TY - JOUR T1 - Nutations in growing plant shoots as a morphoelastic flutter instability JF - Phil. Trans. R. Soc. A Y1 - 2021 A1 - Daniele Agostinelli A1 - Giovanni Noselli A1 - Antonio DeSimone AB -

Growing plant shoots exhibit spontaneous oscillations that Darwin observed, and termed "circumnutations". Recently, they have received renewed attention for the design and optimal actuation of bioinspired robotic devices. We discuss a possible interpretation of these spontaneous oscillations as a Hopf-type bifurcation in a growing morphoelastic rod. Using a three-dimensional model and numerical simulations, we analyse the salient features of this flutter-like phenomenon (e.g. the characteristic period of the oscillations) and their dependence on the model details (in particular, the impact of choosing different growth models) finding that, overall, these features are robust with respect to changes in the details of the growth model adopted.

VL - 379 UR - https://doi.org/10.1098/rsta.2020.0116 ER - TY - JOUR T1 - Nutations in plant shoots: Endogenous and exogenous factors in the presence of mechanical deformations JF - Frontiers in Plant Science Y1 - 2021 A1 - Daniele Agostinelli A1 - Antonio DeSimone A1 - Giovanni Noselli AB -

We present a three-dimensional morphoelastic rod model capable to describe the morphogenesis of growing plant shoots driven by differential growth. We discuss the evolution laws for endogenous oscillators, straightening mechanisms, and reorientations to directional cues, such as gravitropic reactions governed by the avalanche dynamics of statoliths. We use this model to investigate the role of elastic deflections due to gravity loading in circumnutating plant shoots. We show that, in the absence of endogenous cues, pendular and circular oscillations arise as a critical length is attained, thus suggesting the occurrence of an instability triggered by exogenous factors. When also oscillations due to endogenous cues are present, their weight relative to those associated with the instability varies in time as the shoot length and other biomechanical properties change. Thanks to the simultaneous occurrence of these two oscillatory mechanisms, we are able to reproduce a variety of complex behaviors, including trochoid-like patterns, which evolve into circular orbits as the shoot length increases, and the amplitude of the exogenous oscillations becomes dominant.

PB - Cold Spring Harbor Laboratory VL - 12 UR - https://www.frontiersin.org/article/10.3389/fpls.2021.608005 ER - TY - JOUR T1 - MicroMotility: State of the art, recent accomplishments and perspectives on the mathematical modeling of bio-motility at microscopic scales JF - Mathematics in Engineering Y1 - 2020 A1 - Daniele Agostinelli A1 - Roberto Cerbino A1 - Del Alamo, Juan C A1 - Antonio DeSimone A1 - Stephanie Höhn A1 - Cristian Micheletti A1 - Giovanni Noselli A1 - Eran Sharon A1 - Julia Yeomans KW - active matter KW - adhesive locomotion KW - cell motility KW - cell sheet folding KW - knotted DNA KW - topological defects KW - unicellular swimmers KW - unjamming transition AB -

Mathematical modeling and quantitative study of biological motility (in particular, of motility at microscopic scales) is producing new biophysical insight and is offering opportunities for new discoveries at the level of both fundamental science and technology. These range from the explanation of how complex behavior at the level of a single organism emerges from body architecture, to the understanding of collective phenomena in groups of organisms and tissues, and of how these forms of swarm intelligence can be controlled and harnessed in engineering applications, to the elucidation of processes of fundamental biological relevance at the cellular and sub-cellular level. In this paper, some of the most exciting new developments in the fields of locomotion of unicellular organisms, of soft adhesive locomotion across scales, of the study of pore translocation properties of knotted DNA, of the development of synthetic active solid sheets, of the mechanics of the unjamming transition in dense cell collectives, of the mechanics of cell sheet folding in volvocalean algae, and of the self-propulsion of topological defects in active matter are discussed. For each of these topics, we provide a brief state of the art, an example of recent achievements, and some directions for future research.

VL - 2 UR - http://dx.doi.org/10.3934/mine.2020011 ER - TY - JOUR T1 - Nutations in growing plant shoots: The role of elastic deformations due to gravity loading JF - Journal of the Mechanics and Physics of Solids Y1 - 2019 A1 - Daniele Agostinelli A1 - Alessandro Lucantonio A1 - Giovanni Noselli A1 - Antonio DeSimone KW - Circumnutations KW - Flutter instability KW - Gravitropism KW - Hopf bifurcation AB -

The effect of elastic deformations induced by gravity loading on the active circumnutation movements of growing plant shoots is investigated. We consider first a discrete model (a gravitropic spring-pendulum system) and then a continuous rod model which is analyzed both analytically (under the assumption of small deformations) and numerically (in the large deformation regime). We find that, for a choice of material parameters consistent with values reported in the available literature on plant shoots, rods of sufficient length may exhibit lateral oscillations of increasing amplitude, which eventually converge to limit cycles. This behavior strongly suggests the occurrence of a Hopf bifurcation, just as for the gravitropic spring-pendulum system, for which this result is rigorously established. At least in this restricted set of material parameters, our analysis supports a view of Darwin’s circumnutations as a biological analogue to structural systems exhibiting flutter instabilities, i.e., spontaneous oscillations away from equilibrium configurations driven by non-conservative loads. Here, in the context of nutation movements of growing plant shoots, the energy needed to sustain oscillations is continuously supplied to the system by the internal biochemical machinery presiding the capability of plants to maintain a vertical pose.

UR - https://doi.org/10.1016/j.jmps.2019.103702 ER - TY - JOUR T1 - Peristaltic Waves as Optimal Gaits in Metameric Bio-Inspired Robots JF - Frontiers in Robotics and AI Y1 - 2018 A1 - Daniele Agostinelli A1 - François Alouges A1 - Antonio DeSimone KW - Biomimetic robots KW - Crawling motility KW - Lumbricus terrestris KW - Metameric robots KW - Optimization KW - Peristalsis KW - Self-propulsion KW - Soft robotics AB -

Peristalsis, i.e., a motion pattern arising from the propagation of muscle contraction and expansion waves along the body, is a common locomotion strategy for limbless animals. Mimicking peristalsis in bio-inspired robots has attracted considerable attention in the literature. It has recently been observed that maximal velocity in a metameric earthworm-like robot is achieved by actuating the segments using a “phase coordination” principle. This paper shows that, in fact, peristalsis (which requires not only phase coordination, but also that all segments oscillate at same frequency and amplitude) emerges from optimization principles. More precisely, basing our analysis on the assumption of small deformations, we show that peristaltic waves provide the optimal actuation solution in the ideal case of a periodic infinite system, and that this is approximately true, modulo edge effects, for the real, finite length system. Therefore, this paper confirms the effectiveness of mimicking peristalsis in bio-inspired robots, at least in the small-deformation regime. Further research will be required to test the effectiveness of this strategy if large deformations are allowed.

VL - 5 UR - https://doi.org/10.3389/frobt.2018.00099 ER -