Soft machines and the mechanics of growing helical strips

Many natural structures are made of soft tissue that undergoes complicated shape transformations as a result of the distribution of local active deformation of its "elements". Currently, the ability of mimicking this shaping mode in manmade structures is poor.

I will present some results of our study of actively deforming thin sheets.

We formulated a covariant elastic theory from which we derive an approximate 2D plate/shell theory for sheets with intrinsic incompatible metric and curvature tensors. With this theory we study selected cases of special interest.

Experimentally, we use environmentally responsive gel sheets that adopt prescribed metrics upon induction by environmental conditions. With this system we study the shaping mechanism in different cases of imposed metrics and curvature.

I will focus on different mechanisms that form helical ribbons and will show how the mechanism of seed pod opening is related to shape selection in self assembled chiral macromolecules.