Soft Active Mechanics

This page gives a preview of the research on SOFT ACTIVE MECHANICS I am carrying on with a few co-workers. For more information, feel free to check the publications page and/or to contact me!

Swelling dynamics in polymer gels

Modeling solvent dynamics in polymers with solvent-filled cavities

Abstract. Dynamics of solvent release from polymer gels with small solvent-filled cavities is investigated starting from a thermodynamically consistent and enriched multi-physics stress-diffusion model. Indeed, the modeling also accounts for a new global volumetric constraint which makes the volume of the solvent in the cavity and the cavity volume equal at all times. This induces a characteristic suction effect into the model through a negative pressure acting on the cavity walls. The problem is solved for gel-based spherical microcapsules and microtubules. The implementation of the mathematical model into a finite element code allows to quantitatively describe and compare the dynamics of solvent release from full spheres, hollow spheres, and tubules in terms of a few key quantities such as stress states and amount of released solvent under the same external conditions.

M. Curatolo, P. Nardinocchi, L. Teresi. Mechanics of Soft Materials 2(13), 2020.

Other publications on the same topics can be found in the full list of publications; they spread over a period of ten years, involve many co-workers and deal with thermodynamically consistent stress-diffusion models, anisotropic swelling and actuation devices.

Fiber reorientation in soft materials

Researchers: J. Ciambella and P. Nardinocchi

We introduced a continuum model for fibre reinforced materials in which the reference orientation of the fibre field may evolve with time, under the influence of external stimuli. The model has been formulated in the framework of large strain hyper-elasticity and the kinematics of the continuum is described by both a position vector and by a remodelling tensor which, in the present context, is an orthogonal tensor representing the fibre reorientation process. Passive reorientation and magneto-driven fiber reorientation has been studied. In this last case, both the pre-curing and post-curing phases of a fiber-reinforced elastomer have been studied within the unifying framework compatible with nonlinear elasticity and growth theory. The coupling between elasticity and magnetic field has been obtained by considering a proper form of the free energy density which accounts for the mutual orientation between the magnetic field and the fibres. We are now going to study fiber reorientation within the context of large strain viscoelasticity.

Publications: Soft Matter 15, 2019; Int.J.Nonlin.Mech. 117, 2019; JMPS 147, 2021.

Swelling/shrinking-driven morphing of soft structures

Shape-shifting of polymer beams and shells due to oil extraction

Abstract. We investigate the morphing of bilayer naturally curved beams and cylindrical shells due to oil extraction from the outer layers. We fabricate bilayer naturally curved beams and cylindrical shells made of PDMS/(PDMS + silicone oil), use the experimental results to validate an explicit formula delivering the change in curvature of the beams, based on the modeling of oil extraction as a bulk contraction. We show as the same model, set up within a 3D context, delivers the morphing of bilayer cylindrical shells and identify potentially interesting results for designing future experiments. In particular, we show as stable states corresponding to the original cylindrical shells can be got in the form of saddle-like shells and cylindrical shells with the axes of principal curvatures switched with respect to the original axes.

D. Battista, V. Luchnikov, P. Nardinocchi. Extreme Mechanics Letters 36, 2020.

Other publications on the same topics can be found in the full list of publications; they spread over a period of six years, involve many co-workers and deal with soft beams, plates and shells.

Morphing of active gels

Researchers: M. Curatolo, P. Nardinocchi, L. Teresi

We presented a continuum multiphysics model of active polymer gels based on an enriched stress-diffusion model which also takes into account the active behaviour of the polymer network when molecular motors are included in the solvent bath. The latter is described as a remodeling of the polymer network, as the figure from (JMPS 2020) shows, represented by a remodeling tensor and occurs without any storage of elastic energy. As a consequence, the polymer volume-fraction changes because the free length of the polymer chains changes, even under chemical equilibrium conditions. We proposed a contraction-swelling diagram to highlight the chemo-mechanical states of the active gel at equilibrium and described the dynamics of contraction by a proper remodeling law. We observed a stiffening of the polymeric network and studied the effects of bulk contraction on solvent diffusion.

Publications: J.Mech.Phys.Solids 135, 2020; Int. J. Mech. Sci. 193, 2021.

Funded by Ministry of Foreign Affairs and International Cooperation for Italian-Israelian agreements, December 2020 - December 2022.

Myocardium is a worth example of soft active material. We studied the chemo-electro-mechanics of that tissue, focusing on spiral onset and spiral termination (figure from Cherubini et al., Prog. Biophys. Mol. Biol. 97, 2008). We assumed as basic the notion of contraction, a kinematic notion, opposite to that of active tension, stipulating that, when activated, a muscle suffers contraction, which in turn can yield a tension, in case a constraint hampers the motion. Contractions were described as active strains (see also P. Nardinocchi & L. Teresi, "On the active response of soft living tissue", J. Elasticity 88, 2007).
We also modelled cardiac muscle contractions in the framework of anisotropic finite elasticity with large distortions and coupled a mechanical model with reaction–diffusion equations representing electrophysiological activity. The tissue was assumed anisotropic from both the elastic and diffusive point of view, by using anisotropic constitutive relations to relates stresses and elastic strains as well as anisotropic diffusion tensors for both the membrane potential and calcium ions. Activation waves in a small patch of orthotropic tissue are shown in the figure (from Nardinocchi and Teresi, Math Mech Solids 18(6), 2013).
Research on heart mechanics is still going on at the organ level where a synergic approach combining continuum mechanics and echocardiographic imaging has been set up. See here.