Metamaterials, which exhibit properties that go beyond the inherent characteristics of the constituent materials, consist of synthetic, precisely engineered arrangements of structures ranging from the nanoscale to the macroscale. These arrangements collectively influence interactions and responses to mechanical stresses, acoustic waves, electromagnetic waves, heat flow and more. The flexibility in the structural design of metamaterials adds a distinctive dimension to engineering their properties enabling a broad range of applications.

Credit: DAVID SCHARF / SCIENCE PHOTO LIBRARY

Complexity in metamaterials is rapidly increasing, driven by the growing demands for advanced functionality and supported by the development of computational and fabrication tools. Metamaterials now integrate multiscale structures, composite constituents, and aim to achieve multifunctional and dynamically tunable performance. However, this brings challenges in accurate design, scalable fabrication and reliable characterization across various length and time scales. In a Perspective in this issue of Nature Materials, focusing on three-dimensional mechanical metamaterials, James Utama Surjadi and Carlos Portela discuss the shift in focus on the design towards aperiodic architectures, nonlinear and responsive properties, as well as the approaches to fabricating these multiscale architected materials. They emphasize the importance of characterizing behaviours under dynamic or extreme loading conditions, along with high-throughput testing frameworks, which in turn enable precise performance prediction and data-driven designs. Furthermore, they offer insights into the future directions of implementing architected materials into real-world engineering applications, including the development of intelligent devices, characterization standards and integrated multifunctional systems.

The core of metamaterials lies in their structural design. The earlier explorations of metamaterials primarily involved repeating patterns of simple building blocks engineered to manipulate the propagation of electromagnetic waves. They were used as artificial media for applications such as antennas, radar absorbers and negative refraction. Mechanical metamaterials were developed inspired from biological materials such as honeycombs and cellular structures. Researchers have focused on achieving mechanical properties such as negative Poisson’s ratio (auxetics), high strength-to-density ratio and high energy dissipation. Beyond enhancing existing structural frameworks, innovative strategies are emerging. One general idea involves mimicking microstructural features and mechanisms of bulk materials. For instance, the typical microstructures and hardening mechanisms found in crystalline metallic alloys have been encoded into the metamaterial architecture to improve damage tolerance1. Additionally, topological phenomena in condensed-matter systems can be translated into classic systems by metamaterial design2. This raises exciting possibilities for developing metamaterials inspired by microstructure-controlled physical, electrical or chemical processes in functional materials.

Another trend in metamaterial research is the move towards programmable and adaptive behaviours to perform tasks in complex scenarios3,4. Achieving this typically requires hierarchical structures, hybrid components and embedded materials capable of responding to external stimuli. Computational studies are crucial for the inverse design of customized properties. Additionally, these designs can only be realized through fabrication techniques that ensure material quality, structural resolution and the capability to construct multiple functional materials or composites. Achieving the goal for commercial use will also require scalable strategies compatible with industrial processing. An Article in this issue by Minseok Choi and colleagues presents a good example of this vision. They demonstrate a centimetre-scale RGB (red, green and blue) achromatic metalens and explore its potential applications in near-eye displays. Crucially, the device is fabricated through a low-cost, scalable roll-to-plate technique — suitable for commercial deployment — and is integrated with computer-generated holography for a compact near-eye display. As noted in an accompanying News and Views article by T. D. Wilkinson, the combination of several creative solutions produces a high-numerical-aperture optical component that can be made agnostic to chromatic aberrations. Combining this easy-to-fabricate metalens with a holographically based optical engine can pave the way for a true three-dimensional near-eye display.

Metamaterials have progressed far beyond simple repeated units, and towards high-level integration and intelligence. Regardless of how far the field advances, it is closely intertwined with research on responsive materials, innovations in application design, artificial-intelligence-assisted computation and scalable manufacturing. It will be interesting to see how the field progresses based on the advances in some or all of these areas.