initial gas filling of the tracheal system (tracheal filling) in embryos of the tobacco hornworm Manduca sexta (Sphingidae, Insecta). Main focus is the role of cavitation and the importance of solid/liquid/gas interactions at the tracheal wall.

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Embryos of the tobacco hornworm (Manduca sexta) render their tracheal system functional while developing in the egg. The process is remarkable for two reasons. First, tracheal gas filling occurs without contact to outside air; gas bubbles are generated de novo in liquid. Second, the process is very fast. The tracheal system becomes functional in less than five minutes. This indicates that cavitation triggers tracheal filling.The project serves to understand cavitation in the tracheal system of Manduca embryos in unprecedented detail by manipulating factors that affect the likelihood or timing of cavitation. Those factors are the pressure inside the egg, the micro-structure of the tracheal wall, and the change in the surface chemistry of the wall that occurs with sclerotization of the cuticle.A second goal is to uncover the mechanism by which the tracheal liquid is eliminated from the tracheal lumen after cavitation has occurred. Two main alternatives exist. First, water may disappear through the whole tracheal wall. The wall has relatively large surface area, but the sclerotized cuticle is supposed to be impermeable to water. Second, water may disappear only at the tips of the tracheae (tracheoles), where the cuticle is thin and unsclerotized.Tracheal filling provides a biological example of strong surface forces arising from solid-liquid-gas interactions. The proposed project will give insight into the role these three-phase interactions play during a critical respiratory transition in insects. In addition, these kinds of interactions are fundamental in materials science (functional surfaces, lotus effect) and micro-fluidics (lab-on-a-chip applications). We think that detailed study of how biological evolution has shaped these interactions may illuminate basic engineering problems of wide interest.