The intricate structure of butterfly wings has long fascinated scientists and engineers, and now, researchers at MIT have made a groundbreaking discovery that could pave the way for the development of revolutionary new materials. By capturing the earliest moments of butterfly wing scale development, the team has unveiled the mechanics behind the formation of the scales’ ridged structure, offering potential applications in designing advanced photothermal management materials.
The Complexity of Butterfly Wings
Butterfly wings are adorned with tens of thousands of minuscule scales, akin to tiny tiles on a paper-thin rooftop. Each scale, as small as a grain of dust, boasts a remarkable level of complexity. The surface of these scales features wavy ridges that aid in water absorption, heat dissipation, and light reflection, giving butterfly wings their characteristic shimmer.
A Breakthrough in Imaging Technology
Researchers at MIT have developed an innovative method to observe and image the development of these scales during the metamorphosis of butterflies. Utilizing advanced imaging techniques, they have captured the microscale features of butterfly wings as they transform within the pupa.
The team sequentially imaged the growth of individual scales from the wing membrane, revealing for the first time how a smooth surface begins to wrinkle and form tiny parallel ridges. These ridges eventually grow into the fine纹脊 that define the functionality of the adult scales.
The Role of Buckling
The transformation from a smooth to a ridged surface is likely the result of a process called buckling – a general mechanism describing how a smooth surface wrinkles when growing in a confined space.
Mathias Kolle, an associate professor of mechanical engineering at MIT, explains, Buckling is an instability that we, as engineers, typically aim to avoid. But in this case, the organism is harnessing buckling to initiate the growth of these intricate functional structures.
Nature’s Engineering Inspiration
The research team is working to visualize more stages of butterfly wing growth, hoping to gain insights into how they can design advanced functional materials in the future.
Given the multifunctionality of butterfly scales, we aim to understand and emulate these processes to design and fabricate new functional materials sustainably. These materials will exhibit tailor-made optical, thermal, chemical, and mechanical properties, suitable for textiles, building surfaces, vehicles – essentially, any surface that needs to display properties dependent on its microscale and nanoscale structure, adds Kolle.
Research Findings and Implications
The team’s findings were recently published in the journal Cell Reports Physical Science. The study’s co-authors include first author Jan Totz, a former MIT postdoc, co-first author Anthony McDougal, a postdoc, graduate student Leonie Wagner, former postdoc Sungsam Kang, Professor Peter So of mechanical engineering and biomedical engineering, Professor Jörn Dunkel of mathematics, and Professor Bodo Wilts of materials physics and chemistry at the University of Salzburg.
In 2021, McDougal, Kolle, and their colleagues developed a method to continuously capture the microscale details of wing growth during butterfly metamorphosis. They carefully cut open the delicate pupae, peeled back a small piece of the cuticle to expose the wing-growing membrane, and placed a small glass slide over the exposed area. Using a microscopy technique developed by team member Peter So, they captured the growth of scales from the wing membrane.
The team observed the development of scales in Vanessa cardui, a butterfly species with scale structures common to most Lepidoptera. They found that the scales grew in precise overlapping patterns along the wing membrane, much like shingles on a roof. These images provided the most continuous visualization of live butterfly wing scale growth at the microscale to date.
The Development of Ridges
In their new study, the team used the same method to focus on a specific time window in scale development to capture the initial formation of fine ridges on individual scales of a living butterfly. The scientists knew that these ridges, which run parallel along the length of a single scale, are essential for the functionality of wing scales.
The team observed the development of ridges over a 10-day period, taking thousands of measurements of the scale surface changes in a single butterfly. They saw that the early scales were very smooth, but as the butterfly grew, the scale surface began to buckle and form tiny ridges. This process laid the groundwork for the patterned ridges seen in the adult scales.
Investigating the Cause of Buckling
What causes these initial ridges to appear in such precise patterns? The researchers suspected that buckling might be at play. Buckling is a mechanical process where materials bend inward when subjected to compressive forces. For example, an empty soda can will buckle when squeezed from the top.
The scientists noticed that as the butterfly scale’s cell membrane grows, it is effectively fixed in certain places by actin bundles – long filaments that run beneath the growing cell membrane, providing structural support. They proposed that the constraint
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