Fluid Filled Flapper: Modeling hemolymph circulation in a microfluidic insect wing replica

Insect wings bend, twist, and deform during flapping flight. The insect’s circulatory system is made up of thin membranes and tubular veins. Respiratory organs, called trachea, extend into the veins creating a circuit of liquid and air flow in the wing. Distribution of hemolymph (insect blood) is needed for wing hydration and flexibility, sustaining living organs in the wing, and supplying active mechanosensing during flapping. Although insects possess a specific thoracic pump employed for driving hemolymph flow in the wing, the flapping frequency during flight  (20-500 Hz) is much higher than that of pumping (1-3 Hz). How the nominally creeping (Re = 0.1) hemolymph flows in the wing are influenced by this high frequency flapping during flight is unknown. Using the North American grasshopper (Schistocerca americana), a dynamic flier with a complex wing vein network, we built a microfluidic flapping wing model to test hypotheses that flapping motions influence hemolymph circulation in a wing. The flapper was scaled up by a factor of 2.4x with a flow channel design that maintains dynamic similarity (Re = 0.1, Wo = 1.88), and printed using a stereolithography FormLabs Form 3 printer. The channels were seeded with dye droplets and microbeads in two separate experiments, sealed, attached to a sinusoidal oscillator, and then flapped at 3.45 Hz. Fluid movement was visualized in the channels using a high-speed camera (Photron Mini UX100) and analyzed using image processing (FIJI, ImageJ). The experiments confirmed that flapping does influence  hemolymph circulation in the wing.