@article {55, title = {Swimming Euglena respond to confinement with a behavioural change enabling effective crawling}, journal = {Nature Physics}, volume = {15}, year = {2019}, pages = {496-502}, abstract = {

Some euglenids, a family of aquatic unicellular organisms, can develop highly concerted, large-amplitude peristaltic body deformations. This remarkable behaviour has been known for centuries. Yet, its function remains controversial, and is even viewed as a functionless ancestral vestige. Here, by examining swimming Euglena\ gracilis in environments of controlled crowding and geometry, we show that this behaviour is triggered by confinement. Under these conditions, it allows cells to switch from unviable flagellar swimming to a new and highly robust mode of fast crawling, which can deal with extreme geometric confinement and turn both frictional and hydraulic resistance into propulsive forces. To understand how a single cell can control such an adaptable and robust mode of locomotion, we developed a computational model of the motile apparatus of Euglena cells consisting of an active striated cell envelope. Our modelling shows that gait adaptability does not require specific mechanosensitive feedback but instead can be explained by the mechanical self-regulation of an elastic and extended motor system. Our study thus identifies a locomotory function and the operating principles of the adaptable peristaltic body deformation of Euglena cells.

}, keywords = {crawling motility, Euglena gracilis, Metaboly, Spatial confinement}, doi = {10.1038/s41567-019-0425-8}, author = {Noselli, Giovanni and Beran, Alfred and Arroyo, Marino and DeSimone, Antonio} } @article {39, title = {Liquid crystal elastomer strips as soft crawlers}, journal = {Journal of the Mechanics and Physics of Solids}, volume = {84}, year = {2015}, pages = {254-272}, abstract = {

In this paper, we speculate on a possible application of Liquid Crystal Elastomers to the field of soft robotics. In particular, we study a concept for limbless locomotion that is amenable to miniaturisation. For this purpose, we formulate and solve the evolution equations for a strip of nematic elastomer, subject to directional frictional interactions with a flat solid substrate, and cyclically actuated by a spatially uniform, time-periodic stimulus (e.g., temperature change). The presence of frictional forces that are sensitive to the direction of sliding transforms reciprocal, {\textquoteleft}breathing-like{\textquoteright} deformations into directed forward motion. We derive formulas quantifying this motion in the case of distributed friction, by solving a differential inclusion for the displacement field. The simpler case of concentrated frictional interactions at the two ends of the strip is also solved, in order to provide a benchmark to compare the continuously distributed case with a finite-dimensional benchmark. We also provide explicit formulas for the axial force along the crawler body.

}, keywords = {crawling motility, directional surfaces, frictional interactions, liquid crystal elastomers, soft biomimetic robots}, doi = {10.1016/j.jmps.2015.07.017}, author = {Antonio DeSimone and Paolo Gidoni and Giovanni Noselli} } @article {36, title = {Crawling on directional surfaces}, journal = {International Journal of Non-Linear Mechanics}, volume = {61}, year = {2014}, pages = {65-73}, abstract = {

In this paper we study crawling locomotion based on directional frictional interactions, namely, frictional forces that are sensitive to the sign of the sliding velocity. Surface interactions of this type are common in biology, where they arise from the presence of inclined hairs or scales at the crawler/substrate interface, leading to low resistance when sliding {\textquoteleft}along the grain{\textquoteright}, and high resistance when sliding {\textquoteleft}against the grain{\textquoteright}. This asymmetry can be exploited for locomotion, in a way analogous to what is done in cross-country skiing (classic style, diagonal stride). We focus on a model system, namely, a continuous one-dimensional crawler and provide a detailed study of the motion resulting from several strategies of shape change. In particular, we provide explicit formulae for the displacements attainable with reciprocal extensions and contractions (breathing), or through the propagation of extension or contraction waves. We believe that our results will prove particularly helpful for the study of biological crawling motility and for the design of bio-mimetic crawling robots.

}, keywords = {bio-mimetic micro-robots, cell migration, crawling motility, directional surfaces, self-propulsion}, doi = {10.1016/j.ijnonlinmec.2014.01.012}, author = {Paolo Gidoni and Giovanni Noselli and Antonio DeSimone} } @article {35, title = {Discrete one-dimensional crawlers on viscous substrates: achievable net displacements and their energy cost}, journal = {Mechanics Research Communications}, volume = {58}, year = {2014}, pages = {73{\textendash}81}, abstract = {

We study model one-dimensional crawlers, namely, model mechanical systems that can achieve self-propulsion by controlled shape changes of their body (extension or contraction of portions of the body), thanks to frictional interactions with a rigid substrate. We evaluate the achievable net displacement and the related energetic cost for self-propulsion by discrete crawlers (i.e., whose body is made of a discrete number of contractile or extensile segments) moving on substrates with either a Newtonian (linear) or a Bingham-type (stick-slip) rheology. Our analysis is aimed at constructing the basic building blocks towards an integrative, multi-scale description of crawling cell motility.

}, keywords = {cell migration, cell motility, crawling motility, limbless locomotion, motility on a solid substrate, self-propulsion, soft biomimetic robots}, doi = {10.1016/j.mechrescom.2013.10.023}, author = {Giovanni Noselli and Amabile Tatone and Antonio DeSimone} } @article {38, title = {A robotic crawler exploiting directional frictional interactions: Experiments, numerics and derivation of a reduced model}, journal = {Proceedings of the Royal Society A}, volume = {470}, year = {2014}, pages = {20140333}, abstract = {

We present experimental and numerical results for a model crawler which is able to extract net positional changes from reciprocal shape changes, i.e. {\textquoteleft}breathing-like{\textquoteright} deformations, thanks to directional, frictional interactions with a textured solid substrate, mediated by flexible inclined feet. We also present a simple reduced model that captures the essential features of the kinematics and energetics of the gait, and compare its predictions with the results from experiments and from numerical simulations.

}, keywords = {breathing-like deformations, crawling motility, directional interactions, directional surfaces, scallop theorem}, doi = {10.1098/rspa.2014.0333}, author = {Giovanni Noselli and Antonio DeSimone} } @article {30, title = {Crawlers in viscous environments: linear vs. nonlinear rheologies}, journal = {International Journal of Non-Linear Mechanics}, volume = {56}, year = {2013}, pages = {142-147}, abstract = {

We study model self-propelled crawlers which derive their propulsive capabilities from the tangential resistance to motion offered by the environment. Two types of relationships between tangential force and slip velocity are considered: a linear, Newtonian one and a nonlinear one of Bingham-type. Different behaviors result from the two different rheologies. These differences and their implications in terms of motility performance are discussed. Our aim is to develop new tools and insight for future studies of cell motility by crawling.

}, keywords = {cell migration, cell motility, crawling motility, motility on a solid substrate, self-propulsion, soft biomimetic robots}, doi = {10.1016/j.ijnonlinmec.2013.02.007}, author = {Antonio DeSimone and Federica Guarnieri and Giovanni Noselli and Amabile Tatone} }