A team of scientists from Universidad Carlos III de Madrid (UC3M) and Harvard University have experimentally demonstrated that it is possible to reprogram the mechanical and structural behaviour of innovative artificial materials with magnetic properties, known as metamaterials, without the need to modify their composition. This technology opens the door to innovations in fields such as biomedicine and soft robotics, among others.

The study, recently published in the journal Advanced Materials, details how to reprogram these mechanical metamaterials by using flexible magnets distributed throughout their structure. “What is innovative about our proposal is the incorporation of small flexible magnets integrated into a rotating rhomboid matrix that allows the stiffness and energy absorption capacity of the structure to be modified by simply changing the distribution of these magnets or applying an external magnetic field. This confers unique properties that are not present in conventional materials or in nature. When we design new materials, we usually focus on their chemical composition and microstructure, but with metamaterials we can also play with their internal geometry and spatial arrangement,” explains one of the study's authors, Daniel García-González, from UC3M's Department of Continuum Mechanics and Structural Analysis.

This breakthrough represents an important step towards the creation of reconfigurable mechanical structures, useful in sectors such as robotics, impact protection and aerospace engineering. The applications of this type of metastructure are practically infinite, according to the researchers: “From impact protection structures and adaptive components in soft robotics to intelligent shock-absorbing systems in exoskeletons. In the field of sports, they could be used to modify the mechanical response of a sports shoe sole by means of the interactions of the elements incorporated into it, making certain areas more flexible or rigid to improve the footfall of a person or a runner. Innovative possibilities are also opening up in biomedicine. For example, we could introduce modifications of these structures in an obstructed blood vessel and, by applying an external magnetic field, expand the matrix to unblock it,” points out another researcher, Josué Aranda Ruiz, also from UC3M's Department of Continuum Mechanics and Structural Analysis.

To carry out the study, the UC3M and Harvard researchers combined the identification and characterization of different materials with the analysis of their behaviour as a function of magnetic orientations. To this end, they studied how the orientation, residual magnetization and rigidity of the magnets affect the static and dynamic responses of the metamaterial, demonstrating that careful reorientation allows its behaviour to be significantly adjusted. They then analysed its integration into larger structures for dynamic impact testing.

“By modifying the position of the magnets to modulate the magnetic interaction between them, we can achieve completely different behaviours in the material,” adds another of the study's authors, Carlos Pérez-García, a third researcher from UC3M's Department of Continuum Mechanics and Structural Analysis.

This research work has been carried out with the support of the Spanish Ministry of Science and Innovation (MCIN/AEI/10.13039/501100011033), as well as the 4D-BIOMAP project of the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (GA947723). It is also part of the innovation work carried out to transfer technology in soft robotics with the company Monodon (Navantia).