@article {71, title = {Breaking the left-right symmetry in fluttering artificial cilia that perform nonreciprocal oscillations}, journal = {Meccanica}, volume = {In press}, year = {2024}, abstract = {

Recent investigations on active materi- als have introduced a new paradigm for soft robotics by showing that a complex response can be obtained from simple stimuli by harnessing dynamic instabili- ties. In particular, polyelectrolyte hydrogel filaments actuated by a constant electric field have been shown to exhibit self-sustained oscillations as a consequence of flutter instability. Owing to the nonreciprocal nature of the emerging oscillations, these\ artificial cilia\ are able to generate flows along the stimulus. Building upon these findings, in this paper we pro- pose a design strategy to break the left-right symme- try in the generated flows, by endowing the filament with a natural curvature at the fabrication stage. We develop a mathematical model based on morphoe- lastic rod theory to characterize the stability of the equilibrium configurations of the filament, proving the persistence of flutter instability. We show that the emerging oscillations are nonreciprocal and gener- ate thrust at an angle with the stimulus. The results we find at the level of the single cilium open new\ perspectives on the possible applications of artificial ciliary arrays in soft robotics and microfluidics.\ 

}, keywords = {Active matter, Artificial cilia, Flutter instability, left-right symmetry breaking, soft-robotics}, doi = {10.1007/s11012-024-01765-7}, author = {Ariel S. Boiardi and Roberto Marchello} } @article {65, title = {The biomechanical role of extra-axonemal structures in shaping the flagellar beat of Euglena gracilis}, journal = {eLife}, volume = {10:e58610}, year = {2021}, abstract = {

We propose and discuss a model for flagellar mechanics in Euglena gracilis. We show that the peculiar non-planar shapes of its beating flagellum, dubbed {\textquoteright}spinning lasso{\textquoteright}, arise from the mechanical interactions between two of its inner components, namely, the axoneme and the paraflagellar rod. The spontaneous shape of the axoneme and the resting shape of the paraflagellar rod are incompatible. Thus, the complex non-planar configurations of the coupled system emerge as the energetically optimal compromise between the two antagonistic components. The model is able to reproduce the experimentally observed flagellar beats and the characteristic geometric signature of spinning lasso, namely, traveling waves of torsion with alternating sign along the length of the flagellum.\ 

}, keywords = {Euglena gracilis, extra-axonemal structures, flagellar beat, flagellar mechanics, physics of living systems}, doi = {10.7554/eLife.58610}, author = {Giancarlo Cicconofri and Giovanni Noselli and Antonio De Simone} } @article {32, title = {Behavioral study of whisker-mediated vibration sensation in rats}, journal = {Proceedings of the National Academy of Sciences of USA}, volume = {109}, year = {2012}, pages = {971{\textendash}976}, abstract = {

Rats use their vibrissal sensory system to collect information about the nearby environment. They can accurately and rapidly identify object location, shape, and surface texture. Which features of whisker motion does the sensory system extract to construct sensations? We addressed this question by training rats to make discriminations between sinusoidal vibrations simultaneously presented to the left and right whiskers. One set of rats learned to reliably identify which of two vibrations had higher frequency (f1 vs. f2) when amplitudes were equal. Another set of rats learned to reliably identify which of two vibrations had higher amplitude (A1 vs. A2) when frequencies were equal. Although these results indicate that both elemental features contribute to the rats{\textquoteright} sensation, a further test found that the capacity to discriminate A and f was reduced to chance when the difference in one feature was counterbalanced by the difference in the other feature: Rats could not discriminate amplitude or frequency whenever A1f1 = A2f2. Thus, vibrations were sensed as the product Af rather than as separable elemental features, A and f. The product Af is proportional to a physical entity, the mean speed. Analysis of performance revealed that rats extracted more information about differences in Af than predicted by the sum of the information in elemental differences. These behavioral experiments support the predictions of earlier physiological studies by demonstrating that rats are {\textquotedblleft}blind{\textquotedblright} to the elemental features present in a sinusoidal whisker vibration; instead, they perceive a composite feature, the speed of whisker motion.

}, keywords = {barrel cortex, coding}, doi = {10.1073/pnas.1116726109}, author = {Mehdi Adibi and Mathew E. Diamond and Ehsan Arabzadeh} }