Reversible Attachment with Tailored Permeability: The Feather Vane and Bioinspired Designs

In bird flight, the majority of the wing surface consists of highly refined and hierarchically organized feathers. They are composed of barbs that stem from the feather shaft and barbules that branch from barbs, forming a rigid feather vane. Barbules provide adhesion within the vane through an interlocking hook-and-groove mechanism to allow for the effective capture of air. This functional adhesive can reattach if structures unfasten from one another, preventing catastrophic damage of the vane. Here, using pelican primary feathers as a model material, we investigate the in-plane adhesion and stiffness of barbules. With guineafowl, pelican, and dove feathers, we determine the effect of barbules on the feather vane's ability to capture air. The vane is found to have directional permeability, and the effect of detaching barbules on the feather's competency is determined to be a function of barb dimensions. Interestingly, barbule spacing is found to vary within a narrow 8–16 µm range for birds weighing from 4–11 000 g (hummingbird to condor). Additionally, bioinspired barbules are fabricated through additive manufacturing to study the complexities of the vane. Barbules are underexplored structures imperative to the adeptness of the feather in flight, with the potential to provide bioinspired aerospace materials.