The rapid development of micro/nano-electromechanical systems (M/NEMS) under extreme contact conditions require atomic-scale lubricants with ultrathin thickness (<1nm), ultralow friction (coefficient of friction<0.01), and high wear resistance. Two-dimensional (2D) transition metal dichalcogenides (TMDs), such as MoSe2, are promising candidates. However, the role of substrates in governing the friction and wear behavior of monolayer TMDs remains unclear. Here, high-quality monolayer MoSe2 films with a thickness of ~0.7nm were synthesized by chemical vapor deposition on five representative substrates, including SiO2/Si, Si, quartz, a-plane sapphire, and c-plane sapphire. The study systematically investigated the role of interfacial bonding strength in regulating tribological properties. Significantly, MoSe2 on quartz exhibited ultralow friction (COF=0.009) and exceptional wear resistance (40,000 cycles@3.02GPa), significantly outperforming other substrates. Conversely, MoSe2 on Al2O3 showed inferior performance (COF=0.015; <5,000 cycles@3.02GPa), which is attributed to a MoO3-related interfacial layer that reduces bonding strength. Density functional theory (DFT) simulations revealed a positive correlation between tribological performance and interfacial interaction strength. Stronger interfacial interactions provide enhanced anchoring of the monolayer, which can suppress out-of-plane deformation and delamination, thereby reducing energy dissipation. This work identifies interfacial bonding strength as the key factor governing ultrathin 2D material tribology, providing essential guidelines for designing durable, low-friction lubrication systems for future M/NEMS.

Restraining dipole interactions can hinder the formation of conductive pathways in polar polymers, reducing conduction losses and creating deeper charge traps. This enables superior efficiency, high energy density, and enhanced cycling reliability.

High-temperature dielectric energy storage materials are essential for next-generation power electronics and electrical systems operating in extreme environments. However, achieving high-energy storage in polymer dielectrics at ultrahigh temperatures (e.g., 200 degrees C) remains a critical challenge, chiefly owing to the marked enhancement of molecular chain thermal motion, which gives rise to elevated charge conduction losses and diminished breakdown strength. Here, we propose a rigid-flexible synergistic multiple crosslinked network strategy that simultaneously suppresses inter/intra-chain charge transport while inhibiting thermal molecular motion. This rigid crosslinked architecture supports adjacent polymer chains, enhancing local segmental stability while also reducing interchain pi-pi stacking and dipole interactions. Furthermore, enabled by the thermodynamic annealing of flexible segments, the homogenously distributed interchain rigid scaffolds strike a balance between local structural rigidity and global deformability, thereby efficiently mitigating bulk charge conduction and boosting energy storage capabilities under extreme conditions. The resulting material exhibits an exceptional energy storage performance at 200 degrees C, with a discharge energy density of 6.91 J cm-3 at 90% efficiency. Moreover, it demonstrates outstanding cycling stability, maintaining high performance with over 50 000 charge-discharge cycles at 500 MV m-1. This study presents a new design strategy for high-temperature dielectric materials, showcasing the potential of multiple crosslinked structures to meet the demanding requirements of ultrahigh-temperature applications.

Instant adhesion to wet biological surfaces and reduced swelling of tissue adhesives are crucial for rapid wound closure and hemostasis. However, previous strategies to reduce swelling were always accompanied by a decrease in the tissue bonding strength of the adhesive. Moreover, the irreducibility of the covalent bonds in currently reported adhesives results in the adhesives losing their tissue adhesive ability. To tackle the challenge, a superior anti-swelling coacervate adhesive possessing fast self-healing properties through physical interactions (electrostatic interactions, hydrogen bonding) and chemical crosslinking (Schiff base reaction) was obtained with aldehyde-modified gamma-PGA (gamma-PGA-CHO), a natural lysozyme (LZM) and an amyloid fiber reduced lysozyme (RLZM). The instant shear adhesion strength and burst pressure tolerance of the adhesive on wet pig intestine reached 50.8 kPa (2.6 times that of CA glue) and 142.5 mmHg (5.9 times that of CA glue), and it maintained an adhesion strength of 37.4 kPa after exposure to the physical environment for 12 h and the swelling rate was only 34.0% underwater. The in vitro and in vivo experiments provided the coacervate adhesive with potential applicability for emergency rescue and wound care scenarios.

Compounds exhibiting multi-stimulus responsive behavior, exemplified by spiropyran, have demonstrated many potential and practical applications. However, current research primarily focuses on single-spiro systems, where the uniform open-ring state and color render effective differentiation of stimuli sources challenging. In this work, a novel benzene-bridged bis-spiropyran compound has been designed and synthesized, which is covalently bonded to a silicone matrix. This system exhibits orthogonal chromatic responses to mechanical force and ultraviolet (UV) light: mechanical force stimulation only activates one of the spiro-ring units within the benzene-bridged bis-spiropyran, resulting in a red colorimetric response (lambda similar to 515 nm), while UV light irradiation induces the cooperative opening of both spiro rings, generating a green colorimetric response (lambda similar to 645 nm). The red-green colorimetric transition exhibits a high contrast (Delta lambda > 130 nm) and rapid reversibility. Notably, the dual-stimulus orthogonal behavior of mechanical force-induced single-ring opening versus UV light-induced dual-ring activation reported herein stands in stark contrast to the phenomenon of simultaneous opening of dual spiro-rings induced by mechanical force observed in current studies. The covalent integration of the bis-spiropyran with silicone presents a controllable multi-stimulus responsive platform, providing a novel approach for stimulus recognition in complex environments and demonstrating significant potential in programmable smart sensing and dynamic display technologies.

Polymer materials with multiple stimuli-responsive properties have demonstrated many potential and practical applications. By covalently introducing spiropyran (SP1) and spirothiopyran (STP) into the polyurethane backbone, photochromic, mechanochromic, and thermally discolored polymer materials have been prepared. In this work, we report for the first time that white light (violet, blue, and green light) above a certain intensity can activate STP to green color. Based on the above discovery, the polyurethane with SP1 and STP can exhibit reversible three-color changes (brown, green, and purple) in response to four stimuli: ultraviolet irradiation, white light irradiation, mechanical stress, and heat. The color-changing polymer materials have high color contrast and excellent reversibility, and can be used for reversible writing, anticounterfeiting and information encryption, etc.

Injectable adhesive hydrogels combining rapid gelling with robust adhesion to wet tissues are highly required for fast hemostasis in surgical and major trauma scenarios. Inspired by the cross-linking mechanism of mussel adhesion proteins, we developed a bionic double-crosslinked (BDC) hydrogel of poly (γ-glutamic acid) (PGA)/poly (N-(2-hydroxyethyl) acrylamide) (PHEA) fabricated through a combination of photo-initiated radical polymerization and hydrogen bonding cross-linking. The BDC hydrogel exhibited an ultrafast gelling process within 1 s. Its maximum adhesion strength to wet porcine skin reached 254.5 kPa (9 times higher than that of cyanoacrylate (CA) glue) and could withstand an ultrahigh burst pressure of 626.4 mmHg (24 times higher than that of CA glue). Notably, the BDC hydrogel could stop bleeding within 10 s from a rat liver incision 10 mm long and 5 mm deep. The wound treated with the BDC hydrogel healed faster than the control groups, underlining the potential for emergency rescue and wound care scenarios.

Hyaluronic acid (HA) hydrogels have arisen as candidate materials to simulate the extracellular matrix and restore the functions of both cartilage and hard bones. However, integration of bone tissue adhesion and long-term osteogenic properties in one hydrogel is often ignored. Herein, a strategy to construct nanocomposite hydrogel with host tissue adhesive properties, enhanced mechanical strength, improved stability and osteogenic effects was developed. Simvastatin (SIM) was firstly incorporated into zeolitic imidazolate framework-8 (ZIF-8) and surface decoration with hydroxyapatite was realized to obtain SIM loaded and hydroxyapatite modified ZIF-8 particles (SP). As the inorganic strengthening component, SP could further cross-link the mixture of dopamine-hyaluronic acid (dHA) and tannic (TA) via coordination interaction to fabricate the hybrid adhesive hydrogel (dHA/TA/SP). Sufficient phenolic groups endowed dHA/TA/SP with excellent tissue adhesion and antibacterial properties, while incorporation of SP significantly improved the mechanical strength and stability of hydrogel. Further, due to the multiple protective effects of ZIF-8 and hydrogel, SIM was sustainably released from dHA/TA/SP. Together with the active Zn2+ and Ca2+, the expressions of ALP, OCN and RUNX2 were upregulated, and the mineralization was also promoted. With significant osteogenic effect in vitro and in vivo, this nanocomposite adhesive hydrogel holds great potential for bone defects repair.

Polyborosiloxane (PBS) is often referred to as a “shear thickening/stiffening gel” or “dilatant compound”, sometimes actually meaning an increase in modulus with frequency/strain rate rather than the rheological definition of “dilatant compound”, i.e. an increase in viscosity with shear rate. The shear behaviour of bulk PBS and PBS solution has been studied here by steady shear experiments, and it is observed that PBS exhibits shear thickening behaviour only under certain conditions. The shear behaviour of bulk PBS depends on the degree of reaction of the PBS (i.e. the content of B in the PBS). For PBS solution, the shear behaviour is influenced by the concentration of the solution and the type of solvent (with or without oxygen atom in the solvent). The shear behaviour of PBS systems is related to shear induced structural changes, where the formation of new elastically active B:O dynamic dative bonds (interchain cross-linking) contributes to shear thickening.

Soft ionic elastomers have attracted considerable research interest in mimicking the multiple functions of human skin. However, these ionic elastomers struggle to simultaneously achieve controllable ion dynamics and other essential performance, such as self-healing ability and appropriate mechanical robustness. Herein, bioinspired by Piezo proteins and integrins in human skin, thioctic acid (TA)-derived ionic elastomers with skin-like piezo-ionic dynamics are fabricated via a multi-confined interaction network. This bionic network is constructed by introducing a diene comonomer and lithium salt filler into polysulfides (poly (TA)), generating many dynamic interactions (various hydrogen bonds and lithium bonds). These dynamic interactions can bind ions to the polysulfides and be destroyed under external pressure stimulation, achieving controllable ion pumping behavior. This unique design concept enables these ionic elastomers to selectively respond to pressure (the optimal sample exhibits 152 times signal intensity with a sensitivity of 49.53-1.13 kPa-1), along with leak prevention, recyclability, and degradability. Besides, these interactions also serve as sacrificial bonds and self-healing sites to synergistically enhance all aspects of performance, yielding a high modulus of 2.47 MPa and outstanding self-healing efficiency of 98%. It is believed that this work could create a new approach for utilizing sustainable materials in next-generation "green" flexible sensors.

The hydrolysis behaviour of polyborosiloxane (PBS) was investigated, and the hydrolysis resistance was evaluated. The change in chemical structure during the hydrolysis of PBS was characterized by FTIR, 11B-NMR, etc. It was observed that the ternary borate ester in PBS was gradually hydrolyzed into binary and mono borate ester, and finally boric acid (BA) was produced. Rheological tests were used to investigate the effect of hydrolysis on the mechanical properties of PBS. It was observed that the plateau modulus and relaxation time of PBS decreased after immersion due to both the hydrolysis of PBS and the plasticizing effect of free water in the samples. It was also shown that as the free water evaporated during the drying process, the plateau modulus of the immersed PBS recovered somewhat. With regard to the hydrolysis resistance of PBS, the original PBS with a higher content of ternary borate ester has better hydrolysis resistance.

Massive bleeding and wound infection due to severe traumas pose a huge threat to the life and health of sufferers; therefore, it is of clinical importance to fabricate adhesives with rapid hemostatic and superior antibacterial capabilities. However, the weak wet adhesion and insufficient function of existing bioadhesives limits their practical application. In this study, a sandcastle worm protein inspired polyelectrolyte self-coacervate adhesive of poly-γ-glutamic acid (PGA) and lysozyme (LZM) was developed. The adhesive exhibited strong underwater adhesion to various surfaces (>250 kPa for solid plates and >50 kPa for soft tissues) and maintained a 80 kPa even when soaked in water for 7 days. Rat liver and tail defect bleeding models revealed that the hemostatic efficiency was superior to that of commercial samples. The in vitro antimicrobial tests showed that the bacterial inhibition to Staphylococcus aureus and Escherichia coli reached almost 100%. Additionally, the infected wound regeneration model demonstrated that the healing rate of the adhesive group was about 100% within 15 days, which was greater than that of the control group. In vitro and in vivo experiments proved that this facilely prepared adhesive will be a promising material to fulfil the integration functions for rapid wound closure and facilitating wound healing.

Polyborosiloxane is one of the new generation of impact-resistant energy-absorbing materials. A series of polyborosiloxanes with different structures were prepared, which had different boron contents, different shear behavior and different relaxation time scales, and the blends were prepared by combining them with styrene thermoplastic elastomers. The effect of the structure of polyborosiloxane on the impact property of its styrene thermoplastic elastomer blend was analyzed by falling ball impact experiment. The results showed that different structures of polyborosiloxane had no obvious effect on the impact resistance of styrene thermoplastic elastomer blend that with 10% polyborosiloxane, and compared with the thermoplastic elastomer, polyborosiloxane had little effect on the impact resistance of the material. In addition, the influence of the hardness of styrene thermoplastic elastomer on the impact property of the blend was analyzed. The results showed that the peak impact force of the blends whose matrix materials with low hardness to high hardness, increased, unchanged, and decreased, respectively. Polyborosiloxane could improve the impact properties of styrene thermoplastic elastomers with higher hardness, but had no obvious improvement on the impact properties of styrene thermoplastic elastomers with lower hardness.

A B S T R A C TIn hypervelocity impact (HVI) events, the thermo-mechanical behavior of polymeric materials is significantly influenced by viscous effects, which in turn affects energy absorption and protective efficacy. A thermo-mechanical numerical model, which tailored to account for the viscous effects inherent in polymeric materials, was designed to simulate the mechanical behavior and heat generation of materials under HVI. An isotropic viscoelastic-viscoplastic constitutive equation and the Mie-Grüneisen equation of state (EOS) are applied to describe the deviatoric deformation and strongly nonlinear volumetric compression behavior. Moreover, the heat generation is calculated considering contributions of mechanical work (plastic work and viscous dissipation) and irreversible entropy increase, and the temperature increase is calculated based on the apparent heat capacity method. The model is seamlessly integrated into the LS-DYNA program through a user-defined material subroutine. Additionally, the FEM-SPH adaptive method is adopted to accurately model fragmentation which always accompanies in the HVI event, wherein the finite element method (FEM) handles contact and penetration behavior, while the smoothed particle hydrodynamics (SPH) method addresses the formation and motion of debris clouds. Ultra-high molecular weight polyethylene (UHMWPE) is selected as the sample material, and its model parameters are calibrated based on experimental data from dynamic compression testing. A variety of HVI simulations have been conducted and the results demonstrate that the key parameters are in close agreement with the experimental data from literature, such as the perforation diameter and the debris cloud tip velocity, revealing that the model could accurately predict the thermo-mechanical behavior of UHMWPE plates under HVI. An additional noteworthy facet is the capability of the model in capturing the temperature distribution and diverse energy components induced by the impact, including viscous dissipation, plastic work, and residual energy.

选取了 2种分子组成相同硬度不同的热塑性聚氨酯(TPU),将二者共混后得到了不同硬度的TPU共混物,探究了TPU共混物的硬度与冲击性能的关系.通过落球冲击试验、感压纸测试和冲击前后样品表面温度测试对TPU共混物的冲击性能进行表征.当样品的硬度越低时,峰值冲击力越小,冲击持续时间越长,冲击时的最大应变越大,冲击时样品的受力面积增大,对应的冲击时的峰值应力值减小.不同硬度样品的能量耗散比差别不大,但随硬度降低呈现小幅度上升趋势.冲击后的样品表面温度较冲击前有所上升,说明样品通过热的形式耗散了部分能量,各硬度样品的温度差值较为接近,这与不同硬度样品的能量耗散比的变化规律是相似的.所有样品均具有较高的能量耗散比,TPU能耗散大部分冲击能量,具有良好的抗冲击性能.

Thermoplastic polyurethane (TPU) elastomer is widely used in biomedical field because of its good processability, mechanical property and biocompatibility. Most TPUs are composed of macromolecular diols as soft segments, diisocyanate and chain extenders as hard segments, which provide the elasticity of the matrix and the framework rigidity of the chain network, respectively. The structural design of chain extender diol/diamine and diisocyanate is the main method to construct functional TPUs. Researchers designed and prepared the functional monomers according to the specific clinical scene or usage requirements, and developed the corresponding medical TPUs. In this paper, the types and characteristics of macromolecular diols, diisocyanate and chain extenders are introduced. Their unique microphase separation structures are analyzed, and the relationship between the chemical/physical structure and the final performance is discussed. Then, the research progress and advanced applications of TPU in biomedicine at home and abroad are summarized. The applications of TPU as antibacterial, anticoagulant, hydrolytic and oxidation resistant, self-healing and degradable materials are emphasized. Finally, by summarizing and analyzing various standards of biomedical TPU and its device, the key problems of industrial application are put forward, and the future development direction of TPU is prospected.

Expanded poly(ether-block-amide) (EPEBA) bead foams are a new class of advanced thermoplastic elastomer foams with low density and high resilience. Steam-chest molding realizes the fabrication of the molded EPEBA bead foams with complex geometry. However, the evolution of polymer microstructure in autoclave foaming process and the bonding mechanism behind the steam-chest molding of EPEBA beads are still unclear. In this work, the microstructure development of PEBA was characterized by DSC, SAXS and rheological methods. Then, EPEBA beads with an expansion ratio higher than 25-fold were prepared by autoclave foaming, and the molded EPEBA bead foams with a density lower than 0.15 g/cm(3) and a resilience higher than 70% were produced by steam-chest molding. According to the change about thermal properties of EPEBA beads before and after steam-chest molding, a possible inter-bead bonding mechanism during EPEBA beads molding was proposed. The amorphous soft segments and melted low-ordered hard segments promoted the welding process. However, the well-ordered hard segments hindered the interdiffusion of polymer chains at the interface, which leaded to the reduced tensile strength and the narrowed molding temperature window of EPEBA bead foams.

The linear rheological properties of supramolecular polymer networks formed by mixtures of two different bis-Pd(II) cross-linkers with poly(4-vinylpyridine) in dimethyl sulfoxide are examined. The changes in storage and loss moduli of the networks with mixed cross-linkers are compared to those of samples with a single type of cross-linkers. While the plateau moduli, and presumably network topology, of the networks remain equal regardless of the cross-link distribution, the relaxation time contributed by the faster cross-linkers is increased (by a factor of about 1.5 for the specific samples used in this work) by the presence of the slower cross-linkers, while the reverse influences are not significant. This effect can be explained by the fact that a certain fraction of the elastically effective strands cross-linked with fast cross-linkers is pinned on one end by slow cross-linkers, reducing by half the rate of fast chain relaxation. This effect is anticipated to be general for gels with two well-separated relaxation times.

The structure and impact properties of a thermoplastic elastomer/silly putty blend are explored. The impact-resistant materials are made with polyolefin-based thermoplastic elastomer HYBRAR (TM) 5127 and silly putty DOWSIL (TM) 3179. The peak impact force decreases with the content of silly putty, as part of the impact energy might be dissipated by the dissociation of boron-oxygen dynamic dative bonds in silly putty. It is also observed that the crack behavior of samples under impact is related to the phase structure of silly putty in the samples. For the samples with high content of silly putty, a macroscopic crack is observed for these samples under impact, as a crack can spread in the continuous phase structure of silly putty. Different energy dissipation ratios in rheological, compression and impact experiments are also observed. It is concluded that the results of linear dynamic oscillatory shear and compression at a low strain rate cannot give a direct predication of energy dissipation ratios of samples under impact at a high strain rate. (c) 2021 Society of Industrial Chemistry.

Different from the melt foaming of extrusion and injection molding, polymer is in high-elastic state during autoclave foaming. In this study, the critical parameters used to describe the high-elastic state of polymer, i.e., softening temperature (Ts) and viscous flow temperature (Tv), were introduced to explain the autoclave foaming of thermoplastic polyurethane (TPU) and the inter-bead bonding mechanism of expanded TPU (ETPU) beads. Evolution of ordered structure of TPU in high-elastic state was characterized by different methods. The steamchest molding was used to manufacture the ETPU parts, and the molding temperature window was compared with the Ts and Tv of TPU resin, and the endothermic peaks of ETPU beads. The melting of ordered hard segments structure, interface-diffusion of polymer chains, cooling-induced formation of new ordered structure among the diffused polymer chains were the possible mechanism of strong inter-bead bonding in the molded ETPU parts.