Among emerging energy-harvesting technologies, salinity gradient energy via reverse electrodialysis is a promising route to mitigate energy and environmental pressures. Delignified natural wood framework provides natural ion-transport channels for osmotic energy harvesting and holds significant promise, yet its low surface-charge density constrains efficiency. Accordingly, a wood framework/sodium alginate (W/SA) heterogeneous membrane was produced by infiltrating SA, which is rich in negatively charged groups, into the delignified natural wood framework and crosslinking to form a stable, ion-selective architecture. The W/SA membrane delivers a power density of 14.43 W m- 2 under a 50-fold NaCl gradient, 2.88 times the 5.0 W m- 2 commercial standard. In KCl, it reaches 19.76 W m- 2, outperforming most reported wood-based or fiber-based membranes. Ion transport is markedly enhanced, and conductivity at 10- 6 m NaCl rises from 1.12 × 10- 5 to 5.11 × 10- 4 S cm- 1, facilitating ion diffusion and migration. W/SA membrane (0.6 × 5 × 20 mm3) can support 500 g, and a 15-unit series device outputs 2.16 V, evidencing practical feasibility. The construction of this ion-selective membrane not only offers a practical, green and sustainable strategy for low-cost fabrication of high-performance ion-selective membranes but also opens new possibilities for its future application in commercial membrane manufacturing.

Osmotic energy conversion harnesses salinity gradients between seawater and freshwater to generate renewable electricity. Vertically aligned nanochannel membranes show promise for this application owing to their exceptional ion transport characteristics, yet the intricate interplay between channel geometry and energy conversion efficiency remains poorly understood, impeding rational membrane design. Here we present a computational framework that combines finite element simulations, machine learning and multi-objective optimization to elucidate how nanochannel length, diameter, pore density and surface charge govern osmotic energy conversion. We systematically sampled the design space to generate a comprehensive dataset and trained a multilayer perceptron model that achieves prediction accuracy exceeding 95 % while accelerating computations by three orders of magnitude compared with the finite element method (FEM). Shapley additive explanations quantified the relative contributions of each parameter. The analysis revealed synergistic effects, including a critical pore density threshold of 2.5 x 107 pores/cm2. Above this threshold, nanochannel interactions degrade performance. Multi-objective genetic algorithms identified 100 Pareto-optimal solutions that define the parameter ranges for maximizing power output and conversion efficiency. Notably, channel length affects power and efficiency in opposing ways, indicating that design priorities must be carefully balanced. This study provides theoretical guidance for the precise design of vertically aligned nanochannel membranes and highlights the potential of artificial-intelligence-driven materials design in advancing clean energy technologies.

Chiral microstructures exhibit distinctive mechanical, electrical and optical properties, but reliable methods to generate unidirectional rotation with precise control remain limited. Previously, Zeng et al. developed "capillary machines," macroscopic machines with hollow channels that braid microscale wires into specific topologies using interfacial capillary forces. Here, we report a versatile ratcheting mechanism that is flow rate dependent. Under high-flow rate conditions, robust unidirectional rotation of the floating object is generated by the interplay between interfacial flows and capillary forces. Simulations reveal that interfacial flows depend on the actuation direction, leading to the observed hysteresis. Leveraging this principle, we successfully braid multiple microwires into a hierarchically twisted bundle without destructive torsion. By coupling interfacial hydrodynamics with geometric design, this approach establishes a scalable strategy for fabricating delicate chiral architectures, opening transformative paradigms in interface-mediated microassembly.

Geometrical design is a crucial and challenging strategy for improving the performance of type-II superconductors, because the proper placement of intended defects in the current path contribute to flux pinning, a reduction in dissipation, and an increase in achievable current density. Topology optimization is currently one of the most powerful approaches used to determine consistent structural geometries. Therefore, a topology optimization approach is presented to inversely design structural geometries of low-temperature type-II superconductors with superconductor-dielectric/vacuum interfaces.

Osmotic energy has garnered widespread attention in recent years as a stable, efficient, and sustainable clean energy source. However, nanochannel-based osmotic energy conversion systems still face challenges in practical applications due to limited interfacial charge regulation. Most current studies are conducted under steady-state conditions, while the coupling mechanisms among flow fields, ion distributions, and interfacial reactions in complex environments with fluid disturbances remain poorly understood. In this study, using alumina nano-channels as a model system, we constructed four different flow patterns to systematically investigate the effects of fluid flow on ion distribution, surface charge regulation, and energy conversion performance. Both experimental and simulation results consistently demonstrated that applying flow solely on the high-concentration side significantly enhances current output and improves osmotic energy conversion performance. In contrast, other flow modes were found to degrade energy conversion performance to varying degrees. Multiphysics simulations further revealed that flow-induced ion redistribution dynamically modulates the surface charge density within the nanochannels. Specifically, flow at the high-concentration side enhances surface charge density, while the resulting convective flow synergistically promotes ion transport and power output. These findings elucidate a coupled mechanism of flow field-ion distribution-interfacial reactions, demonstrating that directional flow regulation can markedly enhance osmotic energy harvesting. This mechanistic insight not only provides a theoretical foundation for the design of osmotic energy conversion devices but also paves the way for developing smart responsive membranes and advanced nanofluidic energy conversion systems.

To overcome the poor accuracy of classical electrowetting theory in predicting contact-angle saturation and droplet dynamics at high driving voltages in optoelectrowetting (OEW) digital microfluidics, we propose a novel electromechanical model that couples multiple resistance mechanisms. Within a conventional electrodynamic framework, the model embeds electric force, wall-shear resistance, viscous drag from the surrounding medium, and dynamic contact-line friction simultaneously into the source terms of the Navier-Stokes equations, and solves them in concert with an electric-current, phase-field, and laminar-flow multiphysics scheme. Experiments on a self-fabricated OEW chip, carried out over 160-600 V, validate the model against measured contact angles and droplet trajectories. In the high-voltage regime, the improved model limits the contact-angle deviation to ≤2° and the velocity deviation to only 0.05 mm/s-far outperforming both the Lippmann-Young equation and conventional electromechanical formulations. Parametric analyses further show that raising the dielectric constant or reducing the thickness of the dielectric layer markedly enhances the local electric field, thereby increasing droplet speed and displacement, while employing a highly photoconductive a-Si:H layer minimizes voltage drop and optimizes actuation performance. The work provides a solid theoretical and experimental foundation for OEW chip design and material selection, offering a pathway toward high-precision parallel droplet manipulation and fully integrated microfluidic systems.

Osmotic energy conversion in nanochannels relies on the synergistic regulation of ion transport and ion selectivity. However, existing studies have mainly focused on uniformly grafted functional structures or single-field regulation, and the ion transport and energy conversion mechanisms under different axial grafting patterns and multiphysics coupling remain insufficiently understood. Herein, a multiphysics-coupled model of polyelectrolyte brush (PEB)-modified nanochannels was developed to investigate five axial PEB grafting patterns under different concentration gradients, solution pH values, and temperature fields. The results show that, under baseline conditions (pH = 7, 298 K, and without a temperature difference), the outlet-enriched pattern exhibits the best energy conversion performance over different concentration gradients, highlighting the importance of non-uniform axial charge distribution in maintaining ion selectivity. After external-field regulation is introduced, increasing the pH enhances channel selectivity and output power by promoting PEB deprotonation, while temperature regulation further strengthens ion migration and the charge response of the brush layer. Under coupled pH-temperature regulation, the uniformly grafted pattern exhibits the best performance, delivering a maximum output power of 6.81 pW at a 50-fold concentration gradient, pH = 11, and an overall temperature increase of 40 K. These results reveal a condition-dependent transition of the optimal grafting pattern and clarify the synergistic roles of different axial grafting patterns, pH responsiveness, and thermal regulation in determining osmotic energy conversion. This study provides a theoretical basis for the structural design and multiphysics optimization of responsive nanochannels.

Achromatic metalenses face stringent aperture and numerical aperture (NA) constraints, which have become a key bottleneck in metasurface imaging. To this end, a novel achromatic imaging method was first proposed, utilizing the unique wideband consistency of diffracted Bessel spots combined with non-blind image restoration techniques. To address the off-axis aberration issue, off-axis achromatic meta-axicons with eccentric conical phases were further designed to convert oblique plane waves into wideband uniform off-axis Bessel beams. Ultimately, a single metasurface integrating 9 meta-axicons with different design field angles was developed, and a meta-camera was constructed accordingly. After image restoration, the meta-camera achieves achromatic imaging within a 10° stitched field of view (FOV), and an angular resolution close to that of near-diffraction-limit lens with the same aperture throughout the entire FOV. The core idea of achieving achromatic imaging based on natural dispersion laws in this study enables the wideband minimalist optical system based on metasurface to completely circumvent the aperture limitation, providing a highly valuable solution for large-aperture meta-camera design that can simultaneously accommodate wideband and off-axis FOV.

Polyelectrolyte-modified nanochannels are extensively studied in applications such as rectification, sensing, and energy conversion. Effective material design promotes ion transport, and coupling with multiple external fields further enhances performance. Based on this, a mathematical model of polyelectrolyte-modified nanochannels under coupled pH and temperature gradients is developed, and the ion transport and energy conversion performance within the nanochannel are analyzed. The simulations reveal show that the volume charge properties of the polyelectrolyte brush layer are influenced by the solution pH and temperature. Near the isoelectric point of the polyelectrolyte, the charge properties of the polyelectrolyte brush layer can even reverse, altering the ion selectivity. Under both acidic and alkaline conditions, the enhanced ion selectivity significantly improves osmotic energy conversion performance. When an asymmetric temperature gradient is applied, power increased by about 18%, with maximum efficiency reaching up to 47%. Additionally, the study developed three machine learning models capable of effectively predicting output power and energy conversion efficiency, with most prediction errors below 5% compared to finite element method results. The results provide a critical foundation for the integrated application of acid-base wastewater treatment and osmotic energy conversion. The high-accuracy predictions of the machine learning models also offer valuable guidance for subsequent material design.

Quantum optimal control is central to designing spin manipulation pulses. Gradient-based pulse optimization can be facilitated by either accelerating gradient evaluation or enhancing the convergence rate. In this work, we accelerated single-spin optimal control by combining the finite element method with the method of moving asymptotes. By treating discretized time as spatial coordinates, the Liouville - von Neumann equation was reformulated as a linear system, efficiently yielding a joint solution of the spin trajectory and control gradient. The method of moving asymptotes, relying on the ensemble fidelities and gradients, achieves rapid convergence for a target fidelity of 0.995.

Metasurfaces, known for their unique properties such as polarization manipulation, have greatly enhanced wireless systems and optical devices. However, to meet the demand for multi-band functionality and flexibility in wireless systems, there is a need to expand the diversity and integration of polarization conversion devices. Liquid metals, with their excellent electrical conductivity and fluidity, offer a promising opportunity for reconfigurable electromagnetic devices. In this study, we propose an integrated polarization converter based on liquid metal metasurfaces. By adjusting the liquid metal injection, this device can manipulate the polarization state of transmitted or reflected waves, switch between various functions, and adjust the operating frequency. The metasurface consists of four microfluidic layers: the first and third layers contain periodic element arrays, while the second and fourth layers have cavity structures. This design supports multiple functional states, including polarization maintaining, linear-to-left-hand circular polarization, linear-to-right-hand circular polarization, and linear-to-linear polarization conversions. We fabricated a prototype and tested it in a microwave anechoic chamber. The experimental results align with theoretical predictions and simulations, demonstrating the multifunctional capabilities and adaptability of the device, making it ideal for broadband channel multiplexing and integrated antenna systems.

Galinstan liquid metal remains liquid at room temperature and exhibits unique physical properties including fluidity and high electrical conductivity, and its manipulation is a subject of extensive research interest. In contrast to existing control methods, such as electric and magnetic fields, we focus on a novel and efficient approach based on generating liquid metal droplets through microchannels. The present investigation mainly deals with generating liquid metal droplets through establishing a two-dimensional computational model based on the phase-field method for the droplet microfluidics in a T-junction structure. To enhance its performance, a constraint structure is added to expand the adjustment range of droplet formation. The constraint structure and increasing flow rate enhance the viscous shear effect, which reduces the droplet formation length and increases the generation frequency. Polymethyl methacrylate and pressure-sensitive adhesive are laser-cut to fabricate the microchannels. A peristaltic pump is utilized as the driving device, and a high-speed camera is employed to record the liquid metal droplet formation process. Both reducing the constraint ratio and increasing the flow ratio result in accelerated shear rate and increased droplet formation frequency, which is consistent with the simulation results. In experiments, the constraint structure enhanced the viscous shear effect, and relocation of the fracture location was observed. In addition, the high surface tension and inertia of the liquid metal released energy during droplet breakup, leading to noticeable oscillation and deformation of the droplet. Both the simulation and experimental results provide guidelines for the application of liquid metal generation in reconfigurable metasurfaces.

Metasurfaces as advanced artificial materials enable a variety of electromagnetic control functions, especially polarization manipulation. The existing functional switching methods tend to produce a high system complexity and encounter challenges, such as limited working bandwidth and insufficient reconfigurable degrees of freedom, although polarization conversion device based on reconfigurable metasurfaces are extensively investigated. Here, we propose a multifunctional polarization converter employing a liquid metal-based metasurface with various types of integrated microchannels on a single layer. The switching among different functionalities occurs through the injection of liquid metal into various types of microfluidic channels, maintaining the electromagnetic performance of the polarization converter, which encompasses broadband capability and large insensitivity of incident angle. Metasurfaces based on liquid metal microfluidic technology present highly adaptable and reconfigurable materials, offering new possibilities for the development of electromagnetic devices with unprecedented flexibility, with potential applications in microwave imaging, communication systems, remote sensing, among others.

Haematococcus pluvialis (H. pluvialis) is a critical natural source of astaxanthin, recognized for its potent antioxidant capacity, anti-inflammatory properties, and ability to suppress the proliferation of breast and skin cancer cells. The size difference between microalgae such as Chlorella vulgaris (C. vulgaris) and Haematococcus pluvialis (H. pluvialis), coupled with their high research value, makes size-based separation of microalgae essential for efficient extraction of valuable species and advancing directed algal evolution. In this study, we introduce an innovative method utilizing microfluidic devices that integrate spiral channels with contraction-expansion channels. We systematically examine how variables such as flow rate, cell concentration, cell size, and three distinct coupling configurations impact cell sorting. Our results highlight that each coupling configuration of the spiral and contraction-expansion channels exerts unique control over sorting performance, offering promising new approaches for optimizing microchannel design.

Polarization conversion metasurfaces are compact and efficient devices that manipulate the polarization state of electromagnetic waves, offering significant advantages in applications such as antennas, imaging systems, and optical communication. Traditional design methods often struggle to achieve high polarization conversion efficiency across wide bandwidths. To overcome this limitation, we present a gradient-based topology optimization method that uses material distribution approach for the design of broadband polarization conversion metasurfaces. In the broadband optimization process, we adopt a max-min-type objective function, where multiple frequency points within a given frequency band are selected, and the minimum objective value among them is maximized to ensure that the optimized structure performs effectively across the entire frequency range. We applied this method to the inverse design of polarization conversion metasurfaces targeting the X-band, Ku-band, K-band, and Ka-band. Our results demonstrate that the metasurfaces achieve polarization conversion ratios exceeding 90% across these broad frequency bands, significantly enhancing their bandwidth performance. Experimental validation was performed to verify the topologically optimized metasurfaces, where the measured results exhibit remarkable agreement with their numerical counterparts. This approach offers a powerful tool for the design of broadband polarization conversion metasurfaces and holds great promise for various applications, including frequency-selective surfaces, absorbing metasurfaces, and other advanced electromagnetic devices.

Topology optimization for mass and heat transfer has been implemented in three dimensional domains or on two dimensional planes with the lack of extension to 2-manifolds representing the curved surfaces locally similar to two-dimensional Euclidean spaces. In order to enlarge the design space and increase the design freedom, this paper develops topology optimization on variable 2-manifolds for mass and heat transfer in volume flow, where the volume flow is the fluid flow in a three dimensional domain. In the developed topology optimization method, thin-wall patterns are defined on variable curved surfaces represented as implicit 2-manifolds within the three-dimensional domain, where the thin-wall patterns are the structural patterns in the mid-planes of wall-shaped structures with ignorable thickness. The implicit 2-manifolds are homeomorphously defined on preset base manifolds. Fiber bundles is used to describe a thin-wall pattern together with the implicit 2-manifold as an ensemble defined on the base manifold. The topology optimization method on variable 2-manifolds is developed to optimize the fiber bundles for mass and heat transfer in volume flow. It is implemented by using a mixed interfacial condition that combines no-jump and no-slip types. The mixed form is achieved by the interpolation between these two types of interfacial conditions, where the interpolation depends on the material density representing the thin-wall patterns. Two design variables are defined for the thin-wall patterns and the implicit 2-manifolds, respectively. They are regularized by two surface-PDE filters. Variation of the implicit 2-manifolds is controlled by introducing the variable magnitude to the surface-PDE filter. The topology optimization problems are analyzed by using the continuous adjoint method to derive the gradient information of the design objectives and constraints. They are then solved by using the gradient based iterative procedures numerically implemented based on the finite element method. In order to use linear finite elements and reduce the computational cost, the variational formulations of the governing equations are stabilized by using the Brezzi-Pitkäranta, Petrov-Galerkin and general least squares techniques. These methods are applied in the three-dimensional domains, which are deformed according to the implicit 2-manifolds and described by Laplace’s equation. The adjoint equations are derived for the stabilized variational formulations of the governing equations. In the numerical results, the effect of variable amplitude of the implicit 2-manifolds and that of the Reynolds number, Péclet number and pressure drop are investigated to demonstrate the increased design freedom and extended design space.

In practical applications, the optimized design of microchannel heat exchangers is a result of a proper balance between thermal and hydraulic performances. This suggests that material properties and flow conditions determine the upper limit of the performance of microchannel heat exchangers. Exploring the influence of the material properties and flow conditions on the microchannel heat exchangers is beneficial for establishing more cost-effective solutions in the design process of microchannel heat exchangers, i.e., finding the optimal combination of materials, flow conditions, and microchannel structures. To explore the impact of physical conditions on the thermal performance of an optimized microchannel structure, this study innovatively proposes a singleobjective topology optimization method constrained by relaxed fluid energy dissipation. The two-dimensional and three-dimensional topology optimization models were systematically analyzed. The numerical results indicate that the fluid energy dissipation constraint is equivalent to the pressure drop constraint. The performance of microchannel structures greatly varies with physical conditions and exhibits similar regularities in twodimensional and three-dimensional cases. An increase in Reynolds number, an increase in Peclet numbers, a synergistic increase in both numbers, as well as an increase in solid-liquid heat conduction ratio can enhance thermal indicators. In two-dimensional problems, the maximum reductions in objective function are 79.37%, 44.4%, 98.54%, and 99.43%; whereas in three-dimensional problems, the values are 63.64%, 89.67%, 12.08%, and 99.43%, respectively. Based on similar regularities in both two-dimensional and three-dimensional cases, a strategy to improve efficiency of topology optimization design for three-dimensional microchannel heat exchangers is proposed.

Osmotic energy, a clean and renewable energy source, holds vast potential at the confluence of rivers and seas. 2D nanofluidic membranes offer a promising avenue for its efficient harvesting, yet their practical application is hampered by insufficient power density. Here we report a photoresponsive 2D nanofluidic membrane constructed by intercalating molybdenum disulfide with cotton nanofibers to form a stable composite structure. Under 50- and 500-fold salinity gradients, the membrane achieves power densities of 6.48 and 13.57 W m- 2, respectively. By introducing asymmetric illumination on the low-concentration side, we create asymmetric temperature and charge gradients, which substantially enhance the osmotic energy conversion performance. Under a light intensity of 220 mW cm- 2, the membrane achieves a power density of 9.93 W m- 2, representing a 53% increase compared to non-illuminated conditions. This enhancement is accompanied by a 62% rise in the short-circuit current and an 8% increase in the open-circuit voltage. In tests using real seawater, the membrane delivers a power density of 6.06 W m- 2, a 67% improvement over the non-illuminated condition. This study establishes a new strategy for highly efficient osmotic energy harvesting and demonstrates the potential of light-assisted osmotic energy conversion in practical marine environments.

The core advantage of metalenses over traditional bulky lenses lies in their thin volume and lightweight. Nevertheless, as the application scenarios of metalenses extend to the macro-scale optical imaging field, a contradiction arises between the increasing demand for large-aperture metalenses and the synchronous rise in design and processing costs. In response to the application requirements of metalens with diameter reaching the order of 104λ or even 105λ, this paper proposes a novel design method for fixed-height concentric-ring metalenses, wherein, under the constraints of the processing technology, a subwavelength 2D building unit library is constructed based on different topological structures, and the overall cross-section of the metalens is assembled. Compared to global structural optimization, this approach reduces computational resources and time consumption by several orders of magnitude while maintaining nearly identical focusing efficiency. As a result, a concentric-ring metalens with a designed wavelength of 632.8 nm and a diameter of 46.8 mm was developed, and a quasi-telecentric telescope system composed of aperture stop and metalens was constructed, achieving high-resolution detection within a 20° field of view. In the subsequent experiments, the unique weak polarization dependence and narrowband adaptability of the meta-camera are quantitatively analyzed and tested, and excellent imaging results were finally obtained. Our work not only ensures the narrowband optical performance but also promotes the simplicity and light weight of the metalens based telescopic system, which further advances the deep application of large-diameter metalenses in the field of astronomical observation.