Local response and emerging nonlinear elastic length scale in biopolymer matrices

Area of Science:

• Biophysics
• Materials Science
• Cell Biology

Background:

• Nonlinear stiffening is a key property of biopolymers in the extracellular matrix (ECM).
• Cells like fibroblasts and cancer cells exert forces on the ECM, causing local stiffening.
• This cellular force generation is often modeled as monopole forces due to their spindle-like shape.

Purpose of the Study:

• To investigate the nonlinear force-displacement response of the ECM to localized monopole forces.
• To develop a theoretical framework explaining how localized forces induce matrix stiffening.
• To observe and characterize the emergent nonlinear length scale around living cells.

Main Methods:

• Utilizing optical tweezers to apply and measure localized monopole forces on ECM components.
• Developing an effective-probe scaling argument to model the force-induced stiffening.
• Observing the nonlinear length scale around living cells and perturbing it by altering matrix concentration or cell contractility.

Main Results:

• Demonstrated a nonlinear force-displacement response to localized monopole forces.
• Proposed that a nonlinear length scale (R*) characterizes the stiffened region, increasing with force magnitude.
• Showcased the observation of this nonlinear length scale around living cells, which is sensitive to matrix properties and cell contractility.

Conclusions:

• Localized cellular forces lead to nonlinear stiffening of the extracellular matrix.
• An emergent nonlinear length scale (R*) quantifies this stiffening effect.
• This phenomenon is observable in vivo and can be modulated by the cellular and matrix environment.