On the internal architecture of lightweight negative Poisson’s ratio (auxetic) metastructures: A review

Development of lightweight materials with enhanced mechanical properties has been a long-standing challenge in science and engineering. Auxetic metastructures (AMSs) provide a promising approach to this problem. AMSs’ negative Poisson’s ratio is a unique characteristic which results in very interesting practical properties such as high energy absorption. Different properties of metastructures, including anisotropy, are dependent, in addition to their original material, on the unit cell shape and geometrical features which have very high variations. Over the past few years, researchers have developed AMSs with various unit cells, either introducing new internal architecture or enhancing and optimizing the existing ones. Although general reviews on AMSs exist, a detailed comparative analysis of their internal unit cell architectures and their resulting functional properties remains limited. This review addresses this gap by providing a structured classification and comprehensive overview of more than 100 distinct auxetic unit cells. We compare their performance characteristics, discuss practical implementation challenges, and provide the achievable ranges of negative Poisson’s ratio for each category. Finally, the future perspective of the research field and potential developments and applications in this field are discussed.