Stretchable Membrane Research Articles

Ultraconformal Skin-Interfaced Sensing Platform for Motion Artifact-Free Monitoring.

Capable of directly capturing various physiological signals from human skin, skin-interfaced bioelectronics has emerged as a promising option for human health monitoring. However, the accuracy and reliability of the measured signals can be greatly affected by body movements or skin deformations (e.g., stretching, wrinkling, and compression). This study presents an ultraconformal, motion artifact-free, and multifunctional skin bioelectronic sensing platform fabricated by a simple and user-friendly laser patterning approach for sensing high-quality human physiological data. The highly conductive membrane based on the room-temperature coalesced Ag/Cu@Cu core-shell nanoparticles in a mixed solution of polymers can partially dissolve and locally deform in the presence of water to form conformal contact with the skin. The resulting sensors to capture improved electrophysiological signals upon various skin deformations and other biophysical signals provide an effective means to monitor health conditions and create human-machine interfaces. The highly conductive and stretchable membrane can also be used as interconnects to connect commercial off-the-shelf chips to allow extended functionalities, and the proof-of-concept demonstration is highlighted in an integrated pulse oximeter. The easy-to-remove feature of the resulting device with water further allows the device to be applied on delicate skin, such as the infant and elderly.

Directionality of developing skeletal muscles is set by mechanical forces

Formation of oriented myofibrils is a key event in musculoskeletal development. However, the mechanisms that drive myocyte orientation and fusion to control muscle directionality in adults remain enigmatic. Here, we demonstrate that the developing skeleton instructs the directional outgrowth of skeletal muscle and other soft tissues during limb and facial morphogenesis in zebrafish and mouse. Time-lapse live imaging reveals that during early craniofacial development, myoblasts condense into round clusters corresponding to future muscle groups. These clusters undergo oriented stretch and alignment during embryonic growth. Genetic perturbation of cartilage patterning or size disrupts the directionality and number of myofibrils in vivo. Laser ablation of musculoskeletal attachment points reveals tension imposed by cartilage expansion on the forming myofibers. Application of continuous tension using artificial attachment points, or stretchable membrane substrates, is sufficient to drive polarization of myocyte populations in vitro. Overall, this work outlines a biomechanical guidance mechanism that is potentially useful for engineering functional skeletal muscle.

A microfluidic lung-on-a-chip based on biomimetic hydrogel membrane.

Lung-on-chips have showed great promise as a tool to recapitulate the respiratory system for investigation of lung diseases in the past decade. However, the commonly applied artificial elastic membrane (e.g., polydimethylsiloxane, PDMS) in the chip failed to mimic the alveolar basal membrane in the composition and mechanical properties. Here we replaced the PDMS film by a thin, biocompatible, soft, and stretchable membrane based on F127-DA hydrogel that well approached to the composition and stiffness of extracellular matrix in human alveoli for construction of lung-on-a-chip. This chip well reconstructed the mechanical microenvironments in alveoli so that the epithelial/endothelial functions were highly expressed with a well established alveolar-capillary barrier. In opposite to the unexpectedly accelerated fibrotic process on the PDMS-based lung-on-a-chip, HPAEpiCs on hydrogel-based chip only presented fibrosis under nonphysiologically high strain, well reflecting the features of pulmonary fibrosis in vivo. This physiologically relevant lung-on-a-chip would be an ideal model in investigation of lung diseases and for development of antifibrosis drugs.

Cyclic stretch-regulated wound healing

Living cells often experience cyclic stretches in both physiological and pathological conditions, such as those found during wound closure, embryonic development and pulmonary fibrosis. Critical challenges in the field of mechanobiology are understanding whether cells respond to these stimuli via physiological pathways or by pathological pathways, and how to switch back to physiological homeostasis once the latter occurs. A longstanding model for trying to tease this apart is culturing monolayer cells on a stretchable membrane, which simulates these conditions and potentially enables researchers to examine how cells react to cyclic stretch. The results can vary substantially, depending on the cell type, amplitude, duration and frequency of the applied stretch (1, 2). Specifically, a great diversity of cellular responses (1-4) have been reported, including 1) re-alignment of cells, associated with the remodeling of cellular stress fibers and focal adhesions; 2) altered cell proliferation or apoptosis; 3) migration of cells driven by stretch-triggered formation of lamellipodia; 4) secretion of extracellular matrix (ECM) proteins that are critical for tissue remodeling; 5) activation of mitogen-activated protein kinase (MAPK), nuclear factor-kappa B (NF-kB) and Wnt signaling pathways; and 6) upregulation of genes involved in cell adhesion and inflammation.

In Situ Adjustable Nanogaps and In-Plane Break Junctions.

The ability to precisely regulate the size of a nanogap is essential for establishing high-yield molecular junctions, and it is crucial for the control of optical signals in extreme optics. Although remarkable strategies for the fabrication of nanogaps are proposed, wafer-compatible nanogaps with freely adjustable gap sizes are not yet available. Herein, two approaches for constructing in situ adjustable metal gaps are proposed which allow Ångstrom modulation resolution by employing either a lateral expandable piezoelectric sheet or a stretchable membrane. These in situ adjustable nanogaps are further developed into in-plane molecular break junctions, in which the gaps can be repeatedly closed and opened thousands of times with self-assembled molecules. The conductance of the single 1,4-benzenediamine (BDA) and the BDA molecular dimer is successfully determined using the proposed strategy. The measured conductance agreeing well with the data by employing another well-established scanning tunneling microscopy break junction technique provides insight into the formation of molecule dimer via hydrogen bond at single molecule level. The wafer-compatible nanogaps and in-plane dynamical break-junctions provide a potential approach to fabricate highly compacted devices using a single molecule as a building block and supply a promising in-plane technique to address the dynamical properties of single molecules.

Versatile Mechanochromic Sensor based on Highly Stretchable Chiral Liquid Crystalline Elastomer.

A mechanochromic strain sensor that is capable of distinguishing the orientation, the location, and the degree of deformation based on the highly stretchable membrane of main-chain chiral liquid crystalline elastomer (MCLCE) is proposed. The MCLCE film is designed to exhibit uniform and significant color shift upon the small strain by using step-growth polymerization of liquid crystal (LC) oligomer and its phase-stabilization in solvent mesogen. As conformally placed on the bottom elastomer sheet, the MCLCE film shows multimodal, instantaneous color change for sensing arbitrary in-plane deformation, out-of-plane bending, and nonzero Gaussian deformation. Based on high freedom in the device design, it is also demonstrated that this sensor can display color patterns or encrypted images in response to the localized weight or strain. The simple and straightforward concept proposed here can be applicable in the fields of wearable devices, displays, and soft robotics.

Electroactive Soft Actuators Based on Columnar Ionic Liquid Crystal/Polymer Composite Membrane Electrolytes Forming 3D Continuous Ionic Channels.

Here, we report low-voltage-driven fast-response nanostructured columnar ionic liquid crystal/polymer composite actuators that form three-dimensional continuous ion channels. A three-component self-assembly of a zwitterionic rod-like molecule (49.5 wt %), an ionic liquid (27.5 wt %), and poly(vinyl alcohol) (23.0 wt %) provided a free-standing stretchable membrane electrolyte. The dissociated ions can move through a continuous 3D ionophilic matrix surrounding the hydrophobic columns formed by the hexagonally organized rod-mesogens. Three-layer actuators composed of the electrolyte film sandwiched between two conductive polymer film electrodes of doped polythiophene exhibited a bending motion with 0.32% strain and moved 2 mm within 220 ms under 1 V at 0.1 Hz in 70% relative humidity due to the formation of electric double layers at the soft solid electrolyte/electrode interfaces. The bending strain of the columnar nanostructured actuator is comparable to those of polymer iongel actuators and block polymer actuators containing 25-80 wt % of ionic liquids. It is noteworthy that a small number of ions organized into the 3D nanochannels can generate the large bending deformation, which can contribute to reduce the risk of leakage of ions and the production cost. In addition, we have demonstrated a low-voltage-driven deformable mirror actuator that is expected to be applied to optical devices.

Constructing foldable and stretchable proton exchange membranes through spin coating technology

The convenient storage of fuel cells requires the foldable and stretchable membrane electrolytes. However, there was the risk of sacrificing the charge transport mobility and mechanical strength to achieve the foldability and stretchability. The spin coating technology provided an facile strategy to prepare the well-ordered structure of membranes. In this study, the foldable and stretchable proton exchange membranes (PEMs) based on Kevlar nanofibers and polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) were constructed through spin coating technology. After the folded and stretched operations, the membranes exhibited the negligible effect on proton conductivity and mechanical strength. In our opinion, the components of SEBS supported the membranes deformation and Kevlar naonfibers supplied the proton conduction channels. As a result, the prepared (Kevlar/SEBS)5 membranes can be folded in the width direction for 3 times and be stretched up to 10 % strain parallel to the length direction for 50 times. The folded membranes and stretched membranes respectively exhibited the proton conductivities of 9.55 × 10-2 S/cm and 1.98 × 10-1 S/cm, which were comparable with 1.58 × 10-1 S/cm at 160 °C of the original membranes. The tensile stress of (Kevlar/SEBS)5-fold/PA and (Kevlar/SEBS)5–50/PA respectively reached 5.23 MPa and 6.43 MPa, even a little higher than 3.59 MPa of the (Kevlar/SEBS)5/PA membranes. Furthermore, the folded and stretched membranes showed the fine component stability and proton conductivity stability. This study provided the support to exploit foldable and stretchable PEMs with spin coating technique, facilitating the easy storage of PEMs and future portable fuel cells.

Passive suppression of radiation of low-frequency underwater noise

Using an exact solution of the problem of spherical wave diffraction on a fluid sphere, it has been predicted [Godin and Baynes, J. Acoust. Soc. Am. 143, EL67–EL73 (2018)] that passive, broadband suppression of radiation of low-frequency sound can be achieved by placing an acoustically compliant object in the vicinity of the source. In underwater acoustics, the compliant object can be realized as an air-filled bladder. One of the promising applications of the technique is to suppress the noise generated by ship propellers. If implemented on a wide scale, the passive noise suppression technique would help to decrease the noise levels due to commercial and recreational vessels and reduce the detrimental effects of anthropogenic noise on marine life. This paper extends the earlier theoretical treatment of the problem to more realistic models of the compliant object such as a gas volume surrounded by a stretchable membrane (a balloon) and a thin shell. The effect of the finite depths of low-frequency noise source and the compliant object on noise levels in the far field will be discussed.

A Tunable Open Planar Acoustic Notch Filter Utilizing a Pneumatically Modulated Helmholtz Resonator Array

Acoustic filters provide sound insulation unpleasant noises at a specific frequency only. Ordinary passive acoustic filters made up of acoustic metamaterial structures can work without a power supply. However, their working frequency is not adjustable. This study reports a tunable open planar acoustic notch filter that incorporates a pneumatically controlled Helmholtz resonator (HR) array. The HR array consisted of three layers: cavities, a membrane, and microchannels. The cavities function as the HR chambers, whose volume determines the resonant frequency. The acoustic wave is effectively attenuated at this frequency owing to the HR effect. The HR chamber volume can be varied by displacing the stretchable membrane with air pressure through the microchannels. This helps in adjusting the resonant frequency, thereby realizing a tunable acoustic notch filter. We conducted theoretical, and experimental examinations along with simulations of the frequency response for an HR array with three different cavity thicknesses. The prototype device realized a frequency tuning of approximately 4.1–4.9 kHz with 10 dB filtering. Furthermore, an improved notch frequency tunability was observed for the thinner cavities, along with a decrease in the notch performance. Thus, the proposed HR array filter can be useful for high-frequency noise that is generally uncomfortable for humans.

Dielectric Elastomer Actuator Driven Soft Robotic Structures With Bioinspired Skeletal and Muscular Reinforcement.

Natural motion types found in skeletal and muscular systems of vertebrate animals inspire researchers to transfer this ability into engineered motion, which is highly desired in robotic systems. Dielectric elastomer actuators (DEAs) have shown promising capabilities as artificial muscles for driving such structures, as they are soft, lightweight, and can generate large strokes. For maximum performance, dielectric elastomer membranes need to be sufficiently pre-stretched. This fact is challenging, because it is difficult to integrate pre-stretched membranes into entirely soft systems, since the stored strain energy can significantly deform soft elements. Here, we present a soft robotic structure, possessing a bioinspired skeleton integrated into a soft body element, driven by an antagonistic pair of DEA artificial muscles, that enable the robot bending. In its equilibrium state, the setup maintains optimum isotropic pre-stretch. The robot itself has a length of 60 mm and is based on a flexible silicone body, possessing embedded transverse 3D printed struts. These rigid bone-like elements lead to an anisotropic bending stiffness, which only allows bending in one plane while maintaining the DEA's necessary pre-stretch in the other planes. The bones, therefore, define the degrees of freedom and stabilize the system. The DEAs are manufactured by aerosol deposition of a carbon-silicone-composite ink onto a stretchable membrane that is heat cured. Afterwards, the actuators are bonded to the top and bottom of the silicone body. The robotic structure shows large and defined bimorph bending curvature and operates in static as well as dynamic motion. Our experiments describe the influence of membrane pre-stretch and varied stiffness of the silicone body on the static and dynamic bending displacement, resonance frequencies and blocking forces. We also present an analytical model based on the Classical Laminate Theory for the identification of the main influencing parameters. Due to the simple design and processing, our new concept of a bioinspired DEA based robotic structure, with skeletal and muscular reinforcement, offers a wide range of robotic application.

Artificial Perspiration Membrane by Programmed Deformation of Thermoresponsive Hydrogels.

Thermal management is essential for living organisms and electronic devices to survive and maintain their own functions. However, developing flexible cooling devices for flexible electronics or biological systems is challenging because conventional coolers are bulky and require rigid batteries. In nature, skins help to maintain a constant body temperature by dissipating heat through perspiration. Inspired by nature, an artificial perspiration membrane that automatically regulates evaporation depending on temperature using the programmed deformation of thermoresponsive hydrogels is presented. The thermoresponsive hydrogel is patterned into pinwheel shapes and supported by a polymeric rigid frame with stable adhesion using copolymerization. Both shape of the valve and mechanical constraint of the frame allow six times larger evaporation area in the open state compared to the closed state, and the transition occurs at a fast rate (≈1 s). A stretchable membrane is selectively coated to prevent unintended evaporation through the hydrogel while allowing swelling or shrinking of the hydrogel by securing path of water. Consequently, a 30% reduction in evaporation is observed at lower temperature, resulting in regulation of the skin temperature at the thermal model of human skins. This simple, small, and flexible cooler will be useful for maintaining temperature of flexible devices.

All‐Solid‐State Asymmetric Supercapacitors with Metal Selenides Electrodes and Ionic Conductive Composites Electrolytes

AbstractAll‐solid‐state flexible asymmetric supercapacitors (ASCs) are developed by utilization of graphene nanoribbon (GNR)/Co0.85Se composites as the positive electrode, GNR/Bi2Se3 composites as the negative electrode, and polymer‐grafted‐graphene oxide membranes as solid‐state electrolytes. Both GNR/Co0.85Se and GNR/Bi2Se3 composite electrodes are developed by a facile one‐step hydrothermal growth method from graphene oxide nanoribbons as the nucleation framework. The GNR/Co0.85Se composite electrode exhibits a specific capacity of 76.4 mAh g−1 at a current density of 1 A g−1 and the GNR/Bi2Se3 composite electrode exhibits a specific capacity of 100.2 mAh g−1 at a current density of 0.5 A g−1. Moreover, the stretchable membrane solid‐state electrolytes exhibit superior ionic conductivity of 108.7 mS cm−1. As a result, the flexible ASCs demonstrate an operating voltage of 1.6 V, an energy density of 30.9 Wh kg−1 at the power density of 559 W kg−1, and excellent cycling stability with 89% capacitance retention after 5000 cycles. All these results demonstrate that this study provides a simple, scalable, and efficient approach to fabricate high performance flexible all‐solid‐state ASCs for energy storage.

Form-finding with robotics: Rapid and flexible fabrication of glass fiber reinforced concrete panels using thermoformed molds

Abstract We present a process that revisits form-finding within digital media, namely parametric design and robotic fabrication. It is inspired by classical architectural and engineering experiments producing minimal surfaces and tensile structures by physical simulation of materials and natural forces. Fabrication is based on thermoforming, where thin sheets of amorphous PET are heat-treated and while in malleable state, where the material behaves like stretchable membrane, an industrial robot imprints a shape and sheets are rapidly cooled down assuming their final form. Key aspects of the approach include: (a) Speed: as each sheet is formed within seconds; (b) Flexibility, as a wide-range of shapes are produced without fabrication of unique dies; and (c) Resilience, as unlike traditional form-finding processes where the derived forms are ephemeral, the objects produced here are robust, they may be used directly or employed in subsequent fabrication processes. The produced sheets are used here as molds for glass-reinforced concrete casting offering excellent surface quality and the ability to create geometry unlike any conventional fabrication techniques. We present the design and development of the process and a proof-of-concept artwork produced. Highlights A form-finding process that fuses digital and physical computation. Industrial robotics as the forcing system for form-finding material experiments. From delicate physical experimental prototypes to reproducible precise artifacts. Hybrid thermoforming and glass reinforced concrete casting digital and analog fabrication. Presentation of experimental large-scale artwork as demonstration of process.

A windable and stretchable three-dimensional all-inorganic membrane for efficient oil/water separation

There is strong interest in windable and stretchable membranes to meet the technological demands of practical water treatments. Oil/water separating membranes of this type is still significantly underdeveloped. Here, we reported a windable and stretchable membrane with three-dimensional structure for efficient oil/water separation. This membrane is made of ZnO nanorods arrays conformally grown on woven carbon microfibers. This three-dimensional architecture endows the fabricated membrane with highly windable and stretchable properties, at the same time ensures ZnO nanorods fully exposed outwards on the membrane surface. Due to its superior hydrophilicity and oleophobicity of ZnO nanorods, this all-inorganic membrane exhibits outstanding antifouling property, with the foulants on membrane surfaces easily removed by simple physical cleaning without chemicals. The membrane can effectively separate both oil/saline-water mixtures and oil-in-water emulsions, solely driven by gravity, with extremely high permeation flux of 20933.4 L m−2 h−1 and high separation efficiency over 99%.

Fabrication and Characterization of an Upside-Down Carbon Nanotube Microelectrode Array

Microelectrode arrays (MEAs) are widely used in biological application to locally stimulate and record the electrical activity of living cells. Here, a novel fabrication process for a carbon nanotube (CNT)-based MEA integrated on the backside of a free standing stretchable membrane is reported. The new process flow overcomes the manually intensive procedures used in the previous works. The microfabricated upside-down CNT MEA consists of microelectrodes with an area of 110 $\mu \text{m}^{2}$ covered with cobalt-grown CNTs. The surface area enhancement and the foam-like morphology of the CNTs allow an increase of the charge injection per unit area at the electrode–electrolyte interface, resulting in a significantly lower electrochemical impedance of the electrodes. In particular, at 1 kHz, the fabricated CNT-MEA electrodes show a reduction of the overall impedance up to 96% in comparison with benchmark TiN electrodes. The obtained results confirm the effectiveness of the proposed surface texturing through CNT integration. Moreover, the quality and the morphology as well as the biocompatibility of the fabricated CNT-based electrodes were assessed. The obtained results demonstrate that significant improvement can be achieved by integrating structured nanoporous material on MEAs.

PEDOT:PSS: A Conductive and Flexible Polymer for Sensor Integration in Organ-on-Chip Platforms

Sensing and stimulating microstructures are necessary to develop more specialized and highly accurate Organ-on-Chip (OOC) platforms. In this paper, we present the integration of a conductive polymer, poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), on a stretchable membrane, core element of an Heart-on-Chip. The electrical conductivity along with its biocompatibility, high transparency (≈88%) and mechanical elasticity (≈1.2 GPa) make this material a candidate to develop novel microstructures for electrical monitoring and stimulation of cells in flexible-substrate based OOCs. Microstructures with different shapes and geometries of PEDOT:PSS embedded in a 9 μm-thick Polydimethylsiloxane (PDMS) membrane are developed following a wafer-level fabrication approach. PEDOT:PSS layers between 120 nm and 300 nm are obtained by varying the deposition conditions. The layers are successfully patterned and microstructures with lateral dimensions down to 2 μm. The obtained results indicate that this polymer is a suitable material for microfabrication of sensing and stimulating elements in OOC platforms.

Co-ordinated detection of microparticles using tunable resistive pulse sensing and fluorescence spectroscopy.

Tunable resistive pulse sensing (TRPS) has emerged as a useful tool for particle-by-particle detection and analysis of microparticles and nanoparticles as they pass through a pore in a thin stretchable membrane. We have adapted a TRPS device in order to conduct simultaneous optical measurements of particles passing through the pore. High-resolution fluorescence emission spectra have been recorded for individual 1.9 μm diameter particles at a sampling period of 4.3 ms. These spectra are time-correlated with RPS pulses in a current trace sampled every 20 μs. The flow rate through the pore, controlled by altering the hydrostatic pressure, determines the rate of particle detection. At pressures below 1 kPa, more than 90% of fluorescence and RPS events were matching. At higher pressures, some peaks were missed by the fluorescence technique due to the difference in sampling rates. This technique enhances the particle-by-particle specificity of conventional RPS measurements and could be useful for a range of particle characterization and bioanalysis applications.

스트레쳐블 폴리머 디퓨저를 이용한 균질 레이저 디스플레이 해석

본 논문은 스트레쳐블 폴리머 디퓨저를 이용하여서 간섭성이 있는 레이저의 단점인 스페클 효과를 감소하는 결과를 비교 분석하였다. 자체 제작한 RGB 모듈을 기반으로 하여 빔 컴바이너를 거쳐서 레이저빔을 집속한 후 고전압 저주파수를 통해서 레이저빔을 균질화 하였다. 평균 180~300Hz 정도의 주파수를 가한 결과 레이저빔의 균질효과가 나타났다. 컴퓨터 시뮬레이션을 통한 디퓨저와 DMD 반사경을 구현 하였으며, 808nm 레이저빔을 가상으로 조사하여서 디퓨저 유무에 따른 빔의 산란도 및 균질도를 검증 하였다. 결과적으로 디퓨저를 통한 빔의 균질도가 산란효과를 감소시켰고, 이를 통한 디스플레이 선명도를 개선할 수 있을 것으로 기대된다. 청색레이저의 투과도가 83% 정도로 적색이나 녹색 레이저에 비해서 상대적으로 취약하였는데, 이는 디퓨저 내부를 통과시 레이저 빔의 굴절의 양이 많아져서 확산 각이 증가하였기 때문으로 분석되었다. 레이저와 광학 장치 사이에 디퓨저를 사용하여 이미지 구현했을 때 스페클 패턴은 제거되었으며, 레드(650nm), 그린(532nm), 블루(405nm) 파장에서 10-20%정도의 밝기 감소가 나타났으며, 전체적인 밝기 감소는 13%정도 이루어졌다. 또한, 스트레쳐블 폴리머를 이용한 경우 시간축 균질도도 30fs에서 110fs로 개선 되었다. 【A stretchable polymeric membrane shaped diffuser was used to homogenize the coherent laser beam. The developed RGB module was used to focus and defocus test by beam combiners. Average oscillation frequency was set at 180Hz~300Hz and it resulted in the best homogenization effect in visual range. The blue laser module turned out to be the worst case for the transmission and primary reason is believed to be the short length of irradiated laser beam. The developed system removed the speckling and the brightness was decreased by 10 ~ 20% for the RGB laser. Overall the brightness was decreased by 13% and homogenity with respect to the temporal axis was improved from 30fs to 110fs.】

Development of stretchable membrane based nanofilters using patterned arrays of vertically grown carbon nanotubes

A unique process which utilizes membrane based vertically grown carbon nanotubes (CNTs) as nanofilters for a mass transport study is presented here. By using ions, ss-DNA and haemagglutinin as testing molecules of different dimensions, the mass transport function of the CNT membrane is investigated under pressure difference and/or electric field.