Slender fibers amplify local stiffness anisotropy tenfold in stretched fibrous gels.

Cells live inside a mesh of fibers called the extracellular matrix. These fiber networks get stiffer when stretched because the fibers switch from bending to stretching. While scientists often test the whole material at once, cells actually feel tiny, local differences in their surroundings. In this study, researchers investigated how pulling on a fiber network changes stiffness in specific directions at the microscale. They stretched fibrin gels in one direction and measured local stiffness using laser-based optical tweezers. Pulling the gels made them stiffer in both directions, but the stiffness rose much more along the stretch direction, creating direction-dependent stiffness called anisotropyanisotropyWhen the properties of a material (like stiffness) are different depending on the direction you measure, like wood that splits easier along the grain.. Using computer models of fiber networks, they discovered that thinner fibers and more connected networks boost this directional stiffness difference by up to an order of magnitude. These local forces can guide how cells move, and they act differently from the overall material.

Why it matters

This matters because cells sense the stiffness of their surroundings to decide where to move. In tissues, the extracellular matrix is a fibrous network that stiffens when stretched, but until now it was unclear how that stiffening varies at the scale of a single cell. The findings show that local stiffness anisotropy can be tuned by fiber thickness and connectivity, which could explain how cells migrate along stiffness gradients and help design better scaffolds for tissue repair.

Questions answered