Roadmap on mechanical metamaterials

This Roadmap covers the status, current challenges, and new science required to address these challenges, for mechanical metamaterials. This is timely, given the sustained increase in mechanical metamaterials research outputs and patents. Sections are grouped according to anomalous properties. These include auxetic (negative Poisson’s ratio), sub-divided into geometric form, flexible and shape morphing, negative thermal expansion, and negative stiffness. Specific sections also cover naturally and biologically inspired metamaterials (characterised by complex multiscale material architectures), and nanoscale/molecular metamaterials, and applications of mechanical metamaterials. Key challenges raised throughout relate to scaling up manufacturing for reliable, cost-effective production, particularly for high resolution processes nearing the molecular level, and efficiency of modelling approaches required for these multiscale systems. With opportunities to target their new, useful functionalities, such as the extreme hardness of auxetic materials, or extreme vibration damping via negative stiffness, mechanical metamaterials are contributing to rapid evolution of manufacturing and multiscale modelling.