Division of labour is widely thought to increase the task efficiency of eusocial insects. Workers can switch their task to compensate for sudden changes in demand, providing flexible task allocation. In combination with automated tracking technology, we developed a robotic system to precisely control and spatiotemporally manipulate floor temperature over days, which allowed us to predictably drive brood transport behaviour in colonies of the ant Camponotus floridanus. Our results indicate that a small number of workers, usually minors belonging to the nurse social group, are highly specialised for brood transport. There was no difference in the speed at which workers transported brood, suggesting that specialisation does not correlate with efficiency. Workers often started to transport the brood only after having identified a better location. There was no evidence that workers shared information about the presence of a better location. Notably, once brood transporters had been removed, none of the remaining workers performed this task, and the brood transport completely stopped. When brood transporters were returned to their colony, brood transport was immediately restored. Taken together, our study reveals that brood transport is an inflexible task, achieved through the synchronous actions of a few privately informed specialist workers.

Mechanobiology explores how forces regulate cell behaviors and what molecular machinery are responsible for the sensing, transduction, and modulation of mechanical cues. To this end, probing of cells cultured on planar substrates has served as a primary experimental setting for many decades. However, native extracellular matrices (ECMs) consist of fibrous protein assemblies where the physical properties spanning from the individual fiber to the network architecture can influence the transmission of forces to and from the cells. Here, a robotic manipulation platform that allows wireless, localized, and programmable deformation of an engineered fibrous ECM is introduced. A finite-element-based digital twin of the fiber network calibrated against measured local and global parameters enables the calculation of deformations and stresses generated by different magnetic actuation schemes across a range of network properties. Physiologically relevant mechanical forces are applied to cells cultured on the fiber network, statically or dynamically, revealing insights into the effects of matrix-borne forces and deformations as well as force-mediated matrix remodeling on cell migration and intracellular signaling. These capabilities are not matched by any existing approach, and this versatile platform has the potential to uncover fundamental mechanisms of mechanobiology in settings with greater relevance to living tissues.

Bacteria can exploit mechanics to display remarkable plasticity in response to locally changing physical and chemical conditions. Compliant structures play a notable role in their taxis behavior, specifically for navigation inside complex and structured environments. Bioinspired mechanisms with rationally designed architectures capable of large, nonlinear deformation present opportunities for introducing autonomy into engineered small-scale devices. This work analyzes the effect of hydrodynamic forces and rheology of local surroundings on swimming at low Reynolds number, identifies the challenges and benefits of using elastohydrodynamic coupling in locomotion, and further develops a suite of machinery for building untethered microrobots with self-regulated mobility. We demonstrate that coupling the structural and magnetic properties of artificial microswimmers with the dynamic properties of the fluid leads to adaptive locomotion in the absence of on-board sensors.

ABSTRACT Hydrodynamic performance of the marine mussel, Mytilus galloprovincialis, is studied with time-resolved particle image velocimetry. We evaluated inhalant flow, exhalant jet flow, suction performance and flow control capabilities of the mussels quantitatively. Inhalant flow structures of mussels are measured at the coronal plane for the first time in literature. Nutrient fluid is convected into the mussel by three-dimensional sink flow. Inhalant velocity reaches its highest magnitude inside the mussel mantle while it is accelerating outward from the mussels. We calculated pressure gradient at the coronal plane. As inhalant flow approaches the mussel shell tip, suction force generated by the inhalant flow increases and becomes significant at the shell tip. Likewise, exhalant jet flow regimes were studied for 17 mussels. Mussels can control their exhalant jet flow structure from a single potential core region to double potential core region or vice versa. Peak exhalant jet velocity generated by the mussels changes between 2.77 cm s−1 and 11.1 cm s−1 as a function of mussel cavity volume. Measurements of hydrodynamic dissipation at the sagittal plane revealed no interaction between the inhalant and exhalant jet flow, indicating energy-efficient synchronized pumping mechanism. This efficient pumping mechanism is associated with the flow-turning angle between inhalant and exhalant jet flows, ∼90° (s.d. 12°).

The hydrodynamics of suction feeding is critical for the survival of fish larvae; failure to capture food during the onset of autonomous feeding can rapidly lead to starvation and mortality. Fluid mechanics experiments that investigate the suction feeding of suspended particles are limited to adult fishes, which operate at large Reynolds numbers. This manuscript presents the first literature results in which the external velocity fields generated during suction feeding of early zebrafish larvae (2500–20,000 μm total length) are reported using time-resolved microscopic particle image velocimetry. For the larval stages studied, the maximum peak suction velocity of the inflow bolus is measured at a finite distance from the mouth tip and ranges from 1 to 8 mm/s. The average pressure gradient and the velocity profile proximal to the buccal (mouth) cavity are calculated, and two distinct trends are identified. External recirculation regions and reverse flow feeding cycles are also observed and quantified. One of the unresolved questions in fish suction feeding is the shape and dynamics of the buccal cavity during suction feeding; optical coherence tomography imaging is found to be useful for reconstructing the mouth kinematics. The projected area of the mouth cavity during the feeding cycle varies up to 160 and 22 % for the transverse and mid-sagittal planes, respectively. These findings can inspire novel hydrodynamically efficient biomedical and microfluidic devices.

Motile cilia are actively beating hair-like structures that cover the surface of multiple epithelia. The flow that ciliary beating generates is utilized for diverse functions and depends on the spatial location and biophysical properties of cilia. Here we show that the motile cilia in the nose of aquatic vertebrates are spatially organized and stably beat with an asymmetric pattern, resulting in a robust and stereotypical flow around the nose. Our results demonstrate that these flow fields attract odors to the nose pit and facilitate detection of odors by the olfactory system in stagnant environments. Moreover, we show that ciliary beating quickly exchanges the content of the nose, thereby improving the temporal resolution of the olfactory system for detecting dynamic changes of odor plumes in turbulent environments. Altogether, our work unravels a central function of ciliary beating for generating flow fields that increase the sensitivity and the temporal resolution of olfactory computations in the vertebrate brain.

The role of hemodynamic forces within the embryo as biomechanical regulators for cardiovascular morphogenesis, growth, and remodeling is well supported through the experimental studies. Furthermore, clinical experience suggests that perturbed flow disrupts the normal vascular growth process as one etiology for congenital heart diseases (CHD) and for fetal adaptation to CHD. However, the relationships between hemodynamics, gene expression and embryonic vascular growth are poorly defined due to the lack of concurrent, sequential in vivo data. In this study, a long-term, time-lapse optical coherence tomography (OCT) imaging campaign was conducted to acquire simultaneous blood velocity, pulsatile micro-pressure and morphometric data for 3 consecutive early embryonic stages in the chick embryo. In conjunction with the in vivo growth and hemodynamics data, in vitro reverse transcription polymerase chain reaction (RT-PCR) analysis was performed to track changes in transcript expression relevant to histogenesis and remodeling of the embryonic arterial wall. Our non-invasive extended OCT imaging technique for the microstructural data showed continuous vessel growth. OCT data coupled with the PIV technique revealed significant but intermitted increases in wall shear stress (WSS) between first and second assigned stages and a noticeable decrease afterwards. Growth rate, however, did not vary significantly throughout the embryonic period. Among all the genes studied, only the MMP-2 and CASP-3 expression levels remained unchanged during the time course. Concurrent relationships were obtained among the transcriptional modulation of the genes, vascular growth and hemodynamics-related changes. Further studies are indicated to determine cause and effect relationships and reversibility between mechanical and molecular regulation of vasculogenesis.