Swimming bacteria move through a fluid by actuating their moving body parts. They are force-free and can be described as hydrodynamic force dipoles: pushers or pullers. This modelling description is broadly used in biological physics and active matter research, and it has successfully predicted, for example, the superfluid behaviour of suspensions of pushers or the bend instability and emergence of turbulent flows in active nematics. However, this description accounts only for the translational motion of the swimming body and neglects the effects of hydrodynamic torque dipoles, which are relevant to bacteria with rotary motor-driven flagella, such as swimming Escherichia coli. Here we show that the torque dipole of confined swimming E. coli can power the persistent rotation of symmetric discs. The torque dipole leads to a traction force on the discs, an additive mechanism that is both contactless and independent of the orientation of the bacteria. Our results indicate that the torque dipole of swimming E. coli is notable in confined geometries, which is relevant to bacterial transport through porous materials, biofilms and the development of chiral fluids.

Purpose Surface micropatterning is being explored as a strategy to mitigate thrombus formation and reduce long-term anticoagulation requirements in left ventricular assist devices (LVADs). This study investigated whether specific micro-topographies can modulate platelet deposition under LVAD supraphysiological wall shear stress (WSS) conditions. Materials and Methods A custom microfluidic platform was developed to generate a linear WSS gradient from 16 to 130 Pa. Microchannels were patterned with reverse cones and hemispheres in small (1–3 µm) and large (3–9 µm) sizes using two-photon polymerization and nanoimprinting. Human blood was perfused through the microchannels, and platelet deposition was quantified over time as the area coverage ratio (Aₚₗₜ/Aₜₒₜ) and area under the curve (AUC). Platelet detachment events were counted as an indicator of thrombus stability, and computational simulations supported the interpretation of local shear conditions. Results Consistent trends emerged, although no statistical differences were observed relative to flat controls. Aₚₗₜ/Aₜₒₜ increased with WSS for all surfaces. At 16 Pa, small and large cones reduced platelet adhesion by approximately 84 and 98%, respectively, compared to flat controls. At 49 Pa, the reduction was about 95% for small cones and 80% for large cones. Conical geometries also promoted platelet washout at higher WSS. Small hemispherical features showed more than 50% lower platelet adhesion than flat surfaces for WSS > 16 Pa, with limited thrombus growth. Conclusion Conical micropatterns may be most effective at limiting platelet adhesion at lower WSS, while small hemispheres may perform better at higher WSS. These trends suggest a surface–shear interaction that warrants further investigation for LVAD surface optimization.

We present a scalable cryo-CMOS controller for color-center-based quantum processors. A diamond waveguide micro-chiplet with NVs is pick-and-placed on CMOS with a 3D-printed prism for scalable photonic readout. A serial qubit driver array using grid inductors and pulse-width modulators generates a programmable 2.87GHz magnetic field for each qubit with low power and strong confinement. Up to 144 qubits can be operated on a single chip, with 204μW power consumption per qubit under active control.

The success of cardiovascular devices is hindered by non-physiological flow conditions and surface materials, which can trigger platelet activation and lead to thrombus formation with severe consequences for patients. While anticoagulation treatments help prevent thrombus formation, they can compromise hemostasis and thereby increase the risk of bleeding. In this study, physical surface modifications through specific micropatterning, cones, riblets, grids, and hemispheres were investigated as a non-pharmacological strategy to reduce platelet adhesion on blood-contacting devices. Fabrication methods based on two-photon polymerization (2PP) 3D printing combined with nanoimprinting lithography were employed to achieve high micro-scale resolution. Platelet adhesion was investigated under low-WSS conditions, and adhering platelets were reduced by 45%, 29%, 25%, and 41%, respectively, for cones, riblets, grids, and hemispheres compared to the flat reference control. Our findings demonstrate that surface micropatterning at the blood–material interface represents a promising approach to modulate thrombus formation risk in cardiovascular devices.

Shape memory polymers capable of recovering their original form after deformation are highly desirable for applications in soft robotics, biomedical engineering, and microfabrication. However, integrating shape memory properties into 3D-printed microstructures with ultra-low mass remains a challenge, as most existing systems lack sufficient resolution or mechanical robustness at the microscale. In this study, a poly(ε-caprolactone)-based material, crosslinked via thiol–ene chemistry, is developed to fabricate mechanically stable 3D-microstructures using two-photon polymerization. This process enables sub-micron features down to approximately 550 nm. Printing parameters, including laser power, scan speed, hatch distance, and layer height, are optimized to produce complex micro-architectures with high CAD-CAM fidelity. Micrometer-scale geometries are successfully printed, including hollow scaffolds weighing 0.89 µg. These scaffolds exhibit excellent shape memory behavior, fully recovering their original shape upon heating even after compressive loads exceeding five million times their own weight. This microscale demonstration confirms that shape memory functionality translates reliably from macro- to microscale without compromising structural integrity. Macroscale dynamic mechanical analysis shows excellent shape fixity (Rf >99.45%) and shape recovery ratios (Rr >99.07%) across multiple thermal cycles, while nanoindentation validates microscale stiffness and structural integrity.

In the pursuit of realizing reliable clean energy generation via inertial confinement fusion (ICF), wetted foam (WF) capsule targets have long been coveted due to their potential to simplify the target fielding process and suppress hydrodynamic instabilities and material mixing that limit achievable energy output, yet producing and deploying a WF target has proven challenging. In this work, we demonstrate the design, fabrication, metrology, and testing of fully additively manufactured (AM) foam-lined capsules using two-photon polymerization (2PP) for ICF. We successfully fielded an AM polymeric foam capsule with a 3-mm outer diameter, a nominally 15-µm-thick solid outer layer, a 120-µm-thick inner foam layer, and a 250-µm outer diameter copper fill tube on the National Ignition Facility for a polar direct-drive shot, and we showcase deuterium wetting of the capsule foam layer inside an ignition target proofing station. Our exploration showed that 2PP can produce fieldable targets with complex geometries and potentially shorten the design iteration turnaround time and the overall target fabrication time.

We present a modular design strategy for the one-step fabrication of arrays of magnetically responsive microactuators connected to the substrate via compliant hinges. We use direct laser writing in the form of two-photon crosslinking within bilayer films to generate three-dimensional microstructures in which magnetic nanoparticles are embedded in the upper layer. This part of the generated structure drives the actuation, while the hydrogel bottom layer is used to form a mechanically compliant hinge structure. The chemical composition and geometrical features of the hinge control the actuation amplitude, the mechanical properties, and the environmental adaptability. Hydrogel hinges provide stability and strong actuation in an aqueous environment, while stimulus-responsive hinges allow for the dynamic reconfiguration of the actuation and bistable behavior without altering the magnetically driving component. This hinge-based approach establishes a new class of adaptive microactuators and provides a generalizable platform for programmable soft micromachines.

Two-photon polymerization (2PP) has garnered increasing attention for engineering hydrogels with tailored architectures and controlled cellular responses. However, current 2PP strategies typically rely on (meth)acrylated proteins and inefficient chain-growth crosslinking mechanisms. Although thiol-ene photo-click reactions can enhance 2PP efficiency, commercial water-soluble thiol crosslinkers (e.g., DTT—dithiothreitol) tend to form intramolecular loops and introduce structural defects due to their short molecular length. As a result, high polymer concentrations (often up to 20%–50%) are required to achieve satisfactory print fidelity. Here, we develop a series of water-soluble, polyvinyl alcohol macromolecular thiol (PVASH, bearing 10–35 thiol groups) for fast high-fidelity hydrogel microfabrication via 2PP. A two-step synthesis yields PVASH with tunable degrees of substitution and excellent water-solubility. Compared to DTT and polyethylene glycol di-thiol, PVASH-based hydrogels exhibit reduced swelling, enhanced mechanical properties, and significantly improved printing fidelity. Notably, several complex hydrogel structures are fabricated at laser power as low as 20 mW and high scanning speeds of up to 400 mm s−1, achieving sub-micron feature size at 3% polymer concentration. After biofunctionalization with RGD motifs, the micro-scaffolds support cell infiltration, adhesion, proliferation, and osteogenic differentiation. Altogether, this work reports a new strategy for 2PP microfabrication of cell-interactive hydrogel structures with unprecedented printing efficiency and precision.

Optically driven robotic actuators are synthetic materials capable of reversible shape-morphing under the control of incident light.Conventional approaches typically require a favorable illumination condition, that is small incidence angle excitement coveringlarge sample area, which poses challenges for optical integration and applicability in optically restricted environments. Here,we present a method that utilizes two-photon polymerization laser-printing of micromirrors on the surface of a soft actuator toredirect parallel incident light into the material. This mirror reflection enables photomechanical actuation at 90◦ incidence angle.To validate the concept, we employ a liquid crystalline elastomer thin film as the soft actuator operated under photothermalmechanism. The actuator exhibits only moderate deformation at oblique incidence and no deformation at grazing incidence (90◦)without micro mirror assistance. Integrating the micro mirrors manifests the photomechanical deformation at oblique angles.The merits of this micro mirror deflection strategy are illustrated by two demonstrations: a walking robot driven by an opticalbeam that is confined to the locomotive 2D plane, and an optical fiber tip integrated gripper can manipulate objects. These resultsprovide the facts that the photomechanical deformation can be elevated significantly by microscopically constructed pattern onthe actuator surfaces, providing new designs for micro robots.

The integration of biologically inspired materials into photonic device fabrication offers a promising route toward sustainable and biocompatible alternative to conventional in inorganic or petroleum based synthetic materials used in optoelectronic systems. In this work, we present a biosynthetic approach for waveguide fabrication utilizing a biomimetic – de novo designed elastin-like polypeptide (ELP) formulated into an all-water-based photoresist compatible with two-photon polymerization (2PP). The ELP was genetically engineered and recombinantly produced in microbes for enhanced molecular stability, a critical feature for withstanding both localized and bulk temperature increases that occur during high-intensity laser exposure during printing. The resulting ELP formulation supported direct writing of waveguide architecture without the need for organic solvents, harsh processing steps, or post-functionalization. This aqueous resist formulation exhibits high stability during printing and retains its structural integrity upon curing, making it a promising candidate for environmentally friendly, soft-material photonics. This work establishes a foundation for using biosynthetic polypeptides in the fabrication of functional photonic elements and demonstrates a step toward greener, protein-based optoelectronic manufacturing technologies.

The detection of trace gases is crucial in environmental monitoring, industrial safety, and medical diagnostics. Optical sensing technologies, particularly those leveraging photothermal spectroscopy, offer high sensitivity and selectivity, enabling the identification of gases based on their unique absorption spectra. Among these, photothermal interferometry offers exceptional sensitivity due to its use of an interferometric signal transducer. In this work, we performed numerical simulations to systematically explore the influence of cavity geometry and mirror curvature on sensitivity. This guided the design of the most sensitive configurations. To validate the theoretical enhancement, we present a systematic comparison of 18 Fabry–Pérot interferometers (FPI) fabricated via two-photon polymerization (2PP) directly onto optical fiber-tips. These FPIs were rapidly prototyped using a commercial 2PP printer. They span three cavity lengths (110, 200, and 300 µm), each configured with flat or spherical mirrors. Single-cavity and Vernier-enhanced FPIs were implemented. The latter were also modified by gold coating of the terminal interface to enhance reflectivity. We evaluated the sensitivity optimization for collinear photothermal spectroscopy in a wavelength modulation setup. By exploiting the Vernier effect and tailored cavity geometries, we demonstrate a 12-fold improvement in the photothermal 2f-signal compared to a single-cavity FPI configuration. This highlights the versatility of 2PP-printed fiber-tip FPIs for next-generation trace gas sensors.

Microstructured foams are emerging as a promising class of targets, with applications ranging from laser-driven particle acceleration to inertial confinement fusion. To unlock their full potential, a deeper understanding of their properties, especially the changes and behavior of the microstructure under extreme conditions, is required. While recently advancing 3D printed foam targets can be observed by X-ray radiography, the microstructure in chemically produced targets is far below the spatial resolution of conventional radiography. To overcome this limitation, we apply grating-based X-ray dark-field imaging to observe structural changes in foams that are rapidly heated by laser-accelerated proton pulses. The experimental data is compared to synthetic dark-field values obtained from hydrodynamic simulations of a simplified foam model. Both experimental and simulation results demonstrate the viability of utilizing grating-based dark-field imaging for observing microstructural changes in foam targets.

Systemic inflammation associated with obesity impairs skeletal muscle function through paracrine signaling from intermuscular adipose tissue—adipose depots situated between adjacent skeletal muscle groups—as well as from visceral adipose tissue, which consist of infiltrating macrophages surrounding inflamed adipocytes. These signals disrupt metabolic homeostasis and reduce muscle contractility, yet existing models are limited in their ability to recapitulate the crosstalk between skeletal muscle and inflamed adipose tissue in a physiologically relevant context. To address this, a human cell-based microphysiological system is developed that combines engineered muscle tissue (EMT) with an inflamed adipose-macrophage co-culture (IAMC) to model obesity-associated muscle dysfunction. EMTs, derived from human myoblasts on micropillar devices, self-assembled into 3D contractile myobundles. IAMC are generated by co-culturing inflamed adipocytes with pro-inflammatory M1-polarized macrophages, thereby recapitulating the obese inflammatory microenvironment. EMT-IAMC co-culture significantly reduced muscle contractility. Furthermore, cytokine profiling revealed elevated levels of pro-inflammatory mediators, and transcriptomic analysis showed metabolic reprogramming in EMTs, including upregulation of genes linked to fatty acid transport and insulin resistance. Collectively, these findings underscore the detrimental effects of inflamed adipose tissue on skeletal muscle function and suggest the potential utility of an interfaced platform for studying adipose-muscle interactions and screening therapies for obesity-related muscle dysfunction.

Chromosome-less minicells, derived from aberrant polar division events of bacterial cells, have emerged as promising nanocarriers for targeted cancer drug delivery due to their unique characteristics. A major challenge in their purification process lies in effectively isolating such spherical minicells (< 1 μm) from their rod-shaped parental cells (1–10 μm). This study investigates the use of Deterministic Lateral Displacement (DLD) microfluidic systems for minicell purification, leveraging Two-Photon Lithography (TPL) for the rapid prototyping of high-resolution designs optimized for this purpose. Under laminar flow conditions, we investigated key DLD design parameters including symmetric and asymmetric post gaps, outlet widths, dual post arrays, fluidic-resistance-optimized design. To enhance separation efficiency, we developed a two-stage microfluidic separation system combining a spiral inertial chip and an optimized DLD chip in series. Utilizing high-resolution TPL for chip fabrication of an inertial chip with 12 spirals and an asymmetric DLD chip with a 2 μm downstream post gap, we achieved a separation efficiency of 94%. This high efficiency achieved using microfluidics for the separation of cells differing in both shape and size, demonstrates the potential of advanced microfluidic systems in cell sorting.

Fiber-based passive mode-locked lasers (MLLs) are a well-established technology for high-speed optical communications, capable of generating ultrashort pulses with high energy. While most commercial MLLs operate at repetition rates around 100 MHz, increasing this frequency to the GHz range introduces significant challenges, including polarization control, efficient saturation of the saturable absorber, heat dissipation and the achievement of a high free spectral range (FSR). To address these limitations, we propose a system consisting of a metalens and a 3D-printed fiber-tip collimator. The metalens is designed to selectively focus one polarization while diverging the orthogonal component, thereby addressing the polarization control. To enhance its performance and increase tolerance to positional offsets and angular tilts, we fabricated a fiber-tip collimator using two-photon polymerization (TPP). Our model suggests that this integrated system could enable the miniaturization of fiber-based MLLs while controlling polarization, enhancing the efficiency of the saturable absorber through better heat dissipation, and increasing the FSR with a shorter fiber length.

Glasses are utilized for their outstanding optical, mechanical, and thermal properties. However, conventional production methods mostly yield in glasses with uniform compositions and material properties. Here a novel lithographic approach is presented for high-resolution 3D dopant integration at defined positions, which enables property modifications in specific regions. For this, a porous glass matrix derived from nanocomposites is shaped using 3D printing or injection molding. Using volumetric 3D printing like computed axial or two-photon lithography, doping is performed within the porous glass using photocurable metal oxide precursors. The dopant is then permanently integrated within the glass during a final sintering step. The local integration of dopants like Ti4+, Co2+, Eu3+ or Tb3+ allow to selectively change the color, luminescence or refractive index within a 3D-shaped glass with micron resolution. The process enables a wide range of novel applications from integrated optics and photonics to mass customization, anti-counterfeiting, and information storage.

The matrix pencil method (MPM) is an approach for quantitative analysis of the multi-exponential time-domain signals from relaxation and diffusion NMR experiments. In contrast to other signal processing methods, MPM relies on solving the generalized eigenvalue problem of a so-called matrix pencil, resulting in discrete values representing the different relaxation species. In this work, the methodology is extended from relaxation experiments towards assessment of NMR self-diffusion studies in micro-porous media on a length scale suitable for determining pore sizes from signal decays. For this, well-defined 3D nano printed micro-capillary structures are introduced as model porous media to correlate the apparent diffusion coefficients derived by MPM from pulsed gradient spin echo (PGSE) experiments to the pore diameter reported by the root-mean-square displacement (RMSD) of molecules diffusing in an array of many regular pores. Due to the high uniformity of the capillaries, the observed signal decay curves are modulated by diffusive diffraction. This phenomenon occurs when the paths of the diffusing spins are confined in an ensemble of identical pores, leading to repeated refocusing of phase coherence in q space. From the q values of the minima, the pore size can be determined for known pore shapes. This can be used as ground truth to validate the results from diffusometry experiments calculated by quantitative analysis methods such as MPM. Results show that MPM algorithm effectively quantifies the diameter within a restricted diffusion experiment. In addition, MPM separates two diffusion components and predicts the correct pore sizes as well as the respective relative contributions.

Glass materials are essential for microsystems applications in fields ranging from optics and photonics to microfluidics and biomedicine, which has driven growing interest in additive manufacturing—or “three-dimensional (3D) printing”—to enable glass micro/nanotechnologies. Notably, the recent discovery that 3D-nanostructured fused silica glass components can be produced via “two-photon direct laser writing (DLW)” of hybrid organic-inorganic polyhedral oligomeric silsesquioxanes (POSS)-based resins holds unique promise, particularly due to the advantages of sinterless, low-temperature (i.e., 650 °C) post-processing. At present, however, it remains unknown how implementing such methodologies to 3D print larger glass microstructures (e.g., with ≥25-µm-thick features) affects critical material properties, such as the ultimate optical and mechanical characteristics. To address this knowledge gap, here we investigate DLW-printed feature size as a key determinant of the optical and mechanical properties of POSS-based fused silica glass microstructures. Experiments for DLW-printed microlenses reveal comparable optical transparency for initial thicknesses up to 40 µm, but increasing to 60 µm significantly reduces light transmission from 87.87 ± 1.18% to 63.57 ± 5.10%. Similarly, compressive loading studies for hollow glass cylindrical microstructures show consistent behavior for initial DLW-printed wall thicknesses up to 30 µm, but significant performance degradation beyond—e.g., Young’s modulus decreasing from 251.6 ± 71.9 to 99.7 ± 63.9 MPa for the 30 to 40 µm cases, respectively. As an exemplar with relevance to biomedical microinjection applications, we harness this new knowledge to DLW-print POSS-based glass microneedle arrays (MNAs) and demonstrate their ability to penetrate into a medium not possible using standard polymer MNAs. In combination, this study establishes critical optical and mechanical benchmarks that underlie the utility of DLW 3D-printed POSS-based fused silica glass microstructures in emerging applications.

Resonant metallic structures are crucial for telecommunications, biosensors, and microrobotics. However, it presents challenges in obtaining high-quality metallic structures using traditional microfabrication methods. Here, we present a rapid prototyping method that combines two-photon polymerization and electrochemical etching to achieve metallic cantilevers of submillimeter sizes for Micro-Mechanical Oscillators (MMOSs). A mask with cantilever designs for selective etching of spring steel foils is fabricated using fast two-photon polymerization with a submicrometer resolution. Then, electrochemical etching of the foils is performed to make spring steel cantilevers with the mask where the regions exposed to the electrolyte are etched through and the masked regions remain. The fabricated cantilever is then assembled into an MMOS with two self-assembled trapezoidal magnets. Excited oscillation tests show that the MMOSs have high Q-values with long oscillating times. Finally, an MMOS is tested as a small-scale magneto-oscillatory localization (SMOL) device under magnetic excitation. A sensor successfully detects the free oscillation signal and can be used for accurate wireless localization.

Transcatheter arterial embolization (TAE) is a minimally invasive technique used to treat hypervascular tumors, hemorrhage, and vascular abnormalities. Though microspheres (MSs) have achieved widespread clinical use as embolic agents, they often lack imaging opacity, optimal morphology and mechanical properties which can lead to unpredictable trajectories, non-target delivery, and suboptimal embolization. This study developed tantalum-loaded calcium alginate (Ta@Ca-Alg) MSs with intrinsic radiopacity, tunable density, and mechanical properties. Ta@Ca-Alg MSs were synthesized using a gas-shearing method and analyzed for size, morphology, swelling behavior, density, radiopacity, and optimized mechanical properties. The results demonstrated that Ta@Ca-Alg MSs maintained a narrow size distribution, with increasing Ta concentration enhancing radiopacity to levels comparable with the clinical contrast agent OMNIPAQUE 350. Density and Young’s modulus corresponding to different Ta concentrations were also investigated. Phantom model testing validated effective vessel occlusion and controlled penetration. In vitro hemocompatibility, sterility, and cytotoxicity studies confirmed excellent biocompatibility. These findings suggest that Ta@Ca-Alg MSs are a promising radiopaque embolic agent with optimized radiopacity, density, and mechanical properties, offering excellent potential for TAE procedures.

Surfaces become “sticky” at the micro/nano length scale as the gravitational force is no longer effective. Ultragentle, high-contrast switching of interfacial adhesion is the key to reliable small-scale object manipulation. Here, a novel approach is presented for surface adhesion control utilizing a liquid-permeable nanoporous surface, which can switch from off-state adhesion (< 0.002 kPa) to on-state attraction (0.8 kPa) without preload. The surface of the gripper is composed of vertically aligned composite nanowires with an average diameter of 79 nm. When a liquid is injected into the nanoporous membrane, capillary adhesion occurs, allowing the object to be picked up. As the liquid evaporates, the object can be released by extremely sparse contact. The off-state adhesion of a millimeter-scale gripper is even lower than the gravitational force of thin polymer films (0.18 mN cm−2), enabling the solid-contactless release of lightweight materials. We characterize and model the mechanism across length scales and provide pick-and-place demonstrations including LED chips, micro-architected materials, and thin-film electronics.

Electrochemical sensors offer the advantages of low cost, high sensitivity, and miniaturization for a wide range of biological applications, including in situ detection of cell metabolites and monitoring cell behavior in real time. However, the complex matrix in biosystems often leads to electrode fouling and inferior sensing performance. In addition to chemical barriers featuring assorted antifouling molecules or coatings, creating micro/nano hierarchical structures on top of electrodes can provide physical barriers to mitigate matrix interference without affecting electron transfer. The emerging two-photon polymerization (TPP) 3D printing technique with the capability to produce precise submicron to several micrometer features on a variety of substrates has enabled the straightforward fabrication of complex hierarchical structures. In this paper, we integrate the value-added micro/nanostructures made by TPP printing with the interdigitated electrode-based sensors and demonstrate the platform’s advantages in filtering out small interfering micro-objects and thus reducing matrix effects. Applying the novel approach to real-time cell monitoring, a 3D-printed microstructure-integrated platform shows higher sensitivity (i.e., the slope of the calibration curve) to model redox analytes in cell culture medium compared to bare electrodes, which display compromised sensitivity due to cell passivation. This research opens a new avenue for mitigating matrix interference and enhancing electrochemical sensing with significant implications across a broad range of applications.

Two-photon polymerization (2PP) is a cutting-edge technique for fabricating precise micro- and nanostructures, with applications in photonics, biomedical engineering, and micro-optics. A critical factor influencing the optical performance of 2PP-fabricated structures is the refractive index (RI) of the printed parts. This study analyzes the refractive indices of three resins developed by UpNano GmbH. Using a Pulfrich refractometer, dispersion curves of the polymerized resins were measured across the visible to near-infrared spectrum (450 nm – 1550 nm), and temperature-dependent RI behavior was characterized for both liquid and polymerized resins (15°C – 50°C). The RI of the polymerized resins ranges from 1.496 to 1.567. What we believe to be a novel model was developed to account for periodic RI fluctuations inherent in 2PP-printed parts due to voxel-based polymerization patterns. The model fits experimental data well and provides additional insights into the degree of polymerization within printed samples. These findings not only enhance understanding of the optical properties of 2PP-fabricated structures but also suggest opportunities for tailoring materials for gradient-index optics and other advanced optical applications.

Porous scaffolds made of bioactive glass (BG) are of great interest for tissue engineering as they can bond to bone rapidly and promote new bone formation. Pores and channels between 100 and 500 µm provide space for cell intrusion and nutrient supply, facilitating bone ingrowth and vascularization. Furthermore, smaller pores and structural features of a few microns in size influence cell behavior, such as adhesion and osteogenic differentiation. Additive manufacturing (AM) is well suited to fabricate such geometries. However, microstructuring BG is demanding and common AM techniques are unable to achieve features below 100 µm. In this work, two-photon lithography (TPL) is used for the first time to structure BG with single-micron features. A composite containing BG nanoparticles is structured using TPL and thermally processed to receive glass scaffolds. The glass used in this study demonstrates in vitro bioactivity in simulated body fluid (SBF) and cytocompatibility toward human mesenchymal stromal cells (MSCs), making it a suitable material for tissue engineering. This process will open a toolbox for a variety of existing BG particles to be shaped with features as small as 6 µm and will broaden the understanding of the influence of scaffold design on cell behavior.

The ability of a sensor to provide stable and reliable response while operating in harsh environments is crucial for many applications. It is highly dependent on the composition of the material constituting the sensor. In this work, we investigated the 3D printing of three types of materials to evaluate their performance for temperature and pressure sensing. To this end, Fabry-Perrot (FP) optical microsensors were fabricated on optical fiber tip using two-photon polymerization 3D printing. First, we investigated organic and hybrid polymers as sensing materials using commercial resins. The obtained FP microcavities showed good optical characteristics around a temperature of 80 °C for IP-S® and 180 °C for OrmoComp®. Spectral shifts and hysteresis were observed over time, making them unsuitable for using as reliable sensors even at lower temperatures. To overcome this problem, homemade silica-based hybrid resin was used to fabricate FP optical sensors on fiber tips. After debinding and sintering at a temperature up to 1200 °C, inorganic silica-based fiber optic sensors were obtained. Temperature sensing has been recorded in the range of 20 °C to 1000 °C using these silica-based FPs. No hysteresis was recorded in the range 20–800 °C in accordance with the accuracy of our experiment. Furthermore, we evaluated the same type of silica-based FP cavity for pressure sensing in the range of 1–138 bars. The sensor showed a linear response to pressure changes in this range. The obtained results demonstrate that our compact silica-based sensors are promising candidates for temperature and pressure sensing in a harsh environment with very good aging and stability.

This study reports the proof-of-concept demonstration of novel, additively manufactured, droplet-emitting electrospray emitter arrays for CubeSat thruster applications. The modular thruster design incorporates multiscale features by employing two different vat photopolymerization technologies, i.e., digital light processing for defining mesoscale features, and two-photon polymerization for creating microscale features. The thruster design includes optimized, 50 µm-diameter microfluidic channels to attain uniform emitter array operation. Devices with up to 8 modules of 4 emitters were tested in a vacuum to assess their performance. Stable and uniform electrospray emission was achieved across all emitters, with a near 100% transmission across the extractor. Both pressure (flow rate) and voltage modulation are investigated as methods for controlling the emitted current and, by extension, the thrust generated by the devices. The per-emitter current followed a well-known square root relationship with flow rate; in addition, a linear relationship between per-emitter current and extractor voltage is observed. Compared to pressure control, modulating thrust via voltage control simplifies system design, eliminating the need for complex valves and enabling a wider throttle range. Estimated thrust and specific impulse are comparable to, or better than reported droplet-emitting electrospray thrusters. These findings demonstrate the potential of additive manufacturing to implement electrospray propulsion hardware.

A multi-laboratory collaborative effort is currently exploring the feasibility of laser direct drive liquid deuterium–tritium (DT) wetted foam inertial confinement fusion concepts being considered for novel neutron sources on the National Ignition Facility (NIF) laser. In contrast to the laser indirect drive approach that recently demonstrated ignition in the laboratory, these concepts also offer the potential of multi-MJ yields but with less damaging laser drives, improved robustness to target and drive imperfections, and enhanced facility fielding flexibility and orders-of-magnitude less target debris: favorable aspects for neutron exposure environments and inertial fusion energy concepts, alike. We present the current status of the experimental platform and radiation-hydrodynamics modeling development efforts to better understand the potential risks and benefits associated with these designs for the envisioned implementation on the NIF laser encompassing (i) novel two-photon-polymerization additively manufactured capsules, (ii) cryogenic target cooling through a large conductive fill tube, (iii) polar direct drive, and (iv) direct laser ablation of the liquid DT wetted foam layer.

Engineering skeletal muscle tissue with precisely defined alignment is of significant importance for applications ranging from drug screening to biohybrid robotics. Aligning 2D contractile muscle monolayers, which are compatible with high-content imaging and can be deployed in planar soft robots, typically requires micropatterned cues. However, current protocols for integrating microscale topographical features in extracellular matrix hydrogels require expensive microfabrication equipment and multi-step procedures involving error-prone manual handling steps. To address this challenge, we present STAMP (simple templating of actuators via micro-topographical patterning), an easily accessible and cost-effective one-step method to pattern microtopography of various sizes and configurations on the surface of hydrogels using reusable 3D printed stamps. We demonstrate that STAMP enables precisely controlling the alignment of mouse and human skeletal muscle fibers without negatively impacting their maturation or function. To showcase the versatility of our technique, we designed a planar soft robot inspired by the iris, which leverages spatially segregated regions of concentric and radial muscle fibers to control pupil dilation. Optogenetic skeletal muscle fibers grown on a STAMPed iris substrates formed a multi-oriented actuator, and selective light stimulation of the radial and concentric fibers was used to control the function of the iris, including pupil constriction. Computational modeling of the biohybrid robot as an active bilayer matched experimental outcomes, showcasing the robustness of our STAMP method for designing, fabricating, and testing planar biohybrid robots capable of complex multi-DOF motion.

Mechanical forces play a crucial role in many biological processes, including cell–cell and cell–matrix interactions. The generation of surface-attached multilayer micromagnet systems fabricated by two-photon lithography and the use of such systems to perform single-cell actuation are presented. The actuators are generated by two-photon crosslinking and consist of a soft and flexible surface-attached hydrogel layer swollen in aqueous medium and a hydrophobic polymer filled with magnetic nanoparticles. To this, thin copolymer bilayers containing a photoreactive crosslinking moiety are deposited on a solid substrate. The crosslinker units are activated by two-photon excitation and react via a C,H insertion reaction with any nearby aliphatic C,H bonds. This leads to crosslinking and surface-attachment of the forming structures so that arrays of micromagnetic pillars with spatially controlled cell adhesion behavior are formed in a single step. Cells are placed on the pillars and actuation is induced by an external magnetic field allowing for highly controllable dynamic and static actuation. Geometric differences can be used to vary cell morphogenesis and movement of the actuators to stretch the cells resulting in highly customizable actuator systems for specific cell growth and actuation control and the study of cell behavior on the molecular level.

The high mortality associated with certain cancers can be attributed to the invasive nature of the tumor cells. Yet, the complexity of studying invasion hinders our understanding of how the tumor spreads. This work presents a microengineered three-dimensional (3D) in vitro model for studying cancer cell invasion and interaction with endothelial cells. The model was generated by printing a biomimetic hydrogel scaffold directly on a chip using 2-photon polymerization that simulates the brain’s extracellular matrix. The scaffold’s geometry was specifically designed to facilitate the growth of a continuous layer of endothelial cells on one side, while also allowing for the introduction of tumor cells on the other side. This arrangement confines the cells spatially and enables in situ microscopy of the cancer cells as they invade the hydrogel scaffold and interact with the endothelial layer. We examined the impact of 3D printing parameters on the hydrogel’s physical properties and used patient derived glioblastoma cells to study their effect on cell invasion. Notably, the tumor cells tended to infiltrate faster when an endothelial cell barrier was present. The potential for adjusting the hydrogel scaffold’s properties, coupled with the capability for real-time observation of tumor-endothelial cell interactions, offers a platform for studying tumor invasion and tumor–endothelial cell interactions.

X-ray free-electron lasers (XFELs) can probe chemical and biological reactions as they unfold with unprecedented spatial and temporal resolution. A principal challenge in this pursuit involves the delivery of samples to the X-ray interaction point in such a way that produces data of the highest possible quality and with maximal efficiency. This is hampered by intrinsic constraints posed by the light source and operation within a beamline environment. For liquid samples, the solution typically involves some form of high-speed liquid jet, capable of keeping up with the rate of X-ray pulses. However, conventional jets are not ideal because of radiation-induced explosions of the jet, as well as their cylindrical geometry combined with the X-ray pointing instability of many beamlines which causes the interaction volume to differ for every pulse. This complicates data analysis and contributes to measurement errors. An alternative geometry is a liquid sheet jet which, with its constant thickness over large areas, eliminates the problems related to X-ray pointing. Since liquid sheets can be made very thin, the radiation-induced explosion is reduced, boosting their stability. These are especially attractive for experiments which benefit from small interaction volumes such as fluctuation X-ray scattering and several types of spectroscopy. Although their use has increased for soft X-ray applications in recent years, there has not yet been wide-scale adoption at XFELs. Here, gas-accelerated liquid sheet jet sample injection is demonstrated at the European XFEL SPB/SFX nano focus beamline. Its performance relative to a conventional liquid jet is evaluated and superior performance across several key factors has been found. This includes a thickness profile ranging from hundreds of nanometres to 60 nm, a fourfold increase in background stability and favorable radiation-induced explosion dynamics at high repetition rates up to 1.13 MHz. Its minute thickness also suggests that ultrafast single-particle solution scattering is a possibility.

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.

The attributes of implant surfaces are pivotal for successful osseointegration. Among surface engineering strategies, microtopography stands out as a promising approach to promote early cellular interactions. This study aims to design and craft a novel biomimetic osteon-like surface modification and to compare its impact on human mesenchymal stem cells (hMSCs) with four established topographies: blank, inverted pyramids, protrusions, and grooves. Poly-ε-caprolactone samples are fabricated using 2-photon-polymerization and soft lithography, prior to analysis via scanning electron microscopy (SEM), water contact angle (WCA), and protein adsorption assays. Additionally, cellular responses including cell attachment, proliferation, morphology, cytoskeletal organization, and osteogenic differentiation potential are evaluated. SEM confirms the successful fabrication of microtopographies, with minimal effect on WCA and protein adsorption. Cell attachment experiments demonstrate a significant increase on the osteon-like structure, being three times higher than on the blank. Proliferation assays indicate a fourfold increase with osteon-like microtopography compared to the blank, while ALP activity is notably elevated with osteon-like microtopography at days 7 (threefold increase over blank) and 14 (fivefold increase over blank). In conclusion, the novel biomimetic osteon-like structure demonstrates favorable responses from hMSCs, suggesting potential for promoting successful implant integration in vivo.

Silicate-based multicomponent glasses are of high interest for technical applications due to their tailored properties, such as an adaptable refractive index or coefficient of thermal expansion. However, the production of complex structured parts is associated with high effort, since glass components are usually shaped from high-temperature melts with subsequent mechanical or chemical postprocessing. Here for the first time the fabrication of binary and ternary multicomponent glasses using doped nanocomposites based on silica nanoparticles and photocurable metal oxide precursors as part of the binder matrix is presented. The doped nanocomposites are structured in high resolution using UV-casting and additive manufacturing techniques, such as stereolithography and two-photon lithography. Subsequently, the composites are thermally converted into transparent glass. By incorporating titanium oxide, germanium oxide, or zirconium dioxide into the silicate glass network, multicomponent glasses are fabricated with an adjustable refractive index nD between 1.4584–1.4832 and an Abbe number V of 53.85–61.13. It is further demonstrated that by incorporating 7 wt% titanium oxide, glasses with ultralow thermal expansion can be fabricated with so far unseen complexity. These novel materials enable for the first time high-precision lithographic structuring of multicomponent silica glasses with applications from optics and photonics, semiconductors as well as sensors.

Spatiotemporally controlled two-photon photodegradation of hydrogels has gained increasing attention for high-precision subtractive tissue engineering. However, conventional photolabile hydrogels often have poor efficiency upon two-photon excitation in the near-infrared (NIR) region and thus require high laser dosage that may compromise cell activity. As a result, high-speed two-photon hydrogel erosion in the presence of cells remains challenging. Here we introduce the design and synthesis of efficient coumarin-based photodegradable hydrogels to overcome these limitations. A set of photolabile coumarin-functionalized polyethylene glycol linkers are synthesized through a Passerini multicomponent reaction. After mixing these linkers with thiolated hyaluronic acid, semi-synthetic photodegradable hydrogels are formed in situ via Michael addition crosslinking. The efficiency of photodegradation in these hydrogels is significantly higher than that in nitrobenzyl counterparts upon two-photon irradiation at 780 nm. A complex microfluidic network mimicking the bone microarchitecture is successfully fabricated in preformed coumarin hydrogels at high speeds of up to 300 mm s−1 and low laser dosage down to 10 mW. Further, we demonstrate fast two-photon printing of hollow microchannels inside a hydrogel to spatiotemporally direct cell migration in 3D. Collectively, these hydrogels may open new avenues for fast laser-guided tissue fabrication at high spatial resolution.

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.

Since the inception of 3D printing in the 1980s, there have been remarkable advancements that have given rise to a wide array of technologies. In the field of bioprinting, many of these technologies are being leveraged to embed living cells into precisely defined 3D structures. Droplet- and extrusion-based bioprinting, two of the earliest techniques, have undergone significant improvements but still face limitations in resolution and versatility. As the role of the cellular microenvironment becomes increasingly recognized, the need for technologies that operate at the microscale has become more critical. Among high-definition (HD) bioprinting techniques, which achieve resolutions below 50 µm, multiphoton lithography (MPL) stands out for its unparalleled precision and versatility. MPL uses a laser to initiate a chemical reaction within a photosensitive material at the laser’s focal point, resulting in highly precise and truly 3D printing capabilities. Recent innovations have focused on improving cytocompatibility and increasing throughput to levels suitable for creating tissue-relevant structures. UpNano leverages over a decade of expertise in photoinitiator and material development, combined with advanced hardware and sophisticated software solutions, to deliver MPL-based bioprinting at the highest level. In addition to classic photopolymerization, additional processes like photoablation, photocleaving, and photopatterning enable precise temporal and spatial control over cell microenvironments. These photochemical methods hold great promise for enhancing the complexity and functionality of 3D-printed tissue models. As commercial MPL systems become more widespread, a growing number of biofabrication applications are emerging, ranging from organs-on-a-chip, designed to replace animal testing, to tissue engineering, where microscaffolds are used to create millimeter-sized tissue constructs, and vascularization, where MPL’s precision allows for the creation of microvessels.

Background Device-related bacterial infections account for a large proportion of hospital-acquired infections. The ability of bacteria to form a biofilm as a protective shield usually makes treatment impossible without removal of the implant. Topographic surfaces have attracted considerable attention in studies seeking antibacterial properties without the need for additional antimicrobial substances. As there are still no valid rules for the design of antibacterial microstructured surfaces, a fast, reproducible production technique with good resolution is required to produce test surfaces and to examine their effectiveness with regard to their antibacterial properties. Methods In this work various surfaces, flat and with microcylinders in different dimensions (flat, 1, 3 and 9 μm) with a surface area of 7 × 7 mm were fabricated with a nanoprinter using two-photon lithography and evaluated for their antibiofilm effect. The microstructured surfaces were cultured for 24 h with different strains of Pseudomonas aeruginosa and Staphylococcus aureus to study bacterial attachment to the patterned surfaces. In addition, surface wettability was measured by a static contact angle measurement. Results Contact angles increased with cylinder size and thus hydrophobicity. Despite the difference in wettability, Staphylococcus aureus was not affected by the microstructures, while for Pseudomonas aeruginosa the bacterial load increased with the size of the cylinders, and compared to a flat surface, a reduction in bacteria was observed for one strain on the smallest cylinders. Conclusions Two-photon lithography allowed rapid and flexible production of microcylinders of different sizes, which affected surface wettability and bacterial load, however, depending on bacterial type and strain.

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.

Imaging the structure and observing the dynamics of isolated proteins using single-particle X-ray diffractive imaging (SPI) is one of the potential applications of X-ray free-electron lasers (XFELs). Currently, SPI experiments on isolated proteins are limited by three factors: low signal strength, limited data and high background from gas scattering. The last two factors are largely due to the shortcomings of the aerosol sample delivery methods in use. Here we present our modified electrospray ionization (ESI) source, which we dubbed helium-ESI (He-ESI). With it, we increased particle delivery into the interaction region by a factor of 10, for 26 nm-sized biological particles, and decreased the gas load in the interaction chamber corresponding to an 80% reduction in gas scattering when compared to the original ESI. These improvements have the potential to significantly increase the quality and quantity of SPI diffraction patterns in future experiments using He-ESI, resulting in higher-resolution structures.

Biodegradable and bioactive gelatin-based hydrogels improve tissue regeneration and wound healing by supporting cell proliferation. Suitably functionalized gelatin hydrogels can even be processed by light-based 3D printing into any required shape, and their physicochemical and biological properties can be modified by incorporating various comonomers into their structure. However, such hydrogels are difficult to monitor in vivo, which has hampered further developments and clinical translation. Herein, we prepared gelatin-based hydrogels with radiopacity by incorporation with biocompatible and radiopaque comonomer 5-acrylamido-2,4,6-triiodoisophthalic acid (AATIPA) and processing through light-based additive manufacturing. Our results showed that adding AATIPA to the reaction mixture significantly accelerates light-induced cross-linking and improves the storage modulus (G′) and swelling ratio (SR) of the cross-linked hydrogels, providing them with radiopacity for in vivo monitoring by X-ray and computed tomography (CT). Because these AATIPA-containing gelatin-based hydrogels are noncytotoxic and support cell proliferation, they offer a cost-effective and versatile, 3D-printable platform with tunable radiopacity for biomedical applications. Therefore, our findings pave the way toward the clinical translation of photo-cross-linked 3D-printed hydrogels into tissue engineering and regenerative medicine.

Two-photon polymerization (2PP) is becoming increasingly established as additive manufacturing technology for microfabrication due to its high-resolution and the feasibility of generating complex parts. Until now, the high resolution of 2PP is also its bottleneck, as it limited throughput and therefore restricted the application to the production of microparts. Thus, mechanical properties of 2PP materials can only be characterized using nonstandardized specialized microtesting methods. Due to recent advances in 2PP technology, it is now possible to produce parts in the size of several millimeters to even centimeters, finally permitting the fabrication of macrosized testing specimens. Besides suitable hardware systems, 2PP materials exhibiting favorable mechanical properties that allow printing of up-scaled parts are strongly demanded. In this work, the up-scalability of three different photopolymers is investigated using a high-throughput 2PP system and low numerical aperture optics. Testing specimens in the cm-range are produced and tested with common or even standardized material testing methods available in conventionally equipped polymer testing labs. Examples of the characterization of mechanical, thermo-mechanical, and fracture properties of 2PP processed materials are shown. Additionally, aspects such as postprocessing and aging are investigated. This lays a foundation for future expansion of the 2PP technology to broader industrial application.

Purpose Intracytoplasmic sperm injection (ICSI) imparts physical stress on the oolemma of the oocyte and remains among the most technically demanding skills to master, with success rates related to experience and expertise. ICSI is also time-consuming and requires workflow management in the laboratory. This study presents a device designed to reduce the pressure on the oocyte during injection and investigates if this improves embryo development in a porcine model. The impact of this device on laboratory workflow was also assessed. Methods Porcine oocytes were matured in vitro and injected with porcine sperm by conventional ICSI (C-ICSI) or with microICSI, an ICSI dish that supports up to 20 oocytes housed individually in microwells created through microfabrication. Data collected included set-up time, time to align the polar body, time to perform the injection, the number of hand adjustments between controllers, and degree of invagination at injection. Developmental parameters measured included cleavage and day 6 blastocyst rates. Blastocysts were differentially stained to assess cell numbers of the inner cell mass and trophectoderm. A pilot study with human donated MII oocytes injected with beads was also performed. Results A significant increase in porcine blastocyst rate for microICSI compared to C-ICSI was observed, while cleavage rates and blastocyst cell numbers were comparable between treatments. Procedural efficiency of microinjection was significantly improved with microICSI compared to C-ICSI in both species. Conclusion The microICSI device demonstrated significant developmental and procedural benefits for porcine ICSI. A pilot study suggests human ICSI should benefit equally.

Engineering vasculature networks in physiologically relevant hydrogels represents a challenge in terms of both fabrication, due to the cell–bioink interactions, as well as the subsequent hydrogel-device interfacing. Here, a new cell-friendly fabrication strategy is presented to realize perfusable multi-hydrogel vasculature models supporting co-culture integrated in a microfluidic chip. The system comprises two different hydrogels to specifically support the growth and proliferation of two different cell types selected for the vessel model. First, the channels are printed in a gelatin-based ink by two-photon polymerization (2PP) inside the microfluidic device. Then, a human lung fibroblast-laden fibrin hydrogel is injected to surround the printed network. Finally, human endothelial cells are seeded inside the printed channels. The printing parameters and fibrin composition are optimized to reduce hydrogel swelling and ensure a stable model that can be perfused with cell media. Fabricating the hydrogel structure in two steps ensures that no cells are exposed to cytotoxic fabrication processes, while still obtaining high fidelity printing. In this work, the possibility to guide the endothelial cell invasion through the 3D printed scaffold and perfusion of the co-culture model for 10 days is successfully demonstrated on a custom-made perfusion system.

The popularity of two-photon direct laser writing in biological research is remarkable as this technique is capable of 3D fabrication of microstructures with unprecedented control, flexibility and precision. Nevertheless, potential impurities such as residual monomers and photoinitiators remaining unnoticed from the photopolymerization in the structures pose strong challenges for biological applications. Here, the first use of high-precision 3D microstructures fabricated from a one-component material system (without monomers and photoinitiators) as a 3D cell culture platform is demonstrated. The material system consists of prepolymers with built- in crosslinker motieties, requiring only aliphatic C, H units as reaction partners following two-photon excitation. The material is written by direct laser writing using two-photon processes in a solvent-free state, which enables the generation of structures at a rapid scan speed of up to 500 mm s−1 with feature sizes scaling down to few micrometers. The generated structures possess stiffnesses close to those of common tissue and demonstrate excellent biocompatibility and cellular adhesion without any additional modification. The demonstrated approach holds great promise for fabricating high-precision complex 3D cell culture scaffolds that are safe in biological environments.

Two-photon polymerization (2PP) is an efficient technique to achieve high-resolution, three-dimensional (3D)-printed complex structures. However, it is restricted to photocurable monomer combinations, thus presenting constraints when aiming at attaining functionally active resist formulations and structures. In this context, metal nanoparticle (NP) integration as an additive can enable functionality and pave the way to more dedicated applications. Challenges lay on the maximum NP concentrations that can be incorporated into photocurable resist formulations due to the laser-triggered interactions, which primarily originate from laser scattering and absorption, as well as the limited dispersibility threshold. In this study, we propose an approach to address these two constraints by integrating metallic Rh NPs formed ex situ, purposely designed for this scope. The absence of surface plasmon resonance (SPR) within the visible and near-infrared spectra, coupled with the limited absorption value measured at the laser operating wavelength (780 nm), significantly limits the laser-induced interactions. Moreover, the dispersibility threshold is increased by engineering the NP surface to be compatible with the photocurable resin, permitting us to achieve concentrations of up to 2 wt %, which, to our knowledge, is significantly higher than the previously reported limit (or threshold) for embedded metal NPs. Another distinctive advantage of employing Rh NPs is their role as promising contrast agents for X-ray fluorescence (XRF) bioimaging. We demonstrated the presence of Rh NPs within the whole 2PP-printed structure and emphasized the potential use of NP-loaded 3D-printed nanostructures for medical devices.

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.

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.

Since its introduction in the 1980s, 3D printing has advanced as a versatile and reliable tool with applications in different fields. Among the available 3D printing techniques, two-photon polymerization is regarded as one of the most promising technologies for microscale printing due to its ability to combine a high printing fidelity down to submicron scale with free-form structure design. Recently, the technology has been enhanced through the implementation of faster laser scanning strategies, as well as the development of new photoresists. This paves the way for a wide range of applications, which has resulted in an increasing number of available commercial systems. This work aims to provide an overview of the technology capability by comparing three commercial systems in a round-robin test. To cover a wide range of applications, six test structures with distinct features were designed, covering various aspects of interest, from single material objects with sub-micron feature sizes up to multi-material millimeter-sized objects. Application-specific structures were printed to evaluate surface roughness and the stitching capability of the printers. Moreover, the ability to generate free-hanging structures and complex surfaces required for cell scaffolds and microfluidic platform fabrication was quantitatively investigated. Finally, the influence of the numerical aperture of the fabrication objective on the printing quality was assessed. All three printers successfully fabricated samples comprising various three-dimensional features and achieved submicron resolution and feature sizes, demonstrating the versatility and precision of two-photon polymerization direct laser writing. Our study will facilitate the understanding of the technology maturity level, while highlighting specific aspects that characterize each of the investigated systems.

Surfaces with tailored wettability have attracted considerable attention because of their wide range of potential applications. Wettability can be finely designed by controlling the chemistry and/or morphology of a surface. However, the commonly adopted analytical theories of Wenzel and Cassie-Baxter cannot describe a variety of intermediate and metastable states, being a thorough understanding of the combined chemical and morphological effect on surface wettability still lacking. Hence, the design and optimization of these surfaces is generally expensive and time-consuming. In this work, we propose a numerical method based on the phase-field model to predict the wettability of micro-structured surfaces and assist their design. First, we simulated the sessile droplet experiment on flat surfaces to calibrate model parameters. Second, we modelled several surface morphologies, intrinsic contact angles and droplet impact velocities. Finally, we produced and tested 3D printed flat and micro-structured samples to validate the phase-field model, obtaining a reasonable qualitative and quantitative agreement between numerical and experimental results. The validated model proposed here can help design and prototype surfaces with tailored wettability. Furthermore, integrated with atomistic/mesoscopic simulations, it represents the last step of a predictive multi-scale model, where both chemical and morphological features of surfaces can be designed a priori.

Crosslinked poly(aspartic acid) (pAsp) hydrogels have been evaluated in various applications benefitting from their biocompatibility and biodegradability. Several crosslinking mechanisms for pAsp derivatives have been investigated, yet research focusing on functionalization of pAsp with photo-crosslinkable moieties is scarce. However, the latter would be beneficial for processing of pAsp through light-based additive manufacturing techniques. pAsp was functionalized comparing two types of photo-crosslinkable moieties (i.e. norbornene versus methacrylate), resulting in a thiol-ene step-growth crosslinking mechanism and a chain-growth mechanism, respectively. The influence of the crosslinking mechanism on the photo-crosslinking kinetics, mechanical properties and biocompatibility of the hydrogels was studied. Hydrogels based on norbornene-modified pAsp with Li-TPO-L photo-initiator and a thiol-based crosslinker showed fast crosslinking kinetics and a high swelling ratio, along with a relatively low storage modulus of 29.4 ± 1.3 kPa. Methacrylate-modified pAsp formulations with Li-TPO-L crosslinked slower and exhibited a lower swelling ratio, yet a higher storage modulus (135.1 ± 4.7 kPa). Both hydrogel materials were non-cytotoxic to cells growing in their vicinity. The applicability of the hydrogels to serve as materials for digital light processing (DLP) and two-photon polymerization (2PP) was elucidated. Both materials were processable via DLP and 2PP, offering possibilities towards processing of these materials into constructs serving biomedical applications.

Alumina-Zirconium dioxide (Al2O3-ZrO2) Ceramic Composite Material (CCM) is specifically known for its enhanced mechanical and corrosion resistance properties and is widely used as raw material for mechanical parts like, pump components, die inserts, bearings, etc. As a result, industrialists are searching for an efficient method for machining this Al2O3-ZrO2 material. In this regard, a hybrid unconventional machining process called Electrochemical Discharge Machining (ECDM) is adapted to analyze the machinability of Al2O3-ZrO2 CCM. Besides, to ensure the efficiency of the ECDM process, a magnetic field is also given to the tool electrode during this study to improve the Material Removal Rate (MRR) of the ECDM machine. The experiment is designed using Response Surface Methodology (RSM) by changing the magnitudes of input controls, namely Electrolytic Concentration (EC), Inter-electrode Gap (IEG) and Applied Voltage (AV). Moreover, a novel hybrid machine learning optimization strategy called Deep Belief Network based Battle Royal Optimization (DBN-BRO) algorithm is developed to predict and optimize the ECDM process. Finally, the optimum results are perceived from 55 V AV, 22.727% EC and 40.909 mm IEG input levels. The proposed method shows less than 0.6207 Root Mean Square Error (RMSE) and tools nearly 80 iterations for optimizing the results.

Humidity sensors are used in many applications. The design of fast sensors that can operate in explosive environments is a difficult task. Therefore, current research efforts aim at combining reliability, sensitivity and high sensing speed. The use of structured ultrathin hydrogels perfectly meets these requirements. Nanostructures are directly fabricated with a two-photon-polymerisation (2PP) 3D printer to use them as templates for hydrogels. After the 3D printing multiple templates are coated with ultrathin films of poly(2-hydroxyethyl-methacrylate) (pHEMA) using initiated chemical vapor deposition (iCVD). p(HEMA) is a humidity responsive hydrogel which changes its thickness by orders of magnitude depending on the ambient conditions. The 3D printed structures are optimized to give both a fast response time, and an optical read-out method for visible wavelengths. Upon hydrogel swelling, the height of the nanostructure pillars increases, keeping their periodicity constant. This induces a change in intensity of the first -order refraction peak, which can be easily measured also at low humidity levels. The humidity response of the nanostructures is measured and an influence for different hydrogel thicknesses and humidity flow rates is observed. The ultrathin film with the lowest thickness of 50 nm shows the fastest response to relative humidity, which is much faster than commercial sensors with 8 s response time.

Photopolymer derived carbon grows in popularity, yet the range in available feature sizes is limited. Herein, the focus is on expanding the field to low surface to volume ratio (SVR) structures. A high temperature acrylic photopolymerizable precursor with FTIR and DSC is described and a thermal inert-gas treatment is developed for producing architected carbon in the mm scale with SVR of 1.38×10−3 µm−1. Based on thermogravimetric analysis and mass spectrometry, two thermal regimes with activation energies of ≈79 and 169 kJ mol−1 are distinguished, which is reasoned with mechanisms during the polymer’s morphologic conversion between 300 and 500 °C. The temperature range of the major dimensional shrinkage (300–440 °C, 50%) does not match the range of the largest alteration in elemental composition (440–600 °C, O/C 0.25–0.087%). The insights lead to an optimized thermal treatment with an initial ramp (2 °C min−1 to 350 °C), isothermal hold (14 h), post hold ramp (0.5 °C min−1 to 440 °C) and final ramp (10 °C min−1 to 1000 °C). The resulting carbon structures are dimensionally stable, non-porous at the µm scale, and comprise an unprecedented variation in feature sizes (from mm to µm scale). The findings shall advance architected carbon to industrially relevant scales.

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).

Acrylate-endcapped urethane-based precursors constituting a poly(D,L-lactide)/poly(ε-caprolactone) (PDLLA/PCL) random copolymer backbone are synthesized with linear and star-shaped architectures and various molar masses. It is shown that the glass transition and thus the actuation temperature could be tuned by varying the monomer content (0–8 wt% ε-caprolactone, Tg,crosslinked = 10—42 °C) in the polymers. The resulting polymers are analyzed for their physico-chemical properties and viscoelastic behavior (G′max = 9.6–750 kPa). The obtained polymers are subsequently crosslinked and their shape-memory properties are found to be excellent (Rr = 88–100%, Rf = 78–99.5%). Moreover, their potential toward processing via various additive manufacturing techniques (digital light processing, two-photon polymerization and direct powder extrusion) is evidenced with retention of their shape-memory effect. Additionally, all polymers are found to be biocompatible in direct contact in vitro cell assays using primary human foreskin fibroblasts (HFFs) through MTS assay (up to ≈100% metabolic activity relative to TCP) and live/dead staining (>70% viability).

Gallium liquid metal alloys (GLMAs) such as Galinstan and gallium–indium eutectic (EGaIn) are interesting materials due to their high surface tensions, low viscosities, and electrical conductivities comparable to classical solid metals. They have been used for applications in microelectromechanical systems (MEMS) and, more recently, liquid metal microfluidics (LMMF) for setting up devices like actuators. However, their high tendency to alloy with the most common metals used for electrodes such as gold (Au), platinum (Pt), titanium (Ti), nickel (Ni), and tungsten–titanium (WTi) is a major problem limiting the scaleup and applicability, e.g., liquid metal actuators. Stable electrodes are key elements for many applications and thus, the lack of an electrode material compatible with GLMAs is detrimental for many potential application scenarios. In this work, we study the effect of actuating Galinstan on various solid metal electrodes and present an electrode protection methodology that, first, prevents alloying and, second, prevents electrode corrosion. We demonstrate reproducible actuation of GLMA segments in LMMF, showcasing the stability of the proposed protective coating. We investigated a range of electrode materials including Au, Pt, Ti, Ni, and WTi, all in aqueous environments, and present the resulting corrosion/alloying effects by studying the interface morphology. Our proposed protective coating is based on a simple method to electrodeposit electrically conductive polypyrrole (PPy) on the electrodes to provide a conductive alloying-barrier layer for applications involving direct contact between GLMAs and electrodes. We demonstrate the versatility of this approach by direct three-dimensional (3D) printing of a 500 μm microfluidic chip on a set of electrodes onto which PPy is electrodeposited in situ for actuation of Galinstan plugs. The developed protection protocol will provide a generic, widely applicable strategy to protect a wide range of electrodes from alloying and corrosion and thus form a key element in future applications of GLMAs.

Polydimethylsiloxane (PDMS) has been the material of choice for microfluidic applications in cell biology for many years, with recent advances encompassing nano-scaffolds and surface modifications to enhance cell-surface interactions at nano-scale. However, PDMS has not previously been amenable to applications which require complex geometries in three dimensions for cell culture device fabrication in the absence of additional components. Further, PDMS microfluidic devices have limited capacity for cell retrieval following culture without severely compromising cell health. This study presents a designed and entirely 3D-printed microfluidic chip (8.8 mm × 8.2 mm × 3.6 mm) using two-photon polymerization (2PP). The ‘nest’ chip is composed of ten channels that deliver sub-microliter volume flowrates (to ~ 600 nL/min per channel) to 10 individual retrievable cell sample ‘cradles’ that interlock with the nest to create the microfluidic device. Computational fluid dynamics modelling predicted medium flow in the device, which was accurately validated by real-time microbead tracking. Functional capability of the device was assessed, and demonstrated the capability to deliver culture medium, dyes, and biological molecules to support cell growth, staining and cell phenotype changes, respectively. Therefore, 2PP 3D-printing provides the precision needed for nanoliter fluidic devices constructed from multiple interlocking parts for cell culture application.

The rheological characterization of soft suspended bodies, such as cells, organoids, or synthetic microstructures, is particularly challenging, even with state-of-the-art methods (e.g. atomic force microscopy, AFM). Providing well-defined boundary conditions for modeling typically requires fixating the sample on a substrate, which is a delicate and time-consuming procedure. Moreover, it needs to be tuned for each chemistry and geometry. Here, we validate a novel technique, called hydraulic force spectroscopy (HFS), against AFM dynamic indentation taken as the gold standard. Combining experimental data with finite element modeling, we show that HFS gives results comparable to AFM microrheology over multiple decades, while obviating any sample preparation requirements.

Tool based manufacturing processes like injection moulding allow fast and high-quality mass-market production, but for optical polymer components the production of the necessary tools is time-consuming and expensive. In this paper a process to fabricate metal-inserts for tool based manufacturing with smooth surfaces via a casting and replication process from fused silica templates is presented. Bronze, brass and cobalt-chromium could be successfully replicated from shaped fused silica replications achieving a surface roughnesses of Rq 8 nm and microstructures in the range of 5 µm. Injection moulding was successfully performed, using a commercially available injection moulding system, with thousands of replicas generated from the same tool. In addition, three-dimensional bodies in metal could be realised with 3D-Printing of fused silica casting moulds. This work thus represents an approach to high-quality moulding tools via a scalable facile and cost-effective route surpassing the currently employed cost-, labour- and equipment-intensive machining techniques.

Metamaterials are engineered materials conceived and designed to achieve very special or even unique physical properties, which depend on the designed micro or nanostructures, more than on the chemical composition of the raw materials employed for their fabrication. Normally metamaterials are made of periodic repetitions of unit cells or Boolean combinations of lattices or porous building blocks. Metasurfaces are the quasi-two-dimensional version of metamaterials and are generally applied to controlling electromagnetic and acoustic waves reaching them. Metamaterials are mainly created through high-precision additive manufacturing technologies, while metasurfaces are normally obtained using micromanufacturing techniques from the electronics industry and laser patterning methods. Consequently, the potential benefits and industrial applications of multi-scale or hierarchical metastructures, which could be obtained by merging metamaterials and metasurfaces, remain unexplored. Through the innovative combination of 3D CAD modelling resources and specific tools for computational mapping of topographical 2D images this study validates the possibility of texturing the building blocks and unit cells of metamaterials, hence reaching designs with interwoven metamaterials and metasurfaces. These microtextured lattices are additively manufactured, using two-photon polymerisation, to demonstrate the feasibility of bridging the gap between metamaterials and metasurfaces and analyse current challenges and potential applications of these digital materials.

Multi-photon lithography (MPL) has proven to be a suitable tool to precisely control the microenvironment of cells in terms of the biochemical and biophysical properties of the hydrogel matrix. In this work, we present a novel method, based on multi-photon photografting of 4,4′-diazido-2,2′-stilbenedisulfonic acid (DSSA), and its capabilities to induce cell alignment, directional cell migration and endothelial sprouting in a gelatin-based hydrogel matrix. DSSA-photografting allows for the fabrication of complex patterns at a high-resolution and is a biocompatible, universally applicable and straightforward process that is comparably fast. We have demonstrated the preferential orientation of human adipose-derived stem cells (hASCs) in response to a photografted pattern. Co-culture spheroids of hASCs and human umbilical vein endothelial cells (HUVECs) have been utilized to study the directional migration of hASCs into the modified regions. Subsequently, we have highlighted the dependence of endothelial sprouting on the presence of hASCs and demonstrated the potential of photografting to control the direction of the sprouts. MPL-induced DSSA-photografting has been established as a promising method to selectively alter the microenvironment of cells.

A series of nine soluble, symmetric chalcogenophenes bearing hexyl-substituted triphenylamines, indolocarbazoles, or phenylcarbazoles was designed and synthesized as potential two-photon absorption (2PA) initiators. A detailed photophysical analysis of these molecules revealed good 2PA properties of the series and, in particular, a strong influence of selenium on the 2PA cross sections, rendering these materials especially promising new 2PA photoinitiators. Structuring and threshold tests proved the efficiency and broad spectral versatility of two selenium-containing lead compounds as well as their applicability in an acrylate resin formulation. A comparison with commercial photoinitiators Irg369 and BAPO as well as sensitizer ITX showed that the newly designed selenium-based materials TPA-S and TPA-BBS outperform these traditional initiators by far both in terms of reactivity and dose. Moreover, by increasing the ultralow concentration of TPA-BBS, a further reduction of the polymerization threshold can be achieved, revealing the great potential of this series for application in two-photon polymerization (2PP) systems where only low laser power is available.

Advancements in hybrid sol-gel technology have provided a new class of holographic materials as photopolymerizable glasses. Recently, a number of photosensitive glass compositions with high dynamic range and high spatial resolution have been reported and their excellent capability for volume holography has been demonstrated. Nevertheless, challenges remain, particularly in relation to the processing time and environmental stability of these materials, that strongly affect the performance and durability of the fabricated holograms. State-of-the-art photopolymerizable glasses possess long curing times (few days) required to achieve thick films, thus limiting the industrial implementation of this technology and its commercial viability. This article presents a novel, fast curing, water-resistant, photopolymerizable hybrid sol-gel (PHSG) for holographic applications. Due to introducing an amine-based modifier that increases the condensation ability of the sol-gel network, this PHSG overcomes the problem of long curing time and can readily produce thick (up to a few hundred micrometers) layers without cracking and breaking. In addition, this PHSG exhibits excellent water-resistance, providing stable performance of holographic gratings for up to 400 h of immersion in water. This finding moves photopolymerizable glasses to the next development stage and renders the technology attractive for the mass production of holographic optical elements and their use across a wide number of outdoor applications.

Platinum (Pt) is an interesting material for many applications due to its high chemical resilience, outstanding catalytic activity, high electrical conductivity, and high melting point. However, microstructuring and especially 3D microstructuring of platinum is a complex process, based on expensive and specialized equipment often suffering from very slow processing speeds. In this work, organic–inorganic photoresins, which can be structured using direct optical lithography as well as two-photon lithography (TPL) with submicrometer resolution and high-throughput is presented. The printed structures are subsequently converted to high-purity platinum using thermal debinding of the binder and reduction of the salt. With this technique, complex 3D structures with a 3D resolution of 300 nm were fabricated. At a layer thickness of 35 nm, the patterns reach a high conductivity of 67% compared to bulk platinum. Microheaters, thermocouple sensors as well as a Lab-on-a-Chip system are presented as exemplary applications. This technology will enable a broad range of application from electronics, sensing and heating elements to 3D photonics and metamaterials.