COURTESY OF THE RESEARCHERS
Using a special microscopic technique, the team looked through an opening they created in the pupa itself, allowing them to continuously image individual scales as they grew out of the wing membrane during a crucial window of time in the butterfly’s development. These images show for the first time how the initially smooth surface of a scale begins to fold, forming microscopic, parallel waves that resemble the grooves in corduroy. The wave-like structures eventually develop into more finely patterned grooves that enable many of the functions of the adult butterfly’s wing scales.
The transition to a corrugated surface is likely the result of “buckling” – a mechanical process in which a material buckles inward when subjected to compressive forces or trapped in a confined space. In this case, they confirmed using a theoretical model describing the general mechanics of buckling, actin bundles – long filaments that run beneath a growing membrane and support the scale as it shapes – lock the membrane in place like ropes around an inflating hot air balloon.
“Buckling is an instability, something we as engineers normally want to avoid,” says Mathias Kolle, associate professor of mechanical engineering and co-author of a study on the work. “But in this context, the organism uses buckling to initiate the growth of these complicated, functional structures.”
The team is working to visualize further stages of butterfly wing growth, which could serve as inspiration for advanced functional materials in the future.
“These materials would have tailored optical, thermal, chemical and mechanical properties for textiles, building surfaces, vehicles – actually for basically any surface that needs to have properties that depend on its micro- and nanostructure,” says Kolle.
“We want to learn from nature not only how these materials work, but also how they are formed,” says Anthony McDougal, SM ’15, PhD ’22, a postdoc at MIT and another co-author. “For example, if you want to create a wrinkled surface that is useful for a variety of applications, here you have two really simple controls that allow you to adjust the wrinkling of these surfaces. You can either change the distance at which the material is fixed, or you can change the amount of material you grow between the fixed sections. And we’ve seen the butterfly use both strategies.”
