How researchers engineer material behaviour through structure

Three recent studies by Dr Tian (Tim) Chen, Associate Professor in the Department of Aeronautics, and international collaborators demonstrate how entanglement, material imperfections and shape can be engineered to create entirely new material behaviours.

One of the biggest engineering challenges today is developing technologies that are lighter, stronger and more sustainable. Achieving these goals remains challenging, often requiring engineers to balance flexibility against strength, or develop new materials and manufacturing methods. 

To get around these problems, Dr Tim Chen’s group at the Department of Aeronautics has been rethinking the relationship between materials and structure. Rather than focusing solely on the chemical composition of materials, Dr Chen’s research explores how a material’s shape, the arrangement of internal structures, and even carefully controlled imperfections can be used to influence performance.   

We explore three recent studies led by Dr Chen and collaborators across the UK and United States, which reveal approaches that are opening new possibilities in material engineering spanning a range of applications, including flexible electronics, soft robotics, aerospace systems and more.   

Study 1: Knitting beyond textiles 

Read paper in PNAS: Entanglement-driven responses through multiscale 3D-printed knits  

Most of us may associate knitting with fabrics, but the underlying logic of knitting offers a new way to engineer material performance through structure rather than composition. Dr Chen and his collaborators asked whether the interlocking loops that give knitted textiles their unique properties could be reproduced in solid 3D printed materials through additive manufacturing. 

Using advanced 3D printing techniques, the researchers produced structures that mimic the behaviour of knitted textiles across a wide range of scales, from centimetre-sized objects down to microscopic architectures. The smallest have loops that measure about 50 micrometres across, which the researchers believe makes them the smallest knitted structures ever made. 

Although these knits are made from solid materials, they behave in ways that are strikingly similar to textiles: they can stretch, deform and then recover their shape. This happens because of the way the filaments interact with one another. 

In particular, Dr Chen and colleagues found that the interactions between interlocking loops of the material filaments, known as entanglement, play a significant role in determining how the material responds to forces. 

“This work establishes entanglement as a new engineering design principle,” explains Dr Chen. “It allows us to tailor mechanical behaviour of materials like flexibility, resilience and adaptability through geometry and topology, not just through chemistry.”  

The research opens up new possibilities for fields where materials need to be light and multifunctional at the same time, such as soft robotics, wearable technologies, medical implants, flexible electronics and lightweight aerospace systems. 

This study was a collaboration between Dr Chen and researchers at the University of Houston, University of Pennsylvania, Stanford University and MIT. 

Study 2: Turning defects into a design tool 

Read paper in Nature Communications: Vibration-assisted fabrication of thin shells with spatially distributed imperfections 

This study introduces a manufacturing method that uses sound vibrations to create controlled imperfection patterns in thin shell structures. 

Thin shells are widely used in engineering because of their exceptional strength-to-weight ratio. In practice, however, their behaviour is often controlled by tiny flaws introduced during manufacturing. These imperfections can determine when and how a shell buckles or fails.  

Rather than treating these flaws as unavoidable defects, Dr Chen and his colleagues developed a way to create and control them deliberately using sound. In their experiments, a soft mould is mounted on a speaker and vibrated while liquid silicone is poured over it. The vibration generates a slow, steady flow in the liquid, which drives material towards points of maximum motion. As the silicone cures, this flow is frozen into a regular pattern of small thickness variations. 

Notably, the pattern is set by the pitch and volume of the sound. By changing these acoustic inputs, the same mould can produce many different patterns without needing to be physically re-machined. In effect, the mould becomes programmable. 

Imperfections do not have to be random. By deliberately controlling them during manufacturing, we can better understand, predict and potentially improve the behaviour of thin-shell structures. Dr Tim Chen Associate Professor in Aerospace Engineering

“Imperfections do not have to be random. By deliberately controlling them during manufacturing, we can better understand, predict and potentially improve the behaviour of thin-shell structures,” said Dr Chen. 

The implications of this work are twofold. First, it allows researchers to study thin shells that are much closer to what is actually produced in industry, where imperfections are distributed and overlapping rather than isolated. Second, it suggests that imperfections might not always be something to eliminate. In some cases, they could be used deliberately to influence performance, for example to steer where and how a shell buckles. 

By helping engineers understand how imperfections influence structural behaviour, the technique could support the development of lighter and more efficient structures for aerospace, energy, civil engineering and space applications. 

This study was a collaboration between Dr Chen and researchers at the University of Houston and University of Southern California. 

Study 3: Towards deployable electronics from flat wafers

Read paper in Nature Communications: Deployable 3D architectures from wafer-fabricated precursors 

Most modern electronic devices are made on flat wafers using lithography, a process that is extremely precise and scalable but essentially two-dimensional. Many emerging applications, however, require curved, three-dimensional geometries. For example, antennas rely on shape to direct signals, optical systems use curvature to focus light, and devices designed to interface with biological tissues must conform to the complex surfaces of the body. 

While there are techniques to build freeform 3D microstructures directly, they tend to be slow and difficult to scale. As a result, large-scale manufacturing remains largely confined to flat geometries. 

Dr Chen and his team devised a method to move from 2D to 3D electronics while maintaining the advantages of wafer-based fabrication. In their approach, flat precursors are patterned on a wafer using standard processes. These precursors are made up of non-repeating cells that are bistable, so each cell has two different configurations in which it is mechanically stable. When deployed, this enables the entire structure to unfold into a prescribed curved geometry. 

Unlike conventional flexible electronics, which typically require a supporting substrate, these new structures deploy into free-standing structures that remain stable without external support. 

The researchers believe that these deployable architectures represent a shift towards truly three-dimensional devices which can be manufactured, transported and stored flat, then activated when needed.  

The team is already exploring how this concept scales. With funding from NASA, they are working on adapting the same algorithm for the design of potential extraterrestrial habitats and deployable space systems. 

“There is growing demand for devices that conform to curved surfaces such as biological tissues and complex environments,” noted Dr Chen. “We want to show that existing semiconductor manufacturing infrastructure can support a much broader class of devices than people currently imagine. That opens up new possibilities without requiring an entirely new fabrication ecosystem.” 

This study was a collaboration between Dr Chen and researchers at the University of Houston and the Toyota Research Institute of North America.