Elastomer Layer Research Articles

Parametric study on the vertical operational characteristics of carbon fiber reinforced elastomeric isolators using Taguchi approach

This paper investigates the viability of implementing the Taguchi method for conducting a parametric study of fiber reinforced elastomeric isolators (FREIs) in a systematic way. In this regard, the vertical properties of carbon fiber reinforced elastomeric isolators (C-FREIs) were chosen as a case study. Finite element models were first validated with experimental data to model a range of full-scale C-FREIs by varying five different physical and mechanical properties. The Taguchi method assumes minimal interaction between the factors and cannot be applied directly during design due to the highly non-linear behavior of elastomeric isolators. This study addresses this limitation through a unique array design. The C-FREI combinations to be modelled and analyzed were significantly reduced where the additivity of the Taguchi method suggested a very robust manner to test the performance of the bearings. Finally, a comprehensive parametric study was conducted on the vertical stiffness and compression modulus of the introduced C-FREIs. The trends obtained indicated that the vertical stiffness of C-FREIs is more sensitive to variations in most factors compared to the compression modulus. Variations in the carbon fiber reinforcement thickness have the lowest effect on the vertical stiffness whereas variations in the number of elastomer layers have the lowest effect on the compression modulus of C-FREIs. Furthermore, changes in the primary and secondary shape factors obtained by varying the loading area caused the highest variation in the vertical stiffness and compression modulus of C-FREIs.

Multi-sized planar capacitive pressure sensor with ultra-high sensitivity

It is now widely accepted that the capacitive pressure sensor has potential benefits for future robotic technologies, human-machine interface, artificial intelligence and health monitoring devices. Despite this fact, the conventional stacked structure including an intermediate dielectric layer between the neighboring electrode layers usually possesses considerable device thickness and size, thus imposing limits on the applicable scale. Here we develop a planar structured pressure sensor without the integrated elastic dielectric layer, and ultra-high sensitivity is achieved enabled by the emerging charge exchange channels between neighboring electrodes induced by external touching stimuli. Each pixel can be fabricated within a several-micrometer range and a tiny pressure of 0.02 Pa would result in a 750% increase in the relative capacitance (equivalent sensitivity of 3.75 × 10 5 kPa −1 for 0–0.05 Pa, exceeding all the previous reports to date). The working mechanisms are quantitatively investigated and proved to be applicable to macro-sized devices. Simultaneously, we illustrate the capabilities of such sensors by using them to perform static pressure mapping, generating capacitance signals to reflect its own surface morphology when the AFM tip passes by, detecting fingers touching, recording real-time human breath, and distinguishing the contact position. This work develops a planar structured pressure sensor without the integrated elastic dielectric layer, and ultra-high sensitivity (3.75 × 10 5 kPa −1 for 0–0.05 Pa) is achieved enabled by the emerging charge exchange channels between neighboring electrodes induced by external touching stimuli. Such devices can sense external stimuli based on the emerging charge exchange channels and be fabricated within wide scale ranges (from several micrometers to several millimeters). The practical application, like revealing the sample surface morphology in atomic force microscope (AFM), detecting fingers touching, recording real-time human breath, and distinguishing the contact position is also demonstrated in this research. • A planar capacitive pressure sensor is developed based on the emerging charge exchange channels between electrodes. • Multi-sized devices were fabricated from several micrometers to several millimeters without the limits of elastomer layers. • Micro-sized pressure sensor can reach an equivalent sensitivity of 3.75 × 10 5 kPa −1 for 0–0.05 Pa.

Thermomechanical characterization of metal-polyurethane bonded joints: effect of manufacturing parameters and working temperature

ABSTRACT Metal-elastomer bonded joints are typical of different industrial applications, specifically pallet truck wheels, where the solid elastomeric layer is bonded to the metal body. This paper focuses on the effect of manufacturing parameters and working temperature, on the shear strength of a metal-elastomer bonded joint. Through a comprehensive experimental test plan, the paper investigates the effect of thermal conditioning of the adhesive, shot peening of the metal adherend, type of solvent-based adhesive, and working temperature of the joint. The test plan uses a TAST-like specimen with a sandwich configuration (metal-elastomer-metal), loaded in order to originate a nearly pure-shear stress state. The results show which parameters influence most the shear strength of the joint helping the designer in maximizing the load-carrying capacity of the joint.

Experimental analysis of sound absorption effect of specially developed elastomeric thin thermoplastic polyurethane sub-micron fibre web layers placed on rigid layer and flexible layers

ABSTRACT The aim of this study is to determine the effect of sub-micron fibre web layers on sound absorption properties when they are placed on rigid substrate and flexible substrate. Elastomeric thermoplastic polyurethane (TPU) and composite TPU/PS (polystyrene) sub-micron fibre webs with both rigid glass fibre fabric reinforced epoxy composites (GFEC) and flexible polypropylene (PP) spunbond nonwovens have been examined. Elastomeric TPU sub-micron fibres and TPU/PS fibre web before and after soxhlet extraction were studied. Even though a thin layer of (less than 1 mm) electrospun sub-micron fibres were used with GFEC, sound absorption coefficient (SAC) improved from 0.1 to 0.4. Maximum SAC is drawn back to lower frequency (from 1250 to 500–630 Hz), when sub-micron fibre web is used on nonwoven. In conclusion, the mechanism of elastomeric thin sub-micron fibre webs on sound absorption for rigid GFEC and for flexible nonwoven is totally different than each other.

Surface instabilities of constrained elastomeric layers subject to electro-static stressing

Surface instabilities on the top surface of a soft elastomeric dielectric layer bonded on its bottom to a stiff substrate are investigated for two electro-static conditions: (I) a voltage difference imposed across the top and bottom surfaces of the layer which are both conducting, and (II) a voltage difference imposed across a rigid planar electrode above the layer and the conducting top surface of the layer. In the absence of surface energy, the critical voltage associated with the onset of instability of the planar state is shown to be a surface mode with any wavelength that is short compared to the layer thickness. With no layer pre-stretch and no surface energy, the uniform state in (I) has hydrostatic compression while that of (II) has hydrostatic tension, nevertheless the critical voltage is the same for both problems if the permittivity is the same for both systems. The role of equi-biaxial pre-stretch and surface energy is presented for both problems for neo-Hookean materials and for the Gent generalization. The thrust of the study is the investigation of the post-bifurcation behavior involving nonlinear interactions among the simultaneous surface modes associated with the critical voltage. The post-bifurcation response of Problem I is a crease-like mode with the top surface probing downward towards the lower surface. The opposite occurs for Problem II with the formation of a sharp ridge protruding towards the upper electrode. The bifurcation behavior is highly unstable leading to an extreme sensitivity to small imperfections. The study complements earlier work and highlights unresolved issues.

Measurement of turbulent boundary layer unsteady wall pressures beneath elastomer layers of various thicknesses on a plate

The attenuation of turbulence-inducedwall pressure fluctuations through elastomer layers is studied experimentally and analytically. Wall pressure statistics are measured downstream from a backward facing step, with no elastomer present and beneath 2-, 3- and 4-mm-thick elastomers in a water tunnel facility. In the absence of an elastomer layer, the wall pressure spectra, cross-spectra and velocity statistics measured at the various locations downstream from the backward facing step are in excellent agreement with those reported in the archival literature. The streamwise coherence measured beneath the elastomer layers is higher than that measured in the absence of an elastomer layer, an effect which increases with increasing elastomer thickness. It is speculated that this increase in coherence level is due to the ability of the elastomer to support shear stresses, which effectively increases the area over which an eddy influences the normal stresses measured by the pressure sensors. The high-frequency filtering of the elastomers is also observed in the coherence at the smallest streamwise separation. The attenuation of the turbulent boundary layer wall pressure fluctuations through the elastomer layer using an analytical elastomer transfer function is in excellent agreement with the attenuation measured experimentally through all thicknesses of elastomer and at all the free stream velocities at which the experiments are performed.

Ultrasensitive, Stretchable, and Fast-Response Temperature Sensors Based on Hydrogel Films for Wearable Applications.

Conductive hydrogels can be used in wearable electronics integrated with skin, but the bulk structure of existing hydrogel-based temperature sensors limits the wearing comfort, response/recovery speeds, and sensitivity. Here, stretchable and transparent temperature sensors based on a novel thin-film sandwich structure (TFSS) are designed, which display unprecedented thermal sensitivity (24.54%/°C), fast response time (0.19 s) and recovery time (0.08 s), a broad detection range (from -28 to 95.3 °C), high resolution (0.8 °C), and high stability. The thin hydrogel layer (12.15 μm) is encapsulated by two thin elastomer layers, which prevent the water evaporation and enhance the heat transfer, leading to the boosted stability and accelerated response/recovery speeds. The nondrying and antifreezing capabilities are further promoted by the hydratable lithium bromide (LiBr) incorporated in the hydrogel, enabling it to avoid dehydration in an extremely arid environment and freeze below subzero temperatures (freezing point below -120 °C). A comparative study reveals that the thermal sensitivity displayed by the TFSS sensor in capacitance mode is several times higher than that in conventional conductance/resistance mode above room temperature. Importantly, a new mechanism based on a horizontal plate capacitance model is proposed to understand the high sensitivity by considering the permittivity and geometry variations of TFSS. The thin TFSS, stretchability and transparency enable the sensor to be conformally and comfortably attached to human skin for real-time and reliable monitoring of various human motions, physical states, skin temperature, etc., without affecting the appearance.

Shear stress distribution of unbonded reinforced elastomeric bearings after lift-off occurs

Reinforced elastomeric bearings (REBs) are widely used to accommodate displacements in bridges as well as for seismic isolation applications. For unbonded REBs, lift-off (i.e. separation between the superstructure and the bearings) could occur under certain combinations of large rotations and relatively low axial stress. Canadian and American bridge design codes (i.e. CSA S6 and AASHTO) have inconsistent requirements in the regulation of lift-off. The objective of this study is to validate the existing analytical solution of the moment-rotation relationship for unbonded REBs considering lift-off by finite element analysis (FEA). The analytical solution, which accounts for the compressibility of the elastomer and extensibility of the reinforcement, has not yet been validated. The shear strain distribution in the elastomeric layers of unbonded REBs is derived and validated by FEA. Eight infinite strip-shaped bearings with different number of layers are investigated. The results show that the numerical curves fit well with the analytical curves in terms of the overall tendency. The analytical solutions could be used to predict the behaviour of unbonded REBs subjected to lift-off. The numerical results of the moment-rotation relationship were more agreeable to the analytical solutions for the unbonded bearings with fewer number of layers and under smaller loads.

Strain history of 3D printed bilayer structure with flexible elastomer and shape memory polymer filaments during thermal tensile test

This study aimed to investigate the strain history of a 3D-printed shape-memory polymer (SMP) and elastomer bilayer specimen under thermal tensile load. First, printing conditions for producing single-layer and bilayer specimens using a fused deposition modeling 3D printer were determined. Tensile tests under thermal effects were then conducted on both specimens. A 1 kg weight was used as a constant tensile load, and temperature cycles ranging from 25 to 65 °C were implemented to determine the thermal effects. The strain history was measured using a strain gauge attached to the specimen during the tests. An initial bending deformation caused by the shrinkage of the elastomer layer was observed in the bilayer specimen immediately after printing. This initial bending was then removed from the bilayer specimen via uniform heating. Strain relaxation was observed in the strain history of the single-layer SMP specimen. Mismatch strain between the two layers of the bilayer specimens was also confirmed from the thermal tensile test results. Analyses and discussions on the strain history data are provided in this paper. In general, this study determined the empirical deformation characteristics of a 3D-printed SMP–elastomer bilayer structure under combined thermal and tensile loading conditions. The results can be used to comprehend the deformation of bilayer SMP–elastomer structures and will be useful for designing a bilayer structure made of 3D-printed SMP material.

Flexible microhyperboloids facets giant sensitive ultra-low pressure sensor

We report a low-cost, flexible, and highly sensitive capacitive ultra-low pressure sensor using the micro-hyperboloid structure (mHBS). The flexible pressure sensor comprises of the PDMS (poly-dimethylsiloxane) elastomeric dielectric thin layer, and ITO (Indium Tin Oxide) coated PET (poly-ethylene tetra-fluoride) flexible conducting electrodes. The sensor with the hyperboloid structure shows the 0.1–96 % change in capacitance for 1 Pa to 100 kPa pressure range. With the capability of ultra-low pressure detection (1 Pa) and fast response speed (40 ms), this pressure sensor shows the sensitivity of 1.8 kPa−1 in the pressure range of 1 Pa–120 Pa. The sensitivity of the sensor was increased with the increase of its effective area, i.e., the sensor's sensitivity was 0.27 kPa-1, 0.99 kPa-1, and 1.8 kPa-1 for the effective area of 9 × 9 mm2, 12 × 12 mm2, and 15 × 15 mm2, respectively. Furthermore, the sensor shows excellent stability, responsitivity with low power consumption. These results indicate that the fabricated sensor based on the microhyperboloid structure surface of the elastomeric dielectric thin layer enhances the pressure sensor's performance and can be used as a wearable pressure sensor and is applicable for pressure sensing devices.

Experiments and Numerical Implementation of a Boundary Value Problem Involving a Magnetorheological Elastomer Layer Subjected to a Nonuniform Magnetic Field

Abstract This study investigates experimentally and numerically the response of a magnetorheological elastomer (MRE) layer placed atop an electromagnetic coil. The MRE layer is deflected upon application of a current in the coil, which creates highly nonuniform magnetic fields. Isotropic and transversely isotropic layers (i.e., containing chains of magnetic particles) are tested experimentally, and the isotropic layer exhibits the largest deflection. To enhance the energetic efficiency of the model device, an iron core is introduced inside the electromagnetic coil, thereby leading to an increase in the resulting magnetic field near the center of the MRE layer. In parallel, the boundary value problem —including the MRE layer, the coil, the core (if present) and the surrounding air—is modeled numerically. For this, a magneto-mechanical, vector potential-based variational formulation is implemented in a standard three-dimensional finite element model at finite strains. For the material description, a recently proposed analytical homogenization-guided model is used to analyze the MRE in the “coil-only” configuration. It is then employed to predict the response of the layer in the “coil plus core” configuration, thus circumventing the need for a separate material characterization procedure. The proposed numerical simulation strategy provides a deeper understanding of the underlying complexity of the magnetic fields and of their interaction with the MRE layer. This study also reveals the importance of modeling the entire setup for predicting the response of MRE materials and, as a result, constitutes a step toward designing more efficient MRE-based devices.

A nonlinear plane strain finite element analysis for multilayer elastomeric bearings

The purpose of this paper is the prediction of the behaviour of multilayer elastomeric bearings by the finite element analysis. First, the finite element formulation of equilibrium equations of incompressible elasticity problem is presented. This approach is based on the modified potential energy taking into account the incompressibility. The linearized system obtained is solved by the Newton–Raphson iterative method with the total lagrangian formulation. A large plane strain element is developed for the analysis of elastomeric materials under large strain deformation. This element is then integrated into our software. After validating the plane strain element using examples with known exact solutions, an industrial case study made of laminated (metal-rubber) elastomeric component is examined. The stress distribution study is limited to the elastomeric layers, possible sources of crack appearance.

Effect of interfacial stiffness on the stretchability of metal/elastomer bilayers under in-plane biaxial tension

Flexible electronic devices are often subjected to large and repeated deformation, so that their functional components such as metal interconnects need to sustain strains up to tens of percent, which is far beyond the intrinsic deformability of metal materials (~1%). To meet the stringent requirements of flexible electronics, metal/elastomer bilayers, a stretchable structure that consists of a metal film adhered to a stretchable elastomer substrate, have been developed to improve the stretch capability of metal interconnects. Previous studies have predicted that the metal/elastomer bilayers are much more stretchable than freestanding metal films. However, these investigations usually assume perfect bonding between the metal and elastomer layers. In this work, the effect of the metal/elastomer interface with a finite interfacial stiffness on the stretchability of bilayer structures is analyzed. The results show that the assumption of perfect interface (with infinite interfacial stiffness) may lead to an overestimation of the stretchability of bilayer structures. It is also demonstrated that increased adhesion between the metal and elastomer layers can enhance the stretchability of the metal layer.

Unobtrusive, Cuffless Blood Pressure Monitoring Using a Soft Polymer Sensor Array With Flexible Hybrid Electronics

The state-of-the-art systems for blood pressure (BP) monitoring often use cuffed-based rigid sensory systems, bulky electronics, multiple measurement sites, and intermittent measurement. Here, we introduce a new type of epidermal electronics that were specifically designed for cuffless BP-monitoring system, named multiPANI. The proposed fully integrated wearable device is equipped with a wireless-flexible hybrid electronics, a personalized flexible sensor array, and encapsulated with a thin biocompatible elastomer layer for soft-conformal contact with the complex skin surface structure. In addition, a unique capability of multiPANI to monitor multiple local pulse wave velocity (PWV) enabling us to develop a novel hybrid BP estimation algorithm that combine a selective-local PWV and high-signal-to-noise-ratio-based pulse wave analysis (PWA) for robust-cuffless BP-monitoring system. Experimental results indicate that the proposed hybrid selective PWV-PWA BP model outperform the typical single-PWV BP model by ~30%, with an acceptable root-mean-square-error performance of 3.94 ± 0.5 and 1.88 ± 0.9 mmHg, for systolic BP and diastolic BP respectively. Collectively, this study demonstrated a unique solution of fully integrated epidermal electronics and hybrid BP estimation algorithm for a robust, cuffless, and long-term BP monitoring.

An investigation on ice adhesion and wear of surfaces with differential stiffness

Ice adhesion is known to be higher on stiff metallic surfaces and lower on compliant polymeric surfaces. In designing icephobic surfaces, while one approach is to use surfaces with lower stiffness, such surfaces typically exhibit poor wear resistance. The aim of this study is to create a patterned surface with differential stiffness such that there is always a shared contact between stiff and compliant surfaces, and to study the possibility of such surfaces having an optimal balance between low ice adhesion and favorable wear resistance. Patterned surfaces with alternating layers of stiff aluminum and compliant polyurethane elastomer were fabricated, and ice adhesion and wear behavior of such patterned surfaces are reported. Ice adhesion as a function of the metal-polymer contact area ratio was studied, and patterned surfaces exhibited reduced ice adhesion compared to a plain aluminum surface. Reciprocating ball-on-flat sliding tests were used to study the wear behavior of the surfaces. Wear resistance of the patterned surfaces is presented in terms of wear depth, and the patterned surfaces exhibited higher wear resistance than plain polyurethane surface. Simple finite element modeling was used to arrive at stress states of the patterned surfaces and to understand their wear behavior. The novel surface engineering approach outlined in this paper shows promise for realizing durable icephobic surfaces under contact conditions.

Fingerpad-Inspired Multimodal Electronic Skin for Material Discrimination and Texture Recognition.

Human skin plays a critical role in a person communicating with his or her environment through diverse activities such as touching or deforming an object. Various electronic skin (E‐skin) devices have been developed that show functional or geometrical superiority to human skin. However, research into stretchable E‐skin that can simultaneously distinguish materials and textures has not been established yet. Here, the first approach to achieving a stretchable multimodal device is reported, that operates on the basis of various electrical properties of piezoelectricity, triboelectricity, and piezoresistivity and that exceeds the capabilities of human tactile perception. The prepared E‐skin is composed of a wrinkle‐patterned silicon elastomer, hybrid nanomaterials of silver nanowires and zinc oxide nanowires, and a thin elastomeric dielectric layer covering the hybrid nanomaterials, where the dielectric layer exhibits high surface roughness mimicking human fingerprints. This versatile device can identify and distinguish not only mechanical stress from a single stimulus such as pressure, tensile strain, or vibration but also that from a combination of multiple stimuli. With simultaneous sensing and analysis of the integrated stimuli, the approach enables material discrimination and texture recognition for a biomimetic prosthesis when the multifunctional E‐skin is applied to a robotic hand.

Shape memory alloy based 3D printed composite actuators with variable stiffness and large reversible deformation

Soft composite actuators can be fabricated by embedding shape memory alloy (SMA) wires into soft polymer matrices. Shape retention and recovery of these actuators are typically achieved by incorporating shape memory polymer segments into the actuator structure. However, this requires complex manufacturing processes. This work uses multimaterial 3D printing to fabricate composite actuators with variable stiffness capable of shape retention and recovery. The hinges of the bending actuators presented here are printed from a soft elastomeric layer as well as a rigid shape memory polymer (SMP) layer. The SMA wires are embedded eccentrically over the entire length of the printed structure to provide the actuation bending force, while the resistive wires are embedded into the SMP layer of the hinges to change the temperature and the bending stiffness of the actuator hinges via Joule heating. The temperature of the embedded SMA wire and the printed SMP segments is changed sequentially to accomplish a large bending deformation, retention of the deformed shape, and recovery of the original shape, without applying any external mechanical force. The SMP layer thickness was varied to investigate its effect on shape retention and recovery. A nonlinear finite element model was used to predict the deformation of the actuators.

Experimental and numerical study on developed elastomeric layers based on natural and butyl matrix rubbers for viscoelastic dampers

Elastomeric layers, that serve as the base of a viscoelastic (VE) damping system in structures, dissipate energy through shear deformation and transform vibration energy into heat by internal friction between polymer chains. In this study, two compounds, based on natural rubber (NR) matrix and butyl rubber (IIR) matrix, were designed and manufactured. Then, the mechanical and dynamic properties of elastomeric layers were investigated. Dynamic loading tests were conducted on the elastomeric layers using a frequency range of 0.1–1.5 Hz and a shear strain range of 10–150% under harmonic loading in order to analyze their hysteretic behavior. The output of the experiments shows that the both of elastomeric layers have a large deformation capability with a high damping performance, but the IIR damper can provide high energy dissipation capacity compared with the NR damper that has a large restoring force. The results also show an increase in storage modulus and loss factor of VE dampers with increasing frequency and their decrease with increasing strain. However, the dependency of VE damper on strain and strain rate based on NR is more remarkable than that of VE damper based on IIR. The experimental data were also used for validation and calibration of numerical simulation by ABAQUS software. The results proved to be satisfactory.

Aerosol Spray Deposition of Liquid Metal and Elastomer Coatings for Rapid Processing of Stretchable Electronics.

We report a spray deposition technique for patterning liquid metal alloys to form stretchable conductors, which can then be encapsulated in silicone elastomers via the same spraying procedure. While spraying has been used previously to deposit many materials, including liquid metals, this work focuses on quantifying the spraying process and combining it with silicones. Spraying generates liquid metal microparticles (~5 μm diameter) that pass through openings in a stencil to produce traces with high resolution (~300 µm resolution using stencils from a craft cutter) on a substrate. The spraying produces sufficient kinetic energy (~14 m/s) to distort the particles on impact, which allows them to merge together. This merging process depends on both particle size and velocity. Particles of similar size do not merge when cast as a film. Likewise, smaller particles (<1 µm) moving at the same speed do not rupture on impact either, though calculations suggest that such particles could rupture at higher velocities. The liquid metal features can be encased by spraying uncured silicone elastomer from a volatile solvent to form a conformal coating that does not disrupt the liquid metal features during spraying. Alternating layers of liquid metal and elastomer may be patterned sequentially to build multilayer devices, such as soft and stretchable sensors.

Fabrication of a Dual Stimuli-Responsive Assorted Film Comprising Magnetic- and Gold-Nanoparticles with a Self-Assembly Protein of α-Synuclein.

Development of sensing elements for controllable soft materials is crucial to improve their responsiveness toward remotely provided external stimuli. Magnetic nanoparticles (MNPs) and gold nanoparticles (AuNPs) have been coassembled into a flexible free-floating 2D film to produce a shape deformable mobile structure in the presence of magnetic field and light irradiation by employing a self-assembly protein of α-synuclein (αS). αS was demonstrated to be essential for the preparation of a multisensory system because the intrinsically disordered protein led to a complete dispersion of MNPs to an average size of 10 nm in aqueous solution, pH-dependent closely packed single layer adsorption of αS-MNPs, and α-helix-mediated free-floating MNP monolayer film formation upon dissolving the underlying polycarbonate substrate with chloroform. As AuNPs were incorporated into the assorted hybrid film in the presence of MNPs, however, the β-sheet component became prominent. By placing the assorted film between a spin-coated thin layer of thermoresponsive P(AAc-co-NIPAAm) hydrogel comprising acrylic acid and N-isopropylacrylamide and a passive layer of silicone elastomer, the resulting triply structure exhibited not only magnet-induced locomotion but also shape deformation due to asymmetric contraction of the sandwiching two layers caused by the heat generated by AuNPs upon near IR irradiation. In fact, two adjoining planar layers of another triply structure were shown to form a three-dimensional lotus flower with the light. This multisensory system is suggested to be further functionalized by modifying the αS molecules and incorporating additional nanoparticles to react to diverse stimuli, which would make the system be utilized in the areas of not only soft robotics but also foldable electronics, high-performance sensors/actuators, and medical/wearable applications.