Meeting Abstract
Circumnutation, a cyclic endogenous circular pattern exhibited by the tip of a growing root, occurs in a diversity of plants, but its function is not fully understood. A previous study observed that rice roots with circumnutating root tips had a higher probability of finding holes that were uniformly distributed on a horizontal plate than mutant roots that grew without circumnutating (Lehner et al. BioArxiv CITE). To investigate the hypotheses that nutation facilitates substrate penetration and exploration, we built a planar soft robot [Hawkes et al. 2017], which grows from the tip like a plant root and can bend in 2D space by oscillating inflation of the series pneumatic artificial muscles (sPAMs) arranged on the two sides. We studied how tip oscillation affected penetration in a heterogeneous environment, a lattice of rough cylinders (d=8cm) distributed uniformly in a bounded free space (120X120cm2). Systematic variation of initial robot starting positions horizontally across the lattice revealed that the non-oscillating tip strategy led to a high probability of becoming pinned to obstacles; the robot was unable to grow more than an average depth of 23.8±19.7cm . The oscillating tip penetrated the lattice significantly further on average, 55.2±24.9cm , typically via discovery of “corridors” in the lattice. Even in randomized lattices, the nutation facilitated sustained growth. The results from the robotic root model suggest that oscillatory movement of a growing structure increases its exploratory capabilities in a heterogeneous environment.
