@article {54, title = {Smart helical structures inspired by the pellicle of euglenids}, journal = {Journal of the Mechanics and Physics of Solids}, volume = {123}, year = {2019}, pages = {234-246}, abstract = {

This paper deals with a concept for a reconfigurable structure bio-inspired by the cell wall architecture of euglenids, a family of unicellular protists, and based on the relative sliding of adjacent strips. Uniform sliding turns a cylinder resulting from the assembly of straight and parallel strips into a cylinder of smaller height and larger radius, in which the strips are deformed into a family of parallel helices. We examine the mechanics of this cylindrical assembly, in which the interlocking strips are allowed to slide freely at their junctions, and compute the external forces (axial force and axial torque at the two ends, or pressure on the lateral surface) necessary to drive and control the shape changes of the composite structure. Despite the simplicity of the structure, we find a remarkably complex mechanical behaviour that can be tuned by the spontaneous curvature or twist of the strips.\ 

}, keywords = {Bio-inspired structures, Euglenoid pellicle, Helical bundles, Morphing structures, Reconfigurable structures}, doi = {10.1016/j.jmps.2018.09.036}, author = {Noselli, Giovanni and Arroyo, Marino and DeSimone, Antonio} } @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 {51, title = {Spontaneous morphing of equibiaxially pre-stretched elastic bilayers: the role of sample geometry}, journal = {International Journal of Mechanical Sciences}, volume = {In press.}, year = {2017}, abstract = {

An elastic bilayer, consisting of an equibiaxially pre-stretched sheet bonded to a stress-free one, spontaneously morphs into curved shapes in the absence of external loads or constraints. Using experiments and numerical simulations, we explore the role of geometry for square and rectangular samples in determining the equilibrium shape of the system, for a fixed pre-stretch. We classify the observed shapes over a wide range of aspect ratios according to their curvatures and compare measured and computed values, which show good agreement. In particular, as the bilayer becomes thinner, a bifurcation of the principal curvatures occurs, which separates two scaling regimes for the energy of the system. We characterize the transition between these two regimes and show the peculiar features that distinguish square from rectangular samples. The results for our model bilayer system may help explaining morphing in more complex systems made of active materials.\ 

}, keywords = {Bifurcation, Elastic bilayer, Pre-stretch, Shape programming}, doi = {10.1016/j.ijmecsci.2017.08.049}, author = {No{\`e} Caruso and Aleksandar Cvetkovi{\'c} and Alessandro Lucantonio and Giovanni Noselli and Antonio DeSimone} }