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The growing importance of submicrometer‐structured surfaces across a variety of different fields has driven progress in light manipulation, color diversity, water‐repellency, and functional enhancements. To enable mass production, processes like hot‐embossing (HE), roll‐to‐roll replication (R2R), and injection molding (IM) are essential due to their precision and material flexibility. However, these processes are tool‐based manufacturing (TBM) techniques requiring metal molds, which are time‐consuming and expensive to manufacture, as they mostly rely on galvanoforming using templates made via precision microlithography or two‐photon‐polymerization (2PP). In this work, a novel approach is demonstrated to replicate amorphous metals from fused silica glass, derived from additive manufacturing and structured using hot embossing and casting, enabling the fabrication of metal insets with features in the range of 300 nm and a surface roughness of below 10 nm. By partially crystallizing the amorphous metal, during the replication process, the insets gain a high hardness of up to 800 HV. The metal molds are successfully used in polymer injection molding using different polymers including polystyrene (PS) and polyethylene (PE) as well as glass nanocomposites. This work is of significant importance to the field as it provides a production method for the increasing demand for sub‐micron‐structured tooling in the area of polymer replication while substantially reducing their cost of production. [ABSTRACT FROM AUTHOR]

Two‐photon lithography (TPL) is a powerful tool for 3D nanofabrication, however, high‐throughput TPL remains challenging, especially for cationic‐based photoresists. A novel cationic‐based photoresist named TP‐EO is developed for high‐throughput and high‐resolution TPL nanofabrication. High‐speed fabrication is achieved by using a bimolecular photosensitizer‐photo acid generator (PS‐PAG) pair that can effectively solve the photosensitivity bottleneck in cationic‐based photoresists. High‐resolution nanofabrication is achieved by limiting the photoacid diffusion via tuning the monomer's intra‐ and inter‐molecular stereo‐structure. The fabrication of 3D structures is demonstrated with fine features (<200 nm), fast writing speed (100 mm s−1), and low shrinkage, and showcased the rapid fabrication of centimeter‐scale nanodevices. TP‐EO photoresist shows outstanding TPL fabrication speed and resolution among cationic‐based photoresists, making it a promising solution for high‐throughput 3D nanomanufacturing. [ABSTRACT FROM AUTHOR]

The continuous exchange between the neuroscience and neuroengineering communities that took place over the past decades has uncovered a multitude of technological solutions to interface with the brain. In this framework, a fascinating approach relies on the integration of multiple activation and monitoring capabilities in the same implantable neural probe to better study the multifaceted nature of neural signaling and related functions in the deep brain regions. We highlight current challenges and perspectives on technological developments that could potentially enable the integration of multiple functionalities on optical fiber-based non-planar implantable neurophotonics probes. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to provide a microfluidic blood glucose sensing platform based on integrated interdigitated electrode arrays (IDEAs) on a flexible quartz glass substrate, adhering closely to pertinent electrochemical characterizations. Design/methodology/approach: Sensors are the key elements of the modern electronics era through which all the possible physical quantities can be detected and converted into their equivalent electrical form and processed further. But to make the sensing environment better, various types of innovative architectures are being developed nowadays and among them interdigitated electrodes are quite remarkable in terms of their sensing capability. They are a well-qualified candidate in the field of gas sensing and biosensing, but even their sensitivities are getting saturated due to their physical dimensions. Most of the thin film IDEAs fabricated by conventional optical lithographic techniques do not possess a high surface-to-volume ratio to detect the target specified and that reduces their sensitivity factor. In this context, a classic conductive carbon-based highly sensitive three dimensional (3D) IDEA-enabled biosensing system has been conceived on a transparent and flexible substrate to measure the amount of glucose concentration present in human blood. 3D IDEA possesses a way better capacitive sensing behavior compared to conventional thin film microcapacitive electrodes. To transmit the target biological analyte sample property for the detection purpose to the interdigitated array-based sensing platform, the design of a microfluidic channel is initiated on the same substrate. The complex 3D Inter Digital array structure improves the overall capacitance of the entire sensing platform and the reactive surface area as well. The manufactured integrated device displays a decent value of sensitivity in the order of 5.6 µA mM−1 cm−2. Findings: Development of a low-cost array-based integrated and highly flexible microfluidic biochip to extract the quantity of glucose present in human blood. Originality/value: Potential future research opportunities in the realm of integrated miniaturized, low-cost smart biosensing systems may arise from this study. [ABSTRACT FROM AUTHOR]

In this study, we investigate the potential of two-photon lithography (2PL) as a solution to the challenges encountered in conventional membrane fabrication techniques, aiming to fabricate tailor-made membranes with high-resolution submicron pore structures suitable for advanced applications. This approach led to the development of fabrication techniques and printed membranes that can be adapted to various lab-on-a-chip (LOC) devices. Membranes were fabricated with pore diameters as small as 0.57 µm and porosities of 4.5%, as well as with larger pores of approximately 3.73 µm in diameter and very high porosities that reached up to 60%. Direct 3D printing of membranes offers a pathway for fabricating structures tailored to specific applications in microfluidics, enabling more efficient separation processes at miniature scales. This research represents a significant step towards bridging the gap between membrane technology and microfluidics, promising enhanced capabilities for a wide array of applications in biotechnology, chemical analysis, and beyond. [ABSTRACT FROM AUTHOR]

In this study, we investigate the potential of two-photon lithography (2PL) as a solution to the challenges encountered in conventional membrane fabrication techniques, aiming to fabricate tailor-made membranes with high-resolution submicron pore structures suitable for advanced applications. This approach led to the development of fabrication techniques and printed membranes that can be adapted to various lab-on-a-chip (LOC) devices. Membranes were fabricated with pore diameters as small as 0.57 µm and porosities of 4.5%, as well as with larger pores of approximately 3.73 µm in diameter and very high porosities that reached up to 60%. Direct 3D printing of membranes offers a pathway for fabricating structures tailored to specific applications in microfluidics, enabling more efficient separation processes at miniature scales. This research represents a significant step towards bridging the gap between membrane technology and microfluidics, promising enhanced capabilities for a wide array of applications in biotechnology, chemical analysis, and beyond.

Multi‐photon 3D laser printing has gathered much attention in recent years as a means of manufacturing biocompatible scaffolds that can modify and guide cellular behavior in vitro. However, in vivo tissue engineering efforts have been limited so far to the implantation of beforehand 3D printed biocompatible scaffolds and in vivo bioprinting of tissue constructs from bioinks containing cells, biomolecules, and printable hydrogel formulations. Thus, a comprehensive 3D laser printing platform for in vivo and in situ manufacturing of microimplants raised from synthetic polymer‐based inks is currently missing. Here, a platform for minimal‐invasive manufacturing of microimplants directly in the organism is presented by one‐photon photopolymerization and multi‐photon 3D laser printing. Employing a commercially available elastomeric ink giving rise to biocompatible synthetic polymer‐based microimplants, first applicational examples of biological responses to in situ printed microimplants are demonstrated in the teleost fish Oryzias latipes and in embryos of the fruit fly Drosophila melanogaster. This provides a framework for future studies addressing the suitability of inks for in vivo 3D manufacturing. The platform bears great potential for the direct engineering of the intricate microarchitectures in a variety of tissues in model organisms and beyond. [ABSTRACT FROM AUTHOR]

Tailoring the properties of microfabricated ceramics through doping can unlock new avenues for the additive manufacturing (AM) of advanced 3D architectures. The first step to achieving optical functionality is to control material morphology, crystallinity, and defects associated with the composition of the produced AM architecture and dopants. For this purpose, AM of zinc‐doped zirconia (ZrO2:Zn) 3D microarchitectures is proposed using two‐photon lithography and tailor‐made resin. It is found that Zn doping modulates ZrO2:Zn architecture crystallinity and optical properties. The modification of optical properties through Zn doping is confirmed by micro‐photoluminescence, where higher energy photon emission is observed due to the promotion of oxygen vacancies and surface defects. It is also shown that Zn 2.5% and 5 wt% stabilizes the monoclinic ZrO2 at a lower temperature than in the case of undoped ZrO2. Furthermore, there is evidence that Zn tends to form ZnO wurtzite, which is later sublimated. The findings provide a promising route to understand the role of defects ZrO2:Zn optically upon annealing. [ABSTRACT FROM AUTHOR]

Transparent polycrystalline magnesium aluminate (MAS) spinel ceramics are of great interest for industry and academia due to their excellent optical and mechanical properties. However, shaping of MAS is notoriously challenging especially on the microscale requiring hazardous etching methods. Therefore, a photochemically curable nanocomposite is demonstrated that can be structured using high‐resolution two‐photon lithography. The printed nanocomposites are converted intro transparent MAS by subsequent debinding, sintering, and hot isostatic pressing. The resulting transparent spinel ceramics exhibit a surface roughness Sq of only 10 nm and can be shaped with minimum feature sizes of down to 13 µm. This technology will be important for the production of microstructured ceramics used for optics, photonics, or photocatalysis. [ABSTRACT FROM AUTHOR]

This study presents a novel approach for investigating the shrinkage dynamics of 3D‐printed nanoarchitectures during isothermal pyrolysis, utilizing in situ electron microscopy. For the first time, the temporal evolution of 3D structures is tracked continuously until a quasi‐stationary state is reached. By subjecting the 3D objects to different temperatures and atmospheric conditions, significant changes in the resulting kinetic parameters and morphological textures of the 3D objects are observed, particularly those possessing varying surface‐to‐volume ratios. Its results reveal that the effective activation energy required for pyrolysis‐induced morphological shrinkage is approximately four times larger under vacuum conditions than in a nitrogen atmosphere (2.6 eV vs. 0.5–0.9 eV, respectively). Additionally, a subtle enrichment of oxygen on the surfaces of the structures for pyrolysis in nitrogen is found through a postmortem electron energy loss spectroscopy study, differentiating the vacuum pyrolysis. These findings are examined in the context of the underlying process parameters, and a mechanistic model is proposed. As a result, understanding and controlling pyrolysis in 3D structures of different geometrical dimensions not only enables precise modification of shrinkage and the creation of tensegrity structures, but also promotes pyrolytic carbon development with custom architectures and properties, especially in the field of carbon micro‐ and nano‐electromechanical systems. [ABSTRACT FROM AUTHOR]

Photonic integrated circuits (PICs) have long been considered as disruptive platforms that revolutionize optics. Building on the mature industrial foundry infrastructure for electronic integrated circuit fabrication, the manufacturing of PICs has made remarkable progress. However, the packaging of PICs has often become a major barrier impeding their scalable deployment owing to their tight optical alignment tolerance, and hence, the requirement for specialty packaging instruments. Two-photon lithography (TPL), a laser direct-write three-dimensional (3-D) patterning technique with deep subwavelength resolution, has emerged as a promising solution for integrated photonics packaging. This study provides an overview of the technology, emphasizing the latest advances in TPL-enabled packaging schemes and their prospects for adoption in the mainstream photonic industry.

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. [ABSTRACT FROM AUTHOR]

Abstract Transparent polycrystalline magnesium aluminate (MAS) spinel ceramics are of great interest for industry and academia due to their excellent optical and mechanical properties. However, shaping of MAS is notoriously challenging especially on the microscale requiring hazardous etching methods. Therefore, a photochemically curable nanocomposite is demonstrated that can be structured using high‐resolution two‐photon lithography. The printed nanocomposites are converted intro transparent MAS by subsequent debinding, sintering, and hot isostatic pressing. The resulting transparent spinel ceramics exhibit a surface roughness Sq of only 10 nm and can be shaped with minimum feature sizes of down to 13 µm. This technology will be important for the production of microstructured ceramics used for optics, photonics, or photocatalysis.

Abstract Two-photon lithography has emerged as a highly effective method for fabricating intricate three-dimensional (3D) microstructures. It enables the rapid fabrication of 3D microstructures, unlike conventional two-dimensional nanopatterning. Researchers have extensively investigated two-photon polymerization (TPP) for the fabrication of diverse 3D micro/nanodevices with high resolution. TPP can be applied in cell cultures, metamaterials, optical materials, electrical devices, and fluidic devices, to name a few. In this study, we investigate the applications and innovative research pertaining to TPP, which is an effective fabrication technique with significant advancement in various fields. In particular, we attempt to determine the reasons that cause the detachment or delamination of 3D microstructures during the development process and propose some solutions. A step-by-step fabrication process for a glass substrate, from photoresist deposition to laser scanning and the dissolution of the uncured photoresist, is presented. Defects such as pattern delamination are discussed, with emphasis on the cell scaffold structure and microlens array. Understanding and addressing these defects are vital to the success of 3D microstructure fabrication via TPP.

Two‐photon lithography (TPL) is an advanced high‐resolution additive manufacturing technique for objects with feature sizes between 100 nanometers to tens of micrometers and an overall footprint of up to hundreds of micrometers. With recent advances in the TPL technique, writing speeds are becoming faster, rendering the method feasible to print high‐resolution microfluidic chips with a footprint in the centimeter range within a reasonable time frame. In this work, a process flow to fabricate embedded microfluidic chips with channel diameters down to 30 µm is developed. To address the particular difficulty of washing the embedded channels free of uncured material, introduces a developing scheme based on a 3D printed chip‐to‐world‐interface to connect the chips to a pressure‐driven pump. This setup is leakage‐free up to a pressure of 6.9 bar for faster and safer development of embedded microfluidic devices. It manufactures meander chips with channel lengths up to 20 cm, droplet generator chips, and cell sorting chips based on deterministic lateral displacement with pillar diameters of 30 µm and pillar spacing of 4 µm. TPL of microfluidic chips will enable rapid manufacturing of novel designs, significantly reducing concept‐to‐chip times with high resolution in a reasonable amount of time. [ABSTRACT FROM AUTHOR]

Two‐Photon Lithography, thanks to its very high sub‐diffraction resolution, has become the lithographic technique par excellence in applications requiring small feature sizes and complex 3D pattering. Despite this, the fabrication times required for extended structures remain much longer than those of other competing techniques (UV mask lithography, nanoimprinting, etc.). Its low throughput prevents its wide adoption in industrial applications. To increase it, over the years different solutions have been proposed, although their usage is difficult to generalize and may be limited depending on the specific application. A promising strategy to further increase the throughput of Two‐Photon Lithography, opening a concrete window for its adoption in industry, lies in its combination with holography approaches: in this way it is possible to generate dozens of foci from a single laser beam, thus parallelizing the fabrication of periodic structures, or to engineer the intensity distribution on the writing plane in a complex way, obtaining 3D microstructures with a single exposure. Here, the fundamental concepts behind high‐speed Two‐Photon Lithography and its combination with holography are discussed, and the literary production of recent years that exploits such techniques is reviewed, and contextualized according to the topic covered. [ABSTRACT FROM AUTHOR]

Two-photon lithography has emerged as a highly effective method for fabricating intricate three-dimensional (3D) microstructures. It enables the rapid fabrication of 3D microstructures, unlike conventional two-dimensional nanopatterning. Researchers have extensively investigated two-photon polymerization (TPP) for the fabrication of diverse 3D micro/nanodevices with high resolution. TPP can be applied in cell cultures, metamaterials, optical materials, electrical devices, and fluidic devices, to name a few. In this study, we investigate the applications and innovative research pertaining to TPP, which is an effective fabrication technique with significant advancement in various fields. In particular, we attempt to determine the reasons that cause the detachment or delamination of 3D microstructures during the development process and propose some solutions. A step-by-step fabrication process for a glass substrate, from photoresist deposition to laser scanning and the dissolution of the uncured photoresist, is presented. Defects such as pattern delamination are discussed, with emphasis on the cell scaffold structure and microlens array. Understanding and addressing these defects are vital to the success of 3D microstructure fabrication via TPP. [ABSTRACT FROM AUTHOR]

Two-photon lithography (TPL) is a representative fabrication process for micro 3D structures with a sub-micron fabrication resolution. As the TPL process is developed and commercialized, the TPL process requires higher process yield to be a considered reliable manufacturing technique for mass production. However, delamination is one of the main factors that reduce the yield of the TPL process. In this study, a double-step laser scanning method is proposed as a reliable high-yield TPS process to reduce the delamination effect. The method entails a simple process that polymerizes the initial interfacial layer between the structures and substrate twice. The additional laser scanning step induces a strong crosslinking in the polymer, and thereby preventing swelling and delamination. Furthermore, the effectiveness of the method is evaluated with large-scale microlens arrays. Although the process time is slightly increased, the process yield is significantly improved through the use of the double-step laser scanning method. Hence, the double-step laser scanning process can be employed as a reliable additive manufacturing process for various 3D microscale devices, and more importantly, it can be used to increase the manufacturing yield through the reduction of defects caused by surface delamination.

Two-photon lithography (TPL) enables the design of novel micromechanical specimens, down to sub-micron resolution, thus extending the possibilities for device and material characterisation and pushing the boundaries of a broad range of miniaturized technologies such as optics, analytics, and medicine. Employing a push-to-pull geometry, incorporating double edge notched tension specimens loaded in mode I, the specimen manufacturing and testing can be automated to a large extent. This allows for the use of large parameter space characterisation methods as the essential work of fracture, with an experimentally simpler to realize compression testing setup. Within this work, a methodology is outlined for automated specimen direct laser writing with a TPL-device and subsequent testing via a nanoindenter. In total, 2100 specimens were manufactured, of which 1997 could be used for evaluation. Estimations for the essential work of fracture of the used photoresist is presented, with regards to influencing parameters such as testing displacement rate and laser writing power. A discussion of its statistical robustness and validity considerations is included. This will act as a basis framework for further statistical fracture evaluation schemes for other resin materials, as well as for probing thin film systems.

Chiral metasurfaces exhibit extraordinary capabilities of steering polarization of electromagnetic waves; and hence offering enormous potential in development of ultrathin components for advanced photonic technologies such as quantum computing and communication, imaging, optical memories and logics. These structures are realized by periodically arranged subwavelength resolved artificial elements (metaelements). Metaelements are mainly metallic, dielectric or metal-dielectric based and their fabrication is a daunting task due to the associated complex fabrication methodologies involving serial, time-consuming processes and sophisticated instrumentation, hence limiting the growth, and application of these metasurfaces to its true potential. To mitigate these issues, we exploited the single-step fabrication capabilities of two-photon polymerization based lithography to generate a range of all-carbon-based dielectric chiral metasurfaces in a carbon-polymer nanocomposite resin. Additionally, theoretical responses of these structures are also calculated. These structures derive their responses from structural chirality. With the advantages of single-step fabrication of any arbitrary structure with sub-wavelength resolved features, along with the capability of rapid prototyping in the proposed material system; this work holds a great potential towards generation of all-carbon metamaterials and 3D metasurfaces for several advanced photonic and optical technologies. [Display omitted] • Two-photon active acrylate-carbon nanocomposites. • Additive manufacturing of chiral metasurfaces. • Optically active two- and three-dimensional micro/nanostructures. • Sub-wavelength resolved features via maskless, single step processing. [ABSTRACT FROM AUTHOR]

Three-dimensional microprinting by two-photon laser lithography is a promising way to manufacture X-ray lenses. However, as the radius of curvature approaches the voxel size, the refractive surface of the lens deviates from the specified shape, that leads to a deterioration in the focusing of X-ray radiation and astigmatism. In this work we suggest a method for correcting a model for 3D printing of a parabolic X-ray lens taking into account the finite voxel size. [ABSTRACT FROM AUTHOR]

Direct laser writing by two‐photon lithography enables the manufacturing of tailored 3D objects, commonly referred to as 3D‐printing, with submicrometer precision. Thereby, new approaches are enabled for miniaturized optical and mechanical devices, where basic material properties act as design guideline and initial input for finite element simulation‐driven device design. These mechanical properties are accessible through micromechanical testing and suitably adapted miniaturized specimens. With direct laser writing, a micromechanical specimen geometry can be readily manufactured without additional postprocessing, enabling the possibility of repetitive sample production and further high‐throughput testing. Widely overhanging features, as in common bending beam or tension specimens, easily cause floating layers as writing artifacts and thereby undefined geometries. Within this work, an approach to overcome this issue is presented. By introducing a slight taper within the geometry at initially printed layers, a reliable sample geometry is achievable without changing the overall mechanical behavior. As showcase geometries, miniaturized notched cantilever and advanced push‐to‐pull devices incorporating a notched tension specimen are detailed. Mechanical testing is conducted in situ and ex situ, and the mechanical influence from introducing a taper to a straight geometry is assessed via a finite element modeling. Thereby, a comprehensive approach for high‐throughput micromechanical testing is established. [ABSTRACT FROM AUTHOR]

Multi-focal laser direct writing (LDW) based on phase-only spatial light modulation (SLM) can realize flexible and parallel nanofabrication with high-throughput potential. In this investigation, a novel approach of combining two-photon absorption, SLM, and vector path-guided by scalable vector graphics (SVGs), termed SVG-guided SLM LDW, was developed and preliminarily tested for fast, flexible, and parallel nanofabrication. Three laser focuses were independently controlled with different paths, which were optimized according to the SVG to improve fabrication and promote time efficiency. The minimum structure width could be as low as 81 nm. Accompanied by a translation stage, a carp structure of 18.10 μm × 24.56 μm was fabricated. This method shows the possibility of developing LDW techniques toward fully electrical systems, and provides a potential way to efficiently engrave complex structures on nanoscales. [ABSTRACT FROM AUTHOR]

Surface-bound 3D micro-magnets are fabricated from photoreactive copolymers filled with magnetic nanoparticles by maskless 3D writing. The structures are generated by 2-photon crosslinking (2PC), which allows direct writing into solid films of composites consisting of magnetic particles and a photoreactive elastomer precursor. With this strategy, it is possible to directly write complex, surface-bound magnetic actuator structures, which generates new opportunities in the fields of microfluidics and bioanalytical systems. Compared to the common 2-photon polymerization, in which the writing process takes place in a liquid resin, the direct writing based on the 2PC method takes place in a solid polymer film (i.e., in the glassy state). [ABSTRACT FROM AUTHOR]

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.

A novel and versatile shape memory ink system allowing 4D printing with light at the macroscale as well as the microscale is presented. Digital light processing (DLP) and direct laser writing (DLW) are selected as suitable 3D printing technologies to cover both regimes. First, a system based on monofunctional isobornyl acrylate and two crosslinkers consisting of a soft and a hard diacrylate is identified and proven to be compatible with both printing techniques. Employing DLP, a large variety of structures exhibiting distinct complexity is printed. These structures range from simple frames to more demanding 3D geometries such as double platform structures, infinity rings, or cubic grids. The shape memory effect is demonstrated for all the 3D geometries. Excellent shape fixity as well as recovery and repeatability is shown. Furthermore, the formulation is adapted for fast 4D printing at the microscale using DLW. Importantly, the 4D printed microstructures display remarkable shape memory properties. The possibility of trapping and releasing microobjects, such as microspheres, is ultimately demonstrated by designing, smart box‐like 4D microstructures that can be thermally actuated—evidencing the versatility and potential of the reported system. [ABSTRACT FROM AUTHOR]

The dispersion of a chiral polymer in a polymerizable matrix can amplify the chirality of the material, and a helical conformation of the chiral material within the polymerized SU-8 excessively increased the circular dichroism. Here, we demonstrate the fabrication of three-dimensional nanostructures of chiral/achiral mixtures by two-photon lithography. The irradiation of light and annealing caused local changes in the chiral material and finally led to the enhancement of the optical properties. The demonstration of a photopatternable chiral material could expand the usage of optical materials for various applications. [ABSTRACT FROM AUTHOR]

Microneedles (MNs) or microneedle arrays (MNAs) are critical components of minimally invasive devices comprised of a single or a series of micro-scale projections. MNs can bypass the outermost layer of the skin and painlessly access microcirculation of the epidermis and dermis layers, attracting great interest in the development of personalized healthcare monitoring and diagnostic devices. However, MN technology has not yet reached its full potential since current micro- and nanofabrication methods do not address the need of fabricating MNs with complex surfaces to facilitate the development of clinically adequate devices. This work presents a new approach that combines 3D printing technology based on two-photon polymerization with soft lithography for cost-effective and time-saving fabrication of complex MNAs. Specifically, this method relies on printing complex 3D objects efficiently replicated into polymeric substrates via soft lithography, resulting in a free-standing polymeric lattice (PL) membrane that can be transferred onto gold-coated MNs and used for electrochemical biosensing. This platform shows excellent electrochemical performance in detecting metabolite (glucose) and protein (insulin) biomarkers with a dynamic linear range sufficient for detecting biomarkers in healthy individuals and patients. The approach holds great potential for fabricating next-generationMNs, including their transfer into clinically adequate devices., (© 2024 Wiley‐VCH GmbH.)

Two-photon lithography has revolutionized multi-photon 3D laser printing, enabling precise fabrication of micro- and nanoscale structures. Despite many advancements, challenges still persist, particularly in biofunctionalization of 3D microstructures. This study introduces a novel approach combining two-photon lithography with scanning probe lithography for post-functionalization of 3D microstructures overcoming limitations in achieving spatially controlled biomolecule distribution. The method utilizes a diverse range of biomolecule inks, including phospholipids, and two different proteins, introducing high spatial resolution and distinct functionalization on separate areas of the same microstructure. The surfaces of 3D microstructures are treated using bovine serum albumin and/or 3-(Glycidyloxypropyl)trimethoxysilane (GPTMS) to enhance ink retention. The study further demonstrates different strategies to create binding sites for cells by integrating different biomolecules, showcasing the potential for customized 3D cell microenvironments. Specific cell adhesion onto functionalized 3D microscaffolds is demonstrated, which paves the way for diverse applications in tissue engineering, biointerfacing with electronic devices and biomimetic modeling., (© 2024 The Author(s). Small published by Wiley‐VCH GmbH.)

Implementation of more refined structures at the nano to microscale is expected to advance applications in optics and photonics. This work presents the additive manufacturing of 3D luminescent microarchitectures emitting light in the visible range. A tailor‐made organo‐metallic resin suitable for two‐photon lithography is developed, which upon thermal treatment in an oxygen‐rich atmosphere allows the creation of silicon‐free tetragonal (t‐) and monoclinic (m‐) ZrO2. The approach is unique because the tailor‐made Zr‐resin is different from what is achieved in other reported approaches based on sol−gel resins. The Zr‐resin is compatible with the Eu‐rich dopant, a luminescent activator, which enables to tune the optical properties of the ZrO2 structures upon annealing. The emission characteristics of the Eu‐doped ZrO2 microstructures are investigated in detail with cathodoluminescence and compared with the intrinsic optical properties of the ZrO2. The hosted Eu has an orange−red emission showcased using fluorescence microscopy. The presented structuring technology provides a new platform for the future development of 3D luminescent devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Four coumarin-carbazole-based oxime esters were synthesized as photoinitiators (PIs). • PIs exhibit excellent adsorption and initiation ability than commercial OXE 02. • PIs can effectively initiate one/two-photon polymerization of LEDs/NIR light. • PIs have outstanding migration stability and cytocompatibility. • PIs with CF 3 group have higher two-photon lithography capability. Photocuring has developed rapidly in recent years owing to its unique "5E" characteristics, especially in the industrial and manufacturing fields, where photoinitiators (PIs) are essential components of the polymerization system. However, most PIs have limited applications in fields that directly contact the human body, such as food packaging or biomedicine, due to migration stability and toxicity. Here, four oxime esters were designed as PIs by using coumarin-carbazole as the conjugate structure, and their properties were optimized by multisite modification of the molecular structure. First, substituents with different electronic properties were introduced at the 4-position of coumarin. The introduction of electron-withdrawing trifluoromethyl redshifted the molecule and better matched the light-emitting diode (LED) emission spectra (i.e., 365–450 nm). In addition, the introduction of long and branched alkyl chains on carbazole increased the solubility of the four PIs. The initiation efficiency of the PIs was improved by inserting long or cyclized alkyl chains at the α-position of C = N double bond. The experimental results demonstrated that these four PIs are superior to the commercial oxime ester OXE 02 in terms of light absorption and initiation ability under LED irradiation. The migration stability and cytocompatibility of these PIs were validated, ensuring a green and safe application in photocuring applications. Furthermore, these PIs exhibited a considerable writing speed and remarkable nanopatterning capabilities under 780 nm laser in two-photon polymerization. These outstanding properties indicated their great potential for applications in diverse areas of photocuring, especially in food packaging, bio-3D printing, tissue engineering, and nano-additive manufacturing. [ABSTRACT FROM AUTHOR]

Multi-focal laser direct writing (LDW) based on phase-only spatial light modulation (SLM) can realize flexible and parallel nanofabrication with high-throughput potential. In this investigation, a novel approach of combining two-photon absorption, SLM, and vector path-guided by scalable vector graphics (SVGs), termed SVG-guided SLM LDW, was developed and preliminarily tested for fast, flexible, and parallel nanofabrication. Three laser focuses were independently controlled with different paths, which were optimized according to the SVG to improve fabrication and promote time efficiency. The minimum structure width could be as low as 81 nm. Accompanied by a translation stage, a carp structure of 18.10 μm × 24.56 μm was fabricated. This method shows the possibility of developing LDW techniques toward fully electrical systems, and provides a potential way to efficiently engrave complex structures on nanoscales.

Surface-bound 3D micro-magnets are fabricated from photoreactive copolymers filled with magnetic nanoparticles by maskless 3D writing. The structures are generated by 2-photon crosslinking (2PC), which allows direct writing into solid films of composites consisting of magnetic particles and a photoreactive elastomer precursor. With this strategy, it is possible to directly write complex, surface-bound magnetic actuator structures, which generates new opportunities in the fields of microfluidics and bioanalytical systems. Compared to the common 2-photon polymerization, in which the writing process takes place in a liquid resin, the direct writing based on the 2PC method takes place in a solid polymer film (i.e., in the glassy state).

We design and fabricate ultra-broadband achromatic metalenses operating from the visible into the short-wave infrared, 450–1700 nm, with diffraction-limited performance. A hybrid 3D architecture, which combines nanoholes with a phase plate, allows realization in low refractive index materials. As a result, two-photon lithography can be used for prototyping while molding can be used for mass production. Experimentally, a 0.27 numerical aperture (NA) metalens exhibits 60% average focusing efficiency and 6% maximum focal length error over the entire bandwidth. In addition, a 200 μm diameter, 0.04 NA metalens was used to demonstrate achromatic imaging over the same broad spectral range. These results show that 3D metalens architectures yield excellent performance even using low-refractive index materials, and that two-photon lithography can produce metalenses operating at visible wavelengths.

Robotic handling and transfer printing of micrometer‐sized superlight objects is a crucial technology in industrial fabrication. In contrast to the precise gripping with micropatterned adhesives, the reliable release of superlight objects with negligible weight is a great challenge. Slanted deformable polymer microstructures, with typical pillar cross‐section 150 µm × 50 µm, are introduced with various tilt angles that enable a reduction of adhesion by a switching ratio of up to 500. The experiments demonstrate that the release from a smooth surface involves sliding of the contact during compression and subsequent peeling of the object during retraction. The handling of a 0.5 mg perfluorinated polymer micro‐object with high accuracy in repeated pick‐and‐place cycles is demonstrated. Based on beam theory, the forces and moments acting at the tip of the microstructure are analyzed. As a result, an expression for the pull‐off force is proposed as a function of the sliding distance and a guide to an optimized design for these release structures is provided. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms underlying cell-surface interaction is of fundamental importance for the rational design of scaffolds aiming at tissue engineering, tissue repair and neural regeneration applications. Here, we examined patterns of neuroblastoma cells cultured in three-dimensional polymeric scaffolds obtained by two-photon lithography. Because of the intrinsic resolution of the technique, the micrometric cylinders composing the scaffold have a lateral step size of ~200 nm, a surface roughness of around 20 nm, and large values of fractal dimension approaching 2.7. We found that cells in the scaffold assemble into separate groups with many elements per group. After cell wiring, we found that resulting networks exhibit high clustering, small path lengths, and small-world characteristics. These values of the topological characteristics of the network can potentially enhance the quality, quantity and density of information transported in the network compared to equivalent random graphs of the same size. This is one of the first direct observations of cells developing into 3D small-world networks in an artificial matrix.

Hydrogel precursor photoresists (HPR) are being studied widely due to the close similarities between HPR cured microstructures and biological materials. A vast majority of such resists are formulated in water and suffer from swelling-related inhomogeneities during microfabrication. Hence formulation HPRs in non-aqueous media are being studied as an alternative. This approach enables controlled swelling of fabricated structures. In this work, we demonstrate that controlled swelling of hydrogel microstructures fabricated by two-photon lithography (TPL) can be used to drive 2D to 2.5D transitions in flat microstructures. Through fabrication experiments, mechanical analysis and finite element method (FEM) simulations we have shown that swelling delamination leads to bend microstructures, and the height of the resulting bend structure depends on the designed thickness of the structure.

Advances in bioinspired and biohybrid robotics are enabling the creation of multifunctional systems able to explore complex unstructured environments. Inspired by Avena fruits, a biohybrid miniaturized autonomous machine (HybriBot) composed of a biomimetic biodegradable capsule as cargo delivery system and natural humidity-driven sister awns as biological motors is reported. Microcomputed tomography, molding via two-photon polymerization and casting of natural awns into biodegradable materials is employed to fabricate multiple HybriBots capable of exploring various soil and navigating soil irregularities, such as holes and cracks. These machines replicate the dispersal movements and biomechanical performances of natural fruits, achieving comparable capsule drag forces up to ≈0.38 N and awns torque up to ≈100 mN mm -1 . They are functionalized with fertilizer and are successfully utilized to germinate selected diaspores. HybriBots function as self-dispersed systems with applications in reforestation and precision agriculture., (© 2024 The Authors. Advanced Materials published by Wiley‐VCH GmbH.)

Lightweight ceramic nanolattices exhibiting high stiffness and good recoverability are obtained by leveraging base material size effects in combination with smart structural design. Here, the double-wall tube (DWT) lattice architecture is introduced to increase the stiffness of brittle nanolattices, while maintaining their recoverability. The DWT architecture consists of two nested simple-cubic hollow-truss nanolattices. The superposition of two nanolattices leads to a reduced wall thickness for a given relative density thereby preventing the built-up of large stresses at the cell wall level when crushing the lattices. In this work, DWT alumina nanolattices are fabricated and compressed in situ to demonstrate the improvement in recoverability with decreasing alumina wall thickness. The results from finite element simulations reveal that double-wall architectures are up to two times stiffer than their single wall counterparts of equal mass, suggesting that superior recoverability (thinner ceramic coatings) coupled with enhanced stiffness can be achieved. The DWT lattice is proposed as a new architecture to expand the design space of highly recoverable brittle nanolattices. The new double-wall design concept is expected to provide an efficient tool for improving the mechanical performance of shell-nanolattices in general including triply-periodic minimal surfaces.

Interference lithography is a promising method for fabricating large-area, defect-free three-dimensional photonic crystal structures which can be used for facilitating the realization of photonic devices with a fast processing time. Although they can be used in waveguides, resonators, and detectors, their repeated regular array patterns can only be used for limited applications. In this study, we demonstrate a method for fabricating large-area photonic crystal structures with controlled defects by combining interference lithography and two-photon lithography using a light-curable resin. By combining regular array structures and controlled patterns, monotonous but large-area regular structures can be obtained. Furthermore, the patterned structures have considerable potential for use in various applications, such as solar cells, sensors, photodetectors, micro-/nano-electronics, and cell growth. [ABSTRACT FROM AUTHOR]

Vat photopolymerization (VP) is one of the most remarkable additive manufacturing techniques today and has been used for a variety of applications, from materials research to product manufacturing. The main challenge with VP is the limited choice of compatible materials, which motivates significant interest in VP materials development. We provide a brief overview of the materials that are currently accessible via VP and highlight recent advances in the field. We also provide perspective on expanding the library of materials compatible with VP using in situ materials synthesis. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The dispersion of a chiral polymer in a polymerizable matrix can amplify the chirality of the material, and a helical conformation of the chiral material within the polymerized SU-8 excessively increased the circular dichroism. Here, we demonstrate the fabrication of three-dimensional nanostructures of chiral/achiral mixtures by two-photon lithography. The irradiation of light and annealing caused local changes in the chiral material and finally led to the enhancement of the optical properties. The demonstration of a photopatternable chiral material could expand the usage of optical materials for various applications.

A novel approach is demonstrated that extends the resolution of 3D electroforming. Photoresist templates with complex 3D geometries are generated using two‐photon lithography are shrunken by a factor of ≈5 through pyrolysis. A key discovery is that pyrolysis at 500 °C, instead of the higher temperatures normally used for pyrolysis, still shrinks the template by a significant amount but keeps the template nonconductive. This shrunken template is used for electroforming, or template‐assisted electrodeposition, and then etched away to reveal complex 3D structures of pure metal (>99 at%) with linewidths below 200 nm. The versatility of the technique is demonstrated by fabricating octet truss nanolattices from either nanocrystalline gold or microcrystalline copper. In situ micromechanical tests are used as an analytical technique to reveal that these lattices have yield strengths of 325 and 190 MPa for the gold and copper, therefore verifying the fidelity of the architecture. [ABSTRACT FROM AUTHOR]

Shape memory polymers (SMPs) respond to heat by generating programmable movement in devices that require substantial deformation and operate at transient temperatures, including stents and embolization coils. To enable their use in small‐scale applications like retinal vasculature stenting, shape transformations must occur in SMPs with complex 3D geometries with nanoscale features. This work describes the synthesis and sculpting of a benzyl methacrylate‐based SMP into 3D structures with <800 nm characteristic critical dimensions via two photon lithography. Dynamic nanomechanical analysis of 8 µm‐diameter cylindrical pillars reveal the initiation of this SMP's glass transition at 60 °C. Shape memory programming of the characterized pillars as well as complex 3D architectures, including flowers with 500 nm thick petals and cubic lattices with 2.5 µm unit cells and overall dimensions of 4.5 µm × 4.5 µm × 10 µm, demonstrate an 86 +/− 4% characteristic shape recovery ratio. These results reveal a pathway toward SMP devices with nanoscale features and arbitrary 3D geometries changing shape in response to temperature. [ABSTRACT FROM AUTHOR]

Magnetic microrobots have been developed for navigating microscale environments by means of remote magnetic fields. However, limited propulsion speeds at small scales remain an issue in the maneuverability of these devices as magnetic force and torque are proportional to their magnetic volume. Here, a microrobotic superstructure is proposed, which, as analogous to a supramolecular system, consists of two or more microrobotic units that are interconnected and organized through a physical (transient) component (a polymeric frame or a thread). The superstructures consist of microfabricated magnetic helical micromachines interlocked by a magnetic gelatin nanocomposite containing iron oxide nanoparticles (IONPs). While the microhelices enable the motion of the superstructure, the IONPs serve as heating transducers for dissolving the gelatin chassis via magnetic hyperthermia. In a practical demonstration, the superstructure's motion with a gradient magnetic field in a large channel, the disassembly of the superstructure and release of the helical micromachines by a high-frequency alternating magnetic field, and the corkscrew locomotion of the released helices through a small channel via a rotating magnetic field, is showcased. This adaptable microrobotic superstructure reacts to different magnetic inputs, which can be used to perform complex delivery procedures within intricate regions of the human body., (© 2023 The Authors. Advanced Materials published by Wiley‐VCH GmbH.)

Switchable underwater adhesion can be useful for numerous applications, but is extremely challenging due to the presence of water at the contact interface. Here, deformable cupped microstructures (diameter typically 100 µm, rim thickness 5 µm) are reported that can switch between high (≈1 MPa) and low (<0.2 MPa) adhesion strength by adjusting the retraction velocity from 100 to 0.1 µm s–1. The velocity at which the switch occurs is determined by specific design parameters of the cupped microstructure, such as the cup width and angle. The results are compared with theoretical estimates of water penetration into the contact zone and expansion of the cup during retraction. This work paves the way for controlling wet adhesion on demand and may inspire further applications in smart adhesives. [ABSTRACT FROM AUTHOR]

Two-photon lithography (TPL) enables the fabrication of metamaterials exhibiting unprecedented mechanical performance. Such lattice structures consist of micron-scale geometric features and are designed to achieve their envisioned properties through stretching and bending of individual trusses. Here, we present for the first time a comprehensive study of the effect of temperature and strain rate on the mechanical properties of micron-sized 3D printed polymers made by TPL using Nanoscribe’s negative tone photoresist IP-Dip. A strong strain rate dependency was identified for the yield strength, which increased fourfold in compression from 68 MPa to 230 MPa as the strain rate was raised from 7e−4 s−1 to 600 s−1. This trend was also seen in tension. The elastic modulus was found to increase with strain rate in the quasistatic regime but was constant at 3.2 GPa for strain rates of 0.7 s−1 and above. Even slightly elevated temperatures of 80°C led to a significant drop in the yield strength and elastic modulus, though the observed reduction was less severe at higher strain rates. Further, a model based on the strain rate-temperature superposition principle is reported that allows the extrapolation of the mechanical properties even beyond the conditions tested here.

Organ-on-chip (OoC) technology is increasingly used for biomedical research and to speed up the process of bringing a drug from lab to the market. The main fluidic components of an OoC device are microfluidic channels and porous membranes arranged in three dimensions. Current chips are often assembled from several parts. In the development phase a small change in design will cause a delay in the research because a new prototype has to be built and assembled again step-by-step. The research discussed in this paper addresses this point by targeting a monolithic 3D device that can be fabricated in a single lithography and development step, enabling rapid prototyping. Two-photon lithography (TPL) was used in combination with a positive photoresist AZ 4562. The exposure process was characterized, which included an experimental and theoretical study of the voxel size and shape. It was found that the voxel has an hourglass-shape for the laser power settings that were required for process stability. The smallest pores we could produce with these settings measured 250 nm in diameter. The TPL process was then used to fabricate a microfluidic device featuring two crossed channels each one on a separate height-level, connected by a membrane in the centre. Access to the channels was provided through 4 reservoirs from the top-side of the device. The device was successfully filled with water and dried to see whether it can withstand the corresponding capillary forces.