Surface texture can notably reduce friction at contact interfaces with relative motion. However, its limited friction-reduction applicability over wide operating conditions remains a major constraint on technological applications. In this work, machine learning and metaheuristic algorithms are used to determine the optimal texture shape for maximizing the operating condition range (∆H). An eXtreme Gradient Boosting method is proposed to predict the applicable range of regular-shaped textures (circular, rectangular, grooved, triangular, and chevron) for friction reduction under a target coefficient of friction, with data derived from averaged Reynolds equations and Stribeck curves. Particle swarm optimization is used to optimize texture geometric parameters. The chevron texture exhibits the widest operating range, and experiments confirm the superiority of the optimized results. Then, a genetic algorithm-particle swarm optimization algorithm is adopted to automatically obtain the optimal contour of an irregular-shaped texture, yielding a spade-shaped base contour and wedge-shaped bottom contour. Interfacial flow-field analysis indicates that the superior tribological behavior of the obtained texture is predominantly attributed to enhanced hydrodynamic lift. Experiments show that the optimal texture expands the applicable operating range by 12.1% over the chevron texture. This study establishes a data-driven framework for designing surface texture contours with a predictable broad operating range.

Flexible pressure sensors fabricated via fused deposition modeling (FDM) offer promising advantages for wearable electronics and human-machine interfaces. However, conventional FDM suffers from limited printing resolution, hindering the formation of microscale features crucial for high sensing performance. In this work, we propose a direct fabrication strategy that integrates femtosecond laser-engineered microgrooves onto the inner wall of a 3D printing nozzle, enabling the in situ formation of periodic surface microstructures during extrusion. These microstructured elastomeric substrates, combined with a modified PEDOT:PSS conductive coating, form piezoresistive sensors with significantly enhanced sensitivity and mechanical compliance. Compared to unstructured counterparts, the microstructured sensors exhibit an order-of-magnitude improvement in pressure responsiveness (2.1%/kPa vs. 0.13%/kPa), alongside excellent repeatability and stability under dynamic loading. The application of a load induces microstructural reorganization within the sensor, generating new contact points. This establishes parallel circuits at the interlayer interfaces, which significantly enhances its sensitivity. Demonstrations in user interactive scenarios, such as click-mode distinction in a mouse and joint movement monitoring, validate the robustness and versatility of the device. This work establishes a scalable and material-efficient route for the fabrication of next-generation flexible sensors with customizable surface functionalities, paving the way for advanced applications in smart wearables and soft robotics.

Thrombosis in tortuous vessels causes blockages and pathological conditions. Current thrombolytics are inefficient, and mechanical thrombectomies lack adaptability, hindering thrombus clearance in complex geometries. Here, we propose a 4D reconfigurable vascular tunneling machine (VTM) capable of synchronous rotation and elongation, mimicking teredo locomotion. The VTM operates via the reversible nematic-to-isotropic phase transition of liquid crystal elastomers, triggered by the reorientation of liquid crystal mesogens during a coupled contraction-torsion motion. Functionalized with magnetic liquid metals, the VTM achieves remote reconfiguration within 20 s via induction heating, with a temperature rise of only 1.1 °C and uniform heat dissipation. This rapid and safe thermal response facilitates the adaptive locomotion of the VTM within a cerebral artery model. Comprehensive biocompatibility evaluation confirms that the VTM exhibits no cytotoxicity and good hemocompatibility, and the VTM achieves the disruption of thrombus simulants across a stiffness range of 1 kPa to 1 MPa and sample retrieval up to 7.13 mm³. These demonstrations establish the VTM as a promising proof-of-concept platform, highlighting the potential for future development toward thrombus interventions and for operation as an adaptive soft robot in constrained environments.

Re-entrant structures are fundamental to achieving robust liquid repellency, especially for low-surface-tension liquids. However, existing fabrication techniques often face a trade-off among mechanical durability, substrate geometry compatibility, large-area processing, and rapid production. Metals, with their inherent robustness, offer a promising substrate, but direct and efficient machining of metallic re-entrant structures remains a significant challenge. Here, we present a one-step mechanical cutting strategy, termed confined shear-induced structure discretization (CSSD), to directly fabricate high-density re-entrant architectures on planar and curved metallic surfaces. By designing a cave-trapezoid composite tool, we achieve a controlled transition from continuous ridges to discrete re-entrant units during ultra-precision diamond turning. The resulting metallic surfaces sustain a super-repellent Cassie–Baxter state for a broad range of liquids, exhibiting a water contact angle of 161.7 ± 2.2°, indicating non-wetting behavior. Notably, this approach enables rapid, large-area manufacturing, with a material removal rate of 1.068 mm3 s−1 over areas up to 1.5 × 104 mm2. The re-entrant textures retain sufficient structural features after 1000 abrasion cycles to recover superhydrophobicity. This geometry-guided strategy reveals a mechanism for the scalable fabrication of discrete microstructures and offers useful guidance for extending the approach to other machining modalities. Researchers fabricate re-entrant microstructures on metals through a confined shear-induced structure discretization (CSSD) mechanism using a cave-trapezoid cutting tool, resulting in durable, liquid-repellent surfaces.

Facilitating entropic elastic deformation is central to strengthening the mechanical resilience of 3D-printable elastomers. Despite extensive efforts that have focused on enhancing entropy-driven responses through regulating inter-chain interactions, the role of dangling chain conformational constraints in modulating elastic energy dissipation and mechanical reinforcement has remained largely overlooked. Herein, we challenge this prevailing convention by constraining polymer chain termini, thereby eliminating unbound ends and creating a fully connected molecular network. This end-constraint reweights the deformation response by suppressing slippage and enhancing entropic elasticity, unlocking a unique combination of high modulus, creep resistance, and toughness unattainable with conventional designs. By coupling terminal constraint and interchain physical crosslinking, 3D-printable elastomers achieve enhancement of over 571.1% and 388.2% in strength and toughness, while preserving printability and resilience. This work establishes chain-end engineering as a powerful principle for molecular design, opening avenues toward recyclable, durable, and high-performance soft materials for 3D printing, wearable electronics, and soft robotics.

IntroductionMicrotextured surfaces can reduce solid‐solid friction through hydrodynamic effects. However, their friction‐reduction performance often deteriorates as the micro‐geometrical features are progressively worn, limiting their tribological stability and long-term applicability.MethodsA hierarchical microtextured surface with multi‐level depth‐to‐diameter ratios was fabricated on SUS304 stainless steel using femtosecond laser processing. Ball‐on‐flat reciprocating sliding tests under PAO10 lubrication were conducted to evaluate the effects of area density, depth‐to‐diameter ratio, normal load, and sliding speed on the coefficient of friction and friction‐reduction stability.ResultsThe hierarchical microtexture enabled staged recovery of the optimized depth‐to‐diameter ratio during progressive wear, thereby repeatedly restoring favorable hydrodynamic lubrication conditions. Compared with the flat surface, the hierarchical microtextured surface reduced the coefficient of friction by up to 22.7%. Compared with the conventional microtexture, it improved the stability of the friction‐reduction effect by 77.1%.DiscussionThe hierarchical design provides a feasible strategy for maintaining stable solid‐solid friction reduction and enhanced tribological stability during progressive wear.

The effective functioning of a vanadium redox flow battery (VRFB) is heavily dependent on the consistency of its electrolyte distribution. Ultrasound technology has been recognized as a promising method for enhancing the mixing and reaction rates of electrolytes by leveraging acoustic thermal, acoustic cavitation, and acoustic streaming effects. However, previous research on ultrasonic impact on batteries often combined multiple acoustic effects, making it unclear how specifically acoustic streaming affects battery performance. In this study, we introduce localized acoustic streaming to improve electrolyte uniformity in VRFB. By isolating the thermal effect from other ultrasonic effects, we demonstrate that acoustic streaming alone can boost cell energy efficiency by 2.9 %. Additionally, electrolyte uniformity in the negative electrode significantly increases from 0.22 to 0.53, marking a 141.0 % enhancement ratio. This effectively reduces concentration polarization within the battery, thereby enhancing its voltage efficiency. In addition, the energy consumption of an intermittent ultrasonic application strategy is reduced by 90 % when compared to continuous ultrasonic application. The study provides a new paradigm to promote the localized uniformity of electrolytes, leading to potential impacts in enhancing battery performance.

Silk fibroin, known for its biocompatibility and biodegradability, holds significant promise for biomedical applications, particularly in drug delivery systems. The precise fabrication of silk fibroin particles, specifically those ranging from tens of nanometres to hundreds of microns, is critical for these uses. This study introduces elliptical vibration micro-turning as a method for producing silk fibroin particles in the form of cutting chips to serve as carriers for drug delivery systems. A hybrid finite element and smoothed particle hydrodynamics (FE-SPH) model was used to investigate how vibration parameters, such as frequency and amplitude, influence chip formation and morphology. This research is essential for determining the size and shape of silk fibroin particles, which are crucial for their effectiveness in drug delivery systems. The results demonstrate the superior capability of elliptical vibration micro-turning for producing shorter, spiral-shaped chips in the size range of tens of microns, in contrast to the long, continuous chips with zig-zag folds and segmented edges generated by conventional micro-turning. The unique zig-zag shapes result from the interplay between the high flexibility and hierarchical structure of silk fibroin and the controlled cutting environment provided by the diamond tool. Additionally, higher vibration frequencies and lower vertical amplitudes promote chip curling, facilitate breakage, and improve chip control, while reducing cutting forces. Experimental trials further validate the accuracy of the hybrid model. This study represents a significant advancement in the processing of silk fibroin film, offering a complementary approach to fabricating short, spiral-shaped silk fibroin particles with a high surface-area-to-volume ratio compared to traditional spheroids, which holds great potential for enhancing drug-loading efficiency in high-precision drug delivery systems.

Leveraging surface texturing to realize significant friction reduction at contact interfaces has emerged as a preferred technique among tribology experts, boosting tribological energy efficiency and sustainability. This review systematically demonstrates optimization strategies, advanced manufacturing methods, typical applications, and outlooks of technical challenges toward surface texturing for friction reduction. Firstly, the lubricated contact models of microtextures are introduced. Then, we provide a framework of state-of-the-art research on synergistic friction optimization strategies of microtexture structures, surface treatments, liquid lubricants, and external energy fields. A comparative analysis evaluates the strengths and weaknesses of manufacturing techniques commonly employed for microtextured surfaces. The latest research advancements in microtextures in different application scenarios are highlighted. Finally, the challenges and directions of future research on surface texturing technology are briefly addressed. This review aims to elaborate on the worldwide progress in the optimization, manufacturing, and application of microtexture-enabled friction reduction technologies to promote their practical utilizations.

Anchoring flexible macromolecules onto smooth substrates to create liquid-like surfaces (LLSs) has revolutionized repellent surface technologies. However, real-world applications of the LLSs are highly restricted due to the lack of a universal bonding mechanism between those macromolecule termini and diverse surfaces. Herein, a new perspective on interfacial bonding mechanisms for flexible macromolecule immobilization is proposed. A universal flash coating (UFC) technology has been developed based on a rationally designed linear polydimethylsiloxane (PDMS) molecule terminated with catechol at one end (L-PDMS-Cat). The terminated catechol unit enables L-PDMS-Cat to anchor onto various metallic, inorganic, and organic substrates in a mussel adhesion-mimicking manner. A nanoscale coating of 24.3 +/- 1.2 nm thickness is achieved within seconds via a simple spray process. The obtained UFC surface can repel fluids with ultralow surface tensions (gamma < 20 mN m(-1)), exhibit an impressively low ice shear strength of 16.7 +/- 10.5 kPa, and offer exceptional resistance to solvent soaking. Moreover, the theoretical model of temperature-dependent rheology reveals that retaining molecular configurations with unconfined chain segments in the bonded coating is the key to preserving the interfacial slippage of such surfaces. The study provides a new paradigm for molecular design of multifunctional liquid-like surfaces for wide-ranging applications.

The high-performance manufacturing of hard-brittle materials by single-point diamond turning (SPDT) is a very active and challenging research area. The stress-assisted nano-cutting is a promising method for improving the machinability of hard-brittle materials. However, the simulation results in the existing stress-assisted nanocutting model would contradict the actual condition due to the pre-stress being released before tool entry into the workpiece. A modified stress-assisted nano-cutting model with a virtual boundary between the workpiece and tool is proposed for the first time in this paper to investigate the nano-cutting process of GaAs material under different external stresses. The emergence of an atomic flow vortex during stress-assisted nano-cutting significantly enhances the quality of the machined surface, leading to a substantial reduction in both machined surface roughness (34.4 %) and subsurface damage (56.2 %), compared to the normal nano-cutting. By evaluating surface roughness, subsurface damage depth, morphological accuracy, cutting force, and removal efficiency, a pre-strain of 0.06 is determined to be the optimal pre-strain for stress-assisted nano-cutting. Moreover, the selection of optimal pre-strain remains unaffected by variations in the nano-cutting depth. TEM results demonstrate that the nano-cutting mechanism elucidated by the MD analysis accurately reflects the genuine deformation of the GaAs material.

Under ion beam radiation, surface defects in forms of nanodroplet are randomly formed on group III-V semiconductors' surfaces. This work demonstrates the effectiveness of cryo-FIB on suppressing surface nanodroplets formation. Using GaAs as a representative, it was found that the surface nanodroplets derived from a phase transition process of the arsenide atoms. The redundant gallium atoms will then accumulate and eventually form surface nanodroplets. Cryo-FIB at 80 K can effetely suppress this phase transition process, leading to a defect free surface finish. The effectiveness of cryo-FIB on other group III-V semiconductors including InP and InAs are also successfully demonstrated. (c) 2024 CIRP. Published by Elsevier Ltd. All rights reserved.

Polydimethylsiloxane (PDMS) is the most studied organosilicon polymer, finding broad applications in soft lithography of microfluidic devices, wearable electronics insulation, medical tubing, shielding coatings, and sealant elements. However, their cross-linked forms swell severely in nonpolar oils due to the comparable solubility parameters. Here, an oil-stable cross-linked PDMS discovered by grafting flexible PDMS chains onto its polymeric networks is reported, which enables surface-exposed chains with high dynamics. It is found that the synergetic effect of mobile nanopore filling and quasi-liquid lubrication of PDMS brushes endows the cross-linked matrix with a reduced oil absorption ratio of up to 91.7% without altering its surface composition. Moreover, stretching polymeric networks can be re-arranged with an adequate grafting of PDMS chains, further enhancing the antipenetration performance. This discovery of the oil-stable surface configuration of cross-linked PDMS breaks the constraint of siloxane elastomers not being applicable in nonpolar soluble liquid, opening a new era of research in organosilicon chemistry.

The generation of surface acoustic waves (SAW) through electrically driven piezoelectric devices has attracted considerable attention in both fundamental research and practical applications, particularly for suppressing bacterial adhesion on surfaces. However, the precise mechanism by which SAW prevents bacterial attachment remains incompletely understood. This study explores the impact of SAW-induced boundary-driven streaming on the surface adhesion of Escherichia coli and Staphylococcus aureus in a liquid environment, focusing on the prevention of bacterial adhesion through the formation of micrometer-scale shielding fluid layers. We primarily examine the distance and acoustic streaming effects that influence bacterial behavior in the flow field. Our in vitro experiments, supported by numerical simulations, demonstrate that the viscous boundary layer and vortices generated by SAW can inhibit bacterial colonization and biofilm formation when Stokes drag forces predominate. This work provides new insights into the inhibitory mechanism of SAW on bacterial adhesion, offering valuable guidance for the development of advanced antibacterial strategies.

Additive manufacturing based on material extrusion is widely used in industrial production due to low cost, high throughput, and materials compatibility. Surface microstructures endow 3D-printed products with advanced functions, including anti-fouling, anti-corrosion, drag reduction, etc. However, it is challenging to directly achieve surface microstructures during the continuous extrusion of filaments for additive manufacturing. Despite the development of a variety of post- and pre-processing strategies aimed at fabricating microstructured surfaces of 3D printed products, they are unable to online regulate the microscale morphology which often needs additional operations and reduces the manufacturing efficiency. Herein, we propose an online 3D printing strategy based on material extrusion for the direct fabrication of objects stacked with microstructured filaments. It utilizes a microgrooved printing nozzle to extrude microridged filaments. The dimension and geometry of the microridges on surfaces can be controlled by adjusting printing parameters and the microgrooves within the nozzle. The morphology of microridges is influenced by the extrudate swell resulting from the viscoelastic properties of the polymer during extrusion. Triangular, bell-shaped, trapezoidal microridges are fabricated by different cross-sectional profiles. The Bird-Carreau model is applied to describe the flow behavior of melted polymers. Compatibility of the technology with conventional material extrusion-based additive manufacturing is validated by printing a variety of materials and using different diameters of nozzles. The material extrusion additive manufacturing products with anisotropic wetting surfaces are successfully achieved with static contact angles of 155° and 76° in two crossed directions. The technology provides a new paradigm for microstructured 3D printing, leading to potential impacts in the fabrication of smart microfluidic devices, multifunctional tissue engineering scaffolds, and high-performance sensors.

We utilize molecular dynamics simulations to comparably investigate the wetting and motion behavior of droplets on liquid-like surfaces (LLS) with varying grafting conditions. Polydimethylsiloxane (PDMS) and perfluoropolyether (PFPE) have been considered to be flexible molecules versus rigid molecules of trichloro(octadecyl) silane (OTS) and trichloro(1H,1H,2H,2H-perfluorooctyl) silane (PFOS), respectively. Our findings reveal that droplets on surfaces tethered with either PDMS or PFPE brushes can generate indentations and wetting ridges, providing microscopic evidence of their liquid-like nature. The grafting density of mobile chains exerts a dominant influence on the wetting properties compared to the molecular weight. A parameter map is created to pinpoint the precise range of grafting densities essential for the optimal construction of LLS at predetermined molecular weights. Furthermore, the investigation of droplet motion dynamics on LLS demonstrates that droplets consistently exhibit a rolling state, regardless of the intensity of the applied lateral force. The movement pattern of the droplet shifts only under conditions where the grafting density is significantly reduced and the substrate exhibits hydrophilic tendencies. These findings and the developed model are anticipated to offer valuable guidelines for optimal designs of LLS.

To overcome the precision limitation and environmental impact of current chemical-based production methods for manufacturing silk microfibres used for targeted drug delivery, this paper presents a high-precision, scalable, eco-friendly mechanical machining approach to produce such microfibres in the form of discontinuous chips obtained through elliptical vibration turning of silk fibroin film using a diamond tool. The length and waist width of fabricated microfibres can be precisely controlled. As each vibration cycle will produce one silk microfibre, complete and deterministic chip breakage becomes an essential and challenging task in this approach due to its unique two-phase structure. Thus, the hybrid FE-SPH numerical simulations and machining experiments were conducted to gain a pioneering and in-depth exploration of the chip-breaking mechanism in this process. It was found that applying a low depth ratio (ratio of the nominal depth of cut to the tool path vertical amplitude) and a high horizontal speed ratio (the nominal cutting speed versus the critical workpiece velocity) could effectively reduce the average tool velocity angle (the angle from the deepest cut to the tool exit point along the cutting direction). A smaller angle would enhance the diamond tool's shearing action and led to the reduction of hydrostatic pressure in the cutting zone and a consequent decrease in the ductility of silk fibroin due to its unique structure dominated by beta-sheet crystallites. The above adjustments collectively facilitated chip breakage. This paper, therefore, established a governing rule for the controlled and repeatable formation of microfibres based on the average tool velocity angle for the first time and revealed that the cutting chips would undergo complete and deterministic breakages once the angle approached below 22.6°. On this basis, the high-precision and scalable manufacturing of silk microfibres with precisely controllable length and waist width was ultimately achieved.

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