Search for: All records

Abstract This paper seeks to design, develop, and explore the locomotive dynamics and morphological adaptability of a bacteria-inspired rod-like soft robot propelled in highly viscous Newtonian fluids. The soft robots were fabricated as tapered, hollow rod-like soft scaffolds by applying a robust and economic molding technique to a polyacrylamide-based hydrogel polymer. Cylindrical micro-magnets were embedded in both ends of the soft scaffolds, which allowed bending (deformation) and actuation under a uniform rotating magnetic field. We demonstrated that the tapered rod-like soft robot in viscous Newtonian fluids could perform two types of propulsion; boundary rolling was displayed when the soft robot was located near a boundary, and swimming was displayed far away from the boundary. In addition, we performed numerical simulations to understand the swimming propulsion along the rotating axis and the way in which this propulsion is affected by the soft robot’s design, rotation frequency, and fluid viscosity. Our results suggest that a simple geometrical asymmetry enables the rod-like soft robot to perform propulsion in the low Reynolds number ( Re ≪ 1) regime; these promising results provide essential insights into the improvements that must be made to integrate the soft robots into minimally invasive in vivo applications. 

Abstract Microscale propulsion impacts a diverse array of fields ranging from biology and ecology to health applications, such as infection, fertility, drug delivery, and microsurgery. However, propulsion in such viscous drag-dominated fluid environments is highly constrained, with time-reversal and geometric symmetries ruling out entire classes of propulsion. Here, we report the spontaneous symmetry-breaking propulsion of rotating spherical microparticles within non-Newtonian fluids. While symmetry analysis suggests that propulsion is not possible along the fore-aft directions, we demonstrate the existence of two equal and opposite propulsion states along the sphere’s rotation axis. We propose and experimentally corroborate a propulsion mechanism for these spherical microparticles, the simplest microswimmers to date, arising from nonlinear viscoelastic effects in rotating flows similar to the rod-climbing effect. Similar possibilities of spontaneous symmetry-breaking could be used to circumvent other restrictions on propulsion, revising notions of microrobotic design and control, drug delivery, microscale pumping, and locomotion of microorganisms. 

Copepods that catch prey using feeding currents beat their cephalic appendages to generate flow entrainment, and detect the presence of nearby prey through the mechanoreceptional setae on the antennules and other appendages. It remains unclear whether the feeding current can be used by the copepod to gain information about its surroundings by sensing when the current is disturbed by nearby particles. In this article, we present a numerical model to address how much the presence of free‐floating prey can alter the feeding current velocity field, and how these prey‐induced disturbances modify setal deformation patterns. We prescribe the beating strokes of the feeding appendages, and quantify the changes in the bending flows across the setae and setal deformations due to the prey entrainment. We find that, first, the seta bends more due to the time‐averaged velocity component of the feeding current, while filtering out the oscillatory component. Second, 100 μm diameter free‐floating prey do not induce any noticeable change in deformations of the proximal and distal setae unless they are less than 10 or 5.5 prey radii from the antennules, respectively. Larger prey cause bigger flow disturbances than small prey, which are expected to be even harder to detect. Last, if setae are responsive to changes in deformationrelativeto the deformations in the absence of prey, the distal seta may have long‐ranged sensitivity to assist in detection of prey near the proximal seta, but if setae are responsive toabsolutechanges in deformation, both setae have very short‐ranged sensitivity.

 

The modular assembly and actuation of 3D prin- ted milliscale cuboid robots using a globally applied magnetic field is presented. Cuboids are composed of a rectangular resin shell embedded with two spherical permanent magnets that can independently align with any applied magnetic field. Placing cuboids within short distances of each other allows for modular assembly and disassembly by changing magnetic field direction. Assembled cuboids are demonstrated to stably self-propel under sequential field inputs allowing for both rolling and pivot walking motion modes. Swarms of cuboids could be actuated within the working space and exhibit near identical behavior. Specialized ‘trap robots’ were developed to capture objects, transport them within the working space, and subsequently release the payload in a new location. Cuboids with male and female connectors were developed to exhibit the selective mating between cuboids. The results show that cuboids are a diverse and adaptable platform that has the potential to be scaled down to the sub-millimeter regime for use in medical or small-scale assembly applications. 

Copepods sense the hydrodynamic disturbances induced by swimming planktonic prey, potential mates, and predators through the bending of setae on their first antennae and other appendages. While the flows induced by these sources have been studied and are crucial for the mechanoreception of copepods, there is little knowledge on how these flows cause the deformation of the copepod's mechanoreceptional seta. In this article, we present a mechanical model to address how the mechanics of setal deformation by hydrodynamic signals determines the sensing capabilities of copepods. We represent a generic flow around a copepod as a combination of a uniform plus shear flow, and demonstrate that the detailed geometry of the first antenna has non‐negligible effects on the flow profile across the seta. We then proceed to evaluate the setal deformations induced by such a flow oscillating at frequencies relevant for copepod sensing, and find that lower frequency signals lead to larger setal bending and are more easily detected. We investigate the effects of setal length, signal amplitude, and signal frequency on setal bending. Finally, we investigate the response time of setal bending to hydrodynamic signals, and find short response time consistent with the rapid behavioral and neurological response of copepods.