Long-duration spaceflight poses multiple hazards to human health, including physiological changes associated with microgravity. The hemodynamic adaptations occurring upon entry into weightlessness have been associated with retrograde stagnant flow conditions and thromboembolic events in the venous vasculature but the impact of microgravity on cerebral arterial hemodynamics and function remains poorly understood. The objective of this study was to quantify the effects of microgravity on hemodynamics and wall shear stress (WSS) characteristics in 16 carotid bifurcation geometries reconstructed from ultrasonography images using computational fluid dynamics modeling. Microgravity resulted in a significant 21% increase in flow stasis index, a 22–23% decrease in WSS magnitude and a 16–26% increase in relative residence time in all bifurcation branches, while preserving WSS unidirectionality. In two anatomies, however, microgravity not only promoted flow stasis but also subjected the convex region of the external carotid arterial wall to a moderate increase in WSS bidirectionality, which contrasted with the population average trend. This study suggests that long-term exposure to microgravity has the potential to subject the vasculature to atheroprone hemodynamics and this effect is modulated by subject-specific anatomical features. The exploration of the biological impact of those microgravity-induced WSS aberrations is needed to better define the risk posed by long spaceflights on cardiovascular health.

Millimeter-scale robots have many applications in bioengineering fields due to their ability to be actuated remotely. Certain forms of locomotion allow them to achieve high swim speeds while maintaining controllability. The corkscrew locomotions have been achieved in previous soft robot studies, but their swim speeds were much lower than those exhibited by soft robots of different locomotions. In this paper, a corkscrew swimming motion with a high swim speed was achieved with a 3D rotating magnetic field by designing an asymmetrical soft robot made of flexible polymer embedded with magnetic particles and magnetized at a specific orientation. While this robot exhibited a rolling and transient locomotion at magnetic field frequencies lower than 40 Hz, at frequencies above 40 Hz, the robot exhibited corkscrew swimming locomotion. The swimming speed peaked at a velocity of about 30 mm/s at a magnetic field frequency of 49 Hz. Beyond this frequency, the swim speed of the soft robot decreased because the rotational frequency of the robot could not match the frequency of the actuating magnetic field.