NiTi alloys have drawn significant attentions in biomedical and aerospace fields due to their unique shape memory effect (SME), superelasticity (SE), damping characteristics, high corrosion resistance, and good biocompatibility. Because of the unsatisfying processabilities and manufacturing requirements of complex NiTi components, additive manufacturing technology, especially laser powder bed fusion (LPBF), is appropriate for fabricating NiTi products. This paper comprehensively summarizes recent research on the NiTi alloys fabricated by LPBF, including printability, microstructural characteristics, phase transformation behaviors, lattice structures, and applications. Process parameters and microstructural features mainly influence the printability of LPBF-processed NiTi alloys. The phase transformation behaviors between austenite and martensite phases, phase transformation temperatures, and an overview of the influencing factors are summarized in this paper. This paper provides a comprehensive review of the mechanical properties with unique strain-stress responses, which comprise tensile mechanical properties, thermomechanical properties (e.g. critical stress to induce martensitic transformation, thermo-recoverable strain, and SE strain), damping properties and hardness. Moreover, several common structures (e.g. a negative Poisson’s ratio structure and a diamond-like structure) are considered, and the corresponding studies are summarized. It illustrates the various fields of application, including biological scaffolds, shock absorbers, and driving devices. In the end, the paper concludes with the main achievements from the recent studies and puts forward the limitations and development tendencies in the future.

The exceptional physical properties and unique layered structure of two-dimensional (2D) materials have made this class of materials great candidates for applications in electronics, energy conversion/storage devices, nanocomposites, and multifunctional coatings, among others. At the center of this application space, mechanical properties play a vital role in materials design, manufacturing, integration and performance. The emergence of 2D materials has also sparked broad scientific inquiry, with new understanding of mechanical interactions between 2D structures and interfaces being of great interest to the community. Building on the dramatic expansion of recent research activities, here we review significant advances in the understanding of the elastic properties, in-plane failures, fatigue performance, interfacial shear/friction, and adhesion behavior of 2D materials. In this article, special emphasis is placed on some new 2D materials, novel characterization techniques and computational methods, as well as insights into deformation and failure mechanisms. A deep understanding of the intrinsic and extrinsic factors that govern 2D material mechanics is further provided, in the hopes that the community may draw design strategies for structural and interfacial engineering of 2D material systems. We end this review article with a discussion of our perspective on the state of the field and outlook on areas for future research directions.

Atomic layer deposition (ALD) has become an indispensable thin-film technology in the contemporary microelectronics industry. The unique self-limited layer-by-layer growth feature of ALD has outstood this technology to deposit highly uniform conformal pinhole-free thin films with angstrom-level thickness control, particularly on 3D topologies. Over the years, the ALD technology has enabled not only the successful downscaling of the microelectronic devices but also numerous novel 3D device structures. As ALD is essentially a variant of chemical vapor deposition, a comprehensive understanding of the involved chemistry is of crucial importance to further develop and utilize this technology. To this end, we, in this review, focus on the surface chemistry and precursor chemistry aspects of ALD. We first review the surface chemistry of the gas–solid ALD reactions and elaborately discuss the associated mechanisms for the film growth; then, we review the ALD precursor chemistry by comparatively discussing the precursors that have been commonly used in the ALD processes; and finally, we selectively present a few newly-emerged applications of ALD in microelectronics, followed by our perspective on the future of the ALD technology.

Articular cartilage damage caused by trauma or degenerative pathologies such as osteoarthritis can result in significant pain, mobility issues, and disability. Current surgical treatments have a limited capacity for efficacious cartilage repair, and long-term patient outcomes are not satisfying. Three-dimensional bioprinting has been used to fabricate biochemical and biophysical environments that aim to recapitulate the native microenvironment and promote tissue regeneration. However, conventional in vitro bioprinting has limitations due to the challenges associated with the fabrication and implantation of bioprinted constructs and their integration with the native cartilage tissue. In situ bioprinting is a novel strategy to directly deliver bioinks to the desired anatomical site and has the potential to overcome major shortcomings associated with conventional bioprinting. In this review, we focus on the new frontier of robotic-assisted in situ bioprinting surgical systems for cartilage regeneration. We outline existing clinical approaches and the utilization of robotic-assisted surgical systems. Handheld and robotic-assisted in situ bioprinting techniques including minimally invasive and non-invasive approaches are defined and presented. Finally, we discuss the challenges and potential future perspectives of in situ bioprinting for cartilage applications.

Flexible and stretchable transparent electrodes are widely used in smart display, energy, wearable devices and other fields. Due to the limitations of flexibility and stretchability of indium tin oxide electrodes, alternative electrodes have appeared, such as metal films, metal nanowires, and conductive meshes. However, few of the above electrodes can simultaneously have excellent flexibility, stretchability, and optoelectronic properties. Nanofiber (NF), a continuous ultra-long one-dimensional conductive material, is considered to be one of the ideal materials for high-performance transparent electrodes with excellent properties due to its unique structure. This paper summarizes the important research progress of NF flexible transparent electrodes (FTEs) in recent years from the aspects of NF electrode materials, preparation technology and application. First, the unique advantages and limitations of various NF materials are systematically discussed. Then, we summarize the preparation technology of various advanced NF FTEs, and point out the future development trend. We also discuss the application of NFs in solar cells, supercapacitors, electric heating equipments, sensors, etc, and analyze its development potential in flexible electronic equipment, as well as problems that need to be solved. Finally, the challenges and future development trends are proposed in the wide application of NF FTEs in the field of flexible optoelectronics.

Copper matrix composites doped with ceramic particles are known to effectively enhance the mechanical properties, thermal expansion behavior and high-temperature stability of copper while maintaining high thermal and electrical conductivity. This greatly expands the applications of copper as a functional material in thermal and conductive components, including electronic packaging materials and heat sinks, brushes, integrated circuit lead frames. So far, endeavors have been focusing on how to choose suitable ceramic components and fully exert strengthening effect of ceramic particles in the copper matrix. This article reviews and analyzes the effects of preparation techniques and the characteristics of ceramic particles, including ceramic particle content, size, morphology and interfacial bonding, on the diathermancy, electrical conductivity and mechanical behavior of copper matrix composites. The corresponding models and influencing mechanisms are also elaborated in depth. This review contributes to a deep understanding of the strengthening mechanisms and microstructural regulation of ceramic particle reinforced copper matrix composites. By more precise design and manipulation of composite microstructure, the comprehensive properties could be further improved to meet the growing demands of copper matrix composites in a wide range of application fields.

Piezoelectricity in native bones has been well recognized as the key factor in bone regeneration. Thus, bio-piezoelectric materials have gained substantial attention in repairing damaged bone by mimicking the tissue’s electrical microenvironment (EM). However, traditional manufacturing strategies still encounter limitations in creating personalized bio-piezoelectric scaffolds, hindering their clinical applications. Three-dimensional (3D)/four-dimensional (4D) printing technology based on the principle of layer-by-layer forming and stacking of discrete materials has demonstrated outstanding advantages in fabricating bio-piezoelectric scaffolds in a more complex-shaped structure. Notably, 4D printing functionality-shifting bio-piezoelectric scaffolds can provide a time-dependent programmable tissue EM in response to external stimuli for bone regeneration. In this review, we first summarize the physicochemical properties of commonly used bio-piezoelectric materials (including polymers, ceramics, and their composites) and representative biological findings for bone regeneration. Then, we discuss the latest research advances in the 3D printing of bio-piezoelectric scaffolds in terms of feedstock selection, printing process, induction strategies, and potential applications. Besides, some related challenges such as feedstock scalability, printing resolution, stress-to-polarization conversion efficiency, and non-invasive induction ability after implantation have been put forward. Finally, we highlight the potential of shape/property/functionality-shifting smart 4D bio-piezoelectric scaffolds in bone tissue engineering (BTE). Taken together, this review emphasizes the appealing utility of 3D/4D printed biological piezoelectric scaffolds as next-generation BTE implants.

Because of the complex nerve anatomy and limited regeneration ability of natural tissue, the current treatment effect for long-distance peripheral nerve regeneration and spinal cord injury (SCI) repair is not satisfactory. As an alternative method, tissue engineering is a promising method to regenerate peripheral nerve and spinal cord, and can provide structures and functions similar to natural tissues through scaffold materials and seed cells. Recently, the rapid development of 3D printing technology enables researchers to create novel 3D constructs with sophisticated structures and diverse functions to achieve high bionics of structures and functions. In this review, we first outlined the anatomy of peripheral nerve and spinal cord, as well as the current treatment strategies for the peripheral nerve injury and SCI in clinical. After that, the design considerations of peripheral nerve and spinal cord tissue engineering were discussed, and various 3D printing technologies applicable to neural tissue engineering were elaborated, including inkjet, extrusion-based, stereolithography, projection-based, and emerging printing technologies. Finally, we focused on the application of 3D printing technology in peripheral nerve regeneration and spinal cord repair, as well as the challenges and prospects in this research field.

The continual demand for modern optoelectronics with a high integration degree and customized functions has increased requirements for nanofabrication methods with high resolution, freeform, and mask-free. Meniscus-on-demand three-dimensional (3D) printing is a high-resolution additive manufacturing technique that exploits the ink meniscus formed on a printer nozzle and is suitable for the fabrication of micro/nanoscale 3D architectures. This method can be used for solution-processed 3D patterning of materials at a resolution of up to 100 nm, which provides an excellent platform for fundamental scientific studies and various practical applications. This review presents recent advances in meniscus-on-demand 3D printing, together with historical perspectives and theoretical background on meniscus formation and stability. Moreover, this review highlights the capabilities of meniscus-on-demand 3D printing in terms of printable materials and potential areas of application, such as electronics and photonics.

As one of the most promising platforms for wireless communication, radiofrequency (RF) electronics have been widely advocated for the development of sensing systems. In particular, monolayer and few-layer two-dimensional (2D) materials exhibiting extraordinary electrical properties not only can be integrated to improve the performance of RF circuits, but also to display exceptional sensing capabilities. This review provides an in-depth perspective of current trends and challenges in the application of 2D materials for RF biochemical sensing, including: (i) theoretical bases to achieve different sensing schemes; (ii) unique properties of 2D materials for reasoning their applications in RF sensing; (iii) developments in 2D RF sensors to facilitate the practice of biochemical sensors with ever-demanding sensitivities, as well as their potential uses in meeting the requirements and challenges of biochemical sensors in the Internet-of-Things era.

Four-dimensional printing allows for the transformation capabilities of 3D-printed architectures over time, altering their shape, properties, or function when exposed to external stimuli. This interdisciplinary technology endows the 3D architectures with unique functionalities, which has generated excitement in diverse research fields, such as soft robotics, biomimetics, biomedical devices, and sensors. Understanding the selection of the material, architectural designs, and employed stimuli is crucial to unlocking the potential of smart customization with 4D printing. This review summarizes recent significant developments in 4D printing and establishes links between smart materials, 3D printing techniques, programmable structures, diversiform stimulus, and new functionalities for multidisciplinary applications. We start by introducing the advanced features of 4D printing and the key technological roadmap for its implementation. We then place considerable emphasis on printable smart materials and structural designs, as well as general approaches to designing programmable structures. We also review stimulus designs in smart materials and their associated stimulus-responsive mechanisms. Finally, we discuss new functionalities of 4D printing for potential applications and further development directions.

As a new generation of materials/structures, heterostructure is characterized by heterogeneous zones with dramatically different mechanical, physical or chemical properties. This endows heterostructure with unique interfaces, robust architectures, and synergistic effects, making it a promising option as advanced biomaterials for the highly variable anatomy and complex functionalities of individual patients. However, the main challenges of developing heterostructure lie in the control of crystal/phase evolution and the distribution/fraction of components and structures. In recent years, additive manufacturing techniques have attracted increasing attention in developing heterostructure due to the unique flexibility in tailored structures and synthetic multimaterials. This review focuses on the additive manufacturing of heterostructure for biomedical applications. The structural features and functional mechanisms of heterostructure are summarized. The typical material systems of heterostructure, mainly including metals, polymers, ceramics, and their composites, are presented. And the resulting synergistic effects on multiple properties are also systematically discussed in terms of mechanical, biocompatible, biodegradable, antibacterial, biosensitive and magnetostrictive properties. Next, this work outlines the research progress of additive manufacturing employed in developing heterostructure from the aspects of advantages, processes, properties, and applications. This review also highlights the prospective utilization of heterostructure in biomedical fields, with particular attention to bioscaffolds, vasculatures, biosensors and biodetections. Finally, future research directions and breakthroughs of heterostructure are prospected with focus on their more prospective applications in infection prevention and drug delivery.

Nanomaterial-based flexible sensors (NMFSs) can be tightly attached to the human skin or integrated with clothing to monitor human physiological information, provide medical data, or explore metaverse spaces. Nanomaterials have been widely incorporated into flexible sensors due to their facile processing, material compatibility, and unique properties. This review highlights the recent advancements in NMFSs involving various nanomaterial frameworks such as nanoparticles, nanowires, and nanofilms. Different triggering interaction interfaces between NMFSs and metaverse/virtual reality (VR) applications, e.g. skin-mechanics-triggered, temperature-triggered, magnetically triggered, and neural-triggered interfaces, are discussed. In the context of interfacing physical and virtual worlds, machine learning (ML) has emerged as a promising tool for processing sensor data for controlling avatars in metaverse/VR worlds, and many ML algorithms have been proposed for virtual interaction technologies. This paper discusses the advantages, disadvantages, and prospects of NMFSs in metaverse/VR applications.

Porous and functionally graded materials have seen extensive applications in modern biomedical devices—allowing for improved site-specific performance; their appreciable mechanical, corrosive, and biocompatible properties are highly sought after for lightweight and high-strength load-bearing orthopedic and dental implants. Examples of such porous materials are metals, ceramics, and polymers. Although, easy to manufacture and lightweight, porous polymers do not inherently exhibit the required mechanical strength for hard tissue repair or replacement. Alternatively, porous ceramics are brittle and do not possess the required fatigue resistance. On the other hand, porous biocompatible metals have shown tailorable strength, fatigue resistance, and toughness. Thereby, a significant interest in investigating the manufacturing challenges of porous metals has taken place in recent years. Past research has shown that once the advantages of porous metallic structures in the orthopedic implant industry have been realized, their biological and biomechanical compatibility—with the host bone—has been followed up with extensive methodical research. Various manufacturing methods for porous or functionally graded metals are discussed and compared in this review, specifically, how the manufacturing process influences microstructure, graded composition, porosity, biocompatibility, and mechanical properties. Most of the studies discussed in this review are related to porous structures for bone implant applications; however, the understanding of these investigations may also be extended to other devices beyond the biomedical field.

In order to mimic the natural heterogeneity of native tissue and provide a better microenvironment for cell culturing, multi-material bioprinting has become a common solution to construct tissue models in vitro. With the embedded printing method, complex 3D structure can be printed using soft biomaterials with reasonable shape fidelity. However, the current sequential multi-material embedded printing method faces a major challenge, which is the inevitable trade-off between the printed structural integrity and printing precision. Here, we propose a simultaneous multi-material embedded printing method. With this method, we can easily print firmly attached and high-precision multilayer structures. With multiple individually controlled nozzles, different biomaterials can be precisely deposited into a single crevasse, minimizing uncontrolled squeezing and guarantees no contamination of embedding medium within the structure. We analyse the dynamics of the extruded bioink in the embedding medium both analytically and experimentally, and quantitatively evaluate the effects of printing parameters including printing speed and rheology of embedding medium, on the 3D morphology of the printed filament. We demonstrate the printing of double-layer thin-walled structures, each layer less than 200 µm, as well as intestine and liver models with 5% gelatin methacryloyl that are crosslinked and extracted from the embedding medium without significant impairment or delamination. The peeling test further proves that the proposed method offers better structural integrity than conventional sequential printing methods. The proposed simultaneous multi-material embedded printing method can serve as a powerful tool to support the complex heterogeneous structure fabrication and open unique prospects for personalized medicine.

Direct ink writing (DIW) holds enormous potential in fabricating multiscale and multi-functional architectures by virtue of its wide range of printable materials, simple operation, and ease of rapid prototyping. Although it is well known that ink rheology and processing parameters have a direct impact on the resolution and shape of the printed objects, the underlying mechanisms of these key factors on the printability and quality of DIW technique remain poorly understood. To tackle this issue, we systematically analyzed the printability and quality through extrusion mechanism modeling and experimental validating. Hybrid non-Newtonian fluid inks were first prepared, and their rheological properties were measured. Then, finite element analysis of the whole DIW process was conducted to reveal the flow dynamics of these inks. The obtained optimal process parameters (ink rheology, applied pressure, printing speed, etc) were also validated by experiments where high-resolution (<100 patterns="" were="" fabricated="" rapidly="">70 mm s^-1). Finally, as a process research demonstration, we printed a series of microstructures and circuit systems with hybrid inks and silver inks, showing the suitability of the printable process parameters. This study provides a strong quantitative illustration of the use of DIW for the high-speed preparation of high-resolution, high-precision samples.

Additive manufacturing (AM) is a free-form technology that shows great potential in the integrated creation of three-dimensional (3D) electronics. However, the fabrication of 3D conformal circuits that fulfill the requirements of high service temperature, high conductivity and high resolution remains a challenge. In this paper, a hybrid AM method combining the fused deposition modeling (FDM) and hydrophobic treatment assisted laser activation metallization (LAM) was proposed for manufacturing the polyetheretherketone (PEEK)-based 3D electronics, by which the conformal copper patterns were deposited on the 3D-printed PEEK parts, and the adhesion between them reached the 5B high level. Moreover, the 3D components could support the thermal cycling test from -55 ℃ to 125 ℃ for more than 100 cycles. Particularly, the application of a hydrophobic coating on the FDM-printed PEEK before LAM can promote an ideal catalytic selectivity on its surface, not affected by the inevitable printing borders and pores in the FDM-printed parts, then making the resolution of the electroless plated copper lines improved significantly. In consequence, Cu lines with width and spacing of only 60 µm and 100 µm were obtained on both as-printed and after-polished PEEK substrates. Finally, the potential of this technique to fabricate 3D conformal electronics was demonstrated.

Aiming to improve the battery performance of lithium-ion batteries (LIBs), modification of the cathodes and anodes of LIBs using laser beams to prepare through-holes, non-through-holes or ditches arranged in grid and line patterns has been proposed by many researchers and engineers. In this study, a laser processing system attached to rollers, which realizes this modification without large changes in the present mass-production system, was developed. The laser system apparatus comprises roll-to-roll equipment and laser equipment. The roll-to-roll equipment mainly consists of a hollow cylinder with openings on its circumferential surface. Cathode and anode electrodes for LIBs are wound around the cylinder in the longitudinal direction of the electrodes. A pulsed beam reflected from the central axis of the cylinder can continuously open a large number of through-holes in the thin electrodes. Through-holes were formed at a rate of 100 000 holes per second on lithium iron phosphate cathodes and graphite anodes with this system. The through-holed cathodes and anodes prepared with this system exhibited higher C-rate performance than nontreated cathodes and anodes.

Ni₅₁Ti₄₉ at.% bulk was additively manufactured by laser-directed energy deposition (DED) to reveal the microstructure evolution, phase distribution, and mechanical properties. It is found that the localized remelting, reheating, and heat accumulation during DED leads to the spatial heterogeneous distribution of columnar crystal and equiaxed crystal, a gradient distribution of Ni₄Ti₃ precipitates along the building direction, and preferential formation of Ni₄Ti₃ precipitates in the columnar zone. The austenite transformation finish temperature (A_f) varies from −12.65 ◦C (Z = 33 mm) to 60.35 ◦C (Z = 10 mm), corresponding to tensile yield strength (σ_0.2) changed from 120 ± 30 MPa to 570 ± 20 MPa, and functional properties changed from shape memory effect to superelasticity at room temperature. The sample in the Z = 20.4 mm height has the best plasticity of 9.6% and the best recoverable strain of 4.2%. This work provided insights and guidelines for the spatial characterization of DEDed NiTi.

Direct Laser Interference Patterning (DLIP) is used to texture current collector foils in a roll-to-roll process using a high-power picosecond pulsed laser system operating at either fundamental wavelength of 1064 nm or 2nd harmonic of 532 nm. The raw beam having a diameter of 3 mm @ 1/e² is shaped into an elongated top-hat intensity profile using a diffractive so-called FBS®-L element and cylindrical telescopes. The shaped beam is split into its diffraction orders, where the two first orders are parallelized and guided into a galvanometer scanner. The deflected beams inside the scan head are recombined with an F-theta objective on the working position generating the interference pattern. The DLIP spot has a line-like interference pattern with about 15 µm spatial period. Laser fluences of up to 8 J cm⁻² were achieved using a maximum pulse energy of 0.6 mJ. Furthermore, an in-house built roll-to-roll machine was developed. Using this setup, aluminum and copper foil of 20 µm and 9 µm thickness, respectively, could be processed. Subsequently to current collector structuring coating of composite electrode material took place. In case of lithium nickel manganese cobalt oxide (NMC 622) cathode deposited onto textured aluminum current collector, an increased specific discharge capacity could be achieved at a C-rate of 1 ºC. For the silicon/graphite anode material deposited onto textured copper current collector, an improved rate capability at all C-rates between C/10 and 5 ºC was achieved. The rate capability was increased up to 100% compared to reference material. At C-rates between C/2 and 2 ºC, the specific discharge capacity was increased to 200 mAh g⁻¹, while the reference electrodes with untextured current collector foils provided a specific discharge capacity of 100 mAh g⁻¹, showing the potential of the DLIP technology for cost-effective production of battery cells with increased cycle lifetime.

Complex-shaped optical lenses are of great interest in the areas of laser processing, machine vision, and optical communications. Traditionally, the processing of complex optical lenses is usually achieved by precision machining combined with post-grinding or polishing, which is expensive, labor-intensive and difficult in the processing of ultra-complex optical lenses. Additive manufacturing is an emerging technology that provides significant advantages in producing highly intricate optical devices. However, the layer-by-layer method employed in such manufacturing processes has resulted in low printing speeds, as well as limitations in surface quality. To address these challenges, we apply tomographic volumetric printing (TVP) in this work, which can realize the integrated printing of complex structural models without layering. By coordinating the TVP and the meniscus equilibrium post-curing methods, ultra-fast fabrication of complex-shaped lenses with sub-nanometric roughness has been achieved. A 2.5 mm high, outer diameter 9 mm spherical lens with a roughness value of RMS = 0.3340 nm is printed at a speed of 3.1 × 10⁴ mm³ h^-1. As a further demonstration, a complex-shaped fly-eye lens is fabricated without any part assembly. The designed spherical lens is mounted on a smartphone’s camera, and the precise alignments above the circuit board are captured. Upon further optimization, this new technology demonstrates the potential for rapid fabrication of ultra-smooth complex optical devices or systems.

Nano-3D printing has obtained widespread attention owing to its capacity to manufacture end-use components with nano-scale features in recent years. Multiphoton lithography (MPL) is one of the most promising 3D nanomanufacturing technologies, which has been widely used in manufacturing micro-optics, photonic crystals, microfluidics, meta-surface, and mechanical metamaterials. Despite of tremendous potential of MPL in laboratorial and industrial applications, simultaneous achievement of high throughput, high accuracy, high design freedom, and a broad range of material structuring capabilities remains a long-pending challenge. To address the issue, we propose an acousto-optic scanning with spatial-switching multispots (AOSS) method. Inertia-free acousto-optic scanning and nonlinear swept techniques have been developed for achieving ultrahigh-speed and aberration-free scanning. Moreover, a spatial optical switch concept has been implemented to significantly boost the lithography throughput while maintaining high resolution and high design freedom. An eight-foci AOSS system has demonstrated a record-high 3D printing rate of 7.6 × 10⁷ voxel s⁻¹, which is nearly one order of magnitude higher than earlier scanning MPL, exhibiting its promise for future scalable 3D nanomanufacturing.

Surface nanopatterning of semiconductor optoelectronic devices is a powerful way to improve their quality and performance. However, photoelectric devices’ inherent stress sensitivity and inevitable warpage pose a huge challenge on fabricating nanostructures large-scale. Electric-driven flexible-roller nanoimprint lithography for nanopatterning the optoelectronic wafer is proposed in this study. The flexible nanoimprint template twining around a roller is continuously released and recovered, controlled by the roller’s simple motion. The electric field applied to the template and substrate provides the driving force. The contact line of the template and the substrate gradually moves with the roller to enable scanning and adapting to the entire warped substrate, under the electric field. In addition, the driving force generated from electric field is applied to the surface of substrate, so that the substrate is free from external pressure. Furthermore, liquid resist completely fills in microcavities on the template by powerful electric field force, to ensure the fidelity of the nanostructures. The proposed nanoimprint technology is validated on the prototype. Finally, nano-grating structures are fabricated on a gallium nitride light-emitting diode chip adopting the solution, achieving polarization of the light source.

Polycrystalline materials are extensively employed in industry. Its surface roughness significantly affects the working performance. Material defects, particularly grain boundaries, have a great impact on the achieved surface roughness of polycrystalline materials. However, it is difficult to establish a purely theoretical model for surface roughness with consideration of the grain boundary effect using conventional analytical methods. In this work, a theoretical and deep learning hybrid model for predicting the surface roughness of diamond-turned polycrystalline materials is proposed. The kinematic–dynamic roughness component in relation to the tool profile duplication effect, work material plastic side flow, relative vibration between the diamond tool and workpiece, etc, is theoretically calculated. The material-defect roughness component is modeled with a cascade forward neural network. In the neural network, the ratio of maximum undeformed chip thickness to cutting edge radius R_TS, work material properties (misorientation angle θ_g and grain size d_g), and spindle rotation speed n_s are configured as input variables. The material-defect roughness component is set as the output variable. To validate the developed model, polycrystalline copper with a gradient distribution of grains prepared by friction stir processing is machined with various processing parameters and different diamond tools. Compared with the previously developed model, obvious improvement in the prediction accuracy is observed with this hybrid prediction model. Based on this model, the influences of different factors on the surface roughness of polycrystalline materials are discussed. The influencing mechanism of the misorientation angle and grain size is quantitatively analyzed. Two fracture modes, including transcrystalline and intercrystalline fractures at different R_TS values, are observed. Meanwhile, optimal processing parameters are obtained with a simulated annealing algorithm. Cutting experiments are performed with the optimal parameters, and a flat surface finish with Sa 1.314 nm is finally achieved. The developed model and corresponding new findings in this work are beneficial for accurately predicting the surface roughness of polycrystalline materials and understanding the impacting mechanism of material defects in diamond turning.

The development of projection-based stereolithography additive manufacturing techniques and magnetic photosensitive resins has provided a powerful approach to fabricate miniaturized magnetic functional devices with complex three-dimensional spatial structures. However, the present magnetic photosensitive resins face great challenges in the trade-off between high ferromagnetism and excellent printing quality. To address these challenges, we develop a novel NdFeB-Fe₃O₄ magnetic photosensitive resin comprising 20 wt.% solid loading of magnetic particles, which can be used to fabricate high-precision and ferromagnetic functional devices via micro-continuous liquid interface production process. This resin combining ferromagnetic NdFeB microparticles and strongly absorbing Fe₃O₄ nanoparticles is able to provide ferromagnetic capabilities and excellent printing quality simultaneously compared to both existing soft and hard magnetic photosensitive resins. The established penetration depth model reveals the effect of particle size, solid loading, and absorbance on the curing characteristics of magnetic photosensitive resin. A high-precision forming and ferromagnetic capability of the NdFeB-Fe₃O₄ magnetic photosensitive resin are comprehensively demonstrated. It is found that the photosensitive resin (NdFeB:Fe₃O₄ = 1:1) can print samples with sub-40 µm fine features, reduced by 87% compared to existing hard magnetic photosensitive resin, and exhibits significantly enhanced coercivity and remanence in comparison with existing soft magnetic photosensitive resins, showing by an increase of 24 times and 6 times, respectively. The reported NdFeB-Fe₃O₄ magnetic photosensitive resin is anticipated to provide a new functional material for the design and manufacture of next-generation micro-robotics, electromagnetic sensor, and magneto-thermal devices.

Optical fibers are typically used in telecommunications services for data transmission, where the use of fiber tags is essential to distinguish between the different transmission fibers or channels and thus ensure the working functionality of the communication system. Traditional physical entity marking methods for fiber labeling are bulky, easily confused, and, most importantly, the label information can be accessed easily by all potential users. This work proposes an encrypted optical fiber tag based on an encoded fiber Bragg grating (FBG) array that is fabricated using a point-by-point femtosecond laser pulse chain inscription method. Gratings with different resonant wavelengths and reflectivities are realized by adjusting the grating period and the refractive index modulations. It is demonstrated that a binary data sequence carried by a fiber tag can be inscribed into the fiber core in the form of an FBG array, and the tag data can be encrypted through appropriate design of the spatial distributions of the FBGs with various reflection wavelengths and reflectivities. The proposed fiber tag technology can be used for applications in port identification, encrypted data storage, and transmission in fiber networks.

Microwave absorption in radar stealth technology is faced with challenges in terms of its effectiveness in low-frequency regions. Herein, we report a new laser-based method for producing an ultrawideband metamaterial-based microwave absorber with a highly uniform sheet resistance and negative magnetic permeability at resonant frequencies, which results in a wide bandwidth in the L- to S-band. Control of the electrical sheet resistance uniformity has been achieved with less than 5% deviation at 400 Ω sq^-1 and 6% deviation at 120 Ω sq^-1, resulting in a microwave absorption coefficient between 97.2% and 97.7% within a 1.56-18.3 GHz bandwidth for incident angles of 0◦-40◦, and there is no need for providing energy or an electrical power source during the operation. Porous N- and S-doped turbostratic graphene 2D patterns with embedded magnetic nanoparticles were produced simultaneously on a polyethylene terephthalate substrate via laser direct writing. The proposed low-frequency,wideband, wide-incident-angle, and high-electromagnetic-absorption microwave absorber can potentially be used in aviation, electromagnetic interference (EMI) suppression, and 5G applications.