3D Micro-printing Research Articles

Fabricating ordered array of polystyrene spheres on concave structure via 3D micro-printing

Fabricating ordered array of polystyrene spheres on concave structure via 3D micro-printing

Fabrication of Shape‐Controlled Copper Line Arrays by Meniscus‐Confined 3D Microprinting on Insulating Substrates

Meniscus‐confined electrodeposition (MCED), as a 3D printing process, exhibits excellent capabilities in microstructure fabrication. However, it faces numerous challenges, particularly when integrating with different substrates, especially insulating ones and cross‐layer interconnection. This study intends to investigate the impact of factors such as nozzle diameter, flight height of the nozzle over insulating substrates, and applied current by MCED on micro/nanoscale metal structures, to fabricate shape‐controllable and nanogap copper lines. As the flight height of the nozzle increases, there is no significant variation in the line height (≈60 nm) or width (≈15 nm) of the printed copper lines. And copper lines are successfully fabricated with consistent feature size oversteps totaling 1.2 μm in height. Additionally, highly dense copper line arrays are fabricated, achieving a minimum wire spacing of 120 nm. Remarkable stability and simplicity are realized in producing high‐resolution copper microstructures, demonstrating an acceptable degree of variability in insulating substrates and promising applications in integrated microsystems.

Transient charge-driven 3D conformal printing via pulsed-plasma impingement

Seamless integration of microstructures and circuits on three-dimensional (3D) complex surfaces is of significance and is catalyzing the emergence of many innovative 3D curvy electronic devices. However, patterning fine features on arbitrary 3D targets remains challenging. Here, we propose a facile charge-driven electrohydrodynamic 3D microprinting technique that allows micron- and even submicron-scale patterning of functional inks on a couple of 3D-shaped dielectrics via an atmospheric-pressure cold plasma jet. Relying on the transient charging of exposed sites arising from the weakly ionized gas jet, the specified charge is programmably deposited onto the surface as a virtual electrode with spatial and time spans of ~mm in diameter and ~μs in duration to generate a localized electric field accordantly. Therefore, inks with a wide range of viscosities can be directly drawn out from micro-orifices and deposited on both two-dimensional (2D) planar and 3D curved surfaces with a curvature radius down to ~1 mm and even on the inner wall of narrow cavities via localized electrostatic attraction, exhibiting a printing resolution of ~450 nm. In addition, several conformal electronic devices were successfully printed on 3D dielectric objects. Self-aligned 3D microprinting, with stacking layers up to 1400, is also achieved due to the electrified surfaces. This microplasma-induced printing technique exhibits great advantages such as ultrahigh resolution, excellent compatibility of inks and substrates, antigravity droplet dispersion, and omnidirectional printing on 3D freeform surfaces. It could provide a promising solution for intimately fabricating electronic devices on arbitrary 3D surfaces.

From 2D to 3D electrochemical microfabrication of nickel architectures at room temperature: Synthesis and characterization of microstructure and mechanical properties

Recent development in direct electrochemical 3D microprinting allows the fabrication of 3D metallic micro-components of predominantly noble metals with the positive standard reduction potentials (e.g., Cu, Au, or Pt). These pure metals (e.g., Cu, Au, or Pt) have a small shear modulus up to 60 GPa, which limits one of the important strengthening mechanisms, Taylor hardening. Hence, their mechanical strength is relatively low and limits the application in a structural component. 3D printing of mechanically high-strength metals (e.g., Ni), specifically, printing of microscale parts by direct electrodeposition using a voxel-by-voxel printing technique, is so far very challenging due to the negative standard reduction potential, which leads to hydrogen evolution and unstable printing. In this paper, we demonstrate the stable and successful room temperature (RT) electrochemical printing of Ni micro-architectures by using a newly formulated Ni ink and supporting electrolyte, which were developed through 2D voltammetry and deposition analysis. The micro manufacturing of Ni succeeds at a high deposition speed up to ∼61 nm/s, which is the fastest speed reported so far for microprinting of Ni. 3D printed micropillars feature a heterogeneous nanostructure from ∼13 nm at the center to ∼27 nm at the perimeter. By performing micropillar compression tests, the printed pillars exhibit a high compressive yield-strength of 2.3 ± 0.1 GPa, only ∼15 % lower than 2D processed samples (2.7 ± 0.1 GPa) featuring a homogeneous nanostructure of 27 ± 16 nm. Thus, by deposition of stronger, but less noble metals we show a new pathway to enhance the mechanical robustness of 3D-printed structures, opening up new applications where mechanical rigidity is essential.

3D microprinting of QR-code integrated hydrogel tactile sensor for real-time E-healthcare

Stretchable strain sensors have the potential to significantly advance electronic healthcare (E-healthcare). However, current challenges, including a limited detection range, low sensitivity, aggregation of conductive nanoparticles, and the inherent rigidity of conductive polymers within hydrogel matrices, hinder their progress. In our study, we employed a dual approach: we tailored both physical and chemical bond densities and coupled them with conductive polymer nanoparticles. As a result, we developed a stretchable hydrogel strain sensor embedded with a quick response code. This innovation achieved an impressive detection range of up to 1500% and a high gauge factor of 16.6. By modifying the hydrogen bond strength and converting conductive polymer nanoparticles into linear polymer chains, we managed to enhance the sensor's stretchability to 2100%. Moreover, the incorporation of a quick response code enabled the sensor to simultaneously monitor in real-time and encode information. Thus, our sensor emerges as a robust contender for pioneering advancements in E-healthcare, potentially supporting intricate applications like rehabilitation progression tracking.

Lipid membranes supported by polydimethylsiloxane substrates with designed geometry.

The membrane curvature of cells and intracellular compartments continuously adapts to enable cells to perform vital functions, from cell division to signal trafficking. Understanding how membrane geometry affects these processes in vivo is challenging because of the biochemical and geometrical complexity as well as the short time and small length scales involved in cellular processes. By contrast, in vitro model membranes with engineered curvature would provide a versatile platform for this investigation and applications to biosensing and biocomputing. Here, we present a strategy that allows fabrication of lipid membranes with designed shape by combining 3D micro-printing and replica-molding lithography with polydimethylsiloxane to create curved micrometer-sized scaffolds with virtually any geometry. The resulting supported lipid membranes are homogeneous and fluid. We demonstrate the versatility of the system by fabricating structures of interesting combinations of mean and Gaussian curvature. We study the lateral phase separation and how local curvature influences the effective diffusion coefficient. Overall, we offer a bio-compatible platform for understanding curvature-dependent cellular processes and developing programmable bio-interfaces for living cells and nanostructures.

3D microprinting of inorganic porous materials by chemical linking-induced solidification of nanocrystals

Three-dimensional (3D) microprinting is considered a next-generation manufacturing process for the production of microscale components; however, the narrow range of suitable materials, which include mainly polymers, is a critical issue that limits the application of this process to functional inorganic materials. Herein, we develop a generalised microscale 3D printing method for the production of purely inorganic nanocrystal-based porous materials. Our process is designed to solidify all-inorganic nanocrystals via immediate dispersibility control and surface linking-induced interconnection in the nonsolvent linker bath and thereby creates multibranched gel networks. The process works with various inorganic materials, including metals, semiconductors, magnets, oxides, and multi-materials, not requiring organic binders or stereolithographic equipment. Filaments with a diameter of sub-10 μm are printed into designed complex 3D microarchitectures, which exhibit full nanocrystal functionality and high specific surface areas as well as hierarchical porous structures. This approach provides the platform technology for designing functional inorganics-based porous materials.

Bioinspired 3D microprinted cell scaffolds: Integration of graph theory to recapitulate complex network wiring in lymph nodes.

Physical networks are ubiquitous in nature, but many of them possess a complex organizational structure that is difficult to recapitulate in artificial systems. This is especially the case in biomedical and tissue engineering, where the microstructural details of 3D cell scaffolds are important. Studies of biological networks-such as fibroblastic reticular cell (FRC) networks-have revealed the crucial role of network topology in a range of biological functions. However, cell scaffolds are rarely analyzed, or designed, using graph theory. To understand how networks affect adhered cells, 3D culture platforms capturing the complex topological properties of biologically relevant networks would be needed. In this work, we took inspiration from the small-world organization (high clustering and low path length) of FRC networks to design cell scaffolds. An algorithmic toolset was created to generate the networks and process them to improve their 3D printability. We employed tools from graph theory to show that the networks were small-world (omega factor, ω =-0.10±0.02; small-world propensity, SWP=0.74±0.01). 3D microprinting was employed to physicalize networks as scaffolds, which supported the survival of FRCs. This work, therefore, represents a bioinspired, graph theory-driven approach to control the networks of microscale cell niches.

Three-Dimensionally Printed, Vertical Full-Color Display Pixels for Multiplexed Anticounterfeiting.

Information encryption strategies have become increasingly essential. Most of the fluorescent security patterns have been made with a lateral configuration of red, green, and blue subpixels, limiting the pixel density and security level. Here we report vertically stacked, luminescent heterojunction micropixels that construct high-resolution, multiplexed anticounterfeiting labels. This is enabled by meniscus-guided three-dimensional (3D) microprinting of red, green, and blue (RGB) dye-doped materials. High-precision vertical stacking of subpixel segments achieves full-color pixels without sacrificing lateral resolution, achieving a small pixel size of ∼μm and a high density of over 13,000 pixels per inch. Furthermore, a full-scale color synthesis for individual pixels is developed by modulating the lengths of the RGB subpixels. Taking advantage of these unique 3D structural designs, trichannel multiplexed anticounterfeiting Quick Response codes are successfully demonstrated. We expect that this work will advance data encryption technology while also providing a versatile manufacturing platform for diverse 3D display devices.

Electrical stimulation induces anti-tumor immunomodulation via a flexible microneedle-array-integrated interdigital electrode

Immunotherapy has revolutionized cancer therapy, using chemical or biological agents to reinvigorate the immune system. However, most of these agents have poor tumor penetration and inevitable side effects that complicate therapeutic outcomes. Electrical stimulation (ES) is a promising alternative therapy against cancers that does not involve chemical or biological agents but is limited in the fabrication and operation of complex micrometer-scale ES devices. Here, we present an optically microprinted flexible interdigital electrode with a gold-plated polymer microneedle array to generate alternating electric fields for cancer treatment. A flexible microneedle-array-integrated interdigital electrode (FMIE) was fabricated by combining optical 3D microprinting and electroless plating processes. FMIE-mediated ES of cancer cells induced necrotic cell death through mitochondrial Ca2+ overload and increased intracellular reactive oxygen species (ROS) production. This led to the release of damage-associated molecular patterns that activated the immune response and potentiated immunogenic cell death (ICD). FMIE-based ES has an excellent safety profile and systemic anti-tumor effects, inhibiting the growth of primary and distant tumors as well as melanoma lung metastasis. FMIE-based ES-driven cancer immunomodulation provides a new pathway for drug-free cancer therapy.

Macromolecular Engineering: From Precise Macromolecular Inks to 3D Printed Microstructures

Macromolecules with complex, defined structures exist in nature but rarely is this degree of control afforded in synthetic macromolecules. Sequence-defined approaches provide a solution for precise control of the primary macromolecular structure. Despite a growing interest, very few examples for applications of sequence-defined macromolecules exist. In particular, the use of sequence-defined macromolecules as printable materials remains unexplored. Herein, the rational design of precise macromolecular inks for 3D microprinting is investigated for the first time. Specifically, three printable oligomers are synthesized, consisting of eight units, either crosslinkable (C) or non-functional (B) with varied sequence (BCBCBCBC, alternating; BBCCCBB, triblock; and BBBBCCCC, block). The oligomers are printed using two-photon laser printing and characterized. It is clearly demonstrated that the macromolecular sequence, specifically the positioning of the crosslinkable group, plays a critical role in both the printability and final properties of the printed material. Thus, through precise design and printability of sequence-defined macromolecules, an exciting avenue for the next generation of functional materials for 3D printing is created.

Mechanisms of Droplet Formation and Deposition in Drop-On-Demand Needle-Valve Inkjets for Precision 3D Microprinting

Mechanisms of Droplet Formation and Deposition in Drop-On-Demand Needle-Valve Inkjets for Precision 3D Microprinting

Direct 3D microprinting of highly conductive gold structures via localized electrodeposition

Directly 3D-printed metal microstructures could enable hybrid micromanufacturing, combining conventional micromanufacturing with additive micromanufacturing (µAM). The microstructure’s material properties, including the electrical resistivity, are of decisive importance for a wide range of applications in microelectronics, high-frequency communication, and biomedical engineering. In this work, we present a room-temperature process for µAM of gold structures based on local electrodeposition. We demonstrate control of the electrodeposition process by regulating the precursor species supply rate through air pressure and by regulating the reaction rate through the electrodeposition potential. We 3D printed complex gold microscale structures and characterized the resistivity of the printed gold by developing hybrid devices with integrated four-point probe measurement capability. Additionally, we printed copper microwires, building on a previously shown copper µAM process, and characterized the copper resistivity. We demonstrate near-bulk resistivity values of 65 nΩ·m (about 2.5 times higher than bulk) and 19 nΩ·m (only 10% higher than bulk) for the gold and copper wires, respectively, without post-treatment. Microstructural analysis of the gold wires revealed a dense metal deposit free of voids. Finally, we printed gold structures on a pre-patterned substrate, paving the way to hybrid devices in which additive micromanufacturing is combined with existing micromanufacturing techniques.

3D Microprinting of Super‐Repellent Microstructures: Recent Developments, Challenges, and Opportunities

AbstractLiquid super‐repellent surfaces, characterized by a low liquid–solid contact fraction, allow various liquids to bead up and freely roll off. Apart from liquid repellency, these surfaces feature several unique properties, including inter alia, self‐cleaning, low‐friction, anti‐icing, and anti‐biofouling, making them valuable for a vast array of applications involving liquids. Essential to achieve such super‐repellency is the bio‐inspired reentrant or doubly reentrant micro‐topography. However, despite their unique interfacial properties, the fabrication of these delicate 3D topographies by conventional microfabrication methods is extremely challenging. Recently, emerging 3D microprinting technologies, particularly two‐photon lithography, have brought new scope to this field. With unparalleled design freedom and flexibility, 3D microprinting greatly facilitates the design, testing, and studying of complex 3D microstructures. Here, applications of 3D microprinting in the design and fabrication of super‐repellent microstructures are summarized, with a focus on their remarkable properties, and new functionalities offered by these intricate 3D topographies. Current challenges and new opportunities of emerging 3D microprinting techniques to further advance liquid super‐repellent materials are also discussed.

Smart Nematic Liquid Crystal Polymers for Micromachining Advances.

The miniaturization of tools is an important step in human evolution to create faster devices as well as precise micromachines. Studies around this topic have allowed the creation of small-scale objects capable of a wide range of deformation to achieve complex tasks. Molecular arrangements have been investigated through liquid crystal polymer (LCP) to program such a movement. Smart polymers and hereby liquid crystal matrices are materials of interest for their easy structuration properties and their response to external stimuli. However, up until very recently, their employment at the microscale was mainly limited to 2D structuration. Among the numerous issues, one concerns the ability to 3D structure the material while controlling the molecular orientation during the polymerization process. This review aims to report recent efforts focused on the microstructuration of LCP, in particular those dealing with 3D microfabrication via two-photon polymerization (TPP). Indeed, the latter has revolutionized the production of 3D complex micro-objects and is nowadays recognized as the gold standard for 3D micro-printing. After a short introduction highlighting the interest in micromachines, some basic principles of liquid crystals are recalled from the molecular aspect to their implementation. Finally, the possibilities offered by TPP as well as the way to monitor the motion into the fabricated microrobots are highlighted.

Parametric optimization of two-photon direct laser writing process for manufacturing polymeric microneedles

Laser-based additive manufacturing methods have been rapidly developed in recent years and it is anticipated that this new generation of microfabrication tools will dominate the market in the near future. Three-dimensional (3D) microprinting based on two-photon polymerization allows manufacturing of complex microstructures with a resolution down to hundreds of nanometers. In recent years, the technology has been used for the manufacturing of a variety of nano- and micro-sized features such as microfluidic devices, photonics, micro-optics, and microneedle arrays. Microneedles have been mainly studied for transdermal drug delivery of therapeutic agents across the skin and withdrawing bio samples for point-of-care (POC) diagnostics. With significant development being made, it is now possible to 3D print complex microneedle structures directly from computer-aided design (CAD) models by the two-photon direct laser writing technique. However, selecting the optimal parameters and investigating the possible arrangement for the print process often involves intensive optimization process and testing. Herein we report on fabrication of highly detailed microneedles using the two-photon direct laser writing process with a discussion of optimization and parameter selection for microprinting tall microneedles with side-channels and other complex designs. Due to the long printing time, this manufacturing process is currently best suited to print master microneedles. Therefore, we further demonstrate the replication capabilities of the master microneedles by the soft embossing process. Additionally, the mechanical characteristics and insertion force of the microneedle replicas are investigated.

Coupled micromechanical resonator for mass detection

A resonator composed of two coupled doubly-clamped beams is fabricated and used as a mass sensor. Five mass blocks made of IP-L780 photoresist are printed on each resonator beam by 3D microprinting technology as mass loading. The minimum mass which the sensor can detect is as low as 10 ng. The experimental results show that the asymmetric resonant mode of this resonator has a higher Q factor than the symmetric mode when doing mass detection. The responsivity of the coupled resonator for the mass sensing reaches 58.5 Hz/ng.

Meniscus-Guided 3D Microprinting of Pure Metal-Organic Frameworks with High Gas-Uptake Performance.

Metal-organic frameworks (MOFs) are a promising nanoporous functional material system; however, the practicality of shaping freeform MOF monoliths, while retaining their porosity, remains a challenge. Here, we demonstrate that meniscus-guided three-dimensional (3D) printing can produce pure MOF monoliths with high gas-uptake performance. The method exploits a femtoliter precursor ink meniscus to highly confine and guide supersaturation-driven crystallization in a layer-by-layer manner to print a pure HKUST-1 micro-monolith with a high spatial resolution of <3 μm. The proposed 3D printing technique does not involve rheological additives, binders, or mechanical forces. Thus, the resulting HKUST-1 monolith displays a prominently high Brunauer-Emmett-Teller surface area of 1192 m2/g, which is superior to monoliths produced using other 3D printing approaches. This technique enables both structural design freedom and high material performance in the manufacturing of MOFs for practical use.

Direct 3d Microprinting of Highly Conductive Gold Structures Via Localized Electrodeposition

Direct 3d Microprinting of Highly Conductive Gold Structures Via Localized Electrodeposition

Long-Time Behavior of Surface Properties of Microstructures Fabricated by Multiphoton Lithography.

The multiphoton lithography (MPL) technique represents the future of 3D microprinting, enabling the production of complex microscale objects with high precision. Although the MPL fabrication parameters are widely evaluated and discussed, not much attention has been given to the microscopic properties of 3D objects with respect to their surface properties and time-dependent stability. These properties are of crucial importance when it comes to the safe and durable use of these structures in biomedical applications. In this work, we investigate the surface properties of the MPL-produced SZ2080 polymeric microstructures with regard to the physical aging processes during the post-production stage. The influence of aging on the polymeric microstructures was investigated by means of Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). As a result, a time-dependent change in Young’s Modulus, plastic deformation, and adhesion and their correlation to the development in chemical composition of the surface of MPL-microstructures are evaluated. The results presented here are valuable for the application of MPL-fabricated 3D objects in general, but especially in medical technology as they give detailed information of the physical and chemical time-dependent dynamic behavior of MPL-printed surfaces and thus their suitability and performance in biological systems.