In a groundbreaking discovery, researchers at the Massachusetts Institute of Technology (MIT) have delved into the intricate structure of butterfly wings and uncovered a potential key to developing revolutionary new materials. By observing and imaging the development of scales during the butterfly’s metamorphosis, the researchers revealed how the ridged structure of the scales forms through a process called buckling.
The research, published in Cell Reports Physical Science, could pave the way for the development of novel photothermal management materials with applications ranging from textiles and building surfaces to vehicles. The findings offer a deeper understanding of the mechanical properties of scales and highlight the potential of nature-inspired engineering.
Unveiling the Secret of Butterfly Wings
Butterfly wings are covered with tens of thousands of tiny scales, resembling shingles on a thin roof. These scales, each as small as a grain of dust, are incredibly complex. Their surface features wave-like ridges that aid in water absorption, heat dissipation, and light reflection, giving butterfly wings their shimmering appearance.
The MIT research team captured the initial moment of scale development during the butterfly’s metamorphosis. Using advanced imaging techniques, they observed the microstructure of butterfly wings as they transformed from caterpillars. They discovered that the scales’ initial smooth surface begins to wrinkle, forming tiny parallel undulations, which eventually develop into the fine ridges that determine the scales’ function.
Buckling: The Key to Scale Formation
The researchers found that the transformation of scales to the wavy surface is likely the result of buckling, a general mechanism describing how smooth surfaces wrinkle in enclosed spaces as they grow.
Mathias Kolle, an associate professor of mechanical engineering at MIT, explained: Buckling is an instability, and as engineers, we typically don’t want to see this happen. But in this case, the organism uses buckling to initiate the growth of these intricate functional structures.
A Glimpse into Nature’s Engineering
The research team is working to visualize more stages of wing growth in butterflies to provide clues for designing advanced functional materials. Kolle said: Given the multifunctionality of butterfly scales at this scale, we want to understand and mimic these processes to sustainably design and manufacture new functional materials with tailored optical, thermal, chemical, and mechanical properties for textiles, building surfaces, vehicles – really, any surface that needs to exhibit characteristics depending on its micro and nanoscale structure.
Decoding the Development of Ridge Patterns
The research team used the same method to focus on a specific time window in the scale development process to capture the initial formation of the intricate ridges on individual scales. They observed that the parallel ridges, similar to the stripes on corduroy, enable many of the wing scales’ functions.
By studying the development of the scales over a 10-day period, the researchers discovered that the early scales have a very flat surface. As the butterfly grows, the scales begin to slightly bulge, and at around 41% of the development process, they observed a very regular pattern of this bulging original scale. This process lasts about five hours, laying the structural foundation for the subsequent patterned ridges.
Investigating the Causes of Ridge Formation
The researchers suspect that buckling is responsible for the precise arrangement of the initial ridges. They observed that the cell membrane of the butterfly scales is effectively anchored by actin filaments, long fibers that run beneath the growing cell membrane and act as a support scaffold during scale formation. They propose that as the butterfly wing scales grow, they will bulge between the underlying actin filaments, bending to form the initial parallel ridges of the scales.
Theoretical Modeling of Scale Formation
To validate their hypothesis, the MIT research team studied a theoretical model describing the general mechanical principles of buckling. They added image data, such as measurements of the scale membrane’s height at different early stages of development, and the different spacings of actin filaments across the growing membrane, to the model. They then ran the model forward in time to observe whether its mechanical buckling principles would produce the same ridge patterns observed in the actual butterfly.
Through this modeling, the researchers found that it is possible to transform a flat surface into one with greater undulations. From a mechanical perspective, this suggests that membrane buckling is likely the cause of these amazing ordered ridges.
Implications for Material Science
McDougal said: We want to learn from nature, not only to learn about the functions of these materials but also about how they are formed. For example, if you want to make a pleated surface, which is useful for various applications, then this provides two very easy-to-adjust ‘knobs’ to customize the way these surfaces pleat. You can change the spacing of the fixed materials and also change the amount of material between the fixed parts, and we found that butterflies use both strategies.
The research offers a fascinating glimpse into nature’s engineering and its potential to inspire the development of innovative materials. As we continue to explore the intricate structures and processes in the natural world, we may uncover even more remarkable insights that can benefit our society and future technological advancements.
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