Soft Silicone Rubber Research Articles

Wireless and Battery-Free Sensor for Interstitial Fluid Pressure Monitoring.

Congestive heart failure (CHF) is a fatal disease with progressive severity and no cure; the heart's inability to adequately pump blood leads to fluid accumulation and frequent hospital readmissions after initial treatments. Therefore, it is imperative to continuously monitor CHF patients during its early stages to slow its progression and enable timely medical interventions for optimal treatment. An increase in interstitial fluid pressure (IFP) is indicative of acute CHF exacerbation, making IFP a viable biomarker for predicting upcoming CHF if continuously monitored. In this paper, we present an inductor-capacitor (LC) sensor for subcutaneous wireless and continuous IFP monitoring. The sensor is composed of inexpensive planar copper coils defined by a simple craft cutter, which serves as both the inductor and capacitor. Because of its sensing mechanism, the sensor does not require batteries and can wirelessly transmit pressure information. The sensor has a low-profile form factor for subcutaneous implantation and can communicate with a readout device through 4 layers of skin (12.7 mm thick in total). With a soft silicone rubber as the dielectric material between the copper coils, the sensor demonstrates an average sensitivity as high as -8.03 MHz/mmHg during in vitro simulations.

Experimental and theoretical investigation on magnetorheological elastomers containing carbonyl iron particles coated with silane coupling agent

Magnetorheological (MR) elastomer composites, comprising soft silicone rubber, various additives, and different weight fractions of carbonyl iron particles (CIPs) coated with silane coupling agent, are produced via a novel manufacturing process in an anisotropic state. This study encompasses both experimental and modeling investigations into the dynamic viscoelastic properties of magnetorheological elastomer (MREs) in shear mode under varying magnetic fields, displacement amplitudes, and frequencies. Two MRE vibration mitigation devices are fabricated to experimentally assess the shear storage modulus and the loss factor of MREs. The experimental findings reveal a pronounced MR effect in the MRE devices, where both the shear storage modulus and the loss factor increase with rising magnetic fields, frequencies, and particle weight fractions, yet decrease with higher displacement amplitudes. A modified fractional-derivative equivalent parametric model, grounded in a magnetic field- and frequency-dependent shear modulus model along with internal variable theory, is proposed to describe the effects of these key influencing factors on the MREs’ dynamic viscoelastic properties. Comparative analysis of experimental and numerical data demonstrates that this refined mathematical model can accurately represent the dynamic viscoelastic properties of MREs.

Elastic Tactile Sensor Glove for Dexterous Teaching by Demonstration.

We present a thin and elastic tactile sensor glove for teaching dexterous manipulation tasks to robots through human demonstration. The entire glove, including the sensor cells, base layer, and electrical connections, is made from soft and stretchable silicone rubber, adapting to deformations under bending and contact while preserving human dexterity. We develop a glove design with five fingers and a palm sensor, revise material formulations for reduced thickness, faster processing and lower cost, adapt manufacturing processes for reduced layer thickness, and design readout electronics for improved sensitivity and battery operation. We further address integration with a multi-camera system and motion reconstruction, wireless communication, and data processing to obtain multimodal reconstructions of human manipulation skills.

Numerical study of polymer embedded metal hydride-based self-sensing actuator

Metal hydride actuators have amassed increasing attention over the past decade owing to their desirable operational characteristics, such as a high power-to-weight ratio, noiseless and vibration-less operation, lightweight, safety and environmental friendliness. Essentially, there are two ways in which we can attain actuation using hydrides. Primarily, actuation force is generated by the hydrogen gas pressure changes associated with charge–discharge process. Alternatively, the incompressible volumetric changes in the hydride bed during sorption can also result in actuation. However the studies reported on this type of actuators are rare and mostly deal with bimorph actuators. The present study investigates the effect of soft silicone rubber composited metal hydride bed within a hollow stainless steel spring for its potential use as a self-sensing actuator element. LaNi5 is used as the metal hydride alloy. For an equivalent quantity of hydride by mass, the estimated actuation stroke and force for the composite bed actuator are better than their powder bed counterpart (12 mm and 100 N, respectively, in contrast to 5.84 mm and 60 N), due to improved heat transfer. Bed thickness, coil pitch and coil diameter are important geometric parameters which control the performance of the device. As previously reported, hydrogen supply pressure and heat transfer coefficient are found to be important operating parameters controlling the force –stroke characteristics of the actuating element. The simulation study has been executed using COMSOL Multiphysics™ commercial code.

Magnetic training of the soft magnetorheological elastomers

The effect of repetitive quasi-static magnetisation of a magnetorheological elastomer on its magnetic response is discussed. Typical components of this material, namely soft silicone rubber and carbonyl iron powder, are used to produce magnetically sensitive composite samples. The composite specimens are examined by vibrating sample magnetometry. The influence of the elasticity of the composite matrix on the change in magnetic differential susceptibility of the material as a function of the number of repeated magnetisation cycles is evaluated. The soft matrix elastomers are characterised by the presence of maxima in the initial part of the differential susceptibility curves. The sample magnetisation values corresponding to such maxima vary with the number of magnetisation cycles. In addition, the initial magnetic susceptibility curves of soft samples obtained at different polarity of the applied field are not symmetrical. Symmetry is obtained by performing several subsequent magnetisation cycles. The differential susceptibility curves are affected by both reversible and irreversible processes related to particle mobility in the matrix. The magnetic response of composite samples with rigid matrices is more similar to that of classical soft magnetic materials.

Modulating the Configurations of "Gel-Type" Soft Silicone Rubber for Electro-Mechanical Energy Generation Behavior in Wearable Electronics.

Electro-mechanical configurations can be piezo-electric transducers, triboelectric generators, electromagnetic induction, or hybrid systems. Our present study aims at developing energy generation through the piezoelectric principle. Gel-type soft SR with Shore A hardness below 30 was used as a versatile material for an elastomeric substrate. Also, multi-wall carbon nanotube (MWCNT), and diatomaceous earth (DE) were used as reinforcing fillers. This "gel-type" soft SR has crosslinking polymer networks with silicone encapsulated within its structure. Mechanical properties such as modulus or stretchability are of utmost importance for such devices based on "gel-type" soft. From the experiments, some of the mechanical aspect's values are summarized. For example, the stretchability was 99% (control) and changes to 127% (3 phr, MWCNT), 76% (20 phr DE), and 103% (20 phr hybrid). From electro-mechanical tests, the output voltage was 0.21 mV (control) and changed to 0.26 mV (3 phr, MWCNT), 0.19 mV (20 phr DE), and 0.29 mV (20 phr hybrid). Moreover, from real-time biomechanical human motion tests in "gel-type" soft-based composites, a relationship among output voltage from machine to human motions was established. Overall, these configurations make them promising against traditional portable devices such as batteries for small power applications such as mobile phones.

Flexible 1-3 Piezoelectric Composites with Soft Embedded Conductive Interconnects for Underwater Acoustic Transducers

1-3 Piezoelectric composites have been widely used in underwater acoustic transducers because of their advanced electromechanical coupling properties relative to bulk piezoelectric ceramics. However, the existing applied composites are mainly rigid 1-3 PZT–epoxy resin composites, which have rigid structures and cannot be adapted to various sonar carriers with complex surfaces. Here, we design and develop a flexible 1-3 PZT–silicone rubber composite (PSC) for the first time. PSC combines a soft silicone rubber polymer in PZT with flexible embedded island-bridge conductive interconnects to enable the flexibility of both the piezoelectric sensing core and the electrical layer. The flexible wide bridge structure embedded in the polymer can cope with the large bending deformation of PSC with good conductive property, while the rigid thin island structure ensures the high acoustic performance of piezoelectric materials. A PSC sample is prepared with its structural parameters optimized via finite element analysis and is experimentally verified to have good flexibility, high electromechanical coupling coefficient (kt = 0.7), great thermal stability (from 25 to 105 °C), and bending stability (bending angle up to 215°). In addition, a preparation method for flexible 1-3 PSC is introduced, which has the advantages of high efficiency, low cost, no sample size restriction, and no high-temperature operation. The flexible 1-3 PSC in this work paves an important way for the development and application of the next generation of flexible underwater acoustic transducers.

4D printing of hard magnetic soft materials based on NdFeB particles

Magnetic soft materials (MSM) show excellent potential in soft robotics, biomedicine, and sensors because of their excellent magnetic response, reversible deformation, and controlled motion. A hard magnetic soft material (HASM) that can be obtained by adding hard magnetic particles to a soft material matrix. By programing the spatial magnetization profile of the HASM object and manipulating the driving magnetic field, it exhibits excellent shape manipulation performance with unconstrained, reversible deformation transformation and controlled motion. In this study, a HASM ink consisting of hard magnetic NdFeB particles with a soft silicone rubber matrix was prepared. A 4D printing strategy using 3D injection printing technology combined with origami magnetization technology is used to fabricate 3D structured HASM objects for flexible shape programmability. A variety of programed shapes of HASM straight beams with bionic fish tails were fabricated by 4D printing strategy. The HASM straight beam is driven by the magnetic field, which can quickly realize the transformation and change of the preset shape as well as the shape of the HASM beam. The HASM bionic fish tail can swing rapidly under the action of the driving magnetic field. It shows a broad potential in the field of soft and bionic robots.

3D-Printed multi-material liver model with simultaneous mechanical and radiological tissue-mimicking features for improved realism.

89Anatomic models have an important role in the medical domain. However, soft tissue mechanical properties' representation is limited in mass-produced and 3D-printed models. In this study, a multi-material 3D printer was used to print a human liver model featuring tuned mechanical and radiological properties, with the goal of comparing the printed model with its printing material and real liver tissue. The main target was mechanical realism, while radiological similarity was a secondary objective. Materials and internal structure were selected such that the printed model would resemble liver tissue in terms of tensile properties. The model was printed at 33% scaling and 40% gyroid infill with a soft silicone rubber, and silicone oil as a filler fluid. After printing, the liver model underwent CT scanning. Since the shape of the liver is incompatible with tensile testing, tensile testing specimens were also printed. Three replicates were printed with the same internal structure as the liver model and three more out of silicone rubber with 100% rectilinear infill to allow a comparison. All specimens were tested in a four-step cyclic loading test protocol to compare elastic moduli and dissipated energy ratios. The fluid-filled and full-silicone specimens had initial elastic moduli of 0.26 MPa and 0.37 MPa, respectively, and featured dissipated energy ratios of 0.140, 0.167, 0.183, and 0.118, 0.093, 0.081, respectively, in the second, third, and fourth loading cycles. The liver model showed 225 ± 30 Hounsfield units (HU) in CT, which is closer to real human liver (70 ± 30 HU) than the printing silicone (340 ± 50 HU). Results suggest that the liver model became more realistic in terms of mechanical and radiological properties with the proposed printing approach as opposed to printing only with silicone rubber. Thus, it has been demonstrated that this printing method enables new customization opportunities in the field of anatomic models.

Data-driven multi-joint waveguide bending sensor based on time series neural network.

Due to the bulky interrogation devices, traditional fiber optic sensing system is mainly connected by wire or equipped only for large facilities. However, the advancement in neural network algorithms and flexible materials has broadened its application scenarios to bionics. In this paper, a multi-joint waveguide bending sensor based on color dyed filters is designed to detect bending angles, directions and positions. The sensors are fabricated by casting method using soft silicone rubber. Besides, required optical properties of sensor materials are characterized to better understand principles of the sensor design. Time series neural networks are utilized to predict bending position and angle quantitatively. The results confirm that the waveguide sensor demodulated by the data-driven neural network algorithm performs well and can be used for engineering applications.

Synthesis of a grape-like conductive carbon black/Ag hybrid as the conductive filler for soft silicone rubber.

Conductive silicone rubber (CSR) is an outstanding stretchable conductive composite due to its excellent mechanical properties and stable conductivity. In this paper, silver nanoparticles were deposited on carbon black (CB) through a reduction reaction. The uniform dispersion of silver particles on the surface of CB as well as the grape-like branch structure of hybrid particles was formed by the condensation reaction of the hydroxyl groups of CB with (3-mercaptopropyl) trimethoxysilane (KH-590), along with the interattraction between sulfhydryl groups of KH-590 and silver ions. This sulfhydryl modified conductive carbon black/Ag hybrid filler (SMCB@Ag) avoided the high processing viscosity of CSR caused by the hydroxyl groups of CB. The percolation threshold of CSR made from SMCB@Ag was 5.5 wt% according to the percolation equation. With the addition amount of SMCB@Ag increasing to 10 wt%, the conductivity of CSR increased from 10−5 to about 101. Moreover, the conductivity of this CSR showed excellent stability with extension of storage time and increase of stretching-recovery cycles.

Abstract 11290: Mechanical Loading Enhances the Ability to Predict Hypertrophic Cardiomyopathy Phenotypes with Human Induced Pluripotent Stem Cell Derived Cardiac Micro-Tissues

Introduction: Modeling hypertrophic cardiomyopathy (HCM) with human induced pluripotent stem cell (hiPSC) derived cardiomyocytes is challenging because of the immaturity of hiPSC-derived cardiomyocytes along with the need to recapitulate non-genetic factors that contribute to HCM pathogenesis. We assessed the effects of mechanical loading on the action potential waveform morphology of hiPSC-derived micro-heart muscle. We benchmarked these results against action potential morphology measured in primary human cardiomyocytes from HCM patients. Hypothesis: Mechanical loading is necessary for expression of HCM phenotypes in genotype-positive hiPSC cardiomyocyte engineerd tissues Methods: Control and MYBPC3 +/- iPSC were differentiated into cardiomyocytes which were used to form micro-heart muscle atop soft silicone rubber substrates with rigidity matching healthy (15 kPa) or fibrotic heart (65 kPa) muscle. Micro-tissues were stained with voltage sensitive dye to assess action potential duration (APD) under field pacing. Contractility was measured by monitoring the motion of fluorescent beads embedded into the substrates. Freshly isolated surgical specimens from HCM patients were enzymatically digested into single ventricular myocytes and compared to discarded WT donor hearts as controls. Adult cardiomyocytes were stained with the same voltage sensitive dye to measure APD. Results: MYBPC3 +/- micro-tissues had similar action potential waveforms to controls when the tissues worked against a 15 kPa substrate, although the MYBPC3 +/- tissues had higher contractility. On 65 kPa substrates, the degree of hypercontractility in MYBPC3 +/- tissues was less substantial. However, the action potential duration (APD) of these tissues was significantly longer than controls. This increase in APD of hiPSC-cardiomyocytes with an HCM-causing mutation was consistent with an increase in APD observed in primary HCM cardiomyocytes as compared to controls. Conclusions: Mechanical loading may be required to induce electrophysiological aspects of HCM phenotypes in genotype-positive cells to facilitate modeling this disease with iPSC-derived heart tissues.

Soft capacitive tactile sensor using displacement of air–water interface

We propose a soft capacitive tactile sensor using the displacement of an air–water interface. This soft tactile sensor is composed of a soft contact part with a chamber and channel filled with water and a clip-shaped sensing part to detect the position of the interface. This tactile sensor changes the displacement of the air–water interface in the channel when a contact force is applied. The change in displacement is detected as a change in the capacitance at the sensing part. This sensor structure does not require stiff electrical elements to be embedded in the soft silicone rubber body, which improves the flexibility and durability of the sensor. Therefore, the proposed tactile sensor exhibits high flexibility and durability against bending and external stresses. Additionally, the proposed tactile sensor can detect not only press force but also pull force. This results in the detection of a press or pinch in a robot skin. The experimental results show that the proposed sensor can successfully detect both press and pull static forces. The sensitivity of the proposed sensor was 0.169 pF/N for an applied force in the press direction and −0.152 pF/N for a force in the pull direction based on the results of an evaluation of the static sensor characteristics. Furthermore, an evaluation of the dynamic sensor characteristics revealed that the proposed tactile sensor has high repeatability and a quick response to an external force. Additionally, the hysteresis of the proposed tactile sensor is small, especially in the press direction.

О качестве измерений кожно-жировых складок калиперами и скользящим циркулем

A comparative study of the calipers GPM (DKSH, Switzerland), Holtain (Holtain Ltd, Great Britain), the caliper designed by V.E. Deryabin, and the sliding caliper GPM (Martin type) was carried out by the four measurers. The study was conducted using a metal caliper checking gauge GPM, a ‘sandwiches’ of soft silicone rubber kSil™ GP250 (Silicon Engineering, UK), as well as by measurements of subscapular, triceps, suprailiac, and calf skinfolds utilized in the Heath-Carter somatotype assessment scheme, in 20 adult volunteers (10 women and 10 men). Results and discussion. When measuring the caliper checking gauge, the V.E. Deryabin’s and the sliding caliper were accurate, the caliper GPM slightly underestimated (by 0.2 mm), and the caliper Holtain overestimated the exact values (by 0.4-0.6 mm). When measuring ‘sandwiches’ of silicone rubber, the GPM and Holtain calipers showed small but statistically significant differences between measurers (up to 1.4 mm), and for the V.E. Deryabin’s caliper, these differences were more pronounced (up to 5 mm). With a sufficiently high reproducibility of skinfold data, the mean values of their total thickness for the GPM and Holtain calipers differed significantly, and for the V.E. Deryabin and GPM calipers, there were no significant differences. The measurement data using the sliding caliper were consistent with those for the Holtain caliper but showed the largest variation of data between measurers: the maximal difference of the total skinfold thickness averages was 5.2 mm and 7.1 mm in the female and male subgroups, respectively, or 10-14% of the total averages. Conclusion. The results obtained support the need for mutual comparison of skinfold calipers and control of technical measurement errors to ensure data comparability. Cross-calibration of skinfold calipers is a necessary procedure that should precede the anthropometric study. When measured by an experienced anthropologist, the technical error of measuring skinfolds with a sliding caliper can be reduced, but this instrument is not recommended for training and subsequent use for skinfold measurements due to the high risk of obtaining inconsistent data.

A Novel Multi-Axial Pressure Sensor Probe for Measuring Triaxial Stress States Inside Soft Materials.

This paper presents the concept, design, construction, and validation of a novel probe based on the hexadic disposition of six pressure sensors suitable for measuring triaxial stress states inside bulky soft materials. The measurement of triaxial stress states inside bulk materials such as brain tissue surrogates is a challenging task needed to investigate internal organs’ stress states and validate FE models. The purpose of the work was the development and validation of a 17 × 17 × 17 mm probe containing six pressure sensors. To do so, six piezoresistive pressure sensors of 6 mm diameter were arranged into an hexad at three cartesian axes and bisecting angles, based on the analytical solution of the stress tensor. The resulting probe was embedded in a soft silicone rubber of known characteristics, calibrated under cyclic compression and shear in three orientations, and statically validated with combined loads. A calibration matrix was computed, and validation tests allowed us to estimate Von Mises stress under combined stress with an error below 6%. Hence, the proposed probe design and method can give indications about the complex stress state developing internally to soft materials under triaxial high-strain fields, opening applications in the analysis of biological models or physical surrogates involving parenchyma organs.

Investigating an Inverse Finite Element Approach for Characterising Soft Materials

ABSTRACT Soft materials, such as soft biological tissue and soft silicone rubber, are non-linear materials which require the classical uniaxial and biaxial tensile testing methods for characterisation. Unfortunately, in special cases, such as for soft biological tissue, the samples are smaller than 10 mm χ 10 mm in size and these classical tensile testing methods produce unwanted stress and strain gradients due to the fastening techniques associated with these methods. Micro-indentation is proposed as an alternative method for characterising soft materials. Using inverse Finite Element (FE) analysis and a known Mooney-Rivlin three parameter material model, six different micro-indentation tests were proposed. A theoretical approach was used to determine which indentation test best characterised a silicone sample, by using two FE models. The results showed that microindentation is capable of characterising a soft material in ideal conditions with a cylindrical indenter applied in a diagonal orientation over the sample, as the best indentation method. Finally, it was observed that the material model can either match the displacements with the smallest objective function or the stress vs. stretch curve can be matched to 99 % over the whole stretch range but not both simultaneously. Additional keywords: Inverse Finite Elements analysis, Micro-indentation, Gradient optimisation, Mooney-Rivlin hyper-elastic material model.

Design and Development of Artificial Spinal Ligaments for Paediatric Synthetic Spine

A synthetic spine is a model fabricated from artificial materials consisting of the vertebrae, intervertebral discs and ligaments for spinal testing. The synthetic spine overcomes many difficulties associated with biological specimens such as handling, biohazard concerns, high costs, and limited availability of specimens, quality and large inter-specimen variability. This paper presents the design and development of spinal ligaments to mimic the stiffness of the paediatric ligaments for use in the synthetic spine. Spinal ligaments are uniaxial structures in the spine that carry tensile loads along the direction of the fibres. Early in the research, silicone materials were used to cover the whole spinal unit, but it became apparent that the material responses were inadequate. The synthetic spine was revised to use fibreglass tape to more closely simulate the natural spinal structures. The composite design applied in this paper consisted of soft silicone rubber and fibreglass tape to obtain the natural stiffness that normally occurred in the spinal ligaments.

Wavefront shaping in underwater with soft gradient-index metasurfaces at ultrasonic frequencies

Metasurfaces are planar metamaterials with a subwavelength thickness that allows wavefront shaping by introducing in-plane variations, namely, gradients, in the spatial wave response of these flat structures. Most of the recently reported acoustic metasurfaces were designed to control air-borne waves. Here, we report a new class of acoustic gradient-index (GRIN) metasurfaces engineered from soft graded-porous silicone rubber with a high and tunable acoustic index for broadband ultrasonic 3-D wavefront shaping in aqueous media. The functionalities of these soft flat lenses are illustrated through various experiments, which demonstrate beam steering and beam focusing, as well as vortex beam generation in free water. These new GRIN metasurfaces may have important applications in various domains using designed ultrasonic fields (biomedical imaging, industrial non-destructive testing, contactless particle manipulation), since their fabrication is very straightforward with common polymer science engineering. Y. Jin, R. Kumar, O. Poncelet, O. Mondain-Monval, and T. Brunet, Nat. Commun. 10, 143 (2019).

Effect of particle size and size distribution on the permeability of soft magnetic liquid silicone rubber composites

Magnetic composites made of LSR (Liquid Silicone Rubber) and a magnetic filler have been investigated with respect to magnetic field guidance for transcutaneous energy transport. Effects of particle size and size distribution on the effective initial magnetic permeability are analyzed. A simple model is presented to describe the permeability as a function of the degree of filling, particle size and size distribution. From this, a calculus for the relevant size average of the filler was developed at 20 vol% of magnetic filler. The calculus showed self-consistency and can be used to tailor optimized powders for better field guidance.

4 DOFs Hollow Soft Pneumatic Actuator–HOSE

This study reports a novel Hollow Soft Pneumatic Actuator (HOSE), which exhibits 4 degrees of freedom (DOFs). The design consists of a central hollow cylinder surrounded by four twisting symmetric chambers. By virtue of their spiral disposition, each chamber produces a diagonal force along the hollow internal cylinder composed of two components: one parallel to the Z axis and the other one to the plane X-Y. Both top and bottom sections of the actuator are reinforced to avoid deformation, essential for optimal function and dexterity of HOSE. Different movements of the actuator are produced by varying the activation combinations of the 4 chambers. They are constructed from thin walled (0.5 mm) Ecoflex 00–30 super soft silicon rubber, enabling HOSE to perform controlled movements with low pressure not exceeding 35 kPa. HOSE exhibits a maximal extension of 230% of its original length, bends up to i) ±900 around X axis, ii) ±1150 around Y axis, and iii) twists around Z axis with a total range of ±350. The paper describes the manufacturing process together with the actuator performance, reporting the range of motion along each DOF related to the internal pressure, volume versus forces and torques produced along each axis.