Modeling Tools for Soft Robotics

"Muscle is the natural contractile system that artificial systems attempt to emulate.” [1]. This presentation is based on a paradigm: "living matter realizes motions at almost no stress". You can experiment by yourself by flexing your forearm: two large muscles, the biceps and the triceps, will change their shapes by a large amount, the shape-changes are not isotropic at all, but are isochoric—long, slender shapes transform into short, broad ones, and vice versa; more important, your forearm will not spring back to any preferred configuration, meaning that muscles are not storing any elastic energy whatsoever. Our goal is to put forward a theoretical framework to improve our ability to produce controlled motions of soft materials, by mimicking natural muscles. Most of our investigations originated as a question: is it possible to have very large, non-isotropic, shape-changes of a deformable body without varying its elastic energy? The answer is yes: soft matter exhibits noticeable morphological changes, which may arise as a consequence of many different ‘actuations’. Our involvement dates back to the seminal paper [2] that prompted us a thoroughly study of non-linear elasticity with large, evolving distortions. At first, we proposed the use of the notion of large distortions as a modeling tool for soft material [3]; since then, the same tool proved very useful in modeling apparently disparate phenomena such as muscle contractions, [4], director reorientations in nematic elastomers [5], phase transitions in nematic gels [6, 7], actuation of Ionic Polymer Metal Composites [8]. A distinctive attribute for all these phenomena is that large displacements are triggered by evolving distortions; moreover, it is possible to realize, through distortions, very large shape changes at no, or low, change of the elastic energy [9]. References [1] G. Pollack. Cells, Gels and the Engines of Life. Ebner & Sons, (2010). [2] A. DiCarlo, S. Quiligotti. Mechanics Research Communications 29, pp449–456 (2002). [3] P. Nardinocchi, L. Teresi. Journal of Elasticity, 88, pp27–39 (2007). [4] A. Evangelista, P. Nardinocchi, P.E. Puddu, L. Teresi, C. Torromeo, V. Varano. Progress in Biophysics and Molecular Biology, 107, pp.112–121 (2011). [5] A. DeSimone, A. DiCarlo, L. Teresi. European Physical Journal E, 24, pp.303–310 (2007). [6] Y. Sawa, K. Urayama, T. Takigawa, A. DeSimone, L. Teresi. Macromolecules 43, pp.4362–4369 (2010). [7] L. Teresi, V. Varano. Soft Matter, in press (2013). [8] P. Nardinocchi, M. Pezzulla, L. Placidi. Journal of Intelligent Material Systems and Structures, v.22/16, pp.1887–1897 (2011). [9] P. Nardinocchi, L. Teresi, V. Varano. J. Mechanics Physics of Solids, n.60, pp.1420- 1431 (2012).