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Probing the flexural rigidity of micropillars and microfibers is challenging as they are short and difficult to handle. We developed a magnetic torque methodology where a coil-generated uniform magnetic field acts on a magnetic microrod attached to the fiber end, forcing it to turn. It is shown that magnetic torque bends microfibers in a circular arc, whose radius depends on the flexural rigidity. Magnetic microrods were fabricated by electroplating nickel on tungsten microwires. The methodology was validated with synthetic microfibers. Available magnetic stages for optical microscopes offering uniform magnetic fields within a millimeter-wide spot can be implemented to study a variety of beam-like microstructures. 

The proboscis of butterflies and moths is made of two C-shaped tubular strands, each with a crescent cross-section. Together, they form a food canal for fluid uptake. Each strand is sealed at the free end and blood is pumped in at the head. The accepted scenario for proboscis uncoiling assumes that intrinsic muscles deform the proboscis walls like fingers pressing a bicycle tire, decreasing the cross-sectional area and displacing blood that pushes the external walls outward, as does the air in the tire. This scenario requires the external walls of the strands to be softer than the food canal walls. We tensile-tested the proboscis of Manduca sexta hawk moths and discovered that the food canal walls are softer than the external walls, contradicting the accepted scenario. We hypothesize that the proboscis works as a hydraulic spring, requiring no muscular action to uncoil. The model supports this hypothesis: the pump pressurizes the blood, which pushes on the food canal walls, buckling them inward. The crescent edges along which the strands are connected are free to move loosening the coil and unrolling the proboscis. Using X-ray scattering and assuming the same cuticle matrix for both walls of the crescent strands, we showed that the difference in cuticular stiffnesses is achieved through a unidirectional ordering of α-chitin nanofibrils aligned mutually orthogonal in the food canal and external walls of the proboscis, making it a transversely anisotropic tubular composite and preventing buckling. This arrangement opens new engineering opportunities for multifunctional fiber-based hydraulic springs in micromachines. 

In insects vulnerable to dehydration, the mechanistic reaction of blood after wounding is rapid. It allows insects to minimize blood loss by sealing the wound and forming primary clots that provide scaffolding for the formation of new tissue. Using nano-rheological magnetic rotational spectroscopy with nickel nanorods and extensional rheology, we studied the properties of blood dripping from the wound of caterpillars of the Carolina sphinx moth (Manduca sexta) with a high concentration of blood cells. We discovered that wound sealing followed a two-step scenario. First, in a few seconds, the Newtonian low-viscosity blood turns into a non-Newtonian viscoelastic fluid that minimizes blood loss by retracting the dripping blood back into the wound. Next, blood cells aggregate, starting from the interfaces and propagating inward. We studied these processes using optical phase-contrast and polarized microscopy, X-ray imaging, and modeling. Comparative analyses of the cell-rich and cell-poor blood of different insects revealed common features of blood behavior. These discoveries can help design fast-working thickeners for vertebrate blood, including human blood. 

Viscosity determines the resistance of haemolymph flow through the insect body. For flying insects, viscosity is a major physiological parameter limiting flight performance by controlling the flow rate of fuel to the flight muscles, circulating nutrients and rapidly removing metabolic waste products. The more viscous the haemolymph, the greater the metabolic energy needed to pump it through confined spaces. By employing magnetic rotational spectroscopy with nickel nanorods, we showed that viscosity of haemolymph in resting hawkmoths (Sphingidae) depends on wing size non-monotonically. Viscosity increases for small hawkmoths with high wingbeat frequencies, reaches a maximum for middle-sized hawkmoths with moderate wingbeat frequencies, and decreases in large hawkmoths with slower wingbeat frequencies but greater lift. Accordingly, hawkmoths with small and large wings have viscosities approaching that of water, whereas hawkmoths with mid-sized wings have more than twofold greater viscosity. The metabolic demands of flight correlate with significant changes in circulatory strategies via modulation of haemolymph viscosity. Thus, the evolution of hovering flight would require fine-tuned viscosity adjustments to balance the need for the haemolymph to carry more fuel to the flight muscles while decreasing the viscous dissipation associated with its circulation.