Soft and Active Solids

An active material is broadly defined as a material that dynamically respond to external stimuli. Examples include biological material, like growing membranes and tissues, and artificially engineered structures, incluinding swelling gels or interacting robots.

The overarching question to address is what is the emerging, global, behaviour, induced by local rules that control the activity? A natural connected question refer to how the properties at different length-scales interact to define the continuum description in those systems?

In this project we focus on active solids where the activity is embedded, using a phenomenological continuum description, via either a non-mechanical stimuli that introduce a competition with mechanical responses or by using odd elastic constitutive relationship. We also study how shapes induced by instabilites emerge.

In a recent preprint (Taffetani & Pezzulla, 2025) we derived a fully non-linear model of stimuli responsive naturally curved shell to be used in the description of budding and vesiculation of solid-like shell. are currently study odd elastic plates and and limb fromation in growing domains.

Many interesting shapes appearing in the biological world or in artificial devices emerge from mechanical instability. Compressive strains are the most common cause of instabilities, as in residually stressed or indendented pressurized shells. Beads-on-string patterns experimentally observed in solid cylinders for a wide range of material properties and structural lengths, instead, seems to emerge under a state of tension: we have first explored this problem via the competition between bulk elasticity and surface tension, i.e. elastocapillarity; more recently, we accounted for the bending resistance of the surface by introducing a bending modulus and an incompatible mean curvature. This leads to a novel elastobendo mode of beading that gives rise to finite-wavelength patterns with spatially localized modulations in amplitude that have not been seen in this system before and we show how elastobendo beading can provide a new interpretation of the infinite-wavelength instability seen in the elastocapillary version of this problem.