Tunable resins with PDMS-like elastic modulus for stereolithographic 3D-printing of multimaterial microfluidic actuators

Stereolithographic 3D-printing (SLA) permits facile fabrication of high-precision microfluidic and lab-on-a-chip devices. SLA photopolymers often yield parts with low mechanical compliancy in sharp contrast to elastomers such as poly(dimethyl siloxane) (PDMS). On the other hand, SLA-printable elastomers with soft mechanical properties do not fulfill the distinct requirements for a highly manufacturable resin in microfluidics (e.g., high-resolution printability, transparency, low-viscosity). These limitations restrict our ability to print microfluidic actuators containing dynamic, movable elements. Here we introduce low-viscous photopolymers based on a tunable blend of the monomers poly(ethylene glycol) diacrylate (PEGDA, Mw ∼ 258) and the monoacrylate poly(ethylene glycol methyl ether) methacrylate (PEGMEMA, Mw ∼ 300). In these blends, which we term PEGDA-co-PEGMEMA, tuning the PEGMEMA content from 0% to 40% (v/v) alters the elastic modulus of the printed plastics by ∼400-fold, reaching that of PDMS. Through the addition of PEGMEMA, moreover, PEGDA-co-PEGMEMA retains desirable properties of highly manufacturable PEGDA such as low viscosity, solvent compatibility, cytocompatibility and low drug absorptivity. With PEGDA-co-PEGMEMA, we SLA-printed drastically enhanced fluidic actuators including microvalves, micropumps, and microregulators with a hybrid structure containing a flexible PEGDA-co-PEGMEMA membrane within a rigid PEGDA housing. These components were built using a custom "Print-Pause-Print" protocol, referred to as "3P-printing", that allows for fabricating high-resolution multimaterial parts with a desktop SLA printer without the need for post-assembly. SLA-printing of multimaterial microfluidic actuators addresses the unmet need of high-performance on-chip controls in 3D-printed microfluidic and lab-on-a-chip devices.

Cartilage-inspired terpolymer hydrogel with excellent mechanical properties and superior lubricating ability

Osteoarthritis (OA), the most common degenerative joint disorder, seriously affects patients' daily activities. Recently, hydrogels, due to their similar structure to articular cartilage, have shown great potential as cartilage-repairing materials. In the present work, we developed a simple process for fabricating terpolymer [P(acrylamide-co-acrylic acid-co-2-acrylamido-2-methyl-1-propanesulfonic acid)/Fe3+] hydrogel [P(AAm-co-AAc-co-AMPS)/Fe3+]. The content of AMPS was found to show a crucial effect on the mechanical and tribological performance of the terpolymer hydrogel. When the content of AMPS was 0.45 mol L-1, the compressive strength, modulus, and friction coefficient of the terpolymer hydrogel were 66.60 ± 1.79 MPa, 2.10 ± 0.16 MPa, and 0.032, respectively. In addition, the hydrogel showed high wear durability and the friction coefficient was as low as 0.038 after 3.6 × 105 sliding cycles.

A Semi-Crystalline Polymer Semiconductor with Thin Film Stretchability Exceeding 200

Despite the emerging scientific interest in polymer-based stretchable electronics, the trade-off between the crystallinity and stretchability of intrinsically stretchable polymer semiconductors-charge-carrier mobility increases as crystallinity increases while stretchability decreases-hinders the development of high-performance stretchable electronics. Herein, a highly stretchable polymer semiconductor is reported that shows concurrently improved thin film crystallinity and stretchability upon thermal annealing. The polymer thin films annealed at temperatures higher than their crystallization temperatures exhibit substantially improved thin film stretchability (> 200%) and hole mobility (≥ 0.2 cm²  V^-1  s^-1 ). The simultaneous enhancement of the crystallinity and stretchability is attributed to the thermally-assisted structural phase transition that allows the formation of edge-on crystallites and reinforces interchain noncovalent interactions. These results provide new insights into how the current crystallinity-stretchability limitation can be overcome. Furthermore, the results will facilitate the design of high-mobility stretchable polymer semiconductors for high-performance stretchable electronics.

Advanced Stretchable Photodetectors: Strategies, Materials and Devices

Past decades have witnessed the generation of new stretchable photodetectors in electronic eyes, health sensing, wearable devices, intelligent monitoring and other fields. Stretchable devices require not only outstanding performance but also excellent flexibility, adaptability and stability. Innovative strategies have been proposed to realize the stretchability of devices. In addition, novel functional materials including zero-dimensional nanomaterials, one-dimensional inorganic nanomaterials, two-dimensional layered materials, organic materials, and organic-inorganic composite materials with excellent properties are emerging to continuously improve the performance of devices. Here, the recent research progress of stretchable photodetectors in terms of both various design methods and functional materials is outlined. The optical performance and stretchable properties are also comprehensively reviewed. Finally, a summary and the challenges associated with the application of stretchable photodetectors are presented.

Effectiveness of organic solvents for recovering collapsed PDMS micropillar arrays

Polydimethylsiloxane (PDMS) micropillar arrays are widely used in research labs and engineering fields as analytical tools for various purposes. When the micropillar length or density surpasses a critical value, micropillars tend to collapse with each other and become unusable. Restoring collapsed PDMS micropillars typically involves the use of low surface tension solvents and ultrasound sonication, but such approach has received little success to date. In this work, we examined the effectiveness of different types of solvents for restoring collapsed PDMS micropillar arrays and show that the swelling ratio of PDMS in selected solvents constitutes an important factor in the effectiveness of restoring collapsed PDMS micropillars. Our results could be a promoter in recycling PDMS micropillar arrays and achieving economic and social benefits.

Ultra-stable blue-emitting lead-free double perovskite Cs2SnCl6 nanocrystals enabled by an aqueous synthesis on a microfluidic platform

Blue emitting Sn-based lead-free halide perovskite nanocrystals (NCs) are considered to be a promising material in lighting and displays. However, industrialised fabrication of blue-emitting NCs still remains a significant challenge due to the use of toxic solvents and optical instability, not mentioning in large-scale synthesis. In this work, a green-route synthesis of blue-emitting lead-free halide perovskite Cs₂SnCl₆ powders is developed, in which deionized water with a small amount of inorganic acid is used as the solvent and the synthesis of the Cs₂SnCl₆ powders is achieved on a microfluidic platform. Using the Cs₂SnCl₆ powders, we prepare Cs₂SnCl₆ NCs via an ultrasonication process. Changing the volume ratio of the ligands (oleic acid to oleylamine) can alter the photoluminescence (PL) characteristics of the prepared NCs, including the PL-peak wavelength, PL-peak intensity and quantum yield. The highest photoluminescence quantum yield (PLQY) of 13.4% is achieved by the Cs₂SnCl₆ NCs prepared with the volume ratio of oleic acid to oleylamine of 40 μL to 10 μL. A long-term PL stability test demonstrates that the as-synthesized Cs₂SnCl₆ NCs can retain a stable PLQY over a period of 60 days. This work opens up a new path for a large-scale green-route synthesis of blue-emitting Sn-based lead-free NCs, such as Cs₂SnX₆ (Cl, Br and I), towards their applications in optoelectronics.

Affinity of Keratin Peptides for Cellulose and Lignin: A Fundamental Study toward Advanced Bio-Based Materials

Keratin is a potential raw material to meet the growing demand for bio-based materials with special properties. Keratin can be obtained from feathers, a by-product from the poultry industry. One approach for keratin valorization is to use the protein to improve the properties of already existing cellulose and lignin-based materials to meet the requirements for replacing fossil-based plastics. To ensure a successful combination of keratin with lignocellulosic building blocks, keratin must have an affinity to these substrates. Hence, we used quartz crystal microbalance with a dissipation monitoring (QCM-D) technique to get a detailed understanding of the adsorption of keratin peptides onto lignocellulosic substrates and how the morphology of the substrate, pH, ionic strength, and keratin properties affected the adsorption. Keratin was fractionated from feathers with a scalable and environmentally friendly deep eutectic solvent process. The keratin fraction used in the adsorption studies consisted of different sized keratin peptides (about 1-4 kDa), which had adopted a random coil conformation as observed by circular dichroism (CD). Measuring keratin adsorption to different lignocellulosic substrates by QCM-D revealed a significant affinity of keratin peptides for lignin, both as smooth films and in the form of nanoparticles but only a weak interaction between cellulose and keratin. Systematic evaluation of the effect of surface, media, and protein properties enabled us to obtain a deeper understanding of the driving force for adsorption. Both the structure and size of the keratin peptides appeared to play an important role in its adsorption. The keratin-lignin combination is an attractive option for advanced material applications. For improved adsorption on cellulose, modifications of either keratin or cellulose would be required.

Surface acoustic wave-based generation and transfer of droplets onto wettable substrates

Fluid manipulation using surface acoustic waves (SAW) has been utilized as a promising technique in the field of microfluidics due to its numerous advantages, over other active techniques, such as low power requirement, facile fabrication methods, and non-invasive nature. Even though SAW-based generation of micron-sized droplets through atomization has been studied, the role of substrate wettability on the characteristics of the transferred droplets has not been explored to date. Here, we study the generation and effective transfer of micron-sized droplets using SAW onto wettable substrates whose water contact angles vary from 5° to 145°. The characteristics of transferred droplets after impacting the wettable substrates are characterized in terms of the contact line diameter and polydispersity index. A theoretical model is formulated to predict the initial average size of the transferred droplets on the wettable substrates of different contact angles. The variation of polydispersity and number density with contact angle is explained by considering droplet coalescence and bouncing. The relevance of the technique in biological assays is demonstrated by transferring droplets of streptavidin protein samples onto a substrate.

Material Design and Device Fabrication Strategies for Stretchable Organic Solar Cells

Recent advances in the power conversion efficiency (PCE) of organic solar cells (OSCs) have greatly enhanced their commercial viability. Considering the technical standards (e.g., mechanical robustness) required for wearable electronics, which are promising application platforms for OSCs, the development of fully stretchable OSCs (f-SOSCs) should be accelerated. Here, a comprehensive overview of f-SOSCs, which are aimed to reliably operate under various forms of mechanical stress, including bending and multidirectional stretching, is provided. First, the mechanical requirements of f-SOSCs, in terms of tensile and cohesion/adhesion properties, are summarized along with the experimental methods to evaluate those properties. Second, essential studies to make each layer of f-SOSCs stretchable and efficient are discussed, emphasizing strategies to simultaneously enhance the photovoltaic and mechanical properties of the active layer, ranging from material design to fabrication control. Key improvements to the other components/layers (i.e., substrate, electrodes, and interlayers) are also covered. Lastly, considering that f-SOSC research is in its infancy, the current challenges and future prospects are explored.

Adaptive wireless millirobotic locomotion into distal vasculature

Microcatheters have enabled diverse minimally invasive endovascular operations and notable health benefits compared with open surgeries. However, with tortuous routes far from the arterial puncture site, the distal vascular regions remain challenging for safe catheter access. Therefore, we propose a wireless stent-shaped magnetic soft robot to be deployed, actively navigated, used for medical functions, and retrieved in the example M4 segment of the middle cerebral artery. We investigate shape-adaptively controlled locomotion in phantoms emulating the physiological conditions here, where the lumen diameter shrinks from 1.5 mm to 1 mm, the radius of curvature of the tortuous lumen gets as small as 3 mm, the lumen bifurcation angle goes up to 120°, and the pulsatile flow speed reaches up to 26 cm/s. The robot can also withstand the flow when the magnetic actuation is turned off. These locomotion capabilities are confirmed in porcine arteries ex vivo. Furthermore, variants of the robot could release the tissue plasminogen activator on-demand locally for thrombolysis and function as flow diverters, initiating promising therapies towards acute ischemic stroke, aneurysm, arteriovenous malformation, dural arteriovenous fistulas, and brain tumors. These functions should facilitate the robot's usage in new distal endovascular operations.

Revealing the Effect of Skull Deformation on Intracranial Pressure Variation During the Direct Interaction Between Blast Wave and Surrogate Head

Intracranial pressure (ICP) during the interaction between blast wave and the head is a crucial evaluation criterion for blast-induced traumatic brain injury (bTBI). ICP variation is mainly induced by the blast wave transmission and skull deformation. However, how the skull deformation influences the ICP remains unclear, which is meaningful for mitigating bTBI. In this study, both experimental and numerical models are developed to elucidate the effect of skull deformation on ICP variation. Firstly, we performed the shock tube experiment of the high-fidelity surrogate head to measure the ICP, the blast overpressure, and the skull surface strain of specific positions. The results show that the ICP profiles of all measured points show oscillations with positive and negative change, and the variation is consistent with the skull surface strain. Further numerical analysis reveals that when the blast wave reaches the measured point, the peak overpressure transmits directly through the skull to the brain, forming the local positive ICP peak, and the impulse induces the local inward deformation of the skull. As the peak overpressure passes through, the blast impulse impacts the nearby skull supported by the soft and incompressible brain tissue and extrudes the skull outward in the initial position. The inward and outward skull deformation leads to the oscillation of ICP. These numerical analyses agree with experimental results, which explain the appearance of negative and positive ICP peaks and the synchronization of negative ICP with surface strain. The study has implications for medical injury diagnosis and protective equipment design.

On the acoustically induced fluid flow in particle separation systems employing standing surface acoustic waves - Part I

By integrating surface acoustic waves (SAW) into microfluidic devices, microparticle systems can be fractionated precisely in flexible and easily scalable Lab-on-a-Chip platforms. The widely adopted driving mechanism behind this principle is the acoustic radiation force, which depends on the size and acoustic properties of the suspended particles. Superimposed fluid motion caused by the acoustic streaming effect can further manipulate particle trajectories and might have a negative influence on the fractionation result. A characterization of the crucial parameters that affect the pattern and scaling of the acoustically induced flow is thus essential for the design of acoustofluidic separation systems. For the first time, the fluid flow induced by pseudo-standing acoustic wave fields with a wavelength much smaller than the width of the confined microchannel is experimentally revealed in detail, using quantitative three-dimensional measurements of all three velocity components (3D3C). In Part I of this study, we focus on the fluid flow close to the center of the surface acoustic wave field, while in Part II the outer regions with strong acoustic gradients are investigated. By systematic variations of the SAW-wavelength λ_SAW and channel height H, a transition from vortex pairs extending over the entire channel width W to periodic flows resembling the pseudo-standing wave field is revealed. An adaptation of the electrical power, however, only affects the velocity scaling. Based on the experimental data, a validated numerical model was developed in which critical material parameters and boundary conditions were systematically adjusted. Considering a Navier slip length at the substrate-fluid interface, the simulations provide a strong agreement with the measured velocity data over a large frequency range and enable an energetic consideration of the first and second-order fields. Based on the results of this study, critical parameters were identified for the particle size as well as for channel height and width. Progress for the research on SAW-based separation systems is obtained not only by these findings but also by providing all experimental velocity data to allow for further developments on other sites.

Cationic Conjugated Polyelectrolytes with Aggregation-Induced Ratiometric Fluorescence

The molecular diversity of aggregation-induced emission remains to be challenging due to the limitation of conventional synthesis methods. Here, a series of novel neutral and cationic conjugated polymers composed with various ratios of tetraarylethylene (TAE) containing a bridged oxygen (O) and fluorene (F) units are designed and synthesized via the geminal cross-coupling (GCC) of 1,1-dibromoolefins. The incorporation of TAE segments into the conjugated backbone of polyfluorene produces pronounced aggregation-induced ratiometric fluorescence (AIRF), i.e., aggregation-induced emission (AIE) at 520-600 nm grows synergistically with aggregations-caused quenching (ACQ) at 400-450 nm. The content of fluorene unit in the polymer backbones determines the intensity of the initial fluorescence at blue light region. The huge distinction (about 150 nm) in dual emission wavelengths caused by the environment change makes these conjugated polyelectrolytes particularly suitable for ratiometric fluorescence sensing. Based on electrostatic interaction mechanism, the gradual addition of heparin into the cationic conjugated polymers aqueous solutions could induce dual-color fluorescence changes with a detection limit of 9 nM. This work exhibits the great facility of using GCC reaction to synthesis the conjugated TAE polymers with superior AIE properties and special functions. This article is protected by copyright. All rights reserved.

Pancake Jumping of Sessile Droplets

Rapid droplet shedding from surfaces is fundamentally interesting and important in numerous applications such as anti-icing, anti-fouling, dropwise condensation, and electricity generation. Recent efforts have demonstrated the complete rebound or pancake bouncing of impinging droplets by tuning the physicochemical properties of surfaces and applying external control, however, enabling sessile droplets to jump off surfaces in a bottom-to-up manner is challenging. Here, the rapid jumping of sessile droplets, even cold droplets, in a pancake shape is reported by engineering superhydrophobic magnetically responsive blades arrays. This largely unexplored droplet behavior, termed as pancake jumping, exhibits many advantages such as short interaction time and high energy conversion efficiency. The critical conditions for the occurrence of this new phenomenon are also identified. This work provides a new toolkit for the attainment of well-controlled and active steering of both sessile and impacting droplets for a wide range of applications.

Engineering a deformation-free plastic spiral inertial microfluidic system for CHO cell clarification in biomanufacturing

Inertial microfluidics has enabled many impactful high throughput applications. However, devices fabricated in soft elastomer (i.e., polydimethylsiloxane (PDMS)) suffer reliability issues due to significant deformation generated by the high pressure and flow rates in inertial microfluidics. In this paper, we demonstrated deformation-free and mass-producible plastic spiral inertial microfluidic devices for high-throughput cell separation applications. The design of deformable PDMS spiral devices was translated to their plastic version by compensating for the channel deformation in the PDMS devices, analyzed by numerical simulation and confocal imaging methods. The developed plastic spiral devices showed similar performance to their original PDMS devices for blood separation and Chinese hamster ovary (CHO) cell retention. Furthermore, using a multiplexed plastic spiral unit containing 100 spirals, we successfully demonstrated ultra-high-throughput cell clarification (at a processing rate of 1 L min^-1) with a high cell-clarification efficiency of ∼99% (at the cell density changing from ∼2 to ∼10 × 10⁶ cells mL^-1). Benefitting from the continuous and clogging-free separation with an industry-level throughput, the cell clarification device could be a critical breakthrough for the production of therapeutic biologics such as antibodies or vaccines, impacting biomanufacturing in general.

Effects of mixing temperature on the extrusion rheological behaviors of rubber-based compounds

In this study, rim strip (R) and sidewall (S) compounds were prepared at varying initial mixing temperatures. The effects of the mixing temperature on the extrusion rheological behaviors of the compounds were investigated, and the relationships between the compound structure and the extrusion rheological behaviors were studied. The results showed that the tensile stress relaxation rates of both R and S were more sensitive to the mixing temperature than the shear stress relaxation rate, and the former was affected by both the dispersion of carbon black (CB) and the actual molecular weight of the rubbers. Strain sweep results showed that R, which had a higher CB content, had a more obvious Payne effect than S. When the initial mixing temperature increased from 80 °C to 90 °C, both storage modulus (G′) at a low shear strain and the ΔG′ of R obviously decreased, indicating CB dispersion improvement. The S extrudates showed higher die swell ratios (B) than the R extrudates, and the former was more sensitive to mixing temperature. The main factors influencing the B of the R and S were the CB dispersity and the molecular weight, respectively. In addition, at high extrusion rates, a sharkskin phenomenon could be observed for the R extrudate surfaces, whereas the S extrudates were more likely to be integrally distorted.

The carbon black dispersity and rubber molecular weight change during the mixing process were the important factors determining the die swell behavior of the rubber compounds.

Co-precipitation polymerization of dual functional monomers and polystyrene-co-divinylbenzene for ciprofloxacin imprinted polymer preparation

Novel ciprofloxacin composite imprinted materials are synthesized by using co-precipitation polymerization of dual functional monomers (methacrylic acid and 2-vinylpyridine) and polystyrene-co-divinylbenzene. The intermolecular interactions between monomers and template are evaluated by molecular modeling analysis. The physicochemical properties of the obtained polymers are characterized using FT-IR, TGA, and SEM. Batch adsorption experiments are used to investigate adsorption properties (kinetic, pH, and isotherm). These polymers are employed to prepare the solid phase extraction cartridges, and their extraction performances are analyzed by the HPLC-UV method. DFT calculations indicate that hydrogen bonding and π−π stacking are the driving forces for the formation of selective rebinding sites. The obtained polymers exhibit excellent adsorption properties, including fast kinetics and high adsorption capacity (up to 10.28 mg g⁻¹) with an imprinted factor of 2.55. The Scatchard analysis indicates the presence of specific high-affinity adsorption sites on the imprinted polymer. These absorbents are employed to extract CIP in river water with recoveries in the range of 65.97–119.26% and the relative standard deviation of 3.59–14.01%. Furthermore, the used cartridges could be reused at least eight times without decreasing their initial adsorption capacity.

Ciprofloxacin imprinted polymers were prepared using co-precipitation polymerization of methacrylic acid, 2-vinylpyridine and polystyrene-co-divinylbenzene.

Monolithic processing of a layered flexible robotic actuator film for kinetic electronics

Low-invasive soft robotic techniques can potentially be used for developing next-generation body-machine interfaces. Most soft robots require complicated fabrication processes involving 3D printing and bonding/assembling. In this letter, we describe a monolithic soft microrobot fabrication process for the mass production of soft film robots with a complex structure by simple 2D processing of a robotic actuator film. The 45 µg/mm² lightweight film robot can be driven at a voltage of CMOS compatible 5 V with 0.15 mm^-1 large curvature changes; it can generate a force 5.7 times greater than its self-weight. In a durability test, actuation could be carried out over 8000 times without degradation. To further demonstrate this technique, three types of film robots with multiple degrees of freedom and a moving illuminator robot were fabricated. This technique can easily integrate various electrical circuits developed in the past to robotic systems and can be used for developing advanced wearable sensing devices; it can be called "Kinetic electronics".

Gifts from Nature: Bio-Inspired Materials for Rechargeable Secondary Batteries

Materials in nature have evolved to the most efficient forms and have adapted to various environmental conditions over tens of thousands of years. Because of their versatile functionalities and environmental friendliness, numerous attempts have been made to use bio-inspired materials for industrial applications, establishing the importance of biomimetics. Biomimetics have become pivotal to the search for technological breakthroughs in the area of rechargeable secondary batteries. Here, the characteristics of bio-inspired materials that are useful for secondary batteries as well as their benefits for application as the main components of batteries (e.g., electrodes, separators, and binders) are discussed. The use of bio-inspired materials for the synthesis of nanomaterials with complex structures, low-cost electrode materials prepared from biomass, and biomolecular organic electrodes for lithium-ion batteries are also introduced. In addition, nature-derived separators and binders are discussed, including their effects on enhancing battery performance and safety. Recent developments toward next-generation secondary batteries including sodium-ion batteries, zinc-ion batteries, and flexible batteries are also mentioned to understand the feasibility of using bio-inspired materials in these new battery systems. Finally, current research trends are covered and future directions are proposed to provide important insights into scientific and practical issues in the development of biomimetics technologies for secondary batteries.

Functionalized Elastomers for Intrinsically Soft and Biointegrated Electronics

Elastomers are suitable materials for constructing a conformal interface with soft and curvilinear biological tissue due to their intrinsically deformable mechanical properties. Intrinsically soft electronic devices whose mechanical properties are comparable to human tissue can be fabricated using suitably functionalized elastomers. This article reviews recent progress in functionalized elastomers and their application to intrinsically soft and biointegrated electronics. Elastomers can be functionalized by adding appropriate fillers, either nanoscale materials or polymers. Conducting or semiconducting elastomers synthesized and/or processed with these materials can be applied to the fabrication of soft biointegrated electronic devices. For facile integration of soft electronics with the human body, additional functionalization strategies can be employed to improve adhesive or autonomous healing properties. Recently, device components for intrinsically soft and biointegrated electronics, including sensors, stimulators, power supply devices, displays, and transistors, have been developed. Herein, representative examples of these fully elastomeric device components are discussed. Finally, the remaining challenges and future outlooks for the field are presented.

Designing a Highly Stable Slippery Organogel on Q235 Carbon Steel for Inhibiting Microbiologically Influenced Corrosion

Microbiologically influenced corrosion (MIC) accelerates the corrosion and degradation of metal materials due to the settlement of microorganisms on the surface. However, environmentally friendly and efficient methods to fabricate antifouling and anticorrosion surfaces are still lacking. Inspired by Nepenthes, a slippery liquid-infused porous surface (SLIPS) has been proven to be an efficient way to inhibit settlement of microorganisms on the metal surface and the following MIC due to the existence of a mobile defect-free lubricant layer. However, the stability of the lubricant layer and substrate of the SLIPS prevented its long-term antifouling and anticorrosion application. Herein, a highly stable slippery organogel was fabricated by depositing a homogeneous mixture of PDMS (base and curing agent), silicone oil, triethoxyvinylsilane, and SiO₂ on Q235 and curing in an oven. Triethoxyvinylsilane was not only able to cross-link with the curing agent of PDMS through hydrosilylation but also able to interlink the organogel and Q235 through condensation between the -OH of the metal surface and hydrolyzed siloxane. As a result, the adhesion force between the organogel without triethoxyvinylsilane and the substrate (0.45 MPa) increased to 1.50 MPa for the organogel with triethoxyvinylsilane and SiO₂. Also, the tensile strength of the organogel without SiO₂ (0.97 MPa) increased to 3.88 MPa for the organogel with 2 wt % SiO₂ because of the high elastic modulus of SiO₂, which was important to improving its stability under external force. In addition, the organogel showed stable oil distribution and slippery performance after spinning at 4000 rpm for 30 s. Then, the bacterial settlement demonstrated that the organogel could effectively inhibit Pseudoalteromonas sp. settlement on the substrate under both static and dynamic conditions. Finally, an electrochemical test indicated that the MIC could be effectively mitigated by the organogel. This study provides an efficient method to fabricate a highly stable slippery surface on a metal surface for its potential application in mitigating MIC.

Toward Mechanochromic Soft Material-Based Visual Feedback for Electronics-Free Surgical Effectors

A chromogenically reversible, mechanochromic pressure sensor is integrated into a mininvasive surgical grasper compatible with the da Vinci robotic surgical system. The sensorized effector, also featuring two soft-material jaws, encompasses a mechanochromic polymeric inset doped with functionalized spiropyran (SP) molecule, designed to activate mechanochromism at a chosen pressure and providing a reversible color change. Considering such tools are systematically in the visual field of the operator during surgery, color change of the mechanochromic effector can help avoid tissue damage. No electronics is required to control the devised visual feedback. SP-doping of polydimethylsiloxane (2.5:1 prepolymer/curing agent weight ratio) permits to modulate the mechanochromic activation pressure, with lower values around 1.17 MPa for a 2% wt. SP concentration, leading to a shorter chromogenic recovery time of 150 s at room temperature (25 °C) under green light illumination. Nearly three-times shorter recovery time is observed at body temperature (37 °C). To the best of knowledge, this study provides the first demonstration of mechanochromic materials in surgery, in particular to sensorize unpowered surgical effectors, by avoiding dramatic increases in tool complexity due to additional electronics, thus fostering their application. The proposed sensing strategy can be extended to further tools and scopes.

Scalable fluid-spinning nanowire-based inorganic semiconductor yarns for electrochromic actuators

Semiconductor yarns with unique functional characteristics have great potential applications in next-generation electronic devices. However, scalable inorganic semiconductor yarns with excellent mechanical and electrical properties, and environmental stability have not been discovered. In this study, we explored a unique fluid-spinning strategy to obtain a series of scalable inorganic semiconductor yarns including neat and hybrid semiconductor yarns. Different from the conventional yarn spinning strategy through a mechanical motor, we utilized the fluid force from the triple-phase interface to assemble and twist inorganic nanofiber building blocks simultaneously, and eventually obtained highly oriented inorganic nanowire-based semiconductor yarns. The obtained semiconductor yarns showed an excellent flexibility (curvature exceeding 2 cm^-1) and mechanical strength (tensile strength of 443 MPa) because of their highly oriented hierarchical nanostructures, which make them coiling able with highly twisted insertion. Additionally, coiled yarns were obtained by combining the host core material and functional guest sheath in a fluid-spinning process, which are flexible in deep cryogenic temperature owing to the pure inorganic building blocks (26.28% tensile strain in liquid nitrogen). In particular, inorganic yarn-based electrochromic actuators can obtain as high as 15.3% tensile stroke and 0.82 J g^-1 work capacity by electrochemical charge injection-associated multicolor switching.

High-resolution integrated piezoresistive sensors for microfluidic monitoring

Microfluidic devices are traditionally monitored by bulky and expensive off-chip sensors. We have developed a soft piezoresistive sensor capable of measuring micron-level strains that can be easily integrated into devices via soft lithography. We apply this sensor to achieve fast and localized monitoring of pressure, flow, and valve actuation.

Rheological characterization of poly-dimethyl siloxane formulations with tunable viscoelastic properties

Studies from the past two decades have demonstrated convincingly that cells are able to sense the mechanical properties of their surroundings. Cells make major decisions in response to this mechanosensation, including decisions regarding cell migration, proliferation, survival, and differentiation. The vast majority of these studies have focused on the cellular mechanoresponse to changing substrate stiffness (or elastic modulus) and have been conducted on purely elastic substrates. In contrast, most soft tissues in the human body exhibit viscoelastic behavior; that is, they generate responsive force proportional to both the magnitude and rate of strain. While several recent studies have demonstrated that viscous effects of an underlying substrate affect cellular mechanoresponse, there is not a straightforward experimental method to probe this, particularly for investigators with little background in biomaterial fabrication. In the current work, we demonstrate that polymers comprised of differing polydimethylsiloxane (PDMS) formulations can be generated that allow for control over both the strain-dependent storage modulus and the strain rate-dependent loss modulus. These substrates requires no background in biomaterial fabrication to fabricate, are shelf-stable, and exhibit repeatable mechanical properties. Here we demonstrate that these substrates are biocompatible and exhibit similar protein adsorption characteristics regardless of mechanical properties. Finally, we develop a set of empirical equations that predicts the storage and loss modulus for a given blend of PDMS formulations, allowing users to tailor substrate mechanical properties to their specific needs.

We have generated novel formulations of polydimethyl siloxane with varying viscoelastic properties that can be used to study cellular response. We present equations that can be used to predict the storage and loss moduli of these polymers.

Ultrasoft and High-Mobility Block Copolymers for Skin-Compatible Electronics

Polymer semiconductors (PSCs) are an essential component of organic field-effect transistors (OFETs), but their potential for stretchable electronics is limited by their brittleness and failure susceptibility upon strain. Herein, a covalent connection of two state-of-the-art polymers-semiconducting poly-diketo-pyrrolopyrrole-thienothiophene (PDPP-TT) and elastomeric poly(dimethylsiloxane) (PDMS)-in a single triblock copolymer (TBC) chain is reported, which enables high charge carrier mobility and low modulus in one system. Three TBCs containing up to 65 wt% PDMS were obtained, and the TBC with 65 wt% PDMS content exhibits mobilities up to 0.1 cm²  V^-1  s^-1 , in the range of the fully conjugated reference polymer PDPP-TT (0.7 cm²  V^-1  s^-1 ). The TBC is ultrasoft with a low elastic modulus (5 MPa) in the range of mammalian tissue. The TBC exhibits an excellent stretchability and extraordinary durability, fully maintaining the initial electric conductivity in a doped state after 1500 cycles to 50% strain.

Soft skin layers for reconfigurable and programmable nanowrinkles

Wrinkling skin layers on pre-strained polymer sheets has drawn significant interest as a method to create reconfigurable surface patterns. Compared to widely studied metal or silica films, softer polymer skins are more tolerant to crack formation when the surface topography is tuned under applied strain. This Mini-review discusses recent progress in mechano-responsive wrinkles based on polymer skin materials. Control over the skin thickness with nanometer accuracy allows for tuning of the wrinkle wavelength and orientation over length scales from nanometer to micrometer regimes. Furthermore, soft skin layers enable texturing of two-dimensional electronic materials with programmable feature sizes and structural hierarchy because of the conformal adhesion to the substrates. Soft skin systems open prospects to tailor a range of surface properties via external stimuli important for applications such as smart windows, microfluidics, and nanoelectronics.

Relationship between the Processing, Structure, and Properties of Microfibrillar Composites

The relationship between processing, morphology, and properties of polymeric materials has been the subject of numerous studies of academic and industrial research. Finding an answer to this question might result in guidelines on how to design polymeric materials. Microfibrillar composites (MFCs) are an interesting class of polymer-polymer composites. The advantage of the MFC concept lies in developing in situ microfibrils by which a perfect homogeneous distribution of the reinforcement in the matrix can be achieved. Their potentially excellent mechanical properties are strongly dependent on the aspect ratio of the fibrils, which is developed through a three-stage production process: melt blending, fibrillation, and isotropization. During melt blending, the polymers undergo different morphological changes, such as a breakup and coalescence of the droplets, which play a crucial role in defining the microstructure. During processing, various parameters may affect the morphology of the MFCs, which must be taken into account. Besides the processing parameters, the microstructure of the composite is dependent on the composition ratio of the blend and viscosity of the components, as well as the dispersion and distribution of the microfibrils. The objective here is to outline this importance and bring together an overview of the processing-structure-property relationship for MFCs.

3D-printed cellular tips for tuning fork atomic force microscopy in shear mode

Conventional atomic force microscopy (AFM) tips have remained largely unchanged in nanomachining processes, constituent materials, and microstructural constructions for decades, which limits the measurement performance based on force-sensing feedbacks. In order to save the scanning images from distortions due to excessive mechanical interactions in the intermittent shear-mode contact between scanning tips and sample, we propose the application of controlled microstructural architectured material to construct AFM tips by exploiting material-related energy-absorbing behavior in response to the tip–sample impact, leading to visual promotions of imaging quality. Evidenced by numerical analysis of compressive responses and practical scanning tests on various samples, the essential scanning functionality and the unique contribution of the cellular buffer layer to imaging optimization are strongly proved. This approach opens new avenues towards the specific applications of cellular solids in the energy-absorption field and sheds light on novel AFM studies based on 3D-printed tips possessing exotic properties.

The authors investigate 3D-printed tips, based on controlled microstructural architectured materials, as probes for shear-mode atomic force microscopy. They demonstrate that the tailored stiffness and energy-absorbing behaviour of the material are beneficial for improving image quality.