Butterfly Wings: A Blueprint for Revolutionary Materials
Cambridge, MA -Researchers at MIT have discovered a fascinating mechanism behind the formation of the intricate ridges onbutterfly wings, potentially unlocking the key to designing revolutionary new materials. Their findings, published in Cell Reports Physical Science, reveal that the process of buckling – a phenomenon where a flat surface wrinkles under compression – plays a crucial role in shaping these tiny, yet complex structures.
Butterfly wings are adorned with hundredsof thousands of microscopic scales, resembling miniature shingles on a paper-thin roof. These scales, each as small as a dust particle, possess a surprisingly complex structure. Their wavy ridges contribute to water absorption, heat dissipation, and light reflection,giving butterfly wings their mesmerizing shimmer.
The MIT team, led by Associate Professor Mathias Kolle, captured the initial moments of this ridge formation during the butterfly’s metamorphosis, when individual scales begin to develop their distinctive patterns. Using advanced imaging techniques, they observed the microscopic features on the wings of butterflies as they transformed within their chrysalises.
The researchers captured a series of images showing individual scales emerging from the wing membrane. These images, for the first time, revealed how the initially smooth surface of the scales begins to wrinkle, forming tiny parallel undulations.These wavy structures eventually grow into the intricate ridges that determine the functionality of the mature scales.
Buckling is an instability that, as engineers, we typically try to avoid, explained Kolle. But in this case, the organism is using buckling to initiate the growth of these intricate functional structures.
The team’s findings suggest that the transition from a smooth to a wavy surface in the scales is likely a result of buckling. This mechanism, which describes how smooth surfaces wrinkle when growing within a confined space, is a common phenomenon in nature and engineering.
Nature’s Engineering Inspiration
The MIT team is actively working tovisualize more stages of butterfly wing growth, hoping to glean insights that can inform the design of advanced functional materials.
Given the multifunctionality of butterfly scales, we want to understand and mimic these processes to sustainably design and manufacture new functional materials, said Kolle. These materials will exhibit tailored optical, thermal, chemical, and mechanical properties for applications in textiles, building surfaces, vehicles – really anything that needs a surface that performs based on its micro- and nanoscale structural features.
Unveiling the Mechanism of Ridge Development
The team focused on a specific window in the scale development process to capture the initial formation of theintricate ridges on individual scales. Scientists knew that these ridges, running parallel along the length of a single scale like stripes on corduroy, are responsible for many of the scale’s functions.
With limited knowledge about how these ridges form, the MIT team aimed to record the continuous formation of the ridges within a developing butterfly anddecipher the organism’s ridge-forming mechanism.
We looked at the butterfly wing development over 10 days and took thousands of measurements of the surface changes of a single butterfly’s scale, said McDougal. We could see that the early scale surface was very smooth. As the butterfly grew,the scale surface started to undulate a little bit, and then at about 41% of development, we saw this very regular pattern of the fully undulated pro-scale. The whole process took about 5 hours, setting the stage for the patterned ridges that would follow.
Investigating the Cause ofBuckling
What caused these initial ridges to appear in such a precise arrangement? The researchers suspected that buckling was at play. Buckling is a mechanical process where a material bends inward when subjected to compressive forces. For example, an empty soda can buckles when squeezed from the top. Buckling can also occur in materialsas they grow if they are constrained or held in place.
The scientists observed that as the cell membrane of the butterfly scale grows, it is effectively anchored in places by actin bundles – long filaments that run beneath the growing membrane and act as supporting struts as the scale takes shape. The scientists theorized that the constrainingeffect of the actin bundles on the growing membrane is similar to the ropes on a hot air balloon. They proposed that as the butterfly wing scale grows, it would buckle between the underlying actin filaments, forming the initial parallel ridges of the scale in a buckling manner.
A Theoretical Model of Scale Formation
To testthis idea, the MIT team investigated a theoretical model that describes the general mechanical principles of buckling. They incorporated image data into the model, such as measurements of the scale membrane’s height at different early developmental stages and the different spacing of actin bundles across the growing membrane. They then ran the model forward in time to seeif its underlying mechanics of buckling would produce the same ridge patterns observed by the team in real butterflies.
Through this modeling, the researchers found that we could go from a flat surface to a more undulated surface. Mechanically, this suggests that buckling of the membrane is very likely the cause of these amazingly ordered ridges.
Conclusions and Implications for Materials Science
We want to learn from nature, not just the function of these materials, but also how they are formed, said McDougal. Say you want to make a wrinkled surface, which is useful for all sorts of applications, then this provides two very easily tunable ‘knobs’ to customize how those surfaces wrinkle. You can change the spacing of what’s holding the material down, or you can change how much material is growing between the fixed parts, and we found that butterflies use both of these strategies.
The MIT team’s research offers a compelling glimpse into theintricate mechanisms behind the formation of butterfly wing scales. Their findings not only provide valuable insights into the biological processes involved but also hold significant potential for the development of new materials with tailored properties. By mimicking nature’s ingenious design principles, scientists can create materials that are both functional and sustainable, paving the way for a future whereinnovation is inspired by the beauty and complexity of the natural world.
Views: 0