A study analyzes the potential and the challenges of flexible mechanical metamaterials

UC3M/DICYT Research into the field of metamaterials, designed to have unusual properties such as being able to change their shape or stiffness, has advanced a great deal during recent years in technologies along with 3D printing, computer simulation, and some conceptual innovations. This subject is gaining so much importance that it was featured on the cover of Nature Reviews Materials, with an article on the challenges facing flexible mechanical metamaterials published by scientists from the Universidad Carlos III de Madrid (UC3M) and the University of Chicago, Harvard University (both in the US) and Leiden University (The Netherlands).

“Mechanical metamaterials have properties that cannot be realized in conventional materials,” remarked one of the study’s authors, Johan Christensen, from the UC3M department of Materials Science and Engineering and Chemical Engineering. In this article, the researchers reviewed the most recent scientific studies in this area. “These metamaterials exhibit exotic functionalities, such as pattern and shape transformations in response to mechanical forces,” the study reveals. An example are the structures based on origami (the art of paper folding to obtain different shaped figures) or kirigami (the art of paper cutting to obtain polygons).

A large number of scientific studies that are currently being carried out target the design of new topological metamaterials capable of having an adjustable refraction index. This would allow changing and guiding the direction of the waves, which opens the door to materials that divert visible light waves and achieve a certain range of invisibility.

In this study, the researchers have also analyzed some of the challenges faced by the scientists working in this field, such as the impact of some technologies that are currently being developed, such as 3D printing and laser cutting, for example. “Many of these techniques are still in their early stages,” he observed, but they open up the possibility of combining materials with specific functionalities to obtain hybrid metamaterials with “optomechanical, thermomechanical or electromechanical properties.”

Johan Christensen carries out this line of research on metamaterials within the framework of a broader scientific project, a Horizon 2020 ERC Starting Grant funded by the European Union (GA 714577) termed “Frontiers in Phononics: Party-Time Symmetric Phononic Metamaterials” (PHONOMETA). The objective of the project deals with the analysis and design of a new generation of metamaterials based on piezoelectric semiconductors that enables highly unusual sound propagation, which should enable submarines to act acoustically invisible to sonar.

	Bibliographic reference
	Flexible mechanical metamaterials. Katia Bertoldi, Vincenzo Vitelli, Johan Christensen & Martin van Hecke. Nature Reviews Materials 2, article number: 17066 (2017) Published online: 17 Oct. doi:10.1038/natrevmats.2017.66 https://www.nature.com/articles/natrevmats201766