@article {cicconofri_2023, title = {Nonreciprocal oscillations of polyelectrolyte gel filaments subject to a steady and uniform electric field}, journal = {Journal of the Mechanics and Physics of Solids}, volume = {173}, year = {2023}, pages = {105225}, abstract = {Soft actuators typically require time-varying or spatially modulated control to be operationally effective. The scope of the present paper is to show, theoretically and experimentally, that a natural way to overcome this limitation is to exploit mechanical instabilities. We report experiments on active filaments of polyelectrolyte (PE) gels subject to a steady and uniform electric field. A large enough intensity of the field initiates the motion of the active filaments, leading to periodic oscillations. We develop a mathematical model based on morphoelasticity theory for PE gel filaments beating in a viscous fluid, and carry out the stability analysis of the governing equations to show the emergence of flutter and divergence instabilities for suitable values of the system{\textquoteright}s parameters. We confirm the results of the stability analysis with numerical simulations for the nonlinear equations of motion to show that such instabilities may lead to periodic self-sustained oscillations, in agreement with experiments. The key mechanism that underlies such behaviour is the capability of the filament to undergo active shape changes depending on its local orientation relative to the external electric field, in striking similarity with gravitropism, the mechanism that drives shape changes in plants via differential growth induced by gravity. Interestingly, the resulting oscillations are nonreciprocal in nature, and hence able to generate thrust and directed flow at low Reynolds number. The exploitation of mechanical instabilities in soft actuators represents a new avenue for the advancement in engineering design in fields such as micro-robotics and micro-fluidics.}, doi = {10.1016/j.jmps.2023.105225}, url = {https://www.sciencedirect.com/science/article/pii/S0022509623000297}, author = {Giancarlo Cicconofri and Valentina Damioli and Giovanni Noselli} } @article {rossi13085, title = {Kinematics of flagellar swimming in Euglena gracilis: Helical trajectories and flagellar shapes}, journal = {Proceedings of the National Academy of Sciences}, volume = {114}, number = {50}, year = {2017}, pages = {13085-13090}, abstract = {Active flagella provide the propulsion mechanism for a large variety of swimming eukaryotic microorganisms, from protists to sperm cells. Planar and helical beating patterns of these structures are recurrent and widely studied. The fast spinning motion of the locomotory flagellum of the alga Euglena gracilis constitutes a remarkable exception to these patterns. We report a quantitative description of the 3D flagellar beating in swimming E. gracilis. Given their complexity, these shapes cannot be directly imaged with current microscopy techniques. We show how to overcome these limitations by developing a method to reconstruct in full the 3D kinematics of the cell from conventional 2D microscopy images, based on the exact characterization of the helical motion of the cell body.The flagellar swimming of euglenids, which are propelled by a single anterior flagellum, is characterized by a generalized helical motion. The 3D nature of this swimming motion, which lacks some of the symmetries enjoyed by more common model systems, and the complex flagellar beating shapes that power it make its quantitative description challenging. In this work, we provide a quantitative, 3D, highly resolved reconstruction of the swimming trajectories and flagellar shapes of specimens of Euglena gracilis. We achieved this task by using high-speed 2D image recordings taken with a conventional inverted microscope combined with a precise characterization of the helical motion of the cell body to lift the 2D data to 3D trajectories. The propulsion mechanism is discussed. Our results constitute a basis for future biophysical research on a relatively unexplored type of eukaryotic flagellar movement.}, doi = {10.1073/pnas.1708064114}, url = {https://www.pnas.org/content/114/50/13085}, author = {Massimiliano Rossi and Giancarlo Cicconofri and Alfred Beran and Giovanni Noselli and Antonio DeSimone} } @article {Cicconofri2016, title = {Motion planning and motility maps for flagellar microswimmers}, journal = {The European Physical Journal E}, volume = {39}, number = {7}, year = {2016}, month = {Jul}, pages = {72}, abstract = {

We study two microswimmers consisting of a spherical rigid head and a passive elastic tail. In the first one the tail is clamped to the head, and the system oscillates under the action of an external torque. In the second one, head and tail are connected by a joint allowing the angle between them to vary periodically, as a result of an oscillating internal torque. Previous studies on these models were restricted to sinusoidal actuations, showing that the swimmers can propel while moving on average along a straight line, in the direction given by the symmetry axis around which beating takes place. We extend these results to motions produced by generic (non-sinusoidal) periodic actuations within the regime of small compliance of the tail. We find that modulation in the velocity of actuation can provide a mechanism to select different directions of motion. With velocity-modulated inputs, the externally actuated swimmer can translate laterally with respect to the symmetry axis of beating, while the internally actuated one is able to move along curved trajectories. The governing equations are analysed with an asymptotic perturbation scheme, providing explicit formulas, whose results are expressed through motility maps. Asymptotic approximations are further validated by numerical simulations.

}, issn = {1292-895X}, doi = {10.1140/epje/i2016-16072-y}, url = {https://doi.org/10.1140/epje/i2016-16072-y}, author = {Giancarlo Cicconofri and Antonio DeSimone} } @mastersthesis {2015, title = {Mathematical Models of Locomotion: Legged Crawling, Snake-like Motility, and Flagellar Swimming}, year = {2015}, school = {SISSA}, keywords = {Motility}, author = {Giancarlo Cicconofri} } @article {CICCONOFRI2015233, title = {Motility of a model bristle-bot: A theoretical analysis}, journal = {International Journal of Non-Linear Mechanics}, volume = {76}, year = {2015}, pages = {233 - 239}, abstract = {

Bristle-bots are legged robots that can be easily made out of a toothbrush head and a small vibrating engine. Despite their simple appearance, the mechanism enabling them to propel themselves by exploiting friction with the substrate is far from trivial. Numerical experiments on a model bristle-bot have been able to reproduce such a mechanism revealing, in addition, the ability to switch direction of motion by varying the vibration frequency. This paper provides a detailed account of these phenomena through a fully analytical treatment of the model. The equations of motion are solved through an expansion in terms of a properly chosen small parameter. The convergence of the expansion is rigorously proven. In addition, the analysis delivers formulas for the average velocity of the robot and for the frequency at which the direction switch takes place. A quantitative description of the mechanism for the friction modulation underlying the motility of the bristle-bot is also provided.

}, keywords = {Bristle-robots, Crawling motility, Frictional interactions}, issn = {0020-7462}, doi = {https://doi.org/10.1016/j.ijnonlinmec.2014.12.010}, url = {http://www.sciencedirect.com/science/article/pii/S0020746215000025}, author = {Giancarlo Cicconofri and Antonio DeSimone} } @article {doi:10.1098/rspa.2015.0054, title = {A study of snake-like locomotion through the analysis of a flexible robot model}, journal = {Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences}, volume = {471}, number = {2184}, year = {2015}, pages = {20150054}, abstract = {

We examine the problem of snake-like locomotion by studying a system consisting of a planar inextensible elastic rod with adjustable spontaneous curvature, which provides an internal actuation mechanism that mimics muscular action in a snake. Using a Cosserat model, we derive the equations of motion in two special cases: one in which the rod can only move along a prescribed curve, and one in which the rod is constrained to slide longitudinally without slipping laterally, but the path is not fixed a priori (free-path case). The second setting is inspired by undulatory locomotion of snakes on flat surfaces. The presence of constraints leads in both cases to non-standard boundary conditions that allow us to close and solve the equations of motion. The kinematics and dynamics of the system can be recovered from a one-dimensional equation, without any restrictive assumption on the followed trajectory or the actuation. We derive explicit formulae highlighting the role of spontaneous curvature in providing the driving force (and the steering, in the free-path case) needed for locomotion. We also provide analytical solutions for a special class of serpentine motions, which enable us to discuss the connection between observed trajectories, internal actuation and forces exchanged with the environment.

}, doi = {10.1098/rspa.2015.0054}, url = {https://royalsocietypublishing.org/doi/abs/10.1098/rspa.2015.0054}, author = {Giancarlo Cicconofri and Antonio DeSimone} }