Helical Swimming Research Articles

Electro-osmotic propulsion of helical nanobelt swimmers

Micro and nanoscale mobile agents capable of self-propulsion in low Reynolds number fluids would have a great technological impact in many fields. Few known mechanisms are able to propel such devices. Here we describe helical nanobelt (HNB) swimmers actuated by an electric field-generated electro-osmotic force. These HNB swimmers are designed with a head and a tail, similar to natural micro-organisms such as bacteria and their flagella. We show that these electro-osmotic propulsion of HNB swimmers achieve speeds (24 body lengths per second), force (1.3 nN), and pressure (375.5 Pa) above those demonstrated by other artificial swimmers based on physical energy conversion. Although nature’s bacteria are still more dynamic, this paper reports that the demonstrated electro-osmotic HNB microswimmers made a big step toward getting closer to their performances. Moreover, an unusual swimming behavior with discontinuous pumping propulsion, similar to jellyfish, was revealed at or above the speculated marginal limit of linear propulsion. These electro-osmosis propelled HNB swimmers might be used as biomedical carriers, wireless manipulators, and as local probes for rheological measurements.

Determination of the swimming trajectory and speed of chain-forming dinoflagellate Cochlodinium polykrikoides with digital holographic particle tracking velocimetry

The marine dinoflagellate Cochlodinium polykrikoides is a harmful and highly motile algal species. To distinguish between the motility characteristics of solitary and chain-forming cells, the swimming trajectories and speeds of solitary cells and 2- to 8-cell chains of C. polykrikoides were measured using a digital holographic particle tracking velocimetry (PTV) technique. C. polykrikoides cells exhibited helical swimming trajectories similar to other dinoflagellate species. The swimming speed increased as the number of cells in the chain increased, from an average of 391 μm s−1 (solitary cells) to 856 μm s−1 (8-cell chain). The helix radius R and pitch P also increased as the number of cells in the chain increased. R increased from 9.24 μm (solitary cell) to 20.3 μm (8-cell chain) and P increased from 107 μm (solitary cell) to 164 μm (8-cell chain). The free thrust-generating motion of the transverse flagella and large drag reduction in the chain-forming cells seemed to increase the swimming speed compared to solitary cells. The measured swimming speeds agreed with those from field observations. The superior motility of chain-forming C. polykrikoides cells may be an important factor for its bloom, in addition to the factors reported previously.

Culture‐independent characterization of a novel, uncultivated magnetotactic member of theNitrospiraephylum

A magnetotactic bacterium, designated strain LO-1, of the Nitrospirae phylum was detected and concentrated from a number of freshwater and slightly brackish aquatic environments in southern Nevada. The closest phylogenetic relative to LO-1 is Candidatus Magnetobacterium bavaricum based on a 91.2% identity in their 16S rRNA gene sequence. Chemical and cell profiles of a microcosm containing water and sediment show that cells of strain LO-1 are confined to the oxic-anoxic interface and the upper regions of the anaerobic zone which in this case, occurred in the sediment. This microorganism is relatively large, ovoid in morphology and usually biomineralizes three braid-like bundles of multiple chains of bullet-shaped magnetosomes that appeared to be enclosed in a magnetosome membrane. Cells of LO-1 had an unusual three-layered unit membrane cell wall and contained several types of inclusions, some of which are sulfur-rich. Strain LO-1 is motile by means of a single bundle of sheathed flagella and exhibits the typical 'wobbling' motility and helical swimming ('flight') path of the magnetotactic cocci. This study and reports from others suggest that LO-1-like organisms are widespread in sediments of freshwater to brackish natural aquatic environments.

Research on the Kinematic Properties of a Sperm-Like Swimming Micro Robot

Nowadays, it has been one of the hottest topics for scientists to research the interventional micro robots operating in human lumen. In this paper, a novel sperm-like interventional swimming robot with single tail is presented. The kinematic models of the sperm-like helical swimming modes are built, and the motion principles are analyzed numerically. Positions and orientations are displayed graphically during the single-tail micro robot swims in liquid. Also, the displacements and the swimming velocities of the robot in x, y, z directions are plotted. It is shown that, when the single flexible tail screws in liquid environment, it generates both axial and radial propulsion forces, thus to cause the axial and the radial movements. In order to make the swimming micro robot more controllable, an improved sperm-like swimming intervention micro robot with four flexible tails is fabricated and characterized in pipes filled with silicone oil. Experimental results show that the sperm-like micro robot can swim efficiently. With different combinations of the tails' rotation directions, the robot can gain excellent controlled performance.

Estimating 3D Movements from 2D Observations Using a Continuous Model of Helical Swimming

Helical swimming is among the most common movement behaviors in a wide range of microorganisms, and these movements have direct impacts on distributions, aggregations, encounter rates with prey, and many other fundamental ecological processes. Microscopy and video technology enable the automated acquisition of large amounts of tracking data; however, these data are typically two-dimensional. The difficulty of quantifying the third movement component complicates understanding of the biomechanical causes and ecological consequences of helical swimming. We present a versatile continuous stochastic model-the correlated velocity helical movement (CVHM) model-that characterizes helical swimming with intrinsic randomness and autocorrelation. The model separates an organism's instantaneous velocity into a slowly varying advective component and a perpendicularly oriented rotation, with velocities, magnitude of stochasticity, and autocorrelation scales defined for both components. All but one of the parameters of the 3D model can be estimated directly from a two-dimensional projection of helical movement with no numerical fitting, making it computationally very efficient. As a case study, we estimate swimming parameters from videotaped trajectories of a toxic unicellular alga, Heterosigma akashiwo (Raphidophyceae). The algae were reared from five strains originally collected from locations in the Atlantic and Pacific Oceans, where they have caused Harmful Algal Blooms (HABs). We use the CVHM model to quantify cell-level and strain-level differences in all movement parameters, demonstrating the utility of the model for identifying strains that are difficult to distinguish by other means.

Flagellar motions in phototactic steering in a brown algal swarmer.

Using infrared high-speed video microscopy, we observed light-triggered transitory flagellar motions in flagellate reproductive cells (swarmers) of a brown alga, Scytosiphon lomentaria, under primary helical swimming conditions before and during negative phototactic orientation to unilateral actinic light. The posterior flagellum, which is autofluorescent and thought to be light-sensing, was passively dragged in the dark and exhibited one to several rapid lateral beats during orientation changes for phototactic steering. Notably, a brief cessation of anterior flagellar beating was occasionally observed concomitantly with rapid beats of the posterior flagellum. This behavior caused a pause in helical body rotation, which may contribute to the accuracy of phototactic steering. Thus, coordinated regulation of the movement of the two flagella plays a crucial role in phototactic steering.

Artificial bacterial flagella for micromanipulation

This article presents an overview of recent developments in artificial bacterial flagella (ABFs) and discusses challenges and opportunities in pursuing applications. These helical swimmers possess several advantageous characteristics, such as high swimming velocity and precise motion control indicating their potential for diverse applications. One application is the manipulation of small objects within liquid, which is the focus of this review. Preliminary results have shown that ABFs are capable of performing microobject manipulation either directly by mechanical contact or indirectly by generating a localized fluid flow. The latter approach can be used for batch manipulation without direct contact, also implying possibilities for flow control in lab-on-a-chip systems. Miniaturized helical swimmers are also promising for biomedical applications, such as targeted drug delivery and implantation or removal of tissues and other objects.

Spirochete Attachment Ultrastructure: Implications for the Origin and Evolution of Cilia

The fine structure of spirochete attachments to the plasma membrane of anaerobic protists displays variations here interpreted as legacies of an evolutionary sequence analogous to that from free-living spirochetes to undulipodia (eukaryotic "flagella" and homologous structures). Attached spirochetes form a vestment, a wriggling fringe of motile cells at the edge of the plasma membrane of unidentified cellulolytic protist cells in the hypertrophied hindgut of the digestive system of Mastotermes darwiniensis, the large wood-feeding termite from northern Australia. From the membrane extend both undulipodia and a complex of comparably sized (10-12 microm x 0.2-0.3 microm) ectosymbiotic spirochetes that resembles unruly ciliated epithelium. In the intestines are helical (swimming) and round-body morphotypes. Round bodies (RBs) are slow or immotile spirochetes, propagules known to revert to typical swimming helices under culture conditions favorable for growth. The surfaces of both the spirochete gram-negative eubacteria and the parabasalid protists display distinctive attachment structures. The attached hypertrophied structures, some of which resemble ciliate kinetids, are found consistently at sites where the spirochete termini contact the protist plasma membranes.

Rolled-up helical nanobelts: from fabrication to swimming microrobots

AbstractWe present recent developments in rolled-up helical nanobelts in which helical structures are fabricated by the self-scrolling technique. Nanorobotic manipulation results show that these structures are highly flexible and mechanically stable. Inspired by the helical-shaped flagella of motile bacteria, such as E. coli, artificial bacterial flagella (ABFs) are a new type of swimming microrobot. Experimental investigation shows that the motion, force, and torque generated by an ABF can be precisely controlled using a low-strength, rotating magnetic field. These miniaturized helical swimming microrobots can be used as magnetically driven wireless manipulators for manipulation of microobjects in fluid and for target drug delivery.

Evolution of phototaxis.

Phototaxis in the broadest sense means positive or negative displacement along a light gradient or vector. Prokaryotes most often use a biased random walk strategy, employing type I sensory rhodopsin photoreceptors and two-component signalling to regulate flagellar reversal. This strategy only allows phototaxis along steep light gradients, as found in microbial mats or sediments. Some filamentous cyanobacteria evolved the ability to steer towards a light vector. Even these cyanobacteria, however, can only navigate in two dimensions, gliding on a surface. In contrast, eukaryotes evolved the capacity to follow a light vector in three dimensions in open water. This strategy requires a polarized organism with a stable form, helical swimming with cilia and a shading or focusing body adjacent to a light sensor to allow for discrimination of light direction. Such arrangement and the ability of three-dimensional phototactic navigation evolved at least eight times independently in eukaryotes. The origin of three-dimensional phototaxis often followed a transition from a benthic to a pelagic lifestyle and the acquisition of chloroplasts either via primary or secondary endosymbiosis. Based on our understanding of the mechanism of phototaxis in single-celled eukaryotes and animal larvae, it is possible to define a series of elementary evolutionary steps, each of potential selective advantage, which can lead to pelagic phototactic navigation. We can conclude that it is relatively easy to evolve phototaxis once cell polarity, ciliary swimming and a stable cell shape are present.

Characterizing the Swimming Properties of Artificial Bacterial Flagella

Artificial bacterial flagella (ABFs) consist of helical tails resembling natural flagella fabricated by the self-scrolling of helical nanobelts and soft-magnetic heads composed of Cr/Ni/Au stacked thin films. ABFs are controlled wirelessly using a low-strength rotating magnetic field. Self-propelled devices such as these are of interest for in vitro and in vivo biomedical applications. Swimming tests of ABFs show a linear relationship between the frequency of the applied field and the translational velocity when the frequency is lower than the step-out frequency of the ABF. Moreover, the influences of head size on swimming velocity and the lateral drift of an ABF near a solid boundary are investigated. An experimental method to estimate the propulsion matrix of a helical swimmer under a light microscope is developed. Finally, swarm-like behavior of multiple ABFs controlled as a single entity is demonstrated.

Steering Chiral Swimmers along Noisy Helical Paths

Chemotaxis along helical paths towards a target releasing a chemoattractant is found in sperm cells and many microorganisms. We discuss the stochastic differential geometry of the noisy helical swimming path of a chiral swimmer. A chiral swimmer equipped with a simple feedback system can navigate in a concentration gradient of chemoattractant. We derive an effective equation for the alignment of helical paths with a concentration gradient which is related to the alignment of a dipole in an external field and discuss the chemotaxis index.

Artificial bacterial flagella: Fabrication and magnetic control

Inspired by the natural design of bacterial flagella, we report artificial bacterial flagella (ABF) that have a comparable shape and size to their organic counterparts and can swim in a controllable fashion using weak applied magnetic fields. The helical swimmer consists of a helical tail resembling the dimensions of a natural flagellum and a thin soft-magnetic “head” on one end. The swimming locomotion of ABF is precisely controlled by three orthogonal electromagnetic coil pairs. Microsphere manipulation is performed, and the thrust force generated by an ABF is analyzed. ABF swimmers represent the first demonstration of microscopic artificial swimmers that use helical propulsion. Self-propelled devices such as these are of interest in fundamental research and for biomedical applications.

Mechanism of phototaxis in marine zooplankton

The simplest animal eyes are eyespots composed of two cells only: a photoreceptor and a shading pigment cell. They resemble Darwin's 'proto-eyes', considered to be the first eyes to appear in animal evolution. Eyespots cannot form images but enable the animal to sense the direction of light. They are characteristic for the zooplankton larvae of marine invertebrates and are thought to mediate larval swimming towards the light. Phototaxis of invertebrate larvae contributes to the vertical migration of marine plankton, which is thought to represent the biggest biomass transport on Earth. Yet, despite its ecological and evolutionary importance, the mechanism by which eyespots regulate phototaxis is poorly understood. Here we show how simple eyespots in marine zooplankton mediate phototactic swimming, using the marine annelid Platynereis dumerilii as a model. We find that the selective illumination of one eyespot changes the beating of adjacent cilia by direct cholinergic innervation resulting in locally reduced water flow. Computer simulations of larval swimming show that these local effects are sufficient to direct the helical swimming trajectories towards the light. The computer model also shows that axial rotation of the larval body is essential for phototaxis and that helical swimming increases the precision of navigation. These results provide, to our knowledge, the first mechanistic understanding of phototaxis in a marine zooplankton larva and show how simple eyespots regulate it. We propose that the underlying direct coupling of light sensing and ciliary locomotor control was a principal feature of the proto-eye and an important landmark in the evolution of animal eyes.

Periprocedural Stroke and Cardiac Catheterization

Case presentation : During cardiac catheterization, a 65-year-old man suddenly complained of nuchal pain, vertigo, and nausea and rapidly became unconscious, presumably from a stroke. The operator was unsure what type of imaging and management should be undertaken in this infrequent clinical setting. He paged the neurologist, asking him to urgently provide a strategy for diagnosis and management. Although the overall rate of stroke after left heart catheterization or percutaneous coronary intervention (PCI) is low, ranging from 0.2% to 0.4% (Tables 1 and 2⇓),1–5 it is the most debilitating complication from the patient’s perspective, associated with a high rate of morbidity and mortality (Figure 1).1–8 In 20 679 consecutive patients who underwent PCI in a large-volume center, stroke occurred in 0.44%.4 Multivariate analysis has shown that the occurrence of stroke was more frequently associated with diabetes mellitus, hypertension, prior stroke, or renal failure and was independently associated with in-hospital death. Patients who suffered a stroke had previously undergone longer cardiac catheterization procedures, using more contrast, were more likely to have had the procedure for urgent reasons, and to have had intraaortic balloon counterpulsation, a procedure that is itself known to increase the risk of stroke.9 Possible explanations for this latter characteristic include the greater propensity for hemodynamic compromise in these patients, which may increase the risk of ischemic stroke, and less meticulous care in advancing the catheter through the aorta during urgent PCI, which increases the risk of embolization by scraping of aortic plaques with subsequent embolization of debris to the brain. Indeed, scraping of aortic plaques occurs in >50% of PCI cases and more frequently with large than with small catheters.10 Cerebral microembolism is thought to be the main mechanism of periprocedural ischemic stroke occurring with PCI. This finding is supported …

Digital holographic microscopy reveals prey-induced changes in swimming behavior of predatory dinoflagellates

The shallow depth of field of conventional microscopy hampers analyses of 3D swimming behavior of fast dinoflagellates, whose motility influences macroassemblages of these cells into often-observed dense "blooms." The present analysis of cinematic digital holographic microscopy data enables simultaneous tracking and characterization of swimming of thousands of cells within dense suspensions. We focus on Karlodinium veneficum and Pfiesteria piscicida, mixotrophic and heterotrophic dinoflagellates, respectively, and their preys. Nearest-neighbor distance analysis shows that predator and prey cells are randomly distributed relative to themselves, but, in mixed culture, each predator clusters around its respective prey. Both dinoflagellate species exhibit complex highly variable swimming behavior as characterized by radius and pitch of helical swimming trajectories and by translational and angular velocity. K. veneficum moves in both left- and right-hand helices, whereas P. piscicida swims only in right-hand helices. When presented with its prey (Storeatula major), the slower K. veneficum reduces its velocity, radius, and pitch but increases its angular velocity, changes that reduce its hydrodynamic signature while still scanning its environment as "a spinning antenna." Conversely, the faster P. piscicida increases its speed, radius, and angular velocity but slightly reduces its pitch when exposed to prey (Rhodomonas sp.), suggesting the preferred predation tactics of an "active hunter."

Chemotaxis of sperm cells

We develop a theoretical description of sperm chemotaxis. Sperm cells of many species are guided to the egg by chemoattractants, a process called chemotaxis. Motor proteins in the flagellum of the sperm generate a regular beat of the flagellum, which propels the sperm in a fluid. In the absence of a chemoattractant, sperm swim in circles in two dimensions and along helical paths in three dimensions. Chemoattractants stimulate a signaling system in the flagellum, which regulates the motors to control sperm swimming. Our theoretical description of sperm chemotaxis in two and three dimensions is based on a generic signaling module that regulates the curvature and torsion of the swimming path. In the presence of a chemoattractant, swimming paths are drifting circles in two dimensions and deformed helices in three dimensions. The swimming paths can be described by a dynamical system that exhibits different dynamic regimes, which correspond to different chemotactic behaviours. We conclude that sampling a concentration field of chemoattractant along circular and helical swimming paths is a robust strategy for chemotaxis that works reliably for a vast range of parameters.

The Vitamin E analog Trolox reduces copper toxicity in the annelid Lumbriculus variegatus but is also toxic on its own

The ability of the water-soluble Vitamin E analog, Trolox, to prevent the toxic effects of copper exposure on the behavior and neuronal physiology of the freshwater oligochaete Lumbriculus variegatus was examined. Trolox produced a concentration-dependent increase in the 24 h LC 50 for copper exposure, with 100 μM Trolox elevating the LC 50 by almost seven-fold (from 0.36 to 2.43 μM). Copper exposure (0.2 μM) for 24 h produced a reduction in the conduction velocity of the medial and lateral giant nerve fibers, which was prevented by 100 μM Trolox. Copper exposure (0.2 μM) for 24 h also reduced the effectiveness of substrate vibration in eliciting giant nerve fiber spikes. Trolox prevented this reduction in sensory responsiveness. Trolox (100 μM) partially reversed the copper-induced (0.4 μM) decrease in touch-evoked helical swimming behavior, but had no effect on the copper-induced decrement in touch-evoked body reversal. Copper exposure (0.2 μM) for 24 h reduced the amount of spontaneous locomotion (crawling); however, Trolox did not reverse this effect. However, Trolox exposure alone produced a decrease in the distance crawled that was similar in magnitude to copper exposure. In normal worms, rapid spiking activity of the medial giant nerve fiber produces facilitation in the amplitude of the resulting muscle potentials produced by the longitudinal body wall muscles. Copper exposure had no effect on the amount of muscle potential facilitation, but Trolox exposure (100 μM) produced a significant decrease in facilitation. The results of this study indicate that many of the toxic effects of copper exposure on Lumbriculus are prevented or reduced by the antioxidant Trolox. However, the results of this study also indicate that Trolox has toxic effects on behavior and neuronal physiology. The results presented here document one of the few published reports of the detrimental effects of Vitamin E or its analogs on nervous system function or behavior.

The method of regularized Stokeslets in three dimensions: Analysis, validation, and application to helical swimming

The method of regularized Stokeslets is a Lagrangian method for computing Stokes flow driven by forces distributed at material points in a fluid. It is based on the superposition of exact solutions of the Stokes equations when forces are given by a cutoff function. We present this method in three dimensions, along with an analysis of its accuracy and performance on the model problems of flow past a sphere and the steady state rotation of rigid helical tubes. Predicted swimming speeds for various helical geometries are compared with experimental data for motile spirochetes. In addition, the regularized Stokeslet method is readily implemented in conjunction with an immersed boundary representation of an elastic helix that incorporates passive elastic properties as well as mechanisms of internal force generation.

Copper-induced changes in locomotor behaviors and neuronal physiology of the freshwater oligochaete, Lumbriculus variegatus

The behavioral and neurotoxic effects of copper exposure were examined in the freshwater oligochaete, Lumbriculus variegatus. The 24 h LC 50 for worms exposed to copper sulfate in an artificial pond water was 0.45 μM. Almost all animals that died due to copper exposure died during the first day of exposure. Immersion in water containing 0.2 or 0.4 μM copper produced time- and concentration-dependent reductions in the ability of tactile stimulation to evoke two stereotyped locomotory behaviors, body reversal and helical swimming. Helical swimming was more severely affected by copper exposure than was body reversal behavior. Upon return to clean water, both behaviors returned to normal levels within 1–2 days. Noninvasive electrophysiological testing indicated that copper exposure produced time- and concentration-dependent reductions in the conduction velocities of the medial and lateral giant nerve fibers. An 8 h exposure to 0.2 μM copper produced significant reductions in giant fiber conduction velocities that returned to normal levels within 3 days of return to clean water. It is likely that copper exposure can significantly degrade the ability of aquatic oligochaetes to avoid predators.