Inspired by leaf veins and dragonfly wings, MIT team designs more resilient materials

Researchers at the Massachusetts Institute of Technology (MIT) and Northeastern University have developed a new class of materials that can better withstand damage and sudden impacts by taking inspiration from networks found in nature, including leaf veins and dragonfly wings.

Called scale-rich metamaterials, the structures are made up of interconnected beams of different sizes rather than the uniform, repeating patterns commonly used in conventional engineered materials.

The researchers found that this network-based design could improve the materials' ability to distribute damage, absorb energy and protect fragile objects embedded within them. The findings could inform the development of stronger, more resilient materials for applications such as helmets, protective armour and packaging. The study was published in the journal Nature on Nov 11.

Moving beyond conventional material designs

Metamaterials are engineered materials whose internal structures give them properties that are not typically found in naturally occurring materials. Rather than relying only on the substances they are made from, their performance is influenced by the way their internal components are arranged.

Conventional metamaterials are generally designed around a basic structural unit, known as a unit cell, which is repeated across the material to create an organised pattern. Lattice and honeycomb structures are common examples.

Although these designs can improve strength and stiffness, they have limitations. When one section is punctured, cracked or deformed, the damage can spread because neighbouring sections share similar structural patterns.

The new approach uses a different design principle. Instead of repeating identical units, the researchers created networks of interconnected beams that vary in length and thickness.

The idea draws on network patterns found in natural systems, including the branching veins of leaves and the intricate structures within dragonfly wings. The researchers also drew on network science, a field that studies how interconnected elements behave as part of a larger system.

How the researchers developed the materials

The team developed an algorithm to generate networks of beams with different dimensions and arrangements. The programme begins by drawing lines through randomly selected points within a defined area. It then adds progressively shorter and thinner lines, creating a dense network of intersecting structures.

By adjusting the thickness of the initial lines and the rate at which subsequent lines become thinner, the researchers could generate different network patterns and control properties such as stiffness.

They used simulations to examine how these changes affected material performance before producing physical samples through 3D printing.

The researchers deposited polymer into patterns of tiny, interconnected beams. Each sample was approximately the size of a credit card, with internal structures ranging from micrometres to centimetres in scale.

The samples were subjected to physical tests, including compression under increasing force and impacts from a dropped weight. Their performance was compared with that of conventional lattice and honeycomb metamaterials.

The network-inspired materials showed greater resilience to compression and sudden impacts. They were also more effective at distributing damage across their structures rather than allowing a localised failure to cause the entire material to collapse.

According to the researchers, the variation in beam sizes creates multiple pathways through which forces can travel. If one section is damaged, the surrounding network can help support the remaining structure.

A design inspired by pomelo fruit

The team also explored how natural structures could guide the design of materials intended to protect fragile objects.

For this demonstration, the researchers took inspiration from the thick rind of a pomelo, a citrus fruit. Its outer layer has a density-graded structure, with a denser region surrounding a softer interior.

The researchers recreated this principle using a network of beams. They designed a material with a denser structure around its edges and embedded a fragile object at its centre.

The resulting structure was able to cushion and protect the object during testing, demonstrating how variations in internal architecture could be used to improve impact absorption.

Potential applications in protective materials

The researchers said the design approach could be used to develop materials for products that need to withstand physical stress or absorb energy.

Potential applications include helmets, protective armour and packaging designed to prevent damage to fragile objects. The approach could also contribute to the development of acoustic lenses, which use specially designed internal structures to focus sound or vibrations.

The findings may also be relevant to structures that need to carry loads while controlling how forces and vibrations move through them.

However, the research represents a materials-design framework and an experimental demonstration, rather than a commercially available product. Further development and testing would be needed before the materials could be used in applications such as protective equipment.

The study's authors include researchers from MIT, Northeastern University and Utrecht University in the Netherlands. The work received support from the US National Science Foundation's Designing Materials to Revolutionize and Engineer our Future programme.

By applying principles from network science to physical materials, the researchers have demonstrated an alternative to the repeating patterns that have traditionally guided metamaterial design. The approach could open new possibilities for engineering materials that are better able to absorb energy, withstand damage and protect objects.