Flexible Polydimethylsiloxane Substrate Research Articles

Extrusion Printing of Surface-Functionalized Metal-Organic Framework Inks for a High-Performance Wearable Volatile Organic Compound Sensor.

Wearable sensors hold immense potential for real-time andnon-destructive sensing ofvolatile organic compounds (VOCs), requiring both efficient sensing performance and robust mechanical properties. However, conventional colorimetric sensor arrays, acting as artificial olfactory systems for highly selective VOC profiling, often fail to meet these requirements simultaneously. Here, a high-performance wearable sensor array for VOC visual detection is proposed by extrusion printing of hybrid inks containing surface-functionalized sensing materials. Surface-modified hydrophobic polydimethylsiloxane (PDMS) improves the humidity resistance and VOC sensitivity of PDMS-coated dye/metal-organic frameworks (MOFs) composites. It also enhances their dispersion within liquid PDMS matrix, thereby promoting the hybrid liquid as high-quality extrusion-printing inks. The inks enable direct and precise printing on diverse substrates, forming a uniform and high particle-loading (70 wt%) film. The printed film on a flexible PDMS substrate demonstrates satisfactory flexibility and stretchability while retaining excellent sensing performance from dye/MOFs@PDMS particles. Further, the printed sensor array exhibits enhanced sensitivity to sub-ppm VOClevels, remarkable resistance to high relative humidity (RH) of 90%, and the differentiation ability for eight distinct VOCs. Finally, the wearable sensor proves practical by in situ monitoring of wheat scab-related VOC biomarkers. This study presents a versatile strategy for designing effective wearable gas sensors with widespread applications.

The Actin Bundling Protein L-Plastin Mediates Platelet Force Generation and Thrombosis

Within minutes of activation, platelets dramatically change their shape, forming filopodia and lamellipodia, aggregate with other platelets or different cells, and can increase their surface area up to 4 times. This relies on a dynamic actin cytoskeleton, regulated by many actin binding proteins in a time- and spatial-specific manner. Deficiency or inhibition of several actin binding proteins in platelets have been shown with impaired platelet spreading and reduced thrombosis. Recently, we found that an actin bundling protein, L-plastin, is expressed in platelets. Its function in platelets has not been studied. In megakaryocytes, we showed that L-plastin is responsible for maintaining cytoskeletal stiffness; in this study we sought to determine L-plastin's role in platelet functions, including thrombosis. We examined the role of L-plastin in platelets in vivo and ex vivo using L-plastin deficient ( Lcp1 -/-) male and female mice. First, we used the collagen/epinephrine induced pulmonary embolism (PE) model and found that survival times were significantly shorter in Lcp1 -/- mice than in their littermate wildtype (WT) controls (Mean±SEM WT 202±12 sec, Lcp1 -/- 139.5±14 sec, P=0.004), suggesting accelerated thrombosis upon L-plastin deficiency in vivo. Second, we examined L-plastin's role in arterial thrombosis in vivo using the laser-induced cremaster arteriole thrombosis mode. Platelets were labeled with anti-GPIb IgG derivative X488 and the thrombosis formation after laser injury was recorded. Preliminary data indicate that thrombi in Lcp1 -/- mice are larger than those in WT mice. Third, we examined L-plastin's role in platelet adhesion using a microfluidics assay with DiOC6-labelled whole blood. At a shear rate of 200/s, the Lcp1 -/- mice had significantly increased platelet adhesion to both collagen and fibrinogen matrices. Fourth, to evaluate the effect of L-plastin on platelet aggregation in vitro, we stimulated washed platelets with 3 different concentrations of thrombin and measured the platelet aggregation (i.e., 0.1, 0.5 and 1 U/mL). When platelets are stimulated with 0.5U/mL or 1U/mL thrombin, platelets from WT and Lcp1 -/- mice showed comparable aggregation kinetics. At 0.1U/mL thrombin, however, preliminary data showed increased aggregation in the Lcp1 -/- group. The difference between the low and high concentration of thrombin indicates potential regulation of the GPIba mediated actin cytoskeleton rearrangement during platelet aggregation. We next examined under low thrombin concentration, the platelet actin cytoskeleton reorganization and platelet spreading. We seeded washed platelets on a fibrinogen matrix with the presence of thrombin (0.1U/mL). Platelets were then fixed and stained for F-actin and imaged using immunofluorescent confocal microscopy. The spreading area per platelet was calculated using FIJI software. Platelets from Lcp1 -/- mice showed significantly increased average membrane area at 30 min (Median WT 689 pixels, Lcp1 -/- 866 pixels, P<0.0001). This suggests that the actin rearrangement in platelets upon fibrinogen activation and thrombin stimulation is inhibited by L-plastin. Lastly, we examined whether L-plastin is involved in platelet force generation during the actin reorganization. We used a recently developed “black dot” assay. Briefly, a fluorescent pattern (i.e., black dots) was microcontact printed onto a flexible polydimethylsiloxane substrate and coated with fibrinogen. Platelets were seeded onto the matrix and fixed after 30 min. The contractile forces of individual platelets were measured based on the deformation of the fluorescent micropattern as illustrated in Fig 1A. The contractile force in platelets from Lcp1 -/- mice is decreased with altered actin distribution pattern compared to WT mice (Fig 1. Contractile force per platelet, Mean±SEM WT 14.78±0.86nN, Lcp1 -/- 12.03±0.67nN, P=0.01). In summary, we found accelerated thrombosis in Lcp1 -/- mice, associated with accelerated platelet adhesion and spreading ex vivo. Mechanistically, our preliminary data suggest this is due to impaired actin bundle formation and decreased platelet contractile force. L-plastin may be unique among actin binding proteins.

Femtosecond Laser Direct Writing of Gecko-Inspired Switchable Adhesion Interfaces on a Flexible Substrate.

Biomimetic switchable adhesion interfaces (BSAIs) with dynamic adhesion states have demonstrated significant advantages in micro-manipulation and bio-detection. Among them, gecko-inspired adhesives have garnered considerable attention due to their exceptional adaptability to extreme environments. However, their high adhesion strength poses challenges in achieving flexible control. Herein, we propose an elegant and efficient approach by fabricating three-dimensional mushroom-shaped polydimethylsiloxane (PDMS) micropillars on a flexible PDMS substrate to mimic the bending and stretching of gecko footpads. The fabrication process that employs two-photon polymerization ensures high spatial resolution, resulting in micropillars with exquisite structures and ultra-smooth surfaces, even for tip/stem ratios exceeding 2 (a critical factor for maintaining adhesion strength). Furthermore, these adhesive structures display outstanding resilience, enduring 175% deformation and severe bending without collapse, ascribing to the excellent compatibility of the micropillar's composition and physical properties with the substrate. Our BSAIs can achieve highly controllable adhesion force and rapid manipulation of liquid droplets through mechanical bending and stretching of the PDMS substrate. By adjusting the spacing between the micropillars, precise control of adhesion strength is achieved. These intriguing properties make them promising candidates for various applications in the fields of microfluidics, micro-assembly, flexible electronics, and beyond.

Tunable Magnetic Domain Patterns in Thickness-Gradient Nickel Films on Flexible PDMS Substrates.

Flexible magnetoelectronic devices (based on magnetic films) have great application prospects in the fields of information storages, bionic robotics, and electronic skins. The intrinsic stress and external loading are very important to modulate the structures and properties of flexible magnetic films due to the magnetoelastic coupling effect. Here, we report on tunable magnetic domain patterns in thickness-gradient nickel (Ni) films deposited on flexible polydimethylsiloxane substrates. It is found that stripe magnetic domains spontaneously form in the Ni films and their sizes increase with the film thickness. The internal stress evolves from tensile to compressive states with decreasing film thickness, leading to the formation of cracks in thicker regions and wrinkles in thinner regions. Meanwhile, the orientations of stripe magnetic domains change from the gradient direction to the orthogonal direction. The structural features, evolution behaviors, and physical mechanisms of the cracks, wrinkles, and magnetic domains are analyzed based on the stress theory and magnetoelastic coupling. Periodic gradient Ni films with large-scale regulations of stripe magnetic domains are also realized by masking of copper grids. This study helps to better understand the magnetoelastic coupling effect in gradient flexible magnetic films and provides a technique to modulate anisotropic magnetic properties by designing specific film systems.

Wide gamut dynamic color manipulation based on dielectric metasurface on a stretchable substrate

Dynamic color adjustment technology has broad prospects in invisibility, anti-counterfeiting, and display, and is an important research direction in structural color. This study investigates the excitation of magnetic dipole resonances in the visible region by titanium dioxide (TiO2) metasurfaces using elastic dielectric polydimethylsiloxane (PDMS) and applied to dynamic color modulation. The near-field interaction between the resonant dielectric elements can be modulated using the mechanical strain of the PDMS substrate, enabling the advection of the resonance peak of the structure throughout the visible range, thereby achieving a wide color gamut. The color structure of TiO2 metasurface is sensitive to the refractive index of the surrounding medium. Moreover, active switching between the “ON” state (highly reflective at a selected wavelength) and the “OFF” state (transparent) can be achieved through the deformation of the flexible PDMS substrate. The proposed method can be applied to fields such as sensor displays and spectroscopy and for studying stretchable and wearable photonics.

LAP2β transmits force to upregulate genes via chromatin domain stretching but not compression.

There is increasing evidence that force impacts almost every aspect of cells and tissues in physiology and disease including gene regulation. However, the molecular pathway of force transmission from the nuclear lamina to the chromatin remain largely elusive. Here we employ two different approaches of a local stress on cell apical surface via an RGD (Arg-Gly-Asp)-coated magnetic bead and whole cell deformation at cell basal surface via uniaxial or biaxial deformation of a fibronectin-coated flexible polydimethylsiloxane substrate. We find that nuclear protein LAP2β mediates force transmission from the nuclear lamina to the chromatin. Knocking down LAP2β increases spontaneous movements of the chromatin by reducing tethering of the chromatin and substantially inhibits the magnetic bead-stress or the substrate-deformation induced chromatin domain stretching and the ensuing dihydrofolate reductase (DHFR) gene upregulation. Analysis of DHFR gene-containing chromatin domain alignments along or perpendicular to the direction of the stretching/compressing reveals that the chromatin domain must be stretched and not compressed in order for the gene to be rapidly upregulated. Together these results suggest that external-load induced rapid transcription upregulation originates from chromatin domain stretching but not compressing and depends on the molecular force transmission pathway of LAP2β. STATEMENT OF SIGNIFICANCE: How force regulates gene expression has been elusive. Here we show that the orientation of the chromatin domain relative to the stress direction is crucial in determining if the chromatin domain will be stretched or compressed in response to a cell surface loading. We also show that nuclear protein Lap2b is a critical molecule that mediates force transmission from the nuclear laminar to the chromatin to regulate gene transcription. This study reveals the molecular force transmission pathway for force-induced gene regulation.

Shape-altering flexible plasmonics of in-situ deformable nanorings

Nanorings (NRs) with their intrinsic cavities have attracted interest as plasmonic nanoparticles for years, due to the uniform electric field enhancement inside the cavity, lower plasmon damping effects and comparatively high refractive index sensitivities. In the present work, we successfully fabricated a series of Au NR arrays on flexible polydimethylsiloxane substrates by taking advantage of state-of-the-art fabrication methods such as electron beam lithography and wet-etching transfer techniques. In-situ optical measurements on these flexible systems are enabled by implementing a homemade micro-stretcher inside an optical reflection spectroscopy setup. The corresponding dark-field spectra of thin-walled NR arrays exhibit a strong shift to longer wavelengths (i.e., ~ 2.85 nm per 1% strain) under polarization perpendicular to the traction, mainly resulting from the increasing shape deformation of the NRs under strain. Moreover, numerical simulations illustrate that the shifting plasmonic mode has a radially-symmetric charge distribution of the bonding mode and is rather sensitive to the tuning of the NRs’ shape as confirmed by a subsequent in-situ scanning electron microscope characterization. These results explore the possibilities of shape-altering flexible plasmonics for nanoparticles with a cavity and indicate potential applications for plasmonic colors and biochemical sensing in future work.Graphical

Suppressing the mechanochromism of flexible photonic crystals.

Photonic crystal slabs (PCS) are a promising platform for optical biosensing. Yet, flexible applications based on PCS for biosensing have been limited, as the mechanical properties influence the optical ones. Here, we show the suppression of the mechanochromism effect for flexible PCS. We obtained flexible photonic crystal slabs by sputtering of a dielectric 100 nm Nb2O5 high refractive index layer onto a flexible nanostructured polydimethylsiloxane (PDMS) substrate with 370 nm grating period. The PCS exhibit a guided mode resonance at around 650 nm. We demonstrate that these flexible photonic crystal slabs show less than 0.5 nm resonance shift for 4% strain and call them stabilized PCS (sPCS). We compare this to a resonance shift of ∼21 nm for ∼4% strain of a flexible photonic crystal with a flexible nanoparticle high index layer (mechanochromatic PCS, mPCS). This high resonance shift is expected from the Bragg equations, where 4% grating period change correspond to approximately 4% change of the resonance wavelength (i.e., ∼26 nm at a resonance wavelength of 650 nm), if changes in the mode effective refractive index are neglected. In a stretch series we obtain color-to-strain dependencies of 4.79 nm/% strain for mPCS and 0.11 nm/% strain for our stabilized sPCS. We analyze the suppression of the mechanochromism with detailed microscopy results. We observe that fissures and fractures form in the rigid waveguiding layer of the sPCS upon mechanical stress. An algorithm based on Holistically-Nested Edge Detection (HED) is used for automated counting of cracks. Rigid photonic crystal cells with sizes on the order of 10 µm to 100 µm are formed that explain the stable optical properties. Even more stable optical properties with less than 0.03 nm wavelength shift per 1% strain are demonstrated for sPCS with an additional dielectric 100 nm SiO2 low index layer beneath the Nb2O5 waveguide layer decoupling the waveguide further from the flexible PDMS substrate.

Antibacterial Properties of Silver Nanoclusters with Carbon Support on Flexible Polymer.

Here, we aimed at the preparation of an antibacterial surface on a flexible polydimethylsiloxane substrate. The polydimethylsiloxane surface was sputtered with silver, deposited with carbon, heat treated and exposed to excimer laser, and the combinations of these steps were studied. Our main aim was to find the combination of techniques applicable both against Gram-positive and Gram-negative bacteria. The surface morphology of the structures was determined by atomic force microscopy and scanning electron microscopy. Changes in surface chemistry were conducted by application of X-ray photoelectron spectroscopy and energy dispersive spectroscopy. The changes in surface wettability were characterized by surface free energy determination. The heat treatment was also applied to selected samples to study the influence of the process on layer stability and formation of PDMS-Ag or PDMS-C-Ag composite layer. Plasmon resonance effect was determined for as-sputtered and heat-treated Ag on polydimethylsiloxane. The heating of such structures may induce formation of a pattern with a surface plasmon resonance effect, which may also significantly affect the antibacterial activity. We have implemented sputtering of the carbon base layer in combination with excimer laser exposure of PDMS/C/Ag to modify its properties. We have confirmed that deposition of primary carbon layer on PDMS, followed by sputtering of silver combined with subsequent heat treatment and activation of such surface with excimer laser, led to the formation of a surface with strong antibacterial properties against two bacterial strains of S. epidermidis and E. coli.

Design of flexible resistance sensor based on mesh convex microstructure

To solve the problems of large volume and poor flexibility of the traditional pressure sensor prepared by rigid materials, a flexible pressure resistance sensor with mesh convex platform microstructure has been prepared by using polydimethylsiloxane (PDMS) as a substrate and graphene as a conductive functional layer. The preparation process of the graphene conductive layer of the flexible sensor and PDMS substrate are optimized. And the effect of the concentration of graphene on the sensitivity of the sensor is investigated. The experimental results show that the addition of polyurethane to graphene and the hydrophilic treatment of the PDMS can improve the stability of the sensitivity of the sensor. Excessive graphene blocks microstructural gaps, leading to enhanced microstructural resistance to deformation which will reduce sensitivity. The experimental results show that the thicker the PDMS, the smaller the microstructural deformation, resulting in lower sensitivity. Based on the theoretical basis of elastic mechanics, the calculated results show that the microstructural strain decreases with the thickness of PDMS, consistent with the experimental results. Finally, the performance of PDMS microstructure sensor with thickness of 0.2 mm has been tested. The sensor has a high linear sensitivity (0.152 kPa−1) and a wide linear dynamic response range (0–4 kPa), along with a fast response time of 83 ms and reliable stability. The sensor has been attached to the index finger joint for bending test and fixed to the left hand pulse detection beat, which shows the sensor is able to detect human physiological activity.

Dirac Point Modulated Self-Powered Ultrasensitive Photoresponse and Color-Tunable Electroluminescence from Flexible Graphene/Metal–Organic Frameworks/Graphene Vertical Phototransistor

Integrated wearable optoelectronic devices synchronously exhibit contradictory phenomena of exciton generation and recombination with their control by an external electric field, and the mechanical strain associated with this has widespread applications. However, a demonstration of such single-miniaturized multifunctional wearable optoelectronics remains a daunting challenge. A versatile metal–organic framework (MOF) possesses tailorable outstanding optical properties through an inherent multiple charge-transfer mechanism between metal and ligand. Yet, its commercialization remains unsuccessful because of large porosity, poor conductivity, and deficient crystallinity. Graphene is honorable for its outstanding optoelectronic and mechanical behaviors. Combining excellent features of a versatile MOF with monolayer graphene, unprecedently, we report a self-powered ultrasensitive (external quantum efficiency ∼3 × 1010%) and ultrafast (response time ≈ 220 μs) wearable vertical phototransistor by utilizing a graphene/MOF/graphene/poly(vinylidene fluoride-co-trifluoroethylene) heterojunction on a flexible polydimethylsiloxane substrate through the formation of asymmetric Schottky junctions at MOF/graphene interfaces by a judicious incorporation of a piezo-sensitive poly(vinylidene fluoride) layer. Importantly, by the Dirac point modulation of graphene through a mechanical strain, we achieve optical strain sensors that can modify the amplitude and polarity of the photocurrent. Additionally, controlling the Dirac point of graphene and charge-transfer mechanisms of the MOF by a suitable electrical bias and strain, we demonstrate color-tunable broadband light emission from a flexible vertical phototransistor. Our unique discovery will enrich wearable integrated optoelectronics.

Reverse Electrowetting-on-Dielectric Energy Harvesting Using 3-D Printed Flexible Electrodes for Self-Powered Wearable Sensors

Reverse electrowetting-on-dielectric (REWOD) presents a unique low-frequency motion energy harvesting method to self-power wearable sensors for human health monitoring in real-time. However, previous studies in REWOD energy harvesting have mainly focused on enhancing power density using rigid electrodes, which due to their rigidity, are not ideal to be implemented as wearable energy harvesting or motion sensing applications from human motion activities. To be considered as the next generation self-powered wearable sensors, self-powered wearable sensors should operate continuously and sustainably in any kind of electrode bending motion and without an external power source. Herein, we demonstrate ac current generation by repeatedly modulating a liquid droplet of microliter volume on an elastomer-based three-dimensional printed flexible electrode without any external bias source. Flexible electrodes were fabricated by deposition of ∼200 nm of titanium (Ti) and an additional ∼200 nm of aluminum oxide (Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) along with ∼50 nm of chromium (Cr) as an interlayer between the metal and the dielectric layers, and all of these on a flexible polydimethylsiloxane substrate. Using a 50 μL electrolyte droplet and 2.5 mm of electrode displacement at a low-frequency motion of 1–2 Hz, a maximum peak-to-peak ac current of ∼340 nA was measured. Although significant progress has yet to be made toward implementing REWOD energy harvesting as a reliable source of power for wearable self-powered systems, this letter signifies the proof-of-concept in implementing flexible electrodes in REWOD energy harvesting.

Wetting stability of flexible superamphiphobic surfaces under stretching loading

Wetting stability is important for superamphiphobic surfaces used in oil–water environments. Maintaining the wetting stability of flexible superamphiphobic surfaces under stretching is challenging. Here, flexible surfaces with stable superamphiphobicity under stretching were fabricated by covering flexible polydimethylsiloxane substrates with superamphiphobic powders. Superamphiphobic powders composed of micro- and nanoparticles were prepared by a chemical substitution reaction and modification treatment. The fabricated flexible surfaces possessed contact angles for water, kerosene and peanut oil of 155, 152 and 153°, respectively, exhibiting superhydrophobicity and superoleophobicity. The self-cleaning properties of the fabricated flexible surface were studied by removing contaminants from the surfaces using water and oil droplets. Also, the wettability and morphology of the fabricated flexible surface under stretching were investigated. It was found that the fabricated flexible surface maintained stable superhydrophobicity and superoleophobicity when the stretching strain reached 60% due to the fact that it still kept micro–nano double-scale structures after being stretched. The fabricated flexible surface coated with superamphiphobic powders with wetting stability is expected to be used in the field of liquid repellency.

Design and fabrication of SU-8 polymer arrayed waveguide gratings based on flexible PDMS substrates.

We investigated and fabricated 1×8 and 1×16 traditional/saddle arrayed waveguide grating (AWG) wavelength division multiplexing devices on flexible substrates. The core layer was made of the negative epoxy photoresist SU-8, and polydimethylsiloxane (PDMS) material was selected for the cladding based on the high refractive index difference. A chemical modification method of PDMS was proposed to enhance the film-forming characteristics of the SU-8 core layer on PDMS substrates. After fabricating and characterizing the optical properties of the AWGs, the dimensions of the proposed 1×8 and 1×16 AWGs were 0.9×0.8cm2 and 1.1×0.9cm2, respectively. Experimental results showed that the saddle-type 1×8 and 1×16 AWGs had good signal transmission characteristics, and the insertion losses were only 5.1 dB and 6.8 dB, respectively, which were lower than those of traditional-type AWGs with the same dimensions and number of waveguides.

Regenerative Flexible Upconversion-Luminescence Biosensor for Visual Detection of Diethylstilbestrol Based on Smartphone Imaging.

Diethylstilbestrol (DES), an endocrine disrupting chemical, has been linked to serious health problems in humans. In this work, a regenerative flexible upconversion-fluorescence biosensor was designed for the detection of DES in foodstuffs and environmental samples. Herein, amino-functionalized upconversion nanoparticles (UCNPs) were synthesized and immobilized on the surface of a flexible polydimethylsiloxane substrate, which was further modified with complementary DNA and dabcyl-labeled DES aptamer. The fluorescence resonance energy transfer (FRET) system was established for DES detection between dabcyl and UCNPs as the acceptor and donor pairs, respectively, which resulted in the quenching of the upconversion luminescence intensity. In the presence of a target, the FRET system was destroyed and upconversion fluorescence was restored due to the stronger affinity of the aptamer toward DES. The designed biosensor was also implemented in a dual-mode signal readout based on images from a smartphone and spectra from a spectrometer. Under the optimized experimental conditions, good linear relationships were achieved based on imaging (y = 53.055x + 36.175, R2 = 0.9851) and spectral data (y = 1.1582x + 1.9561, R2 = 0.9897). The designed biosensor revealed great practicability with a spiked recovery rate of 77.91-97.95% for DES detection in real environment and foodstuff samples. Furthermore, the proposed biosensor was regenerated seven times with an accuracy threshold of 80% demonstrating its durability and reusability. Thus, this biosensor is expected to be applied to point-of-care and on-site detection based on the developed portable smartphone device and android application.

Super Flexible Transparent Conducting Oxide‐Free Organic–Inorganic Hybrid Perovskite Solar Cells with 19.01% Efficiency (Active Area = 1 cm2)

Highly efficient organic–inorganic hybrid perovskite solar cells (OIHP‐SCs) are often fabricated on a transparent conducting oxide (TCO) substrate such as indium tin oxide (ITO). However, the presence of TCOs is disadvantageous to the development of flexible OIHP‐SCs due to the brittle nature of ITO which is easily breakable during bending. Herein, a flexible TCO‐free OIHP‐SC is demonstrated by using lithium bis(trifluoromethane)sulfonimide (Li‐TFSI) as a codopant for the single‐layer graphene transparent conducting electrode and poly(triarylamine) hole‐transporting material (HTM) on a flexible polydimethylsiloxane substrate. The optical and electrical properties of the Li‐TFSI‐doped graphene substrate are measured by controlling the doping amount and the best conditions for charge extraction are established at a doping concentration of 20 mm Li‐TFSI, thus optimizing the device photovoltaic performance. As a result, a highest power conversion efficiency of 19.01% is demonstrated by the flexible TCO‐free OIHP‐SC devices with an active area of 1 cm2. In addition, the flexible TCO‐free OIHP‐SCs exhibit good bending stability after 5000 bending cycles at radii of 6, 4, and 2 mm and excellent light soaking stability under 1 Sun light intensity over 1000 h as opposed to the poor stability when using poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate as the HTM.

Eye-Movement-Controlled Wheelchair Based on Flexible Hydrogel Biosensor and WT-SVM.

To assist patients with restricted mobility to control wheelchair freely, this paper presents an eye-movement-controlled wheelchair prototype based on a flexible hydrogel biosensor and Wavelet Transform-Support Vector Machine (WT-SVM) algorithm. Considering the poor deformability and biocompatibility of rigid metal electrodes, we propose a flexible hydrogel biosensor made of conductive HPC/PVA (Hydroxypropyl cellulose/Polyvinyl alcohol) hydrogel and flexible PDMS (Polydimethylsiloxane) substrate. The proposed biosensor is affixed to the wheelchair user’s forehead to collect electrooculogram (EOG) and strain signals, which are the basis to recognize eye movements. The low Young’s modulus (286 KPa) and exceptional breathability (18 g m−2 h−1 of water vapor transmission rate) of the biosensor ensures a conformal and unobtrusive adhesion between it and the epidermis. To improve the recognition accuracy of eye movements (straight, upward, downward, left, and right), the WT-SVM algorithm is introduced to classify EOG and strain signals according to different features (amplitude, duration, interval). The average recognition accuracy reaches 96.3%, thus the wheelchair can be manipulated precisely.

Kirigami-Inspired Highly Stretchable, Conductive, and Hierarchical Ti3C2Tx MXene Films for Efficient Electromagnetic Interference Shielding and Pressure Sensing.

Although Ti3C2Tx MXene sheets are highly conductive, it is still a challenge to design highly stretchable MXene electrodes for flexible electronic devices. Inspired by the high stretchability of kirigami patterns, we demonstrate a bottom-up methodology to design highly stretchable and conductive polydimethylsiloxane (PDMS)/Ti3C2Tx MXene films for electromagnetic interference (EMI) shielding and pressure sensing applications by constructing wrinkled MXene patterns on a flexible PDMS substrate to create a hierarchical surface with primary and secondary surface wrinkles. The self-controlled microcracks created in the valley domains of the hierarchical film via a nonuniform deformation during prestretching/releasing cycles endow the hierarchical PDMS/MXene film with a high stretchability (100%), strain-invariant conductivity in a strain range of 0%-100%, and stable conductivities over an 1000-cycle fatigue measurement. The stretchable film exhibits a highly stable EMI shielding performance of ≈30 dB at a tensile strain of 50%, and its EMI shielding efficiency increases further to 103 dB by constructing a two-film structure. Furthermore, a highly stretchable and sensitive iontronic sensor array with integrated MXene-based electrodes and circuits is fabricated by a stencil printing process, exhibiting high sensitivity (66.3 nF kPa-1), excellent dynamic cycle stability over 1000 cycles under different frequencies, and sensitive pressure monitoring capability under a tensile strain of 50%.

Measuring Single-Cell Platelet Forces via Microcontact-Printed, Reference-Free Traction Force Microscopy Reveals Relationships between Cell Shape, F-Actin Localization, and Force

Platelets bind, spread, and contract to stop bleeding and reinforce hemostatic plugs. Platelet contraction occurs when interactions between actin and myosin create cytoskeletal tension and force generation. In this study, single-cell platelet forces were measured using a novel microcontact-printed, reference-free traction force microscopy approach. This approach facilitates single-cell force measurement on a contiguous topology that enables unrestricted platelet spreading without necessitating platelet removal to calculate force. Microcontact printing is used to deposit a grid of fluorescent bovine serum albumin onto a flexible polydimethylsiloxane substrate. Platelets from healthy donors were washed and seeded onto von Willebrand Factor-coated substrates. Platelets were fixed, stained, and imaged via confocal microscopy to simultaneously visualize fluorescently labeled platelets and grid displacement (used to calculate single-cell force.) Because microcontact-printing facilitates printing the grid on large, scalable surfaces, platelet forces were able to be measured on >100 single-cells per donor (N = 6 donors). Donor-to-donor platelet force variability was examined, and some donors produce significantly more force per platelet than other donors (p<0.01). Even within each donor, ∼15-fold variability in single platelet forces exists. A well-established area-force relationship (more spread cells produce more force) accounts for some variability in force generation, but for cells spread equally, there is still ∼5-fold differences in force generation. After examining the relationship between cell shape and force, a relationship was observed wherein platelets that are more circular produce more force. Additionally, amongst spread platelets, platelets with more spread F-actin produce more force. This versatile method that facilitates measurement of single-cell forces over large areas without restricting cell spreading or requiring cell removal reveals donor variability, cell shape, and F-actin localization as contributors to the large variability of single-platelet forces.

Gold Nanoparticle Thin Film-Based Strain Sensors for Monitoring Human Pulse

A concise and economical way to build nanoparticle thin-film strain sensors of high gauge factors on a flexible polydimethylsiloxane substrate is developed. The gauge factors for resistance change and capacitance change are much larger than those of many other competing sensors. The small bulk modulus of the substrate provides the sensor a large responsivity for pressure with a frequency bandwidth of kHz. It can be used for tactile sensing that is capable of monitoring human pulse for pre-clinical diagnosis, by resolving minor structures such as peaks of dicrotic pulse and before dicrotic pulse in the waveforms.