Periodic Shape Changes Research Articles

Bubble oscillations at low frequency ultrasound for biological applications

Bubbles oscillating in the presence of ultrasound is commonly employed in biomedical applications for drug delivery, ultrasound enhanced thrombolysis, and the transport and manipulation of cells. This is possible because bubbles tend to interact with the ultrasound to undergo periodic shape changes known as shape-mode oscillation, concomitant with the generation of liquid agitation or streaming. This phenomenon is examined both experimentally and theoretically on a single bubble at a frequency of (45 ± 1) kHz. Effects of ultrasonic frequency and power on the flowfield were explored. Experiments revealed different trends in the development of liquid streaming velocities at different acoustic forcing conditions (5.53, 6.80 and 7.02 Vpp), with lowest (0.5 mm/s) and highest (1.1 mm/s) values of time-averaged mean streaming velocity occurring at 6.80 Vpp and 7.02 Vpp, respectively. Simulations captured the simultaneous evolution of bubble-shapes that helped create flow vortices in the liquid surrounding the bubble. These vortices collectively responsible in generating signature patterns in the liquid for a dominant shape-mode of the bubble, and could also generate localised shear stresses for practical application. The velocity and pressure profiles in the liquid around the bubble confirmed the connection of the applied and reflected soundwaves in driving this phenomenon.

Myosin waves and a mechanical asymmetry guide the oscillatory migration of Drosophila cardiac progenitors.

Heart development begins with the formation of a tube as cardiac progenitors migrate from opposite sides of the embryo. Abnormal cardiac progenitor movements cause congenital heart defects. However, the mechanisms of cell migration during early heart development remain poorly understood. Using quantitative microscopy, we found that in Drosophila embryos, cardiac progenitors (cardioblasts) migrated through a sequence of forward and backward steps. Cardioblast steps were associated with oscillatory non-muscle myosin II waves that induced periodic shape changes and were necessary for timely heart tube formation. Mathematical modeling predicted that forward cardioblast migration required a stiff boundary at the trailing edge. Consistent with this, we found a supracellular actin cable at the trailing edge of the cardioblasts that limited the amplitude of the backward steps, thus biasing the direction of cell movement. Our results indicate that periodic shape changes coupled with a polarized actin cable produce asymmetrical forces that promote cardioblast migration.

Numerical analysis of thermal stress evolution of pulsed-wave laser direct energy deposition

Residual stresses and deformation in additive manufactured (AM) are two main barriers which hinder its extensive application seriously. In recent years, pulsed laser additive manufacturing has been widely examined for its advantages such as lower finer microstructure, more excellent mechanical properties, and heat accumulation in comparison with continuous-wave laser additive manufacturing. Few researches about residual stress of pulsed laser additive manufacturing, however, have been studied, and the development law of stain and residual stress is not clear. In this work, a three-dimensional (3D) transient uncoupled thermo-elastic-plastic model for pulsed-wave laser additive manufacturing procedure is carried through to examine the residual stress distribution and thermal history in 316L laser cladding. Excellent acceptance between the experimental measurements and the numerical results is obtained. It is discovered that pulsed-wave laser additive that manufactures attributes melt pools with periodic shape changes, the thermal stress evolution process moves like heartbeat periodically, and the residual stress distribution in laser cladding direction is similar to zigzag inhomogeneity. Furthermore, the influence of laser pulse parameters on residual stress distribution has been studied, and the results indicated that decreasing constant duty cycle and laser pulse length reduces the size and stress gradient of maximum stress’ region for x-direction tensile stresses. It provides operation parameters’ optimization choice with guidance to control or reduce residual stress.

In-plane gait planning for earthworm-like metameric robots using genetic algorithm

Locomotion of earthworm-like metameric robots results from shape changes of deformable segments. Morphologically, the segments could stretch, contract or bend by changing their states. Periodic shape changes are recognized as gaits of the robots. Robots could employ different gaits for different locomotion tasks. However, earthworm-like robots generally possess a number of independent segments and their hyper-redundant morphology (Chirikjian G S and Burdick J W 1995 IEEE Trans. Robot. Autom. 11 781–93) poses a challenge to gait planning for their locomotion. Hence, the goal of this paper is to establish a framework of in-plane gait planning for earthworm-like robots. To this end, a generic model of earthworm-like robots modelled in our prior work (Zhan X et al 2019 Int. J. Robot. Res. 38 1751–1774) is firstly reviewed and in-plane gaits of the robot are parameterized by adopting the principle of retrograde peristaltic wave (Quillin K J 1999 J. Exp. Biol. 202 661–674). Following this, gaits of earthworm-like robots could be uniquely determined by gait parameters, and gait planning of the robots is then reduced to optimizing the gait parameters. The framework mainly consists of a locomotion simulation module and a genetic algorithm module. In the locomotion simulation, the performance of each gait would be evaluated, and then gait parameters get evolved based on the fitness in the genetic algorithm module. To evaluate the fitness of each gait, two objective functions, i.e., the distance to goals and the number of locomotion steps the earthworm-like robot taken before reaching the goals, are to be minimized in the optimization. Besides, two stopping criteria are proposed to improve the efficiency of evaluation. The framework proposed in the paper could plan in-plane gaits of earthworm-like robots, in contrast, only rectilinear locomotion is considered in similar works. This greatly advances the state of art of earthworm-like robots.

Geometric Gait Design for a Starfish‐Inspired Robot Using a Planar Discrete Elastic Rod Model

A starfish‐inspired robotic platform consisting of multiple soft fluidic bending actuator arms arranged with radial symmetry about a rigid hub is described. Intrinsic properties of the soft actuators are estimated via computer vision for varying input fluid pressures. The dynamic motion of individual arms and the full robot are modeled using the planar discrete elastic rod (PDER) theory. Locomotion gaits (periodic shape changes) that result in translation in the plane, separately considering fixed or rotating anchors at the end of each arm, are derived. Gait efficiency is defined as the displacement magnitude divided by a measure of the input control effort over each gait cycle, including a cost for anchor attachment. Through numerical computation, optimally efficient gaits are found and the desired motion with a pneumatic hardware prototype is demonstrated.

Mechanism of Interaction Between the Boundary Layer of a Polymer Membrane and a Gas Environment

The initial stage at the penetration of air molecules through a polymer membrane has been studied experimentally. A transient process giving rise to an equilibrium between the gas and the boundary layer of the membrane is revealed. This process looks like damped pressure oscillations associated with a periodic shape changes of polymer chains in the boundary layer driven by the “ball–globule” transition. A hypothesis is put forward that a similar phenomenon governs the influence of atmospheric pressure variations on the human organism.

Magnetically Propelled Fish-Like Nanoswimmers.

The swimming locomotion of fish involves a complex interplay between a deformable body and induced flow in the surrounding fluid. While innovative robotic devices, inspired by physicomechanical designs evolved in fish, have been created for underwater propulsion of large swimmers, scaling such powerful locomotion into micro-/nanoscale propulsion remains challenging. Here, a magnetically propelled fish-like artificial nanoswimmer is demonstrated that emulates the body and caudal fin propulsion swimming mechanism displayed by fish. To mimic the deformable fish body for periodic shape changes, template-electrosynthesized multisegment nanowire swimmers are used to construct the artificial nanofishes (diameter 200 nm; length 4.8 μm). The resulting nanofish consists a gold segment as the head, two nickel segments as the body, and one gold segment as the caudal fin, with three flexible porous silver hinges linking each segment. Under an oscillating magnetic field, the propulsive nickel elements bend the body and caudal fin periodically to generate travelling-wave motions with speeds exceeding 30 μm s-1 . The propulsion dynamics is studied theoretically using the immersed boundary method. Such body-deformable nanofishes exhibit a high swimming efficiency and can serve as promising biomimetic nanorobotic devices for nanoscale biomedical applications.

Stick-slip motion and elastic coupling in crawling cells

Crawling cells exhibit a variety of cell shape dynamics, ranging from complex ruffling and bubbling to oscillatory protrusion and retraction. Periodic shape changes during cell migration are recorded in fast-moving fish epithelial keratocytes where sticking and slipping at opposite sides of the cell's broad trailing edge generate bipedal locomotion. Barnhart et al. [Biophys. J. 98, 933 (2010)] recently proposed a mechanical spring model specifically designed to capture bipedal locomotion in these cells. We extend their model by benchmarking the dynamics of four mechanical configurations against those of crawling keratocytes. Our analysis shows that elastic coupling to the cell nucleus is necessary to generate its lateral motion. We select one configuration to study the effects of cell elasticity, size, and aspect ratio on crawling dynamics. This configuration predicts that shape dynamics are highly dependent on the lamellipodial elasticity but less sensitive to elasticity at the trailing edge. The model predicts a wide range of dynamics seen in actual crawling keratocytes, including coherent bipedal, coherent nonbipedal, and decoherent motions. This work highlights how the dynamical behavior of crawling cells can be derived from mechanical properties through which biochemical factors may operate to regulate cellular locomotion.

Dynamical Analysis of an Undulatory Wheeled Locomotor: a Trident Steering Walker

This paper presents a novel methodology of dynamical analysis of an undulatory wheeled locomotor: a trident steering walker based on Lagrangian mechanics. The trident steering walker moves by undulatory locomotion in which it transforms its periodic changes in shape into its displacement and it is a mechanical system subject to nonholonomic constraints in which all wheels roll without slipping on a horizontal plane. The dynamical equations of the trident steering walker consist of the Euler-Lagrange equations and the time derivatives of the equations of the nonholonomic constraints. The nonholonomic constraints are especially incorporated through the Lagrangian undetermined multipliers. I demonstrate the effectiveness of a dynamical control law which is derived from a path-following feedback kinematical control law previously designed by the author by performing a path-following motion in which the trident steering walker follows a third-order Bezier curve path. The dynamical equations are numerically integrated and the simulated state variables of Lagrangian mechanics exactly correspond with those of a commercial multibody dynamics simulator, LMS Virtual. Lab Motion. Therefore, the validity of the dynamical analysis of Lagrangian mechanics is verified by the comparison with the commercial multibody dynamics simulator.

Stokesian jellyfish: viscous locomotion of bilayer vesicles

Motivated by recent advances in vesicle engineering, we consider theoretically the locomotion of shape-changing bilayer vesicles at low Reynolds number. By modulating their volume and membrane composition, the vesicles can be made to change shape quasi-statically in thermal equilibrium. When the control parameters are tuned appropriately to yield periodic shape changes which are not time-reversible, the result is a net swimming motion over one cycle of shape deformation. For two classical vesicle models (spontaneous curvature and bilayer coupling), we determine numerically the sequence of vesicle shapes through an enthalpy minimization, as well as the fluid-body interactions by solving a boundary integral formulation of the Stokes equations. For both models, net locomotion can be obtained either by continuously modulating fore-aft asymmetric vesicle shapes, or by crossing a continuous shape-transition region and alternating between fore-aft asymmetric and fore-aft symmetric shapes. The obtained hydrodynamic efficiencies are similar to that of other low Reynolds number biological swimmers, and suggest that shape-changing vesicles might provide an alternative to flagella-based synthetic microswimmers.

Can the light-addressable potentiometric sensor (LAPS) detect extracellular potentials of cardiac myocytes?

The light-addressable potentiometric sensor (LAPS) measures localized photo-induced currents from a silicon wafer, which are dependent on the local surface potential and on the intensity of the light pointer. In this study the ability of the LAPS to record extracellular potentials of adherent cells was investigated. Time dependent LAPS photocurrent signals that correlated in time with contractions were recorded from beating cardiac myocytes cultured on LAPS surfaces. Signals could be recorded both when the LAPS was biased to working points where the photocurrent was maximally sensitive to potential changes and when it was biased to working points where the photocurrent was insensitive to changes in surface potential. Therefore, signals could not be predominantly created by changes in extracellular potential and might be related to mechanical contractions. One possible explanation might be, that the cell-induced modulation of photocurrents arose as a result of cell shape changes. Such alterations in cell shape might have focused and defocused the light pointer and, thus, modulated its intensity. To further test this hypothesis, height changes of beating cardiac myocytes were measured with an atomic force microscope (AFM). They were found to match well with signals derived from LAPS measurements. Therefore, it can be concluded, that LAPS signals were mainly determined by the periodic changes in shape of beating heart cells, and this interference precludes the measurements of extracellular electrophysiological potentials from these cells.

Shape oscillations of human neutrophil leukocytes: characterization and relationship to cell motility.

When neutrophil leukocytes are stimulated by chemotactic factors or by substratum contact, they change their shape. Shape changes are a prerequisite for cellular migration and typically involve the extrusion of thin, veil-like lamellipods and the development of morphological polarity. Stimulation also leads to changes in the neutrophil content of filamentous actin (F-actin), which is the major cytoskeletal component. Suspensions of human neutrophils stimulated with chemoattractants exhibit sinusoidal light-scattering oscillations with a period of approximately 8 s at 37 degrees C. These oscillations arise from periodic fluctuations in the cell body size caused by lamellipod extension and retraction cycles. The light-scattering oscillations are paralleled by corresponding oscillations in F-actin content. This raises the interesting possibility that cyclic actin polymerization constitutes the driving force for shape oscillations of suspended neutrophils. Similar periodic shape changes are present in neutrophils crawling on a surface, suggesting that shape oscillations are important for neutrophil motion. This review summarizes our present knowledge about shape oscillations in suspended and crawling neutrophils and discusses a possible role for these oscillations in neutrophil motility.