Plant root growth can be altered by introducing obstacles in the path of growth. This principle is used in design to produce planar grid structures composed of interweaving roots. The Engineered Plant Root Materials (EPRMs) grown with this method have the potential to serve as environmentally sensitive alternatives for conventional materials, but their applications are delimited by their material properties. To bridge the gap in the wider application of these materials, the role of plant root structure and an agar-agar matrix are explored in relation to the mechanical properties of the EPRMs. Tensile tests were performed on five root configurations, ranging from single roots to grids of varying sizes. Heterogeneities in each configuration suggest poor load distribution throughout the structure. Agar-agar was introduced as a biopolymer matrix to improve load distribution and tensile properties. Digital microscopy at the intersection of grid cells suggests a correlation between cell size, root tip density, and material strength. The largest cell size (2 cm) had the highest root tip density and yield strength (0.568 ± 0.181 roots/mm² and 0.234 ± 0.018 MPa, respectively), whereas the structure with the least root tips (1 cm) was 31 % weaker.

Technological and economic opportunities, alongside the apparent ecological benefits, point to biodesign as a new industrial paradigm for the fabrication of products in the twenty-first century. The presented work studies plant roots as a biodesign material in the fabrication of self-supported 3D structures, where the biologically and digitally designed materials provide each other with structural stability. Taking a material-driven design approach, we present our systematic tinkering activities with plant roots to better understand and anticipate their responsive behaviour. These helped us to identify the key design parameters and advance the unique potential of plant roots to bind discrete porous structures. We illustrate this binding potential of plant roots with a hybrid 3D object, for which plant roots connect 600 computationally designed, optimized, and fabricated bioplastic beads into a low stool.