A new study by researchers from Tel Aviv University (TAU) shows how defects induced in metamaterials – artificial materials with different properties compared to natural materials – produce different effects and consistencies.A material's structure influences its behavior and function, and how it would respond to stimulus. For example, paper is normally flat and floppy. However, its texture changes when it is crumpled, becoming stiff and round.In order to get a controlled, desired response in texture and functionality from a material, one can exploit topological defects, which are essentially small errors in the material that influence the response.Now, by incorporating intentional defects, researchers are able to design metamaterials in a way to get a better desired reaction when stimulus is applied.“We’ve seen non-symmetric effects of a topological imperfection before. But we’ve now found a way to create these imperfections in a controlled way," said the study's co-author, Prof. Yair Shokef of TAU’s School of Mechanical Engineering. “It’s a new way of looking at mechanical metamaterials – to borrow concepts from condensed-matter physics and mathematics to study the mechanics of materials.“Since we’ve developed general design rules, anyone can use our ideas.”The study is the result of a collaboration between Shokef and Dr. Erdal Oğuz of TAU, and Prof. Martin van Hecke and Anne Meeussen of Leiden University and AMOLF in Amsterdam, and was published on January 27 in the journal Nature Physics. “We were inspired by LCD-screens that produce different colors through tiny, ordered liquid crystals,” Shokef explained. “When you create a defect – when, for example, you press your thumb against a screen – you disrupt the order and get a rainbow of colors. The mechanical imperfection changes how your screen functions. That was our jumping off point.”The researchers created a complex metamaterial construct with 3D printing, and added intentional defects in the structure to show how they influenced the response.This material was flat and made of triangular pieces connected to one another, which moved by bulging and contracting when stress was applied. Depending on where the stress is applied, the material can be soft or simply soft on one side and stiff on the other, or stiff if no stress is applied at all.This, Shokef explained, is a global topological imperfection.“It’s an irregularity that you can’t just remove by locally flipping one puzzle piece. Specifically, we demonstrated how we can use such defects to steer mechanical forces and deformations to desired regions in the system.”The research paves the way for greater understanding of structural defects, and has far-reaching applications. For example, it can lead to developing a way to protect passengers in car crashes; safely launching delicate equipment into space; and developing minimally invasive surgery.The team plans to expand their research from flat metamaterials into three-dimensional ones.