treatments, inhibiting cell contractility and activity of matrix metalloproteinases, respectively, was also dependent on ECM type. Given differential effect of tested ECMs on peri-cellular stiffness landscape, treatment effect and cell properties, this study underscores the need for peri-cellular and not bulk stiffness measurements in studies on cellular mechanotransduction. 

Studies of cell-extracellular matrix (ECM) interactions within fibrous systems such as collagen or fibrin are challenging, particularly if peri-cellular stiffness cannot be monitored. Here we present our light-based method for non-invasive patterning of molecular crosslinking combined with multi-axes optical tweezers active microrheology to map ECM stiffness landscapes. This method allows us to generate prescribed stiffness gradients and associated anisotropies, which model stiffness of the natural peri-cellular ECM. Patterned crosslinking induces strain hardening and measured stiffness gradients are in agreement with predicted strain fields. Migratory cells respond to these gradients as assessed by change in F-actin distribution and morphological properties.