Elastomer Shell Research Articles

Highly compressive aerogel-elastomer hybrid porous material with redistributed strain for high-sensitive soft pressure sensors

Owing to the good sensitivity and simple fabrication process, flexible piezoresistive pressure sensors based on aerogels shows great applications in soft robotics, bioelectronics and so on. However, the poor compressibility and stability of the aerogel is still challenging the development of aerogel based flexible piezoresistive pressure sensors, simultaneously, it is urgent to pave a way to enhance the sensitivity of these sensors. Here, for the first time, we propose a universal strategy to prepare aerogel skeleton-elastomer shell hybrid porous material with enhanced compressibility for high-sensitive and stable flexible pressure sensors. We found that the elastomer shell disperses the strain in the aerogel skeleton and enhances the compressibility of the aerogel, which improve the stability of the sensor (10000 cycles of compression). More importantly, there are elastomer micro-blocks formed in the hybrid material, these micro-blocks redistribute the strain in the material which contributes to the high sensitivity (10.25 kPa−1) of the sensors. Furthermore, the sensors are successful in monitoring both of the large joint bending and subtle skin vibration, as well as remote controlling toy car and artificial hand. This work provides an effective and universal strategy to enhance the sensitivity and stability of the aerogel based flexible pressure sensors and promotes their development towards practical applications.

Efficient large-deformation shell elements for the simulation of electromechanical coupling effects in incompressible dielectric elastomers

So-called electro-active polymers are not only capable of undergoing very large deformations, but they also exhibit different electromechanical coupling effects due to their dielectric or electrostrictive characteristics. In the present paper the sub-class of dielectric elastomers is studied; in particular, we focus on thin dielectric elastomer shells, which undergo large deformations under an applied electric field. We develop a framework for the modeling and subsequent efficient simulation of thin structures made from incompressible dielectric elastomers. A thermodynamically consistent phenomenological continuum model based on the free energy density is adapted imposing the kinematic assumptions of Kirchhoff-Love shells in combination with including the thickness deformation and the electric field as independent unknown fields. To make the formulation accessible to finite element simulations, existing non-linear elastic shell mixed finite elements are extended to the present hyperelastic electromechanically coupled formulation for dielectric elastomer shells. Computational results of the shell theory are compared to three-dimensional results validating the proposed modeling and numerical simulation methodology, and showing high accuracy already for coarse finite element discretizations of the shell.

Analysis of quasi-periodic and chaotic motion of a dielectric elastomer shell under alternating voltage

Analysis of quasi-periodic and chaotic motion of a dielectric elastomer shell under alternating voltage

Microballoons: Osmotically-inflated elastomer shells for ultrafast release of encapsulants and mechanical energy

HypothesisMicrocapsules with osmotically-inflated elastic shells exhibit an ultrafast release of encapsulants while mechanically stimulating the microenvironments, akin to popping balloons. ExperimentsTo prepare elastic shells with uniform thickness and size, monodisperse water-in-oil-in-water (W/O/W) double-emulsion drops are produced in a capillary microfluidic device. The polydimethylsiloxane (PDMS)-containing oil phase is thermally cured to create the elastic shell. The elastic shells are inflated by pumping water into the lumen in hypotonic conditions. The inflated microcapsules produced undergo mechanical compression, and their release properties are studied. FindingsBy controlling the osmotic pressure difference, Microballoons are inflated into a diameter of 200 μm – 316 μm and shell thickness of 7.8 μm – 0.7 µm, respectively. The inflated shell pops due to mechanical failure when subjected to mechanical stress above a certain threshold, resembling a balloon. During popping, the stretched shell rapidly retracts to the original uninflated state, resulting in an ultrafast release of encapsulants from the lumen within a millisecond. This process converts elastic potential energy stored in the shell into mechanical energy with substantial power. The microballoons mechanically stimulate the local environment, leading to the direct and rapid release of encapsulants. This has the potential to improve absorption efficiency.

Progressive adhesion mechanics of elastomeric shells against a rigid substrate: From thin to thick

Hemispherical elastomeric shells with a range of thickness, h, press against a planar glass plate in the presence of interfacial adhesion. The applied load, P, is measured as a function of approach distance, δ, while the contact radius, a, is simultaneously monitored. Thick shells with thickness exceeding 3/10 of the hemispherical radius, R, behaves as the classical Hertz-JKR solid sphere, as manifested by the pull-off tensile force and contact radius. As the shell gets thinner, the detachment trajectory deviates and the pull-off force decreases. Very thin shells with h/R falling below 0.05, an uptick in adhesion is observed. Measurements are performed in shells fabricated in two common polymers. Experimental data are fairly consistent with computational results generated by finite element analysis.

Electrostatic-hydraulic coupled soft actuator for micropump application

The development of a soft actuator with high displacement is crucial for the effective operation of micropumps, ensuring a high fluid pump rate. This study introduces an innovative approach by presenting the design and fabrication of a novel electrostatic-hydraulic coupled soft actuator for a micropump within a microfluidic system. This pioneering soft actuator, leveraging electrostatic-hydraulic coupling, showcases a unique solution to enhance the performance of micropumps. The versatility of such a soft actuator makes it particularly promising for biomedical applications. The actuator comprises dielectric fluid in an elastomeric shell and electrodes to form the out-of-plane fluid-amplified displacement. This displacement amplification was used to generate a pumping actuation in the micropump. The actuator was characterized in terms of dielectric fluid volume, electrode size, temporal response, and amplification displacement. The soft actuator showed a maximum amplified displacement of 0.51 mm at 10 kV of the applied voltage, but a higher voltage caused a dielectric breakdown. Moreover, the actuator demonstrated the ability to operate at frequencies of 0.25 Hz and 0.1 Hz. The results of the study indicate that the fabricated electrostatic-hydraulic coupled soft actuator is a dependable and effective method of actuation for a micropump in a microfluidic system. The experimental characterization of the micropump revealed a maximum flow rate of 2304 μl min−1.

Stress-strain state of a composite tractive element with a broken structure due to elastomer shell rheology

Purpose. Establishing a dependency of change in a stress-strain state for a rubber-cable tractive element with broken structure due to rheology of a rubber shell. Methods. Analytical solution of a model of a rubber-cable tractive element with a broken structure due to rheology of a rubber shell. Results. An algorithm for determining a stress-strain state of a rubber-cable tractive element with a broken structure due to rheology of a rubber shell is developed. The suggested algorithm involves splitting the rope into two parts, which allows considering the influence of a dependency of shear modulus on deformations in a form of a broken line constructed of two segments. Splitting the rope in the area of integrity breakage into three or more parts allows considering a more complex dependency of shear modulus on shear deformations. A mechanism of changing a stress-strain state of a rubber-cable rope due to rheology of a rubber shell is established. The local influence of changes in properties of elastic material interacting with a damaged cable on a stress-strain state of a rubber-cable tractive element with a broken structure is analyzed. Scientific novelty. A mechanism of influence of a shear modulus of rubber shell material in the rubber-cable rope (belt) with a cable integrity breakage on stress-strain state of composite tractive element is established to be time-varying and nonlinearly dependent on deformations. Practical significance. Consideration of shell rubber rheology makes it possible to predict a rope stress state considering a non-linear law of changes in properties of rubber during its use and to increase safety and operational reliability of rubber-cable tractive elements. A local change in mechanical parameters does not increase the danger of using a rope with continuity breakages of cables. An increase in lengths of redistribution of forces and displacements requires an increase in length of steps in butt-joint connections.

A Soft Capsule for Magnetically Driven Drug Delivery Based on a Hard-Magnetic Elastomer Foam.

Drug delivery systems based on porous soft biomaterials have been widely reported because of stimuli-responsive drug release and their inherent reservoirs for drug storage. Especially, magnetic-responsive porous soft biomaterials achieve rapid and real-time control of drug release due to the magnetic field-triggered large deformation. However, the drug release profiles of these materials are difficult to predict and repeat, which restrict them from releasing drugs in the required dosage. Here, we report a soft capsule based on a flexible hard-magnetic elastomer foam (HEF) for magnetically controlled on-demand drug delivery. The HEF capsule contains an inner HEF and an outer elastomer shell. The HEF exhibits low elastic modulus (10 kPa) and highly interconnected pores (81% interconnected pores). Benefitting from the novel precompressed magnetization, the compressive deformation of HEF reaches 66%. Thus, an adjustable drug release rate ranging from 0.02 to 1.7 mL/min in the HEF capsule is achieved. The deformation-triggered drug release profiles of the HEF capsule under the magnetic field are accurately predicted, allowing 85% accuracy in drug dosage regulation and more than 90% maximum cumulative drug release. Especially, the HEF capsule is proven capable of acting as a soft robot to perform magnetically driven drug delivery in a human stomach model. HEF can potentially serve as a soft robot for biomedical applications in the human body.

Preparation of Linear Actuators Based on Polyvinyl Alcohol Hydrogels Activated by AC Voltage.

Currently, the preparation of actuators based on ionic electroactive polymers with a fast response is considered an urgent topic. In this article, a new approach to activate polyvinyl alcohol (PVA) hydrogels by applying an AC voltage is proposed. The suggested approach involves an activation mechanism in which the PVA hydrogel-based actuators undergo extension/contraction (swelling/shrinking) cycles due to the local vibration of the ions. The vibration does not cause movement towards the electrodes but results in hydrogel heating, transforming the water molecules into a gaseous state and causing the actuator to swell. Two types of linear actuators based on PVA hydrogels were prepared, using two types of reinforcement for the elastomeric shell (spiral weave and fabric woven braided mesh). The extension/contraction of the actuators, activation time, and efficiency were studied, considering the PVA content, applied voltage, frequency, and load. It was found that the overall extension of the spiral weave-reinforced actuators under a load of ~20 kPa can reach more than 60%, with an activation time of ~3 s by applying an AC voltage of 200 V and a frequency of 500 Hz. Conversely, the overall contraction of the actuators reinforced by fabric woven braided mesh under the same conditions can reach more than 20%, with an activation time of ~3 s. Moreover, the activation force (swelling load) of the PVA hydrogels can reach up to 297 kPa. The developed actuators have broad applications in medicine, soft robotics, the aerospace industry, and artificial muscles.

Thin Membranes Based on FBG Sensors for Real-Time Subbandage Pressure Monitoring

This work focuses on the manufacturing and testing of a new device for medical bandage monitoring. Excessive pressure exerted from the compression bandage can block the blood flow of the patient, causing different medical complications to the skin, nerves, and circulatory system. On the contrary, if the pressure applied is low, the therapy is not effective. The utility, therefore, arises from a device capable of quantitatively indicating the correct adjustment of the bandage. The technological demonstrators developed consist of a polyurethane elastomeric shell with a thin composite supporting core. Fiber Bragg grating sensors (FBGSs) embedded within this core permit the detection of the subbandage pressure applied during compression therapy. The two prototypes were applied under arm bandages to evaluate their capability to transmit the applied pressure to the embedded FBGS. We demonstrated the ability to monitor the bandaging action by measuring the level of pressure exerted with the rounds of bandages. Moreover, the thin membranes permit the monitoring of the heartbeat of the patient, giving feedback about blood irrotation. The device developed is, therefore, promising to improve the results of compression therapy.

Procedure to categorize wheelchair cushion performance using compliant buttock models

Purpose: Wheelchair cushion prescription often seeks to address tissue integrity in addition to other clinical indicators. Because hundreds of wheelchair cushion models are available, a benefit would result if cushions were classified in a more valid manner to help guide selection by clinicians and users. The objective of this research was to develop an approach to evaluate and classify wheelchair cushion performance with respect to pressure redistribution. Materials and methods: Two anatomically-based buttock models were designed consisting of an elastomeric shell that models overall buttock form and a rigid substructure that abstracts load-bearing aspects of the skeleton. Model shapes were based upon elliptical and trigonometric equations, respectively. Two performance parameters were defined, pressure magnitude and pressure redistribution. The pressure magnitude parameter compared internal pressure values of the test cushion to a flat foam reference material, resulting in three classifications, superior, comparable, and inferior. Surface sensors were used to distinguish cushions with high, moderate or low pressure redistribution performance. Ten wheelchair cushions were evaluated by both models using two loads that represent a range of body weights expected for 41–43 cm wide cushions. Results and Conclusion: A classification matrix is proposed using both models and performance parameters. Two cushions met criteria for the highest level of performance, and one cushion was deemed to have inadequate performance for therapeutic value. The proposed method has a sensitivity to discern differences, compatibility with different sized cushions, and a versatility in classification. As such, it stands as an improvement over existing classification approaches.

Birefringence-modulated total internal reflection in liquid crystal shells

The combination of anisotropic boundary conditions and topological constraints acting on a spherical shell of nematic liquid crystal confined between aqueous phases gives rise to peculiar but well-defined configurations of the director field, and thus of the optic axis that defines the impact of the nematic birefringence. While the resulting optics of nematic shells has been extensively investigated in transmission, studies of the reflection behavior are scarce. Here we show that nematic shells exhibit specific light guiding paths mediated by birefringence-modulated total internal reflection (TIR) within the shell. With stabilizers promoting tangential boundary conditions, shells show immobile antipodal spots revealing the locations of maximum effective refractive index, but their intensity is modulated by the polarization of the illuminating light. With normal-aligning stabilizers, shells instead show bright arcs separated by dark spots, and these follow the rotation of the polarization of the illuminating light. Reflection polarizing microscopy thus offers a valuable complement to the more common characterization in transmission, adding data that can be helpful for accurately mapping out director fields in shells of any liquid crystal phase. Moreover, the TIR-mediated light guiding paths may offer interesting handles to localize photopolymerization of reactive liquid crystal shells or to dynamically modulate the response of light-triggered liquid crystal elastomer shell actuators.

Atypical rupture of a Poly Implant Prothése implant and fluid shifting: a case report

Women have undergone augmentation mammoplasty for decades, and if implant rupture is suspected, imaging modalities such as magnetic resonance imaging (MRI) and ultrasonography are available. The linguine sign, keyhole sign, and noose sign are all suggestive of rupture. However, earlier-generation implants with alternative filler materials demonstrate rupture signs that differ from those of today’s better-known implant materials. A 60-year-old female patient who had undergone augmentation mammoplasty 20 years ago presented with left breast swelling and pain in the lower-outer quadrant. Ultrasonography and MRI confirmed extracapsular diffuse wall enhancement with suspected, but not apparent, discontinuity in the patient’s left breast implant. Therefore, both implants were removed. It was determined that these were Poly Implant Prothése implants. The left breast implant differed from the contralateral implant in that it contained fluctuating fluid. This could be attributed to an osmotic gradient that caused the implant to swell and weakened the elastomer shell, resulting in micro rupture without a gross tear. Patients who undergo augmentation mammoplasty should have regular follow-up examinations, even if there are no symptoms. Furthermore, clinicians should be aware that some patients who have had breast augmentation mammoplasty may experience atypical symptoms and signs if the implant ruptures.

3D Printed Spring‐Type Electronics with Liquid Metals for Highly Stretchable Conductors and Inductive Strain/Pressure Sensors (Adv. Mater. Technol. 7/2022)

Spring-Type Electronics In article number 2101657, Tomoyuki Yokota, Takao Someya and colleagues develop soft spring-type electronic devices formed by core–sheath structures of liquid metals and 3D-printed elastomeric shells. The spring devices work not only as stretchable conductors with minor resistance change, but also as inductive strain/pressure sensors for robotic applications by using the change in the magnetic flux caused by the spring deformation.

‘Pasta-Bly’ the best radiologic imaging sign—I saw the linguine sign

The linguine sign is a radiologic sign seen on magnetic resonance imaging (MRI) that indicates intracapsular rupture of silicone breast implants. It refers to multiple curvilinear lines that appear on MRI, representing the outline of the elastomeric shell of the silicone implant floating freely within the silicone gel. The term first appeared in literature in 1992 when optimal imaging techniques and modalities for implant rupture were still unclear, and since then the term “linguine sign” has been widely used to describe evidence of intracapsular rupture.

Multistable shape programming of variable-stiffness electromagnetic devices.

Programmable shape morphing enables soft machines to safely and effectively interact with the environment. Stimuli-responsive materials can transform 2D sheets into 3D geometries. However, most solutions cannot hold their shape at zero power, are limited to predetermined configurations, or lack sufficient mechanical stiffness to manipulate common objects. We demonstrate here segmented soft electromagnetic actuators integrated with shape memory polymer (SMP) films, capable of deforming and latching into a broad range of configurations. The device consists of liquid metal (LM) coils in an elastomer shell, laminated between two SMP films. The coils are linked by narrow joints, on which stretchable heaters are patterned. Heating the SMP greatly reduces its stiffness. Driving current through an LM coil in the presence of a magnetic field then leads to large bending or twisting. Cooling the SMP locks in the shape, leading to load-bearing capacity. Complex shapes are obtained from an initially flat device.

Integrated and shape-adaptable multifunctional flexible triboelectric nanogenerators using coaxial direct ink writing 3D printing

Triboelectric nanogenerators (TENGs), particularly those with high flexibility and sophisticated geometry, have shown great application foreground in portable and wearable electronics. However, traditional fabrication approaches remain complicated and non-versatile, which are also impractical in the preparation of complex shapes and structures. Herein, a one-pot coaxial direct ink writing (DIW) 3D printing technique has been proposed to fabricate a fully flexible single-electrode TENG (FFTENG) with sophisticated shapes and 3D structures for the purpose of harvesting and utilizing biomechanical energy. This FFTENG is made up of a silicone elastomer shell as the triboelectric layer and an inner silicone/carbon black (CB) core as the flexible electrode. Various factors that affect the output electric performance, including the ratio of the inner and outer diameter of the printed fiber, CB content, loading frequency, applied contact force, specimen size, and external load resistance, are investigated in detail via the contact-separation test. The results show that a standard square FFTENG with a size of 30 × 30 mm2 can yield an open-circuit voltage (Voc), a short-circuit current (Isc) and a short-circuit transferred charge (Qsc) of as high as 60 V, 0.23 μA and 58 nC, respectively, and a maximum output peak power density of 15.59 mW m−2 at a matched resistance of 80 MΩ. More importantly, various shape-adaptable FFTENGs can be designed and tailored to meet the diverse needs of different applications, such as self-powered LED systems, self-charging power systems, LED control devices, self-powered tactile sensors, flexible self-monitoring grip exercisers, and flexible self-powered keyboards, and open up new avenues for use in multifunctional self-powered electronic systems, including biomechanical energy harvesting and utilization, self-powered sensing and human-machine interaction.

Большие упругие деформации эластомерной торовой оболочки (резиновой муфты) при совместном действии крутящих моментов и центробежных сил

The article considers solving the problem of large axisymmetric deformations of elastomeric torus shells of revolution, loaded with jointly acting torques, axial and centrifugal forces. The task is posed due to the calculation of rubber elements of couplings. The calculations are performed according to the momentless shell theory by solving a nonlinear one-dimensional boundary value problem using the shooting method, as well as in a three-dimensional formulation using the finite element method. The calculation results are presented both for convex and concave torus shells. The load characteristics are compared for free and constrained torsion. The dependence of axial reactions in supports on torque and centrifugal forces has been investigated.

Liquid crystal elastomer shells with topological defect-defined actuation: Complex shape morphing, opening/closing, and unidirectional rotation

We produce hollow sphere liquid crystal elastomer (LCE) actuators from a nematic precursor mixture, brought into the shape of a self-closing shell with tangential anchoring of the director field n(r), using a solvent-assisted microfluidic technique. By separating the shell production from the polymerization and cross-linking, the precursor is allowed to approach its equilibrium n(r) configuration in the shell, spontaneously forming topological defects of total strength +2. However, the photopolymerization into an LCE induces a brief but strong distortion of the overall n(r) and the defect configuration, even changing the ground state shape in the case of thick shells. The resulting LCE shells show a rich capacity for reversible shape morphing upon heating and cooling, the exact actuation mode defined by n(r), and the final defect configuration stabilized at the end of polymerization. In regions with a single +1 defect, a reversal of curvature from concave to convex is found, punctured shells exhibit a strong shape change between a nearly closed sphere at low temperature and an open-ended spherocylinder at high temperature, and all shells rotate upon actuation when suspended in a fluid. As the rotation is stronger during relaxation than during actuation, thus breaking the symmetry, the net rotation is unidirectional.

125 A Case of Mistaken Identity: An Obsolete Anti-Reflux Device in An Older Patient with Variable Gastrointestinal Symptoms

Abstract Background A frail 93-year-old lady presented with delirium and hypoxia, on a background of heart failure, constipation, cerebrovascular disease, and osteoporosis. A CTPA on admission revealed an unusual appearance of the left hypochondrium, leading to subsequent CT abdomen. This unexpectedly reported the presence of a gastric band. We therefore considered a possible misidentification as this procedure seemed unlikely in someone of her age. Her GP records revealed that she underwent surgical insertion of an Angelchik prosthesis in 1984. It transpired that our patient had experienced several longstanding symptoms, including reflux, bloating and constipation, which have all been observed in patients with Angelchik prostheses in situ. Discussion The Angelchik prosthesis is an anti-reflux device for patients with chronic reflux disease with or without hiatus hernia, introduced in 1979. It comprised of an elastomer shell ring filled with silicone gel, that was sited at the lower oesophagus and secured with DACRON tapes. It was initially lauded for its replicable insertion technique and promising early results with around 30,000 being inserted in mainly British and American Hospitals. However, over time it became apparent that a significant proportion of patients reported ongoing gastrointestinal symptoms due to device failure. Serious complications such as gastric perforations were also recognised. Surgical removal was noted to be technically complex, providing further challenges. The Angelchik prosthesis therefore fell from favour after a period of use of only fifteen years, and is now rarely encountered. We discovered that our patient had experienced multiple long-standing gastrointestinal complaints potentially linked to her prosthesis, though this association had not previously been considered. Whilst her frailty meant that removal would not be pragmatic, it is uncertain if this could have been a possible consideration in the past. This device is relevant to geriatricians as many recipients are now elderly, and may report ongoing symptoms.