Mechanical interactions of growing roots with their environment

Plant roots are considered the most efficient soil explorers among living organisms. As opposed to the penetration strategy of other organisms, which is based on pushing through soil, roots penetrate by growing, adding new cells at the tip, and elongating over a well-defined growth zone. This growth-based strategy provides anchorage and minimal lateral friction and has recently inspired design of self-growing robot. Currently, however, the mechanics underlying growth-driven penetration into a medium and the mechanical interaction between roots and their environment are not well understood. Here, we perform experiments of Arabidopsis Thaliana roots growing into agar gel environment and measure the displacements and stresses generated in the gel as the root grows forward by traction force microscopy. To gain insights into the mechanical mechanism of growing versus pushing into medium, we develop a computational finite element model that is based on the geometrical and mechanical characteristics of the experimental system. We validate our model against a needle experiment that is pushed in the medium. Our findings provide better understanding of the mechanical principles of root growth and pave the way for a new generation of root-inspired growing robots with efficient penetrations and searching capabilities.