title: Drag Reduction in a Natural High-Frequency Swinging Micro-Articulation: Mouthparts of the Honey Bee.
abstract: Worker-bee mouthparts consist of the glossa, the galeae and the vestigial labial palp, and it is these structures that enable bees to feed themselves. The articulation joints, 60∼70 µm in diameter, are present on the tip of the labial palp and are covered with olfactory sensilla, allowing movements between the segments. Using a specially designed high-speed camera system, we discovered that the articulation joint could swing in the nectar at a frequency of ∼50 Hz, considerably higher than the usual motion frequency of mammalian joints. To understand the potential drag reduction in this tiny organ, we examined its microstructure and also its surface wettability. We found that chitinous semispherical protuberances (4∼6 µm in diameter) are uniformly scattered on the surface of the joint and, moreover, that the surface is hydrophobic. We proposed a hydrodynamic model and revealed that the specialized surface can effectively reduce the mean equivalent friction (Ff) by ∼10%, through the use of protuberances immersed in the liquid feed. Theoretical results indicated that the dimensions of such protuberances are the predominant factor in minimizing Ff, and that the natural dimensions of the protuberances are close to the theoretical optimum at which friction is at a minimum. These discoveries may inspire the design of high-frequency micro-joints for engineering applications, such as in micro-stirrers.
authors.affiliation: Division of Intelligent and Biomechanical Systems, State Key Laboratory of Tribology, Department of Mechanical Engineering, Tsinghua University, Beijing, People's Republic of China.|Department of Automotive Engineering, Tsinghua University, Beijing, People's Republic of China.
authors.forename: Guanya
authors.initials: G
authors.lastname: Shi
authors.affiliation: Division of Intelligent and Biomechanical Systems, State Key Laboratory of Tribology, Department of Mechanical Engineering, Tsinghua University, Beijing, People's Republic of China.
authors.forename: Jianing
authors.initials: J
authors.lastname: Wu
authors.affiliation: Division of Intelligent and Biomechanical Systems, State Key Laboratory of Tribology, Department of Mechanical Engineering, Tsinghua University, Beijing, People's Republic of China.
authors.forename: Shaoze
authors.initials: S
authors.lastname: Yan
mesh_terms: D000818:Animals; D001516:Bees / Q000033:anatomy & histology / Q000502:physiology* / Q000648:ultrastructure; D001696:Biomechanical Phenomena; D057446:Hydrodynamics; D008855:Microscopy, Electron, Scanning; D009055:Mouth / Q000033:anatomy & histology / Q000502:physiology / Q000648:ultrastructure; D009068:Movement; D057048:Plant Nectar; D017155:Wettability
chemical_list: D057048:Plant Nectar
keywords: articulation; honey bee; labial palp; lubrication modelling