Elastomer Balloon Research Articles

Chaotic self-beating of left ventricle modeled by liquid crystal elastomer

Self-vibration systems using active materials generate sustained vibrations spontaneously through synergistic actions between internal structure and external environment. Therefore, the self-vibration systems have a wide application prospect in bionic design and soft robots. Inspired by the human left ventricle, a novel chaotic self-beating system modeled by an electrothermal responsive liquid crystal elastomer balloon is proposed. To study the self-beating characteristics of the liquid crystal elastomer left ventricle, a simplified theoretical framework is formed by combining the electric joule heat conduction model, the left ventricle circulatory system model and the dynamic principle. The numerical results show that the left ventricle has two typical self-beating modes: periodic beating and chaotic beating. The mechanisms of periodic beating and chaotic beating are elucidated by analyzing the balance between the work done by each force on the left ventricle. In addition, the effects of key system parameters on self-beating behavior are investigated in detail. This research will promote the application of chaotic dynamics in artificial hearts and medical devices, while providing a new perspective for the study of chaotic behavior and mechanism in biology.

Approximate analytical solutions of nonlinear vibration and bifurcation of dielectric elastomer balloon

Dielectric elastomers (DE), a novel class of actuators, are increasingly employed in fields such as soft robotics and vibration control. Most existing studies investigating the dynamic characteristics of DE structures neglect the viscoelasticity and strain-stiffening effects of materials, with only a few offering approximate analytical solutions. This paper establishes the governing equation for the dynamics of a DE balloon, utilizing the principle of virtual work and considering material viscoelasticity and strain-stiffening effects through linear damping and the Gent hyperelastic model, respectively. The nonlinear governing equations are simplified using the Chebyshev polynomial approximation. The multiple scales method is applied to derive approximate solutions for the structure's free vibration under static voltage excitation and parametrically excited vibration under harmonic voltage excitation. The accuracy of these approximate analytical solutions is validated by comparison with numerical solutions. Additionally, the paper analyzes stability and bifurcation phenomena through time-domain response curves, amplitude-frequency curves, and phase trajectories. Furthermore, the influence of the stretching limit, voltage, and damping on the nonlinear vibration of the balloon structure is studied, providing a valuable theoretical foundation for the future design and utilization of dielectric elastomers.

Dynamic Modeling and Analysis of Soft Dielectric Elastomer Balloon Actuator with Polymer Chains Crosslinks, Entanglements and Finite Extensibility

Soft dielectric elastomers (SDEs) represent a category of intelligent electroactive materials utilized in electro-mechanical actuation technology. The dynamic performance of these materials during actuation is notably affected by intrinsic factors like crosslinks, entanglements and the limited extensibility of polymer chains. In this paper, we provide a theoretical framework for modeling the dynamic behavior of a balloon actuator made up of soft dielectric elastomer. To account for the inherent characteristics of polymer chain networks, we employ a physics-based nonaffine material model proposed by Davidson and Goulbourne. The governing equation for dynamic motion is established using Euler–Lagrange’s equation of motion for conservative systems. The reported dynamic modeling framework is then utilized to explore the transient response, stability, periodicity and resonance properties of a dielectric elastomer balloon (DEB) actuator for varying levels of polymer chain crosslinks, entanglements and finite extensibility parameters. To assess the periodicity and stability of the nonlinear vibrations exhibited by the DEB actuator, we present Poincaré maps and phase-plane plots. The results demonstrate that changes in the density of polymer chain entanglements lead to transitions between quasi-periodic and aperiodic vibrations. These findings represent an essential initial step toward the design and production of intelligent soft actuators with diverse applications in future technologies.

Light-powered sustained chaotic jumping of a liquid crystal elastomer balloon

Chaotic systems comprising of active materials have the capability to absorb energy directly from the external environment to preserve their own sustained motion, holding tremendous potential for utilization in diverse fields, for instance, controllable sensors, energy harvesting, motion behavior control of smart materials and more. In this paper, a sustained jumping system consisting of photosensitive liquid crystal elastomer (LCE) balloon is developed innovatively, in which the LCE balloon can transition from a static state to a sustained jumping state under periodic illumination. Given the dynamic constitutive model of LCE and Hertz contact theory, the nonlinear dynamics model of the sustained jumping LCE balloon system is established. Numerical calculations demonstrate the existence of two jumping modes for the LCE balloon, i.e., periodic jumping and chaotic jumping. The mechanism of sustained jumping that counterbalances the energy dissipation by the net work combining contact expansion and buoyancy variation, as well as the mechanism of chaotic phenomena, are revealed. In addition, the influences of vital parameters on the jumping mode of the balloon are examined, and the conversion of the jumping modes with parameters is illustrated by bifurcation diagrams. This work can broaden the knowledge of the dynamic behavior of smart materials, which is of guiding significance for the research on chaos control and chaotic system design.

Self-Sustained Chaotic Jumping of Liquid Crystal Elastomer Balloon under Steady Illumination.

Self-sustained chaotic jumping systems composed of active materials are characterized by their ability to maintain motion through drawing energy from the steady external environment, holding significant promise in actuators, medical devices, biomimetic robots, and other fields. In this paper, an innovative light-powered self-sustained chaotic jumping system is proposed, which comprises a liquid crystal elastomer (LCE) balloon and an elastic substrate. The corresponding theoretical model is developed by combining the dynamic constitutive model of an LCE with Hertz contact theory. Under steady illumination, the stationary LCE balloon experiences contraction and expansion, and through the work of contact expansion between LCE balloon and elastic substrate, it ultimately jumps up from the elastic substrate, achieving self-sustained jumping. Numerical calculations reveal that the LCE balloon exhibits periodic jumping and chaotic jumping under steady illumination. Moreover, we reveal the mechanism underlying self-sustained periodic jumping of the balloon in which the damping dissipation is compensated through balloon contact with the elastic substrate, as well as the mechanism involved behind self-sustained chaotic jumping. Furthermore, we provide insights into the effects of system parameters on the self-sustained jumping behaviors. The emphasis in this study is on the self-sustained chaotic jumping system, and the variation of the balloon jumping modes with parameters is illustrated through bifurcation diagrams. This work deepens the understanding of chaotic motion, contributes to the research of motion behavior control of smart materials, and provides ideas for the bionic design of chaotic vibrators and chaotic jumping robots.

Analysis of stretch distribution of high compliant elastomers within folded lumen vessels

Abstract Elastomer based high compliant balloons containing strain sensing element(s) (SEs) is currently under development intended for in-vivo biomechanical diagnostics of vessels. It could potentially reveal local lumen features based on patterns derived from the sensing elements. A Finite Element based, simulation study in COMSOL® (v5.6) focusses on in-vivo inflation behavior of an elastomeric balloon being equipped with SE, whose compliance is ideally magnitudes higher than the surrounding tissue in an idealized 2D setup. We hypothesized the vessel’s inner wall as a closed convexconcave 4-fold structure correlated to surface structures found in urethrae and parameterized the fold depth. A set of SEs consisted of one SE over the inner surface of balloon while the other over the outer wall. Out of the three adjacent placed sets, The first set was closer to the tissue lumen while the third set the farthest. We assessed the stretch of balloon over its inner circumference through SEs. At conformal contact with the tissue wall, The first SE shows a higher value, while the third element undergoes the least stretch within the three sensing elements. The SE’s over the outer circumference show the exact opposite relation. The differences between the sensing elements over the inner and outer circumferences show a correlation with the curvature of the tissue it conforms to. With use of balloon that was 10x thicker (10μm vs 1μm), around 10x larger stretch differences were captured suggesting possibility to use less sensitive measuring system. For the ideal situations performed, the curvature and depth information may be comprehended by observing differences between inner and outer SEs while thicker balloons prove to be more useful to generate differences that are easier to capture in practical situations. This semiquantitative study suggests that simulation studies are powerful tools to obtain new analytical techniques for shape characterization.

Finite element analysis of the interaction between high-compliant balloon catheters and non-cylindrical vessel structures: towards tactile sensing balloon catheters.

Aiming for sensing balloon catheters which are able to provide intraoperative information of the vessel stiffness and shape, the present study uses finite element analysis(FEA) to evaluate the interaction between high-compliant elastomer balloon catheters with the inner wall of a non-cylindrical-shaped lumen structure. The contact simulations are based on 3D models with varying balloon thicknesses and varying tissue geometries to analyse the resulting balloon and tissue deformation as well as the inflation pressuredependent contact area. The wrinkled tissue structure is modelled by utilizing a two-layer fibre-based Holzapfel-Gasser-Ogden constitutive model and the model parameters are adapted based on available biomechanical data for human urethral vessel samples. The balloon catheter structure is implemented as a high-compliant hyper-elastic silicone material (based on polydimethylsiloxane (PDMS)) with a varying catheter wall thickness between 0.5 and 2.5µm. Two control parameters are introduced to describe the balloon shape adaption in reaction to a wrinkled vessel wall during the inflation process. Basic semi-quantitative relations are revealed depending on the evolving balloon deformation and contact surface. Based on these relations some general design guidelines for balloon-based sensor catheters are presented. The results of the conducted in-silico study reveal some general interdependencies with respect to the compliance ratio between balloon and tissue and also in respect of the tissue aspect ratio. Further they support the proposed concept of high-compliant balloon catheters equipped for tactile sensing as diagnosis approach in urology and angioplasty.

Tunable morphing of electroactive dielectric-elastomer balloons

Designing smart devices with tunable shapes has important applications in industrial manufacture. In this paper, we investigate the nonlinear deformation and the morphological transitions between buckling, necking and snap-through instabilities of layered dielectric elastomer (DE) balloons in response to an applied radial voltage and an inner pressure. We propose a general mathematical theory of nonlinear electro-elasticity able to account for finite inhomogeneous strains provoked by the electro-mechanical coupling. We investigate the onsets of morphological transitions of the spherically symmetric balloons using the surface impedance matrix method. Moreover, we study the nonlinear evolution of the bifurcated branches through finite-element numerical simulations. Our analysis demonstrates the possibility to design tunable DE spheres, where the onset of buckling and necking can be controlled by geometrical and mechanical properties of the passive elastic layers. Relevant applications include soft robotics and mechanical actuators.

Light-Propelled Self-Swing of a Liquid Crystal Elastomer Balloon Swing

Light-propelled self-oscillation based on liquid crystal elastomers (LCEs) has been widely harnessed in designing soft robotics and actuating automatic machine fields due to no additional human control, precise manipulation and fast response. In this study, the light-propelled self-swing manner of an LCE balloon swing upon constant illumination is originally constructed and the corresponding nonlinear dynamic model is built. The solution strategy for evolving equation with respect to the swing angle is presented in light of Runge–Kutta explicit iterative approach. Two representative motion manners, i.e., static manner and self-swing manner, are presented. Self-swing mechanism is elucidated where the contraction and relaxation of the LCE balloon is coupled with the back-and-forth swing process and constant light energy from the environment is absorbed by the LCE balloon to compensate for the damping dissipation of the system. The impact of system parameters on self-swing is elaborated. The obtained results evince that self-swing motion can be triggered and tuned by virtue of some system parameters involved. Meanwhile, the frequency and amplitude of self-swing can be tailored to practical needs. Further, the results also furnish new insights into understanding of self-swing phenomenon and present new designs for future self-actuated soft micro-robotics system.

Self-sustained chaotic floating of a liquid crystal elastomer balloon under steady illumination

Self-sustained chaotic system has the capability to maintain its own motion through directly absorbing energy from the steady external environment, showing extensive application potential in energy harvesters, self-cleaning, biomimetic robots, encrypted communication and other fields. In this paper, a novel light-powered chaotic self-floating system is proposed by virtue of a nonlinear spring and a liquid crystal elastomer (LCE) balloon, which is capable of self-floating under steady illumination due to self-beating. The corresponding theoretical model is formulated by combining dynamic LCE model and Newtonian dynamics. Numerical calculations show that the periodic self-floating of LCE balloon can occur under steady illumination, which is attributed to the light-powered self-beating of LCE balloon with shading coating. Furthermore, the chaotic self-floating is presented to be developed from the periodic self-floating through period doubling bifurcation. In addition, the effects of system parameters on the self-floating behaviors of the system are also investigated. The detailed calculations demonstrate that the regime of self-floating LCE balloon depends on a combination of system parameters. The chaotic self-floating system of current study may inspire the design of other chaotic self-sustained motion based on stimuli-responsive materials, and have guiding significance for energy harvesters, self-cleaning, biomimetic robots, encrypted communication and other applications.

Self-oscillating floating of a spherical liquid crystal elastomer balloon under steady illumination

Self-oscillations have the advantages of direct energy harvest from the constant environment, autonomy, and portability of the equipment, and it is desired to develop a wealth of new self-excited motion modes for greatly expanding the application of active machines. In this paper, a self-oscillating floating balloon is creatively constructed, which consists of an optically-responsive liquid crystal elastomer (LCE) spherical balloon under steady layered illumination. A theoretical model is developed based on the well-established dynamic LCE model and the ideal gas model, and dynamics of the self-floating balloon is calculated numerically. The results show that the LCE balloon can self-float continuously up and down by the steady layered illumination, which is elucidated to arise from the coupling between the process-related buoyancy and the constant gravity. The self-floating of the LCE balloon can be maintained by the energy of the constant illumination, which compensates for the damping dissipation of the system. Furthermore, the effects of the system parameters on the triggering condition, amplitude and equilibrium position of the self-floating are extensively investigated. The self-floating balloon constructed in this paper will expand the application scope of self-oscillations, and its simple operation and accurate control will enjoy great application prospects in the fields of soft robotics, targeted therapy, military monitoring and environmental measurement.

Self-Jumping of a Liquid Crystal Elastomer Balloon under Steady Illumination.

Self-oscillation capable of maintaining periodic motion upon constant stimulus has potential applications in the fields of autonomous robotics, energy-generation devices, mechano-logistic devices, sensors, and so on. Inspired by the active jumping of kangaroos and frogs in nature, we proposed a self-jumping liquid crystal elastomer (LCE) balloon under steady illumination. Based on the balloon contact model and dynamic LCE model, a nonlinear dynamic model of a self-jumping LCE balloon under steady illumination was formulated and numerically calculated by the Runge–Kutta method. The results indicated that there exist two typical motion regimes for LCE balloon under steady illumination: the static regime and the self-jumping regime. The self-jumping of LCE balloon originates from its expansion during contact with a rigid surface, and the self-jumping can be maintained by absorbing light energy to compensate for the damping dissipation. In addition, the critical conditions for triggering self-jumping and the effects of several key system parameters on its frequency and amplitude were investigated in detail. The self-jumping LCE hollow balloon with larger internal space has greater potential to carry goods or equipment, and may open a new insight into the development of mobile robotics, soft robotics, sensors, controlled drug delivery, and other miniature device applications.

Nonlinear Vibration and Stability of a Dielectric Elastomer Balloon Based on a Strain-Stiffening Model

Limiting chain extensibility is a characteristic that plays a vital role in the stretching of highly elastic materials. The Gent model has been widely used to capture this behaviour, as it performs very well in fitting stress-stretch data in simple tension, and involves two material parameters only. Recently, Anssari-Benam and Bucchi (Int. J. Non. Linear. Mech. 128:103626, 2021) introduced a different form of generalised neo-Hookean model, focusing on the molecular structure of elastomers, and showed that their model encompasses all ranges of deformations, performing better than the Gent model in many respects, also with only two parameters. Here we investigate the nonlinear vibration and stability of a dielectric elastomer balloon modelled by that strain energy function. We derive the deformation field in spherical coordinates and the governing equations by the Euler-Lagrange method, assuming that the balloon retains its spherical symmetry as it inflates. We consider in turn that the balloon is under two types of voltages, a pure DC voltage and an AC voltage superimposed on a DC voltage. We analyse the dynamic response of the balloon and identify the influential parameters in the model. We find that the molecular structure of the material, as tracked by the number of segments in a single chain, can control the instability and the pull-in/snap-through critical voltage, as well as chaos and quasi-periodicity. The main result is that balloons made of materials exhibiting early strain-stiffening effects are more stable and less prone to generate chaotic nonlinear vibrations than when made of softer materials, such as those modelled by the neo-Hookean strain-energy density function.

Beating of a Spherical Liquid Crystal Elastomer Balloon under Periodic Illumination.

Periodic excitation is a relatively simple and common active control mode. Owing to the advantages of direct access to environmental energy and controllability under periodic illumination, it enjoys broad prospects for application in soft robotics and opto-mechanical energy conversion systems. More new oscillating systems need to be excavated to meet the various application requirements. A spherical liquid crystal elastomer (LCE) balloon model driven by periodic illumination is proposed and its periodic beating is studied theoretically. Based on the existing dynamic LCE model and the ideal gas model, the governing equation of motion for the LCE balloon is established. The numerical calculations show that periodic illumination can cause periodic beating of the LCE balloon, and the beating period of the LCE balloon depends on the illumination period. For the maximum steady-state amplitude of the beating, there exists an optimum illumination period and illumination time rate. The optimal illumination period is proved to be equivalent to the natural period of balloon oscillation. The effect of system parameters on beating amplitude are also studied. The amplitude is mainly affected by light intensity, contraction coefficient, amount of gaseous substance, volume of LCE balloon, mass density, external pressure, and damping coefficient, but not the initial velocity. It is expected that the beating LCE balloon will be suitable for the design of light-powered machines including engines, prosthetic blood pumps, aircraft, and swimmers.

Light-Activated Elongation/Shortening and Twisting of a Nematic Elastomer Balloon.

Nematic elastomer balloons with inflation-induced axial contraction and shear/torsion effect can be used as actuators for soft robots, artificial muscles, and biomedical instruments. The nematic elastomer can also generate drastic shape changes under illumination, and thus light can be utilized to activate the deformation of nematic elastomer balloons with huge advantages of being accurate, fast, untethered, and environmentally sustainable without chemical byproducts. To explore light-activated deformation behaviors of the balloon, a phenomenological relationship between light intensity and material parameters describing polymer backbone anisotropy is proposed from experiments, and a theoretical model of an optically-responsive nematic elastomer balloon is established based on the nematic elastomer theory. Various light-activated elongation/shortening and twisting behaviors in the cases of free-standing and axial-loading are presented and their mechanisms are elucidated. The light intensity and initial mesogen angle have great influences on the light-activated deformations including the radius, length, shearing angle and mesogen angle. Light can be easily controlled to trigger rich deformation processes, including elongation/shortening and torsion. The results of this paper are expected to promote the understanding of the light-activated deformation behaviors of the nematic elastomer balloon, and the applications in light-activated actuators and machines.

Ultra‐Compliant Indwelling Elastomer Balloons Improve Stability and Performance of Bioengineered Human Mini‐Hearts

Animal models used by the pharmaceutical industry to define drug safety and efficacy are expensive, resource‐intensive, subject to interspecies differences, and often fail to predict human responses. Therefore, engineered human tissue preparations are gaining importance as in vitro models to address translation from preclinical data to clinical outcome. Methods that improve fabrication consistency, usability, and physiological relevance of tissues are crucial. For cardiac applications, the goal is to form a miniature 3D chamber that mimics the physiology and biomechanical properties of the ventricle, allowing the measurement of clinically relevant endpoints, such as pressure–volume relationships, which cannot be obtained with simpler constructs. Despite advances in biofabrication, a perfusable mini‐ventricle with a competent endocardium remains an unmet challenge, resulting in thin‐walled organoids that are fluid permeable. A novel method is developed and validated for improving the stability and performance of the herein described human mini‐heart model by creating an ultra‐compliant elastomer balloon for hollow‐organ engineering applications. Balloon properties, tissue formation, and biological data are examined. Findings demonstrate a thin permanent lining, which is retained during testing and permits tissue contraction, functions to eliminate leakage, increase uniformity, and enable multiday longitudinal measurements. Biological data presented herein show reduced variability across measured cardiac parameters when compared to our previously published fabrication method.

A light-fueled self-oscillating liquid crystal elastomer balloon with self-shading effect

Developing new self-oscillating systems would greatly expand their applications in intelligent machines, advanced robotics, and biomedical devices, due to their advantages of directly harvesting ambient energy and self-control. In this paper, we creatively proposed a light-fueled self-oscillating liquid crystal elastomer (LCE) balloon with self-shading coating, which is capable of self-oscillating under steady ambient illumination. Based on the well-established dynamic LCE model and the ideal gas model, the governing equation of the free-standing LCE balloon is formulated, and dynamics of the self-oscillation is studied theoretically. Numerical calculations show that the balloon always evolves into two kinds of motion modes: static mode and oscillation mode. The mechanism of the self-oscillation is elucidated by the self-shading effect of the opaque power coating, and the conditions for triggering the self-oscillation are further obtained numerically. In addition, the effects of system parameters on amplitude, frequency and equilibrium position are also investigated. Amplitude and frequency are mainly affected by light intensity, damping coefficient, mass density and contraction coefficient, while are independent on initial velocity. It is anticipated that the self-oscillating balloon constructed in this paper would be of benefit in autonomous, self-sustained machines and devices with the core feature of photo-mechanical transduction.

Inflation-induced torsion and bulging of a nematic elastomer balloon

The liquid crystal mesogens in a nematic elastomer film under simple uniaxial tension may reorientate and in turn lead to shear of the film. This shear effect under simple loading has potential applications in artificial muscles, micro nano devices, biomedical instruments and other fields. When a nematic elastomer film is fabricated into a cylindrical balloon as a pneumatic artificial muscle, it has presented abnormal inflation behaviors including inflation-induced axial contraction. During the inflation process, the nematic elastomer balloon may also have shear/torsion effect due to the reorientation of the helically distributed liquid crystal mesogens. Based on the nematic elastomer theory proposed by Bladon et al., the torsion and bulging of a cylindrical nematic elastomer balloon under the combined action of axial tension and inflating pressure are theoretically investigated in this paper. In the cases of different axial tensions, the inflation process of the balloon shows a variety of torsion and bulging performances. The initial mesogen director also has a great influence on its torsion and bulging behaviors. The results of this paper further deepen the understanding of the inflation behaviors of a nematic elastomer balloon, and provide guidance for its applications in artificial muscles, soft robots and other fields.

Nonlinear dynamic behaviors and PID control of viscoelastic dielectric elastomer balloons

As a type of intelligent electroactive polymer, dielectric elastomer (DE) exhibits viscoelastic properties. It’s worth pointing out that the relaxation time has great significance for studying the mechanical behavior of viscoelastic polymer. In this paper, a generalized Maxwell model is used to describe the viscoelastic property of dielectric elastomer balloon. Meanwhile, a theoretical model with multiple relaxation times is used and the natural frequency of small amplitude oscillation is derived. Subsequently, the model is validated by comparing with experimental results. The model with double relaxation times can describe the deformation of the dielectric elastomer balloon effectively. Then the effect of relaxation time and shear modulus on the dynamic response of DE balloon is studied. Furthermore, the dielectric elastomer balloons in practical application exhibit the strong nonlinearity and the viscoelastic dissipation. Therefore, it is important to precisely control the dynamic response. The proportional-integral-differential (PID) controller in the form of nonlinear combination is adopted to control the above nonlinear dynamic systems actively. The results indicate that it is feasible to achieve desired control effect.

Stochastic dynamics of dielectric elastomer balloon with viscoelasticity under pressure disturbance

Abstract Dielectric elastomers are widely used in many fields due to their advantages of high deformability, light weight, biological compatibility, and high efficiency. In this study, the stochastic dynamic response and bifurcation of a dielectric elastomer balloon (DEB) with viscoelasticity are investigated. Firstly, the rheological model is adopted to describe the viscoelasticity of the DEB, and the dynamic model is deduced by using the free energy method. The effect of viscoelasticity on the state of equilibrium with static pressure and voltage is analysed. Then, the stochastic differential equation about the perturbation around the state of equilibrium is derived when the DEB is under random pressure and static voltage. The steady-state probability densities of the perturbation stretch ratio are determined by the generalized cell mapping method. The effects of parameter conditions on the mean value of the perturbation stretch ratio are calculated. Finally, sinusoidal voltage and random pressure are applied to the viscoelastic DEB, and the phenomenon of P-bifurcation is observed. Our results are compared with those obtained from Monte Carlo simulation to verify their accuracy. This work provides a potential theoretical reference for the design and application of DEs.