Mechanical metamaterials exhibit a plethora of extreme mechanical functionalities, such as shape-changing or programmable stiffness. For their design, a purely geometrical framework was used.
However, before the start of the project, they had been mostly considered in idealised scenarios, with homogeneous loading, without defects and in the case where energy is conserved. However, in real world applications, these idealised scenarios don't hold, the loading is never homogeneous, there are defects and energy is not conserved. Therefore the purely geometrical framework falls short.
In Extr3Me, we set out to unveil the extreme mechanics of metamaterials in this realistic setting. We have followed three routes: the role of (i) non-homogeneous loading, (ii) disorder and (iii) breaking of energy conservation.
We have therefore started to establish a much needed conceptual framework, with new experimental, numerical and theoretical tools to capture the extreme mechanics of metamaterials. This is important to establish metamaterials as a viable technology in energy absorption, wave guiding and soft robotic applications.
The main conclusions we have drawn are that in the case of inhomogeneous loading, the deformations of metamaterials can be captured by new continuum theories that based on higher order gradients (Nat. Comm. 2022, Nature 2023) and concepts of topology (PNAS 2020, PNAS 2024a) that have beautiful mathematical implications (e.g. using conformal maps, Moebius strips, and topology).
In the case of torsional loading (Adv Science 2021, Nat Commun 2024b), the preferential deformations of metamaterials in specific directions enable unconventional responses under shear, such as a negative Poynting effect and a delayed torsional buckling. All these results were only possible because of the new framework of compliant mechanisms that we used. These studies have allowed up to expand it.
The main conclusions we have drawn from studying the effect of disorder (PNAS 2024b) is that unconventional properties such as auxeticity permeate into the physics of disordered materials, such as friction and yield. Auxeticity allows to tune these otherwise immutable properties. Hence auxetic granular metamaterials could be used in many scenarios where granular media need to flow in confined spaces.
The main conclusion we have drawn from studying the effect of dissipation (PNAS 2021, Soft Matter 2022, Adv Mater 2023, Nature 2024b, Nature Comm 2024a, JMPS 2025) is that buckling tends to amplify dissipative phenomena such as viscoelasticity and plasticity. At the same time, before the onset of buckling, metamaterials have a large structural integrity. This means that metamaterials can combine usually impossible properties: high stiffness and high dissipation (Adv. Mater. 2023, Nature 2024b, JMPS 2025, patent pending). In addition, this buckling enable tunable dissipation and can be used to create materials with multifunctional responses and life-like responses (PNAS 2021, Nat. Commun. 2024). Additionally, we have discovered that energy injection allows to create novel types of waves that are unidirectionally amplified and create nonlinear patterns and waves (PNAS 2020, Nature 2024a, Nature 2025).
The overall conclusion is that by embracing deviations from the traditional purely geometrical framework, this ERC allowed us to open a whole new world. This touches upon beautiful theoretical developments, and also enables the development of new technologies in energy damping applications (we secured two ERC-PoC along those lines) and soft robotic applications.
