CFM: Confinement Force Microscopy-a dynamic, precise and stable microconfiner for traction force microscopy in spatial confinement

Using this system, we identify two distinct mechanical responses to single-step confinement: an immediate, short-term stress spike that likely reflects a passive response from nuclear compression against the gel, and a slower, long-term active response involving actomyosin contraction and cellular adaptation.

The short-term response scales with confinement severity, while the long-term adaptation drives internal pressure buildup, bleb formation, and sustained force generation. We further show that myosin II inhibition suppress the active stress buildup and attenuate the passive, short-term stress jump by markedly lowering the instantaneous elastic modulus and reducing effective viscosity, thereby weakening load transmission at the step.