Flexible Mechanical Properties Research Articles

Contacting of Bicomponent TPU-Fibers with a Conductive Core: A Method for Data Acquisition and Analysis of the Electrical Properties

With the megatrend of digitalization, the demand for sensors in previously difficult-to-access scenarios is increasing. Filament-shaped sensors (FSS) are ideal for this demand, especially in applications in which the monitoring of textile structures is the focus. Electrically conductive bicomponent filaments based on thermoplastic polyurethane (TPU) and doped with carbon nanotubes (CNTs) offer great potential due to their flexible mechanical properties. Through the core-conducting, bicomponent structure, the sensing material is protected from environmental factors such as surrounding conductive materials and external moisture. The insulating material, however, simultaneously complicates the contacting method in order to measure sensing changes in the conductive core. In this work, laser cutting is employed as a technology in order to expose the conductive core of the filaments. The filament is then coated with silver and mechanically crimped, providing both a conductive interface for the data acquisition device as well as a protective layer. Laser parameters (power 20–100 W and speed 5–50 mm/s) are investigated to identify the parameters with the best cutting properties for which the filaments are analyzed visually and electrically. This work provides a robust and reproducible method for contacting core-conducting TPU filaments for strain-sensing applications. This study shows that while the choice of laser parameter influences the morphology of the cut surface, its impact on the resulting linear resistivity is negligible.

Rigidity‐Tunable Materials for Soft Engineering Systems

Engineering systems that leverage the flexibility and softness of soft materials have been fostering revolutionary progress and broad interest across various applications. The inherently flexible mechanical properties of these materials lay the groundwork for engineering systems that can adapt comparably to biological organisms, enabling them to adjust to unpredictable environments effectively. However, alongside the positive benefits of softness, these systems face challenges such as low durability, continuous energy demands, and compromised task performance due to the inherently low stiffness of soft materials. These limitations pose significant obstacles to the practical impact of soft engineering systems in the real world beyond innovative concepts. This review presents a strategy that employs materials with variable stiffness to balance adaptability advantages with the challenge of low rigidity. We summarize developments in materials capable of stiffness modulation alongside their applications in electronics, robotics, and biomedical fields. This focus on stiffness modulation at the material unit level is a critical step toward enabling the practical application of soft engineering systems in real‐world scenarios.This article is protected by copyright. All rights reserved.

Robust ultrahigh electromagnetic interference shielding effectiveness based on engineered structures of carbon nanotube films

High-performance electromagnetic interference (EMI) shielding materials with ultrathin, flexible, and pliable mechanical properties are highly desired for high-end equipments, yet there remain large challenges in the manufacture of these materials. Here, carbon nanotube film (CNTF)/copper (Cu) nanoparticle (NP) composite films are fabricated via a facile electrodeposition method to achieve high electromagnetic shielding efficiency. Notably, a CNTF/Cu NP composite film with 15μm thickness can achieve excellent EMI shielding efficiency of ∼248 dB and absolute EMI shielding effectiveness as high as 2.17×105 dB cm2 g-1, which are the best values for composite EMI shielding materials with similar or greater thicknesses. These engineered composite films exhibit excellent deformation tolerance, which ensures the robust reliability of EMI shielding efficiency after 20,000 cycles of repeated bending. Our results represent a critical breakthrough in the preparation of ultrathin, flexible, and pliable shielding films for applications in smart, portable and wearable electronic devices, and 5G communication.

Accelerated Polymer Photodegradation

Abstract: This article presents preliminary results of the accelerated degradation of polymers using concentrated solar radiation. For this purpose, a passive solar concentration prototype was designed, which consists of four trapezoidal mirrors placed in the shape of an inverted truncated square pyramid. The mirrors are placed at an angle of 30° respect to the zenith. The prototype has a square base of 46 cm x 46 cm where the polymers to be irradiated are placed and a geometric concentration ratio, CRg, of 1.89. The mass change was determined after 30 days of exposure to solar radiation, and the temperature variation of some samples as a function of irradiance was obtained. In addition, a computer simulation was carried out using the free access software Energy2D. Some polymers maintained their flexible mechanical properties, such as PET (type 1), others were partially embrittled, while type 2, 5 and 7 polymers were completely embrittled. It was possible to reduce the degradation time of different types of commercial polymers, while polymers exposed to non-concentrated radiation and without exposure remains intact. Embrittled polymers can be used as waterproof material in slabs and pre-cast walls, as well in applications where they are not exposed to solar radiation. On the other hand, the polymers that remained intact must be used in applications with permanent radiation exposure, such as in flower pots, plastic parts for automobiles, etc.

Mechanical Field Guiding Structure Design Strategy for Meta-Fiber Reinforced Hydrogel Composites by Deep Learning.

Fiber-reinforced hydrogel composites are widely employed in many engineering applications, such as drug release, and flexible electronics, with more flexible mechanical properties than pure hydrogel materials. Comparing to the hydrogel strengthened by continuous fiber, the meta-fiber reinforced hydrogel provides stronger individualized design ability of deformation patterns and tunable stiffness, especially for the elaborate applications in joint, cartilage, and organ. In this paper, a novel structure design strategy based on deep learning algorithm is proposed for hydrogel reinforced by meta-fiber to achieve targeted mechanical properties, such as stress and displacement fields. A solid mechanic model for meta-fiber reinforced hydrogel is first developed to construct the dataset of fiber distribution and the corresponding mechanical properties of the composite. Generative adversarial network (GAN) is then trained to characterize the relationship between stress or displacement field, and meta-fiber distribution. The well-trained GAN is implemented to design meta-fiber reinforced hydrogel composite structure under specific operation conditions. The results show that the deep learning method may efficiently predict the structure of the hydrogel composite with satisfied confidence, and has great potential for applications in drug delivery and flexible electronics.

Preparation of MoS2@PDA-Modified Polyimide Films with High Mechanical Performance and Improved Electrical Insulation.

Polyimide (PI) has been widely used in cable insulation, thermal insulation, wind power protection, and other fields due to its high chemical stability and excellent electrical insulation and mechanical properties. In this research, a modified PI composite film (MoS2@PDA/PI) was obtained by using polydopamine (PDA)-coated molybdenum disulfide (MoS2) as a filler. The low interlayer friction characteristics and high elastic modulus of MoS2 provide a theoretical basis for enhancing the flexible mechanical properties of the PI matrix. The formation of a cross-linking structure between a large number of active sites on the surface of the PDA and the PI molecular chain can effectively enhance the breakdown field strength of the film. Consequently, the tensile strength of the final sample MoS2@PDA/PI film increased by 44.7% in comparison with pure PI film, and the breakdown voltage strength reached 1.23 times that of the original film. It can be seen that the strategy of utilizing two-dimensional (2D) MoS2@PDA nanosheets filled with PI provides a new modification idea to enhance the mechanical and electrical insulation properties of PI films.

A smart superwetting PET-Anthocyanin membrane for pH monitoring in water and emulsion separation

Smart superwetting membranes with anti-oil pollutions and process water pH monitoring show great potential before downstream processing. Herein, a flexible intelligent monitoring membrane with strong anti-oil fouling properties was developed by utilizing a PET-Anthocyanin mixed solution through electrospinning. Specifically, using waste PET plastic bottles as raw materials, a dual-solvent system is used to dissolve the PET, and then anthocyanins are added to blend to form an electrospinning solution. The obtained A/PET showed excellent porous morphology and wettability, and its underwater oil contact angle could reach up to 150°. The introduction of anthocyanins (5 %) rich in hydroxyl functional groups reduced the formation of hydrophobic domains and promoted the hydration layer on the membrane surface, showing excellent oil resistance property. Furthermore, the stress–strain test of the A/PET5 membrane shows that the strain is significantly enhanced after the yield phenomenon, which shows that the membrane has a flexible mechanical property. Most importantly, based on the pH-sensitivity of anthocyanins, it can be intuitively found that color response changes from the original pink to light pink, and then to white, showing excellent monitoring the pH of the continuous phase. Moreover, the developed membrane possesses water flux of 7440 L m-2h−1 and oil rejection up to 99.4 % for O/W emulsions, surpassing that of the superhydrophilic PET base membrane (956 L m-2h−1, 99.3 %). Briefly, this work provides a novel multifunctional smart membrane with excellent anti-fouling, flexible mechanical, and outstanding separation performance, which can visually monitor the separation process of oily wastewater.

Tailored self-assembly of semi-transparent polymer/clay nanocomposites for gas-barrier applications assisted by aqueous liquid crystalline scaffolds

A new strategy for preparing flexible and semi-transparent gas-barrier coatings was developed using tailored self-assembly of montmorillonite (MMT)/polyvinylpyrrolidone (PVP) nanocomposites assisted by aqueous liquid crystalline (LC) scaffolds. First, we established a composition wherein aqueous MMT exhibited the LC phase in the presence of polyethyleneimine (PEI) and hydrochloric acid (HCl). The viscoelastic rheological features of MMT LC enable the formation of uniform and conformal MMT coatings on various types of substrates, including flat or topographically featured surfaces. Moreover, the MMT LC serves as a structural scaffold that enables the rapid transport of PVP within the inner gallery space of the MMT LC, resulting in the formation of stacked MMT/PVP nanosheets after drying. Owing to its highly aligned layered structure, MMT/PVP exhibited flexible mechanical properties with enhanced hardness and modulus compared to neat MMT. Furthermore, the MMT/PVP can suppress gas permeation, as demonstrated by 0.1 Barrer of H2 permeability for the best coating conditions (containing 63 wt% MMT and 37 wt% PVP), while maintaining semi-transparent optical properties. Considering the aforementioned properties and that all components in MMT/PVP are bio-safe materials, this coating system has potential applications as a gas-barrier coating in conventional packaging materials, food packaging, and H2 storage tanks.

One-step generation of droplet-filled hydrogel microfibers for 3D cell culture using an all-aqueous microfluidic system

Hydrogel microfibers, which are characterized by flexible mechanical properties, a uniform spatial distribution, large surface areas, and excellent biocompatibility, hold great potential for various biomedical applications. However, the fabrication of heterogeneous hydrogel microfibers with high cell-loading capacity and the ability to carry multiple components via an environmentally friendly method remains challenging. In this study, we developed a novel pneumatic pump-assisted all-aqueous microfluidic system that enables the one-step fabrication of all-aqueous droplet-filled hydrogel microfibers with unique morphologies and adjustable configurations. By designing a pump-valve cycling system and selecting two immiscible fluids with stable water interfaces (dextran and polyethylene glycol), we successfully fabricated alginate microfibers with equidistantly arranged droplets through the ionotropic gelation reaction between sodium alginate and calcium chloride. The droplet size, interdroplet spacing, and microfiber dimensions could be flexibly controlled by adjusting the flow rates of the inner-phase, middle-phase, and outer-phase inlets. The results showed that the system enabled the high-throughput in situ formation of functional three-dimensional cell spheroids. The generated cell spheroids exhibited excellent cell viability and drug-testing functionality, indicating their potential applications in cell cultures. The developed technique offers strong support for future biomedical research and applications, and provides a new approach for the preparation of multifunctional hydrogel microfibers for materials science, tissue engineering, and drug testing.

Electropolymerisation Technologies for Next-Generation Lithium-Sulphur Batteries.

Lithium-sulphur batteries (LiSBs) have garnered significant attention as the next-generation energy storage device because of their high theoretical energy density, low cost, and environmental friendliness. However, the undesirable "shuttle effect" by lithium polysulphides (LPSs) severely inhibits their practical application. To alleviate the shuttle effect, conductive polymers have been used to fabricate LiSBs owing to their improved electrically conducting pathways, flexible mechanical properties, and high affinity to LPSs, which allow the shuttle effect to be controlled. In this study, the applications of various conductive polymers prepared via the simple yet sophisticated electropolymerisation (EP) technology are systematically investigated based on the main components of LiSBs (cathodes, anodes, separators, and electrolytes). Finally, the potential application of EP technology in next-generation batteries is comprehensively discussed.

Prediction of mechanical properties for a grafted polypropylene system via transfer learning with a small database

The increasing demand for polymer dielectrics in different scenarios, such as electrical insulation cable, requires elevated electrical and mechanical properties. In order to understand the relationship between mechanical properties and the structure of grafted monomers in a grafted polypropylene (PP) system, a design framework based on the transfer-learning method has been proposed for designing grafted side chain structure in PP system. 22 samples of polypropylene-grafted polymer are synthesized. Through a well-trained multi-layer perceptron model for predicting glass transition temperature (Tg), mechanical properties of the grafted PP have been well predicted by the transfer-learning method. Meanwhile, the grafting group structures are divided into nine substructures. By assembling these substructures, the chemical space is established for prediction. Moreover, candidates with satisfied deep traps and flexible mechanical properties are screened out for reference. This work turns qualitative understanding into a quantitative analysis based on mathematical models and broadens the application of polymer materials design with a small dataset.

Current Progress in Conductive Hydrogels and Their Applications in Wearable Bioelectronics and Therapeutics.

Wearable bioelectronics and therapeutics are a rapidly evolving area of research, with researchers exploring new materials that offer greater flexibility and sophistication. Conductive hydrogels have emerged as a promising material due to their tunable electrical properties, flexible mechanical properties, high elasticity, stretchability, excellent biocompatibility, and responsiveness to stimuli. This review presents an overview of recent breakthroughs in conductive hydrogels, including their materials, classification, and applications. By providing a comprehensive review of current research, this paper aims to equip researchers with a deeper understanding of conductive hydrogels and inspire new design approaches for various healthcare applications.

Exosome inspired photo-triggered gelation hydrogel composite on modulating immune pathogenesis for treating rheumatoid arthritis

Although exosome therapy has been recognized as a promising strategy in the treatment of rheumatoid arthritis (RA), sustained modulation on RA specific pathogenesis and desirable protective effects for attenuating joint destruction still remain challenges. Here, silk fibroin hydrogel encapsulated with olfactory ecto-mesenchymal stem cell-derived exosomes (Exos@SFMA) was photo-crosslinked in situ to yield long-lasting therapeutic effect on modulating the immune microenvironment in RA. This in situ hydrogel system exhibited flexible mechanical properties and excellent biocompatibility for protecting tissue surfaces in joint. Moreover, the promising PD-L1 expression was identified on the exosomes, which potently suppressed Tfh cell polarization via inhibiting the PI3K/AKT pathway. Importantly, Exos@SFMA effectively relieved synovial inflammation and joint destruction by significantly reducing T follicular helper (Tfh) cell response and further suppressing the differentiation of germinal center (GC) B cells into plasma cells. Taken together, this exosome enhanced silk fibroin hydrogel provides an effective strategy for the treatment of RA and other autoimmune diseases.

Versatile Hydrogel Dressing with Skin Adaptiveness and Mild Photothermal Antibacterial Activity for Methicillin-Resistant Staphylococcus Aureus-Infected Dynamic Wound Healing.

Bacterial infection often induces chronic repair of wound healing owing to aggravated inflammation. Hydrogel dressing exhibiting intrinsic antibacterial activity may substantiallyreducethe use of antibiotics for infected wound management. Hence, a versatile hydrogel dressing (rGB/QCS/PDA-PAM) exhibiting skin adaptiveness on dynamic woundsand mild photothermal antibacterial activity is developed for safe and efficient infected wound treatment. Phenylboronic acid-functionalized graphene (rGB) and oxadiazole-decorated quaternary carboxymethyl chitosan (QCS) are incorporated into a polydopamine-polyacrylamide (PDA-PAM) network with multiple covalent and noncovalent bonds, which conferred the hydrogel with flexible mechanical properties, strong tissue adhesion and excellent self-healing ability onthe dynamic wounds. Moreover, the glycocalyx-mimicking phenylboronic acid on the surface of rGB enables the hydrogel to specifically capture bacteria. The enhanced membrane permeability of QCS enhanced bacterial vulnerability to photothermaltherapy（PTT）, which is demonstrated by efficient mild PTT antibacteriaagainst methicillin-resistant Staphylococcus aureus in vitro and in vivo at temperatures of <49.6°C. Consequently, the hydrogel demonstrate accelerated tissue regeneration on MRSA-infected wound in vivo, with an intact epidermis, abundant collagen deposition and prominent angiogenesis. Therefore, rGB/QCS/PDA-PAM is a versatile hydrogel dressing exhibiting inherent antibacterial activity and has considerable potential in treating wounds infected with drug-resistant bacteria.

Selenide-linked polydopamine-reinforced hybrid hydrogels with on-demand degradation and light-triggered nanozyme release for diabetic wound healing

BackgroundMultifunctional hydrogels with controllable degradation and drug release have attracted extensive attention in diabetic wound healing. This study focused on the acceleration of diabetic wound healing with selenide-linked polydopamine-reinforced hybrid hydrogels with on-demand degradation and light-triggered nanozyme release.MethodsHerein, selenium-containing hybrid hydrogels, defined as DSeP@PB, were fabricated via the reinforcement of selenol-end capping polyethylene glycol (PEG) hydrogels by polydopamine nanoparticles (PDANPs) and Prussian blue nanozymes in a one-pot approach in the absence of any other chemical additive or organic solvent based on diselenide and selenide bonding-guided crosslinking, making them accessible for large-scale mass production.ResultsReinforcement by PDANPs greatly increases the mechanical properties of the hydrogels, realizing excellent injectability and flexible mechanical properties for DSeP@PB. Dynamic diselenide introduction endowed the hydrogels with on-demand degradation under reducing or oxidizing conditions and light-triggered nanozyme release. The bioactivity of Prussian blue nanozymes afforded the hydrogels with efficient antibacterial, ROS-scavenging and immunomodulatory effects, which protected cells from oxidative damage and reduced inflammation. Further animal studies indicated that DSeP@PB under red light irradiation showed the most efficient wound healing activity by stimulating angiogenesis and collagen deposition and inhibiting inflammation.ConclusionThe combined merits of DSeP@PB (on-demand degradation, light-triggered release, flexible mechanical robustness, antibacterial, ROS-scavenging and immunomodulatory capacities) enable its high potential as a new hydrogel dressing that can be harnessed for safe and efficient therapeutics for diabetic wound healing.

Prediction of 2D IV-V semiconductors: flexible monolayers with tunable band gaps and strong optical absorption as water-splitting photocatalysts.

Seeking novel photocatalysts for water splitting is one of the tasks in developing 2D materials. In the framework of density functional theory, we predict a family of 2D pentagonal sheets called penta-XY2 (X = Si, Ge, and Sn; Y = P, As, and Sb), and modulate their properties via strain engineering. Penta-XY2 monolayers exhibit flexible and anisotropic mechanical properties, due to their low in-plane Young's modulus in the range of 19-42 N m-1. All six XY2 sheets are semiconductors with a band gap ranging from 2.07 eV to 2.51 eV, and the positions of their conduction and valence band edges match well with the reaction potentials of H+/H2 and O2/H2O, so they are suitable for photocatalytic water splitting. Under tensile/compression strains, the band gaps, band edge positions and light absorption of GeAs, SnP2 and SnAs2 could be tuned to improve their photocatalytic performance.

The effect of water and sodium hydrogen carbonate content on flexible polyurethane's microstructure, water, and mechanical properties

AbstractIt is well known that blowing agents (BAs) and polyol are essential components in polyurethane (PU) composition. Utilizing renewable sources in the material's formulation might reduce its environmental hazards while extending its possible engineering applications. In this study, the samples have been synthesized by using palm kernel oil‐based polyol (PKOP). Water and sodium hydrogen carbonate (SHB) have been used as BAs. Scanning electron microscopy (SEM) has shown that adding the mix of BAs is causing the cells' average size to increase up to 227% and have reduced the lamellae width by up to 2% in comparison with the reference sample. The water tests have illustrated that combining two parts per hundred polyol by weight (php) water and 25 php SHB to the sample has increased its water capacity up to 617%. However, the samples are only able to retain 6% of the absorbed water at the 7th day. It has been also found that porosity has affected the water uptake and all the samples are following Fick's diffusion law, and diffusion is correlated to the square root of time. Multivariable power least squares method (MPLSM) and moving least squares method (MLSM) have been applied to find the relation between tear resistance value and BAs ratio. It is found that both methods have a dominant variable compared to the other variables, but MLSM provided optimizable equation with better R2.

Ag-catalyzed GaSb nanowires for flexible near-infrared photodetectors

High-quality narrow bandgap semiconductors nanowires (NWs) challenge the flexible near-infrared (NIR) photodetectors in next-generation imaging, data communication, environmental monitoring, and bioimaging applications. In this work, complementary metal oxide semiconductor-compatible metal of Ag is deposited on glass as the growth catalyst for the surfactant-assisted chemical vapor deposition of GaSb NWs. The uniform morphology, balance stoichiometry, high-quality crystallinity, and phase purity of as-prepared NWs are checked by scanning electron microscopy, energy dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, and X-ray diffraction. The electrical properties of as-prepared NWs are studied by constructing back-gated field-effect-transistors, displaying a high I on/I off ratio of 104 and high peak hole mobility of 400 cm2/(V·s). Benefiting from the excellent electrical and mechanical flexibility properties, the as-fabricated NW flexible NIR photodetector exhibits high sensitivity and excellent photoresponse, with responsivity as high as 618 A/W and detectivity as high as 6.7 × 1010 Jones. Furthermore, there is no obvious decline in NIR photodetection behavior, even after parallel and perpendicular folding with 1200 cycles.

Crushing resistance tailoring of honeycomb material via vertex-derivative strategy

To support the high protection requirements of advanced equipment, honeycomb materials are encountering more demanding challenges on their flexible design and mechanical properties. Therefore, a novel hierarchical topology, namely vertex-derived strategy, is proposed to pursue a superior crushing resistance for honeycomb materials. Based on this strategy, the honeycombs with vertex-derivative characteristic are developed to investigate their energy absorption mechanism and mechanical property under the axial impact. An efficient energy-absorbing progressive folding mechanism is experimentally triggered due to the refinement of the material distribution by sub-cells. Further, a numerical study is conducted to uncover the effect of the derivative index and the thickness-length ratio of the sub-cell on the crushing resistance of honeycomb. The result shows that the derivative index and the thickness-length ratio can improve the energy dissipation capacity and crushing force efficiency of vertex-derivative honeycomb (VDH). A numerical comparison on the material utilization indicates that the vertex-derivative hexagonal topology is a superior geometry for energy dissipation than the vertex-derivative quadrilateral topology under the same geometric parameters. In addition, a theoretical solution derived by the simplified super folding element (SSFE) theory reveals the quantitative relationship of the derivative index and the sub-cell geometry parameters on the energy absorption. The present study looks forward to proposing effective suggestions to enhance the crushing resistance of the hierarchical honeycomb by the vertex-derived strategy.

De Novo Design of Molecules with Low Hole Reorganization Energy Based on a Quarter-Million Molecule DFT Screen: Part 2.

Organic semiconductors have many desirable properties including improved manufacturing and flexible mechanical properties. Due to the vastness of chemical space, it is essential to efficiently explore chemical space when designing new materials, including through the use of generative techniques. New generative machine learning methods for molecular design continue to be published in the literature at a significant rate but successfully adapting methods to new chemistry and problem domains remains difficult. These challenges necessitate continual method evaluation to probe method viability for use in alternative applications not covered in the original works. In continuation of our previous work, we evaluate four additional machine-learning-based de novo methods for generating molecules with high predicted hole mobility for use in semiconductor applications. The four generative methods evaluated here are (1) Molecule Deep Q-Networks (MolDQN), which utilizes Deep-Q learning to directly optimize molecular structure graphs for desired properties instead of generating SMILES, (2) Graph-based Genetic Algorithm (GraphGA), which uses a genetic algorithm for optimization where crossovers and mutations are defined in terms of RDKit's reaction SMILES, (3) Generative Tensorial Reinforcement Learning (GENTRL), which is a variational autoencoder (VAE) with a learned prior distribution and optimized using reinforcement learning, and (4) Monte Carlo tree search exploration of chemical space in conjunction with a recurrent neural network (RNN) decoder (ChemTS). The generated molecules were evaluated using density functional theory (DFT) and we discovered better performing molecules with the GraphGA method compared to the other approaches.