Femtosecond laser programmed artificial musculoskeletal systems

Generation of Tailored Multi-Material Microstructures Through One-Step Direct Laser Writing

Direct laser writing has gained remarkable popularity by offering architectural control of 3D objects at submicron scales. However, it faces limitations when the fabrication of microstructures comprising multiple materials is desired. The generation processes of multi-material microstructures are often very complex, requiring meticulous alignment, as well as a series of step-and-repeat writing and development of the materials. Here, a novel material system based on multilayers of chemically tailored polymers containing anthraquinone crosslinker units is demonstrated. Upon two-photon excitation, the crosslinkers only require nearby aliphatic C,H units as reaction partners to form a crosslinked network. The desired structure can be written into a solid multi-layered material system, wherein the properties of each material can be designed at the molecular level. In this way, C,H insertion crosslinking (CHic) of the polymers within each layer, along with simultaneous reaction at their interfaces, is performed, leading to the one-step fabrication of multi-material microstructures. A multi-material 3D scaffold with a sixfold symmetry is produced to precisely control the adhesion of cells both concerning surface chemistry and topology. The demonstrated material system shows great promise for the fabrication of 3D microstructures with high precision, intricate geometries and customized functionalities.

Biocompatible polymer-based micro/nanorobots for theranostic translational applications

Recently, micro/nanorobots (MNRs) with self-propulsion have emerged as a promising smart platform for diagnostic, therapeutic and theranostic applications. Especially, polymer-based MNRs have attracted huge attention due to their inherent biocompatibility and versatility, making them actively explored for various medical applications. As the translation of MNRs from laboratory to clinical settings is imperative, the use of appropriate polymers for MNRs is a key strategy, which can prompt the advancement of MNRs to the next phase. In this review, we describe the multifunctional versatile polymers in MNRs, and their biodegradability, motion control, cargo loading and release, adhesion, and other characteristics. After that, we review the theranostic applications of polymer-based MNRs to bioimaging, biosensing, drug delivery, and tissue engineering. Furthermore, we address the challenges that must be overcome to facilitate the translational development of polymeric MNRs with future perspectives. This review would provide valuable insights into the state-of-the-art technologies associated with polymeric MNRs and contribute to their progression for further clinical development.

Femtosecond laser writing of ant-inspired reconfigurable microbot collectives

Microbot collectives can cooperate to accomplish complex tasks that are difficult for a single individual. However, various force-induced microbot collectives maintained by weak magnetic, light, and electric fields still face challenges such as unstable connections, the need for a continuous external stimuli source, and imprecise individual control. Here, we construct magnetic and light-driven ant microbot collectives capable of reconfiguring multiple assembled architectures with robustness. This methodology utilizes a flexible two-photon polymerization strategy to fabricate microbots consisting of magnetic photoresist, hydrogel, and metal nanoparticles. Under the cooperation of magnetic and light fields, the microbots can reversibly and selectively assemble (e.g., 90° assembly and 180° assembly) into various morphologies. Moreover, we demonstrate the ability of assembled microbots to cross a one-body-length gap and their adaptive capability to move through a constriction and transport microcargo. Our strategy will broaden the abilities of clustered microbots, including gap traversal, micro-object manipulation, and drug delivery.

Free-space direct nanoscale 3D printing of metals and alloys enabled by two-photon decomposition and ultrafast optical trapping

Nanoscale three-dimensional (3D) printing of metals and alloys has faced challenges in speed, miniaturization and deficiency in material properties. Traditional nanomanufacturing relies on lithographic methods with material constraints, limited resolution and slow layer-by-layer processing. This work introduces polymer-free techniques using two-photon decomposition and optical force trapping for free-space direct 3D printing of metals, metal oxides and multimetallic alloys with resolutions beyond optical limits. This method involves the two-photon decomposition of metal atoms from precursors, rapid assembly into nanoclusters via optical forces and ultrafast laser sintering, yielding dense, smooth nanostructures. Enhanced near-field optical forces from laser-induced localized surface plasmon resonance facilitate nanocluster aggregation. Our approach eliminates the need for organic materials, layer-by-layer printing and complex post-processing. Printed Mo nanowires show an excellent mechanical performance, closely resembling the behaviour of single crystals, while Mo-Co-W alloy nanowires outperform Mo nanowires. This innovation promises the customizable 3D nanoprinting of high-quality metals and metal oxides, impacting nanoelectronics, nanorobotics and advanced chip manufacturing.

Single-Cell Synchro-Subtractive-Additive Nanoscale Surgery with Femtosecond Lasers

Herein, an in situ "synchro-subtractive-additive" technique of femtosecond laser single-cell surgery (FLSS) is presented to address the inadequacies of existing surgical methods for single-cell manipulation. This process is enabled by synchronized nanoscale three-dimensional (3D) subtractive and additive manufacturing with ultrahigh precision on various parts of the cells, in that the precise removal and modification of a single-cell structure are realized by nonthermal ablation, with synchronously ultrafast solidification of the specially designed hydrogel by two photopolymerizations. FLSS is a minimally invasive technique with a post-operative survival rate of 70% and stable proliferation. It opens avenues for bottom-up synthetic biology, offering new methods for artificially synthesizing organelle-like 3D structures and modifying the physiological activities of cells.

Finite element simulation and experimental validation of thermal damage to isolated porcine skin tissue by femtosecond laser welding

The welding effect of the laser on skin tissue is reduced by thermal damage to skin tissue, and greater thermal damage to skin tissue caused by the laser is prevented by predicting thermal damage. In this paper, a finite element model is established for the temperature field of skin tissue scanned by a femtosecond laser to obtain the influence of laser process parameters and scanning path on the thermal damage parameters of skin tissue and the thermal damage area, and verified experimentally. The results show that the established finite element model is accurate and can accurately reflect the temperature distribution during the process of femtosecond laser welding of porcine skin tissues; used to predict the thermal damage parameters of the skin tissues and the thermal damage area; and provide guidance for the study of the femtosecond laser welding of the skin tissues process to obtain the optimal process parameters.

Direct Laser Writing of Silica Nanoparticle Nanocomposites: Probing Mechanical Reinforcement and Understanding Structural Color from Design Parameters

Nanocomposite materials have been thoroughly exploited in additive manufacturing, as a means to alter physical, chemical, and optical properties of resulting structures. Herein, nanocomposite materials suitable for direct laser writing (DLW) by two-photon polymerization are presented. These materials, comprising silica nanoparticles, bring significant added value to the technology through physical reinforcement and controllable photonic properties. Incorporation into acrylate photoresists, via a one-step fabrication process, enables the formation of complex structures with large overhangs. The inclusion of 150 nm silica nanoparticles in DLW photoresists at high concentrations, allows for the fabrication of composite microstructures that show reflected color, a product of the relative contributions from the quasi-ordering and random scattering. Using common DLW design parameters, such as slicing distance and structure dimension, a wide gamut of structural color, in solution, using a set concentration of nanoparticles is demonstrated. Numerical modeling is employed to predict the reflected wavelength of the pixel arrays, across the visible spectrum, and this information is used to encode reflected colors into different pixel arrays.

Wide-Size Range and High Robustness Self-Assembly Micropillars for Capturing Microspheres

Capillary force driven self-assembly micropillars (CFSA-MP) holds immense promise for the manipulation and capture of cells/tiny objects, which has great demands of wide size range and high robustness. Here, we propose a novel method to fabricate size-adjustable and highly robust CFSA-MP that can achieve wide size range and high stability to capture microspheres. First, we fabricate a microholes template with an adjustable aspect ratio using the spatial-temporal shaping femtosecond laser double-pulse Bessel beam-assisted chemical etching technique, and then the micropillars with adjustable aspect ratio are demolded by polydimethylsiloxane (PDMS). We fully demonstrated the advantages of the Bessel optical field by using the spatial-temporal shaping femtosecond laser double-pulse Bessel beams to broaden the height range of the micropillars, which in turn expands the size range of the captured microspheres, and finally achieving a wide range of capturing microspheres with a diameter of 5-410 μm. Based on the inverted mold technology, the PDMS micropillars have ultrahigh mechanical robustness, which greatly improves the durability. CFSA-MP has the ability to capture tiny objects with wide range and high stability, which indicates great potential applications in the fields of chemistry, biomedicine, and microfluidics.

3D nanofabricated soft microrobots with super-compliant picoforce springs as onboard sensors and actuators

Microscale organisms and specialized motile cells use protein-based spring-like responsive structures to sense, grasp and move. Rendering this biomechanical transduction functionality in an artificial micromachine for applications in single-cell manipulations is challenging due to the need for a bio-applicable nanoscale spring system with a large and programmable strain response to piconewton-scale forces. Here we present three-dimensional nanofabrication and monolithic integration, based on an acrylic elastomer photoresist, of a magnetic spring system with quantifiable compliance sensitive to 0.5 pN, constructed with customized elasticity and magnetization distributions at the nanoscale. We demonstrate the effective design programmability of these 'picospring' ensembles as energy transduction mechanisms for the integrated construction of customized soft micromachines, with onboard sensing and actuation functions at the single-cell scale for microrobotic grasping and locomotion. The integration of active soft springs into three-dimensional nanofabrication offers an avenue to create biocompatible soft microrobots for non-disruptive interactions with biological entities.

Variable Stiffness Fibers Enabled Universal and Programmable Re-Foldability Strategy for Modular Soft Robotics

Origami is a rich source of inspiration for creating soft actuators with complex deformations. However, implementing the re-foldability of origami on soft actuators remains a significant challenge. Herein, a universal and programmable re-foldability strategy is reported to integrate multiple origami patterns into a single soft origami actuator, thereby enabling multimode morphing capability. This strategy can selectively activate and deactivate origami creases through variable stiffness fibers. The utilization of these fibers enables the programmability of crease pattern quantity and types within a single actuator, which expands the morphing modes and deformation ranges without increasing their physical size and chamber number. The universality of this approach is demonstrated by developing a series of re-foldable soft origami actuators. Moreover, these soft origami actuators are utilized to construct a bidirectional crawling robot and a multimode soft gripper capable of adapting to object size, grasping orientation, and placing orientation. This work represents a significant step forward in the design of multifunctional soft actuators and holds great potential for the advancement of agile and versatile soft robots.

Advanced Nanomaterials in Medical 3D Printing

3D printing is now recognized as a significant tool for medical research and clinical practice, leading to the emergence of medical 3D printing technology. It is essential to improve the properties of 3D-printed products to meet the demand for medical use. The core of generating qualified 3D printing products is to develop advanced materials and processes. Taking advantage of nanomaterials with tunable and distinct physical, chemical, and biological properties, integrating nanotechnology into 3D printing creates new opportunities for advancing medical 3D printing field. Recently, some attempts are made to improve medical 3D printing through nanotechnology, providing new insights into developing advanced medical 3D printing technology. With high-resolution 3D printing technology, nano-structures can be directly fabricated for medical applications. Incorporating nanomaterials into the 3D printing material system can improve the properties of the 3D-printed medical products. At the same time, nanomaterials can be used to expand novel medical 3D printing technologies. This review introduced the strategies and progresses of improving medical 3D printing through nanotechnology and discussed challenges in clinical translation.

Evolution of the Microrobots: Stimuli-Responsive Materials and Additive Manufacturing Technologies Turn Small Structures into Microscale Robots

The development of functional microsystems and microrobots that have characterized the last decade is the result of a synergistic and effective interaction between the progress of fabrication techniques and the increased availability of smart and responsive materials to be employed in the latter. Functional structures on the microscale have been relevant for a vast plethora of technologies that find application in different sectors including automotive, sensing devices, and consumer electronics, but are now also entering medical clinics. Working on or inside the human body requires increasing complexity and functionality on an ever-smaller scale, which is becoming possible as a result of emerging technology and smart materials over the past decades. In recent years, additive manufacturing has risen to the forefront of this evolution as the most prominent method to fabricate complex 3D structures. In this review, we discuss the rapid 3D manufacturing techniques that have emerged and how they have enabled a great leap in microrobotic applications. The arrival of smart materials with inherent functionalities has propelled microrobots to great complexity and complex applications. We focus on which materials are important for actuation and what the possibilities are for supplying the required energy. Furthermore, we provide an updated view of a new generation of microrobots in terms of both materials and fabrication technology. While two-photon lithography may be the state-of-the-art technology at the moment, in terms of resolution and design freedom, new methods such as two-step are on the horizon. In the more distant future, innovations like molecular motors could make microscale robots redundant and bring about nanofabrication.

Laser manufacturing of spatial resolution approaching quantum limit

Atomic and close-to-atom scale manufacturing is a promising avenue toward single-photon emitters, single-electron transistors, single-atom memory, and quantum-bit devices for future communication, computation, and sensing applications. Laser manufacturing is outstanding to this end for ease of beam manipulation, batch production, and no requirement for photomasks. It is, however, suffering from optical diffraction limits. Herein, we report a spatial resolution improved to the quantum limit by exploiting a threshold tracing and lock-in method, whereby the two-order gap between atomic point defect complexes and optical diffraction limit is surpassed, and a feature size of <5 nm is realized. The underlying physics is that the uncertainty of local atom thermal motion dominates electron excitation, rather than the power density slope of the incident laser. We show that the colour centre yield in hexagonal boron nitride is transformed from stochastic to deterministic, and the emission from individual sites becomes polychromatic to monochromatic. As a result, single colour centres in the regular array are deterministically created with a unity yield and high positional accuracy, serving as a step forward for integrated quantum technological applications.

Precise Focal Spot Positioning on an Opaque Substrate Based on the Diffraction Phenomenon in Laser Microfabrication

The precise positioning of the laser focal spot on the substrate is an important issue for laser microfabrication. In this work, a diffraction pattern-based focal spot positioning method (DFSPM) is proposed to achieve the precise positioning of the laser focal spot on opaque substrates. A series of diffraction patterns of laser focus under-positioning, exact positioning and over-positioning were obtained to investigate the cross-section light distribution of the laser focal spot. According to the monotonic tendency of FWHM to exhibit light intensity at the focal spot cross-section away from the focal plane, the FWHM threshold of polynomial fitted curves was used to determine the exact positioning of laser focus. The ascending scanning method was used to obtain the diffraction patterns at various vertical positions and the FWHM threshold of light distribution at the exact position. The polynomial fitted curves verify the FWHM monotonic tendency of light intensity distribution at the focal spot cross-section along the optical axis. Precise positioning can be achieved with a 100 nm adjustment resolution. This work was expected to provide references for laser microfabrication on opaque materials.

High-Transmission Biomimetics Structural Surfaces Produced via Ultrafast Laser Manufacturing

Inspired by periodically aligned micro/nanostructures on biological surfaces, researchers have been fabricating biomimetic structures with superior performance. As a promising and versatile tool, an ultrafast laser combined with other forms of processing technology has been utilized to manufacture functional structures, e.g., the biomimetic subwavelength structures to restrain the surface Fresnel reflectance. In this review paper, we interpret the biomimetic mechanism of antireflective subwavelength structures (ARSSs) for high-transmission windows. Recent advances in the fabrication of ARSSs with an ultrafast laser are summarized and introduced. The limitations and challenges of laser processing technology are discussed, and the future prospects for advancement are outlined, too.

Experimental study on the effect of scanning path on skin tissue properties of femtosecond laser welding

To study the influence pattern of femtosecond laser scanning path on the welding effect of skin tissue, this experiment analyzed the influence of scanning path on the surface morphology, degree of thermal damage, tensile strength, and microstructure of skin samples after skin attachment by designing nine scanning paths to weld skin tissue. The results showed that the skin samples connected by interrupted parallel mattress eversion sewing method with d = 0.2 mm showed no obvious color changes in morphology, the skin samples were connected on both front and back sides, the tensile strength was the highest, reaching 12.80 N/cm2 , the thermal damage parameter was low at 1.08 × 10-2 , the microstructure had obvious directionality, and the texture was clear and uniformly distributed.

A Multidrug Delivery Microrobot for the Synergistic Treatment of Cancer

Multidrug combination therapy provides an effective strategy for malignant tumor treatment. This paper presents the development of a biodegradable microrobot for on-demand multidrug delivery. By combining magnetic targeting transportation with tumor therapy, it is hypothesized that loading multiple drugs on different regions of a single magnetic microrobot can enhance a synergistic effect for cancer treatment. The synergistic effect of using two drugs together is greater than that of using each drug separately. Here, a 3D-printed microrobot inspired by the fish structure with three hydrogel components: skeleton, head, and body structures is demonstrated. Made of iron oxide (Fe3 O4 ) nanoparticles embedded in poly(ethylene glycol) diacrylate (PEGDA), the skeleton can respond to magnetic fields for microrobot actuation and drug-targeted delivery. The drug storage structures, head, and body, made by biodegradable gelatin methacryloyl (GelMA) exhibit enzyme-responsive cargo release. The multidrug delivery microrobots carrying acetylsalicylic acid (ASA) and doxorubicin (DOX) in drug storage structures, respectively, exhibit the excellent synergistic effects of ASA and DOX by accelerating HeLa cell apoptosis and inhibiting HeLa cell metastasis. In vivo studies indicate that the microrobots improve the efficiency of tumor inhibition and induce a response to anti-angiogenesis. The versatile multidrug delivery microrobot conceptualized here provides a way for developing effective combination therapy for cancer.

Dual-Stimuli Cooperative Responsive Hydrogel Microactuators Via Two-Photon Lithography

With the development of bionics as well as materials science, intelligent soft actuators have shown promising applications in many fields such as soft robotics, sensing, and remote manipulation. Microfabrication technologies have enabled the reduction of the size of responsive soft actuators to the micron level. However, it is still challenging to construct microscale actuators capable of responding to different external stimuli in complex and diverse conditions. Here, this work demonstrates a dual-stimuli cooperative responsive hydrogel microactuator by asymmetric fabrication via femtosecond laser direct writing. The dual response of the hydrogel microstructure is achieved by employing responsive hydrogel with functional monomer 2-(dimethylamino)ethyl methacrylate. Raman spectra of the hydrogel microstructures suggest that the pH and temperature response of the hydrogel is generated by the changes in tertiary amine groups and hydrogen bonds, respectively. The asymmetric hydrogel microstructures show opposite bending direction when being heated to high temperature or exposed to acid solution, and can independently accomplish the grasp of polystyrene microspheres. Moreover, this work depicts the cooperative response of the hydrogel microactuator to pH and temperature at the same time. The dual-stimuli cooperative responsive hydrogel microactuators will provide a strategy for designing and fabricating controllable microscale actuators with promising applications in microrobotics and microfluidics.

Optical force brush enabled free-space painting of 4D functional structures

Femtosecond laser-based technique called two-photon polymerization (TPP) has emerged as a powerful tool for nanofabrication and integrating nanomaterials. However, challenges persist in existing three-dimensional (3D) nanoprinting methods, such as slow layer-by-layer printing and limited material options due to laser-matter interactions. Here, we present an approach to 3D nanoprinting called free-space nanopainting, using an optical force brush (OFB). OFB enables precise spatial writing paths, instantaneous adjustment of linewidths and concentrations, and unrestricted resolution beyond optical limits. OFB allows rapid aggregation and solidification of radicals, resulting in narrower lines at lower polymerization thresholds and enhanced sensitivity to laser energy. This advancement enables high-accuracy free-space painting, analogous to Chinese brush painting on paper. The printing speed is increased substantially compared to layer-by-layer methods, from 100 to 1000 times faster. We successfully printed various bionic muscle models derived from 4D nanostructures with tunable mechanical properties, responsive to electrical signals, and excellent biocompatibility.

Femtosecond Laser Direct Writing of Gecko-Inspired Switchable Adhesion Interfaces on a Flexible Substrate

Biomimetic switchable adhesion interfaces (BSAIs) with dynamic adhesion states have demonstrated significant advantages in micro-manipulation and bio-detection. Among them, gecko-inspired adhesives have garnered considerable attention due to their exceptional adaptability to extreme environments. However, their high adhesion strength poses challenges in achieving flexible control. Herein, we propose an elegant and efficient approach by fabricating three-dimensional mushroom-shaped polydimethylsiloxane (PDMS) micropillars on a flexible PDMS substrate to mimic the bending and stretching of gecko footpads. The fabrication process that employs two-photon polymerization ensures high spatial resolution, resulting in micropillars with exquisite structures and ultra-smooth surfaces, even for tip/stem ratios exceeding 2 (a critical factor for maintaining adhesion strength). Furthermore, these adhesive structures display outstanding resilience, enduring 175% deformation and severe bending without collapse, ascribing to the excellent compatibility of the micropillar's composition and physical properties with the substrate. Our BSAIs can achieve highly controllable adhesion force and rapid manipulation of liquid droplets through mechanical bending and stretching of the PDMS substrate. By adjusting the spacing between the micropillars, precise control of adhesion strength is achieved. These intriguing properties make them promising candidates for various applications in the fields of microfluidics, micro-assembly, flexible electronics, and beyond.

Four-Dimensional Micro/Nanorobots via Laser Photochemical Synthesis towards the Molecular Scale

Miniaturized four-dimensional (4D) micro/nanorobots denote a forerunning technique associated with interdisciplinary applications, such as in embeddable labs-on-chip, metamaterials, tissue engineering, cell manipulation, and tiny robotics. With emerging smart interactive materials, static micro/nanoscale architectures have upgraded to the fourth dimension, evincing time-dependent shape/property mutation. Molecular-level 4D robotics promises complex sensing, self-adaption, transformation, and responsiveness to stimuli for highly valued functionalities. To precisely control 4D behaviors, current-laser-induced photochemical additive manufacturing, such as digital light projection, stereolithography, and two-photon polymerization, is pursuing high-freeform shape-reconfigurable capacities and high-resolution spatiotemporal programming strategies, which challenge multi-field sciences while offering new opportunities. Herein, this review summarizes the recent development of micro/nano 4D laser photochemical manufacturing, incorporating active materials and shape-programming strategies to provide an envisioning of these miniaturized 4D micro/nanorobots. A comparison with other chemical/physical fabricated micro/nanorobots further explains the advantages and potential usage of laser-synthesized micro/nanorobots.

High-sensitivity fiber optic temperature sensor based on CTFBG-FPI and Vernier effect

A novel high-sensitivity temperature sensor based on a chirped thin-core fiber Bragg grating Fabry-Perot interferometer (CTFBG-FPI) and the Vernier effect is proposed and demonstrated. With femtosecond laser direct writing technology, two CTFBG-FPIs with different interferometric cavity lengths are inscribed inside a thin-core fiber to form a Vernier effect system. The two FPIs consist of two pairs of CTFBGs with a full width at half maximum (FWHM) of 66.5 nm staggered in parallel. The interferometric cavity lengths of the two FPIs were designed to be 2 mm and 1.98 mm as the reference arm and sensing arm of the sensor, respectively. The temperature sensitivity of this sensor was measured to be -1.084 nm/°C in a range of 40-90°C. This sensor is expected to play a crucial role in precision temperature measurement applications.

Light-triggered multi-joint microactuator fabricated by two-in-one femtosecond laser writing

Inspired by the flexible joints of humans, actuators containing soft joints have been developed for various applications, including soft grippers, artificial muscles, and wearable devices. However, integrating multiple microjoints into soft robots at the micrometer scale to achieve multi-deformation modalities remains challenging. Here, we propose a two-in-one femtosecond laser writing strategy to fabricate microjoints composed of hydrogel and metal nanoparticles, and develop multi-joint microactuators with multi-deformation modalities (>10), requiring short response time (30 ms) and low actuation power (<10 mW) to achieve deformation. Besides, independent joint deformation control and linkage of multi-joint deformation, including co-planar and spatial linkage, enables the microactuator to reconstruct a variety of complex human-like modalities. Finally, as a proof of concept, the collection of multiple microcargos at different locations is achieved by a double-joint micro robotic arm. Our microactuators with multiple modalities will bring many potential application opportunities in microcargo collection, microfluid operation, and cell manipulation.

Ultracompact single-nanowire-morphed grippers driven by vectorial Lorentz forces for dexterous robotic manipulations

Ultracompact and soft pairwise grippers, capable of swift large-amplitude multi-dimensional maneuvering, are widely needed for high-precision manipulation, assembly and treatment of microscale objects. In this work, we demonstrate the simplest construction of such robotic structures, shaped via a single-nanowire-morphing and powered by geometry-tailored Lorentz vectorial forces. This has been accomplished via a designable folding growth of ultralong and ultrathin silicon NWs into single and nested omega-ring structures, which can then be suspended upon electrode frames and coated with silver metal layer to carry a passing current along geometry-tailored pathway. Within a magnetic field, the grippers can be driven by the Lorentz forces to demonstrate swift large-amplitude maneuvers of grasping, flapping and twisting of microscale objects, as well as high-frequency or even resonant vibrations to overcome sticky van de Waals forces in microscale for a reliable releasing of carried payloads. More sophisticated and functional teamwork of mutual alignment, precise passing and selective light-emitting-diode unit testing and installation were also successfully accomplished via pairwise gripper collaborations. This single-nanowire-morphing strategy provides an ideal platform to rapidly design, construct and prototype a wide range of advanced ultracompact nanorobotic, mechanical sensing and biological manipulation functionalities.

Microfluidic Approaches for Microactuators: From Fabrication, Actuation, to Functionalization

Microactuators can autonomously convert external energy into specific mechanical motions. With the feature sizes varying from the micrometer to millimeter scale, microactuators offer many operation and control possibilities for miniaturized devices. In recent years, advanced microfluidic techniques have revolutionized the fabrication, actuation, and functionalization of microactuators. Microfluidics can not only facilitate fabrication with continuously changing materials but also deliver various signals to stimulate the microactuators as desired, and consequently improve microfluidic chips with multiple functions. Herein, this cross-field that systematically correlates microactuator properties and microfluidic functions is comprehensively reviewed. The fabrication strategies are classified into two types according to the flow state of the microfluids: stop-flow and continuous-flow prototyping. The working mechanism of microactuators in microfluidic chips is discussed in detail. Finally, the applications of microactuator-enriched functional chips, which include tunable imaging devices, micromanipulation tools, micromotors, and microsensors, are summarized. The existing challenges and future perspectives are also discussed. It is believed that with the rapid progress of this cutting-edge field, intelligent microsystems may realize high-throughput manipulation, characterization, and analysis of tiny objects and find broad applications in various fields, such as tissue engineering, micro/nanorobotics, and analytical devices.

Towards understanding the mechanism of 3D printing using protein: femtosecond laser direct writing of microstructures made from homopeptides

Femtosecond laser direct write (fs-LDW) is a promising technology for three-dimensional (3D) printing due to its high resolution, flexibility, and versatility. A protein solution can be used as a precursor to fabricate 3D proteinaceous microstructures that retain the protein's native function. The large diversity of protein molecules with different native functions allows diverse applications of this technology. However, our limited understanding of the mechanism of the printing process restricts the design and generation of 3D microstructures for biomedical applications. Therefore, we used eight commercially available homopeptides as precursors for fs-LDW of 3D structures. Our experimental results show that tyrosine, histidine, glutamic acid, and lysine contribute more to the fabrication process than do proline, threonine, phenylalanine, and alanine. In particular, we show that tyrosine is highly beneficial in the fabrication process. The beneficial effect of the charged amino acids glutamic acid and lysine suggests that the printing mechanism involves ions in addition to the previously proposed radical mechanism. Our results further suggest that the uneven electron density over larger amino acid molecules is key in aiding fs-LDW. The findings presented here will help generate more desired 3D proteinaceous microstructures by modifying protein precursors with beneficial amino acids. STATEMENT OF SIGNIFICANCE: Femtosecond laser direct write (fs-LDW) offers a three-dimensional (3D) printing capability for creating well-defined micro-and nanostructures. Applying this technology to proteins enables the manufacture of complex biomimetic 3D micro-and nanoarchitectures with retention of their original protein functions. To our knowledge, amino acid homo-polymers themselves have never been used as precursor for fs-LDW so far. Our studygainsseveral new insights into the 3D printing mechanism of pure protein for the first time. We believe that the experimental evidence presented greatly benefits the community of 3D printing of proteinin particular and the biomaterial science community in general. With the gained insight, we aspire toexpand the possibilitiesof biomaterial and biomedical applications of this technique.

Post-Processing Trimming of Silicon Photonic Devices Using Femtosecond Laser

Fabrication errors inevitably occur in device manufacturing owing to the limited processing accuracy of commercial silicon photonic processes. For silicon photonic devices, which are mostly processing-sensitive, their performances usually deteriorate significantly. This remains an unsolved issue for mass production, particularly for passive devices, because they cannot be adjusted once fixed in processes. This study presents a post-processing trimming method to compensate for fabrication errors by changing the cladding equivalent refractive indices of devices with femtosecond lasers. The experimental results show that the resonant wavelengths of micro-ring resonators can be regularly shifted within their free spectral range via tuning the illuminating area, focusing position, emitting power, and scanning speed of the trimming femtosecond laser with an acceptable loss increase. These experiments, as well as the trimming experiments in improving the phase balance of Mach-Zehnder interferometer switches, indicate that the femtosecond laser trimming method is an effective and fast method for silicon photonic devices.

Femtosecond Laser Ablation of Quantum Dot Films toward Physical Unclonable Multilevel Fluorescent Anticounterfeiting Labels

Femtosecond laser ablation (FsLA) technology has been demonstrated to achieve programmable ablation and removal of diverse materials with high precision. Owing to the cross-scale and digital processing characteristics, the FsLA technology has attracted increasing interest. However, the moderate repeatability of FsLA limits its application in the fabrication of advanced micro-/nanostructures due to the nonidentity of each laser pulse and fluctuation of environment. Fortunately, moderate repeatability combined with programmable ablation and high precision perfectly matches with the technical requirements of a physical unclonable fluorescent anticounterfeiting label. Herein, we applied FsLA to quantum dot (QD) films to fabricate a physical unclonable multilevel fluorescent anticounterfeiting label. Visual Jilin University logos, quick response (QR) codes, microlines, and microholes have been achieved for the multilevel anticounterfeiting functions. Of particular significance, the microholes with a macroidentical and microidentifiable geometry guarantee the physical unclonable functions (PUFs). Moreover, the fluorescent anticounterfeiting label is compatible with deep learning algorithms that facilitate authentication to be convenient and accurate. This work shows a fantastic future potential to be a core anticounterfeiting technique for commercial products and drugs.

Microfluidic Chip with Fiber-Tip Sensors for Synchronously Monitoring Concentration and Temperature of Glucose Solutions

Monitoring the properties of fluids in microfluidic chips often requires complex open-space optics technology and expensive equipment. In this work, we introduce dual-parameter optical sensors with fiber tips into the microfluidic chip. Multiple sensors were distributed in each channel of the chip, which enabled the real-time monitoring of the concentration and temperature of the microfluidics. The temperature sensitivity and glucose concentration sensitivity could reach 314 pm/°C and -0.678 dB/(g/L), respectively. The hemispherical probe hardly affected the microfluidic flow field. The integrated technology combined the optical fiber sensor with the microfluidic chip and was low cost with high performance. Therefore, we believe that the proposed microfluidic chip integrated with the optical sensor is beneficial for drug discovery, pathological research and material science investigation. The integrated technology has great application potential for micro total analysis systems (μ-TAS).

Optimization mechanism and applications of ultrafast laser machining towards highly designable 3D micro/nano structuring

Three-dimensional (3D) micro/nano structures are significant in many applications because of their novel multi-functions and potential in high integration. As is known, the traditional methods for the processing of 3D micro/nano structures exhibit disadvantages in mass production and machining precision. Alternatively, ultrafast laser machining, as a rapid and high-power-density processing method, exhibits advantages in 3D micro/nano structuring due to its characteristics of extremely high peak power and ultra-short pulse. With the development of ultrafast laser processing for fine and complex structures, it is attracting significant interest and showing great potential in the manufacture of 3D micro/nano structures. In this review, we introduce the optimization mechanism of ultrafast laser machining in detail, such as the optimization of the repetition rate and pulse energy of the laser. Furthermore, the specific applications of 3D micro/nano structures by laser processing in the optical, electrochemical and biomedical fields are elaborated, and a valuable summary and perspective of 3D micro/nano manufacturing in these fields are provided.

Femtosecond Laser Induced Lattice Deformation in KTN Crystal

In recent years, many novel optical phenomena have been discovered based on perovskite materials, but the practical applications are limited because of the difficulties of device fabrication. Here, we propose a method to directly induce localized lattice modification inside the potassium tantalate niobate crystal by using the femtosecond laser. This selective modification at the processed regions and the surrounding areas is characterized by two-dimensional Raman spectrum mapping. The spectrum variations corresponding to specific lattice vibration modes demonstrate the lattice structure deformation. In this way, the lattice expansion at the femtosecond laser irradiated regions and the lattice compression at the surrounding areas are revealed. Furthermore, surface morphology measurement confirms this lattice expansion and suggests the extension of lattice structure along the space diagonal direction. Moreover, the existence of an amorphization core is revealed. These modifications on the sample lattice can induce localized changes in physicochemical properties; therefore, this method can realize the fabrication of both linear diffraction and nonlinear frequency conversion devices by utilizing the novel optical responses of perovskite materials.

Emerging applications of femtosecond laser fabrication in neurobiological research

As a typical micro/nano processing technique, femtosecond laser fabrication provides the opportunity to achieve delicate microstructures. The outstanding advantages, including nanoscale feature size and 3D architecting, can bridge the gap between the complexity of the central nervous system in virto and in vivo. Up to now, various types of microstructures made by femtosecond laser are widely used in the field of neurobiological research. In this mini review, we present the recent advancement of femtosecond laser fabrication and its emerging applications in neurobiology. Typical structures are sorted out from nano, submicron to micron scale, including nanoparticles, micro/nano-actuators, and 3D scaffolds. Then, several functional units applied in neurobiological fields are summarized, such as central nervous system drug carriers, micro/nano robots and cell/tissue scaffolds. Finally, the current challenges and future perspective of integrated neurobiology research platform are discussed.

Reconfigurable, Reversible, and Redefinable Deformation of GO Based on Quantum-Confined-Superfluidics Effect

Graphene oxide (GO) films with natural "quantum-confined-superfluidics" (QSF) channels for moisture actuation have emerged as a smart material for actuators and soft robots. However, programming the deformation of GO by engineering QSF nanochannels around 1 nm is extremely challenging. Herein, we report the reconfigurable, reversible, and redefinable deformation of GO under moisture actuation by tailoring QSF channels via moisture-assisted strain-induced wrinkling (MSW). The shape fixity ratio of a general GO film can reach ∼84% after the MSW process, and the shape recovery ratio is ∼83% at room temperature under moisture actuation. The flexible shaping and deformation abilites, as well as the self-healing property of GO make it possible to fabricate soft robots using GO. Besides, as a proof-of-concept, passive electronics and soft robots capable of crawling, turning, switching circuit, and automatic somersault are demonstrated. With unique shaping and deformation abilities, GO may bring great implications for future soft robotics.

Edge State, Localization Length, and Critical Exponent from Survival Probability in Topological Waveguides

Edge states in topological phase transitions have been observed in various platforms. To date, verification of the edge states and the associated topological invariant are mostly studied, and yet a quantitative measurement of topological phase transitions is still lacking. Here, we show the direct measurement of edge states and their localization lengths from survival probability. We employ photonic waveguide arrays to demonstrate the topological phase transitions based on the Su-Schrieffer-Heeger model. By measuring the survival probability at the lattice boundary, we show that in the long-time limit, the survival probability is P=(1-e^{-2/ξ_{loc}})^{2}, where ξ_{loc} is the localization length. This length derived from the survival probability is compared with the distance from the transition point, yielding a critical exponent of ν=0.94±0.04 at the phase boundary. Our experiment provides an alternative route to characterizing topological phase transitions and extracting their key physical quantities.

Femtosecond Laser-Assisted Ophthalmic Surgery: From Laser Fundamentals to Clinical Applications

Femtosecond laser (FSL) technology has created an evolution in ophthalmic surgery in the last few decades. With the advantage of high precision, accuracy, and safety, FSLs have helped surgeons overcome surgical limits in refractive surgery, corneal surgery, and cataract surgery. They also open new avenues in ophthalmic areas that are not yet explored. This review focuses on the fundamentals of FSLs, the advantages in interaction between FSLs and tissues, and typical clinical applications of FSLs in ophthalmology. With the rapid progress that has been made in the state of the art research on FSL technologies, their applications in ophthalmic surgery may soon undergo a booming development.

A fine single Pd microwire H2 sensor fabricated by using a femtosecond laser for a wide detection range at room temperature

We reported a fine H2 sensor based on single Pd microwires (SPMs) by femtosecond-laser-induced deposition of palladium nanoparticles (PdNPs), which exhibits excellent H2 sensing performance. The PdNPs with good dispersion were prepared by ultrasonic assisted one-step solution synthesis. The sensor has a wide detection range of 0.001-4.0% H2 sensing at room temperature. With the increase of the H2 concentration, the SPM sensor presents two sensing mechanisms, the formation of PdH x and hydrogen induced lattice expansion regulating the conductivity of SPMs. This fine hydrogen sensor is promising to be applied to human health monitoring, environmental air detection and other integrated intelligent devices.

Femtosecond laser direct writing of a 3D microcantilever on the tip of an optical fiber sensor for on-chip optofluidic sensing

Real-time detection of the concentration of input fluid is essential for optofluidic sensing, especially in the case of biochips and organ-on-a-chip systems. In this paper, a microcantilever structure that enables temperature and liquid concentration sensing was fabricated on the tip of the optical fiber by femtosecond laser direct writing (two-photon polymerization, TPP) technology. An open Fabry-Pérot interferometer (F-P) structure was formed between the end of the optical fiber and the cantilever, so the sensor becomes quite sensitive to the localized temperature, concentration and refractive index of the target liquids. The reasonable size parameters of the cantilever were determined by structural stress analysis and interference spectrum analysis. By integrating the fiber sensor with a microfluidic chip, an on-chip optofluidic sensing platform is developed, which shows high sensitivities of the temperature (92.7 pm °C^-1), concentration (0.3287 nm (g L^-1)^-1), and refractive index (1385.819 nm RIU^-1). The reported optofluidic sensing platform demonstrates reasonably high stability and satisfactory sensing effect, holding great promise for applications in lab-on-a-chip systems.

Miniature optoelectronic compound eye camera

Inspired by insect compound eyes (CEs) that feature unique optical schemes for imaging, there has recently been growing interest in developing optoelectronic CE cameras with comparable size and functions. However, considering the mismatch between the complex 3D configuration of CEs and the planar nature of available imaging sensors, it is currently challenging to reach this end. Here, we report a paradigm in miniature optoelectronic integrated CE camera by manufacturing polymer CEs with 19~160 logarithmic profile ommatidia via femtosecond laser two-photon polymerization. In contrast to μ-CEs with spherical ommatidia that suffer from defocusing problems, the as-obtained μ-CEs with logarithmic ommatidia permit direct integration with a commercial CMOS detector, because the depth-of-field and focus range of all the logarithmic ommatidia are significantly increased. The optoelectronic integrated μ-CE camera enables large field-of-view imaging (90°), spatial position identification and sensitive trajectory monitoring of moving targets. Moreover, the miniature μ-CE camera can be integrated with a microfluidic chip and serves as an on-chip camera for real-time microorganisms monitoring. The insect-scale optoelectronic μ-CE camera provides a practical route for integrating well-developed planar imaging sensors with complex micro-optics elements, holding great promise for cutting-edge applications in endoscopy and robot vision.

Rapid and Multimaterial 4D Printing of Shape-Morphing Micromachines for Narrow Micronetworks Traversing

Micromachines with high environmental adaptability have the potential to deliver targeted drugs in complex biological networks, such as digestive, neural, and vascular networks. However, the low processing efficiency and single processing material of current 4D printing methods often limit the development and application of shape-morphing micromachines (SMMs). Here, two 4D printing strategies are proposed to fabricate SMMs with pH-responsive hydrogels for complex micro-networks traversing. On the one hand, the 3D vortex light single exposure technique can rapidly fabricate a tubular SMM with controllable size and geometry within 0.1 s. On the other hand, the asymmetric multimaterial direct laser writing (DLW) method is used to fabricate SMMs with designable 3D structures composed of hydrogel and platinum nanoparticles (Pt NPs). Based on the presence of ferroferric oxide (Fe₃ O₄ ) and Pt NPs in the SMMs, efficient magnetic, bubble, and hybrid propulsion modes are achieved. Finally, it is demonstrated that the spatial shape conversion capabilities of these SMMs can be used for narrow micronetworks traversing, which will find potential applications in targeted cargo delivery in microcapillaries.

Bubble-pen lithography: Fundamentals and applications: Nanoscience: Special Issue Dedicated to Professor Paul S. Weiss

Developing on-chip functional devices requires reliable fabrication methods with high resolution for miniaturization, desired components for enhanced performance, and high throughput for fast prototyping and mass production. Recently, laser-based bubble-pen lithography (BPL) has been developed to enable sub-micron linewidths, in situ synthesis of custom materials, and on-demand patterning for various functional components and devices. BPL exploits Marangoni convection induced by a laser-controlled microbubble to attract, accumulate, and immobilize particles, ions, and molecules onto different substrates. Recent years have witnessed tremendous progress in theory, engineering, and application of BPL, which motivated us to write this review. First, an overview of experimental demonstrations and theoretical understandings of BPL is presented. Next, we discuss the advantages of BPL and its diverse applications in quantum dot displays, biological and chemical sensing, clinical diagnosis, nanoalloy synthesis, and microrobotics. We conclude this review with our perspective on the challenges and future directions of BPL.

Functional Shape-Morphing Microarchitectures Fabricated by Dynamic Holographically Shifted Femtosecond Multifoci

Functional microdevices based on responsive hydrogel show great promise in targeted delivery and biomedical analysis. Among state-of-the-art techniques for manufacturing hydrogel-based microarchitectures, femtosecond laser two-photon polymerization distinguishes itself by high designability and precision, but the point-by-point writing scheme requires mechanical apparatuses to support focus scanning. In this work, by predesigning holograms combined with lens phase modulation, multiple femtosecond laser spots are holographically generated and shifted for prototyping of three-dimensional shape-morphing structures without any moving equipment in the construction process. The microcage array is rapidly fabricated for high-performance target capturing enabled by switching environmental pH. Moreover, the built scaffolds can serve as arrayed analytical platforms for observing cell behaviors in normal or changeable living spaces or revealing the anticancer effects of loaded drugs. The proposed approach opens a new path for facile and flexible manufacturing of hydrogel-based functional microstructures with great versatility in micro-object manipulation.

Fabry-Perot Interferometer Based on a Fiber-Tip Fixed-Supported Bridge for Fast Glucose Concentration Measurement

Blood glucose concentration is important for metabolic homeostasis in humans and animals. Many diabetic patients need to detect blood glucose daily which burdens community hospitals and family healthcare. Optical fiber sensors are widely used in biomedical detection because of their compact structure, fast response, high sensitivity, low cost, and ease of operation. In this work, we constructed a Fabry-Perot (FP) cavity biosensor for the fast detection of glucose concentration in serum. The femtosecond laser micromachining was applied to fabricate the FP cavity by printing the fiber-tip fixed-supported bridge at the end face of the optical fiber. An additional hemisphere was printed at the center of the outer surface of the bridge to avoid multi-beam interference. The results demonstrated that the proposed biosensor had high refractive index (RI) detection sensitivity, roughly 1039 nm/RIU at a wavelength of 1590 nm, and the detection sensitivity for glucose was around 0.185 nm/ (mg/mL) at a wavelength of 1590 nm. Due to its high sensitivity, compact structure, and fast response, the FP cavity biosensor has great potential to be applied in family healthcare for glucose concentration detection of diabetic patients.

Creating three-dimensional magnetic functional microdevices via molding-integrated direct laser writing

Magnetically driven wireless miniature devices have become promising recently in healthcare, information technology, and many other fields. However, they lack advanced fabrication methods to go down to micrometer length scales with heterogeneous functional materials, complex three-dimensional (3D) geometries, and 3D programmable magnetization profiles. To fill this gap, we propose a molding-integrated direct laser writing-based microfabrication approach in this study and showcase its advanced enabling capabilities with various proof-of-concept functional microdevice prototypes. Unique motions and functionalities, such as metachronal coordinated motion, fluid mixing, function reprogramming, geometrical reconfiguring, multiple degrees-of-freedom rotation, and wireless stiffness tuning are exemplary demonstrations of the versatility of this fabrication method. Such facile fabrication strategy can be applied toward building next-generation smart microsystems in healthcare, robotics, metamaterials, microfluidics, and programmable matter.

Recent Advances in Silver Nanowires Electrodes for Flexible Organic/Perovskite Light-Emitting Diodes

Flexible organic light-emitting diodes and perovskite light-emitting diodes (PeLEDs) have been investigated as an innovative category of revolutionary LED devices for next-generation flat display and lighting applications. A transparent conductive electrode is a key component in flexible OLEDs and PeLEDs, and has been the limitation of the development in this area. Silver nanowires (AgNWs) have been regarded as the most suitable alternative material in TCEs, due to the economical solution synthesis and compatibility with roll-to-roll technology. This mini-review addresses the advances in silver nanowires electrodes for flexible organic/perovskite light-emitting diodes, and the relationship between electrode optimization and device performance is demonstrated. Moreover, the potential strategies and perspectives for their further development of AgNWs-based flexible OLEDs and PeLEDs are presented.

All-fiber mode-locked gigahertz femtosecond laser at 1610 nm using a self-developed long-wavelength gain fiber

We report a compact all-fiber passively mode-locked ultrafast laser with a fundamental repetition rate of 1.6 GHz that uses a self-developed long-wavelength active fiber, i.e., a fluoro-sulfo-phosphate-based Er³⁺/Yb³⁺ co-doped fiber (only 6.2 cm in length). This active fiber can provide a net gain coefficient of 0.6 dB/cm at 1610 nm. The high-repetition-rate all-fiber mode-locked laser operates at a low pump power of only approximately 90 mW. The mode-locked pulse train has a period of 625 ps and a 3 dB bandwidth of 7.0 nm, which can support a transform-limited pulse width of 390 fs.

Polarization-dependent Bloch oscillations in optical waveguides

Optical systems provide a new and practical platform for studying Bloch oscillations. This study investigates the fundamental-mode propagation of polarization-dependent Bloch oscillations. By using the three-dimensional properties of femtosecond laser direct writing, we fabricate a polymer-based gradient waveguide array and determine the Bloch oscillations under different polarization inputs by using the birefringence gradient and the equivalent refractive index, thus exhibiting a polarization-dependent Bloch period. Our results provide a new, to the best of our knowledge, paradigm for two-dimensional optical Bloch modes and highlight the influence of optical polarization in the same system, which provides a possibility to observe richer physics related to Bloch oscillations in one structure.

High-resolution in situ patterning of perovskite quantum dots via femtosecond laser direct writing

Colloidal quantum dots (QDs) have exhibited great potential for optoelectronic applications, including displays, lasers, anti-counterfeiting and information storage. However, the high-resolution patterning technique of QDs is still a challenge, while precise patterned QDs are of great value for practical applications. Here, a femtosecond laser direct writing strategy was demonstrated for the in situ fabrication of high-resolution-patterned perovskite quantum dots (PQDs) by the laser-induced Marangoni flow to aggregate and deposit the PQDs based on the opto-thermoelectric mechanism. By regulating the laser power and the exposure time, the minimum line width could reach 1.58 μm. Importantly, through the patterning of red, green and blue PQDs, the strategy exhibited the applicability in full-color PQD materials. Moreover, the deposited PQDs can preserve the original photophysical properties including photoluminescence spectra and excited state lifetime. The approach provides a strategy to fabricate high-resolution patterned PQDs in situ, which is a promising alternative in photonic applications including high-resolution displays and anti-counterfeiting.

Fully Room-Temperature Reprogrammable, Reprocessable, and Photomobile Soft Actuators from a High-Molecular-Weight Main-Chain Azobenzene Crystalline Poly(ester-amide)

Azobenzene (azo) polymer photoactuators with full room-temperature reprogrammability, reprocessability, and photomobility are highly desirable for large-scale applications, but their development remains a daunting challenge. Herein, a strategy is first presented for fabricating such advanced photoactuators from a high-molecular-weight main-chain azo crystalline poly(ester-amide) (PEA) prepared via Michael addition polymerization. This azo PEA can be readily processed into both physically cross-linked, uniaxially oriented fibers and films with high mechanical robustness and reversible photoinduced bending/unbending at room temperature. Importantly, the presence of both amide unit-induced hydrogen bonding and crystalline domains in such films and fibers endows them with dynamic, yet stable cross-linking points, which enable their easy reprogrammability under strain at room temperature into various three-dimensional (3D) shapes (e.g., film helicoid and spiral ribbon, fiber spring) capable of showing completely different shape-dependent photomobile modes. In particular, these reshaped photoactuators can maintain their accurate 3D shapes and highly reversible photoinduced motions even after being kept at 80 °C for 20 days or at 100 °C for 2 days. They can also be reprocessed and recycled from solution at room temperature. Such a multifunctional main-chain azo crystalline PEA can serve as a versatile platform for fabricating various photoactuators with desired 3D shapes and motion modes under mild ambient conditions.

Micro-/Nano-Structures Fabricated by Laser Technologies for Optoelectronic Devices

Due to unique optical and electrical properties, micro-/nano-structures have become an essential part of optoelectronic devices. Here, we summarize the recent developments in micro-/nano-structures fabricated by laser technologies for optoelectronic devices. The fabrication of micro-/nano-structures by various laser technologies is reviewed. Micro-/nano-structures in optoelectronic devices for performance improvement are reviewed. In addition, typical optoelectronic devices with micro-nano structures are also summarized. Finally, the challenges and prospects are discussed.