Indentation mechanics of healthy and fibrotic murine lung reveals homogeneous surface stiffness

This study investigates how pulmonary fibrosis alters the microscale mechanical properties of lung tissue by performing high-resolution spherical indentation across multiple lobes in healthy and bleomycin-injured mice. Contrary to expectations that fibrotic remodeling would produce regionally heterogeneous stiffening, the findings reveal that surface stiffness remains remarkably homogeneous across the lung, even under pathologic ECM deposition. Finite element simulations and small-amplitude oscillatory indentation help decouple geometric contributions from intrinsic material behavior, showing that curvature, thickness, and inflation state strongly influence apparent stiffness. These results suggest that surface indentation alone may not capture the full mechanical consequences of fibrotic remodeling and highlight the need for depth-dependent and structural analyses when interpreting lung mechanics.