Mechanics of Fibrous Materials
Many biological materials are made of microscopic fibers that have small thickness compared to length. The mechanical behavior of fibrous materials is complicated, because it results from the collective action of the fibers, each of which can bend, stretch, and buckle in response to applied forces. We quantify the mechanics of fibrous materials at length scales ranging from the microscale of a fiber to the macroscale of the bulk material. Applications of this work are in understanding how cells sense and respond to their environment and in developing new materials having desirable properties such as low weight and resistance to fracture.
Imaging Fiber Alignment and Buckling During Loading
The mechanics of fibrous materials result from deformations of each fiber, but it is challenging to quantify the mechanics while simultaneously imaging the fibers. We have developed experimental methods to apply localized deformations to fibrous materials while simultaneously imaging the fibers to observe fiber alignment and buckling. Our method has provided important insights into the sources of nonlinearity and heterogeneity within fibrous materials.
Force Chains in Fibrous Materials
It is thought that tissue formation and progression of disease requires cells to reliably transmit forces over space, but the random structure of the fibrous materials in which the cells reside makes force transmission difficult to predict. We have studied how force transmission depends on the network structure and established that localized paths of force transmission, called force chains, are an important factor in nonlinear strain stiffening.
Strain Localization
For over a century, biologists have been interested in highly localized deformations in fibrous materials wherein the fibers align and become locally denser. These deformations result from forces produced by cells to the surrounding fibers and are thought to be important in tissue formation and cell migration. Using experiments that observe the fiber densification and quantify the local strain fields, we have shown that buckling of fibers is an important factor causing fiber densification and alignment.
Physics of Collective Cell Migration
We are studying the physics of collective migration, focusing on the relationship between cell forces and motion. In particular, we are interested in what factors lead to production of cell forces in space and time and how cell forces are transmitted to the cell’s neighbors and the surrounding environment. We experimentally measure both forces and motion, and we frequently compare our experiments to predictions from physics-based models.
Force and Motion in Model Systems for Wound Healing
During wound healing, cells must migrate collectively to cover the wound area. We mimic this collective cell migration process in the lab using experiments like the one in the movie below, showing expansion of a cell collective along with the cell-substrate and cell-cell forces.
Multicellular Coordination of Motion
Shown in the movie is a sheet of cells moving collectively. The arrows indicate the cell velocities, and the colors indicate the direction. Clusters of cells can be seen with arrows of the same color, indicating groups of cells that move together within the larger collective. We are interested in how cells communicate with their neighbors to produce these collective groups and how the size of the collective groups affects wound healing and essential processes in tissue development.
Cell Alignment and Topological Defects
Some epithelial cell types are elongated rather than circular. To cover all available space, the cells must align with their neighbors. Flaws in the alignment are called topological defects. It is not yet clear how alignment and defects affect the stress state within the cell layer. We are experimentally measuring the stresses along with the cell motion, which gives valuable data for comparison to physics-based models that predict how the alignment and defects affect cell migration.
