3D Microfabrication Research Articles

Multiphoton Lithography of Interpenetrating Polymer Networks for Tailored Microstructure Thermal and Micromechanical Properties.

Multiphoton lithography (MPL), an emerging truly 3D microfabrication technique, exhibits substantial potential in biomedical applications, including drug delivery and tissue engineering. Fabricated micro-objects are often expected to undergo shape morphing or bending of the entire structure or its parts. Furthermore, ensuring precise property tuning is detrimental to the realization of the functionality of MPL microstructures. Herein, novel MPL materials based on interpenetrating polymer networks (IPNs) are presented that effectively combine the advantages of acrylate and epoxy systems. IPNs with varying component ratios are investigated for their microfabrication performance and structural integrity with respect to thermal and micromechanical properties. A variety of high-resolution techniques is applied to comprehensively evaluate IPN properties at the bulk, micron, and segmental levels. This study shows that the MPL laser scanning velocity and power, photoinitiator content, and multi-step exposure can be used to tune the morphology and properties of the IPN. As a result, a library of 3D MPL IPN microstructures with high 3D structural stability and tailored thermal and micromechanical properties is achieved. New IPN microstructures with Young's moduli of 3-4MPa demonstrate high-to-fully elastic responses to deformations, making them promising for applications in morphable microsystems, soft micro-robotics, and cell engineering.

Highly Efficient Ultraviolet Third-Harmonic Generation in an Isolated Thin Si Meta-Structure.

Nonlinear nanophotonic devices have shown great potential for on-chip information processing, quantum source, 3D microfabrication, greatly promoting the developments of integrated optics, quantum science, nanoscience and technologies, etc. To promote the applications of nonlinear nanodevices, improving the nonlinear efficiency, expanding the spectra region of nonlinear response and reducing device thickness are three key issues. Herein, this study focuses on the nonlinear effect of third-harmonic generation (THG), and present a thin Si meta-sructure to improve the THG efficiency in the ultraviolet (UV)region. The measured THG efficiency is up to 10-5 at an emission wavelength of 309nm. Also, the THG nanosystem is only 100nm in thickness, which is two-five times thinner than previous all-dielectric nanosystems applied in THG studies. These findings not only present a powerful thin meta-structure with highly efficient THG emission in UV region, but also provide a constructive avenue for further understanding the light-matter interactions at subwavelength scales, guiding the design and fabricating of advanced photonic devices in future.

Soft Actuators and Actuation: Design, Synthesis, and Applications.

Soft actuators are one of the most promising technological advancements with potential solutions to diverse fields' day-to-day challenges. Soft actuators derived from hydrogel materials possess unique features such as flexibility, responsiveness to stimuli, and intricate deformations, making them ideal for soft robotics, artificial muscles, and biomedical applications. This review provides an overview of material composition and design techniques for hydrogel actuators, exploring 3D printing, photopolymerization, cross-linking, and microfabrication methods for improved actuation. It examines applications of hydrogel actuators in biomedical, soft robotics, bioinspired systems, microfluidics, lab-on-a-chip devices, and environmental, and energy systems. Finally, it discusses challenges, opportunities, advancements, and regulatory aspects related to hydrogel actuators.

Ultrathin and Deformable Graphene Etch Mask for Fabrication of 3D Microstructures.

Three-dimensional (3D) microfabrication techniques play a crucial role across various research fields. These techniques enable the creation of functional 3D structures on the microscale, unlocking possibilities for diverse applications. However, conventional fabrication methods have limits in producing complex 3D structures, which require numerous fabrication steps that increase the costs. Graphene is an atomically thin material known for its deformability and impermeability to small gases and molecules, including reactive gases like XeF2. These features make graphene a potential candidate as an etch mask for 3D microfabrication. Here, we report the fabrication of various 3D microstructures using graphene etch masks directly grown and patterned on a Si substrate. The patterned graphene deforms and wraps the etched structures, allowing for the fabrication of complicated 3D microstructures, such as mushroom-like and step-like microstructures. As a practical demonstration of the graphene etch mask, we fabricate an omniphobic surface of reentrant 3D structures on a Si substrate. Our work provides a method for fabricating complex 3D microstructures using a graphene etch mask, contributing to advancements in etching and fabrication processes.

Micro‐Casting/Assembly Technology Based on Bismuth‐Based Liquid Metal

AbstractComplex and precise 3D microfabrication technology is the basis for the development of fields including chip‐based bioassay, microelectronic communication, and micromachine manufacturing. Among them, assembled 3D structures provide new ideas to the development of 3D integration of 2D components due to their convenience and high efficiency. In this work, a micro‐casting/assembly technique that can create 3D micro devices is provided with bismuth‐based liquid metal (LM). The liquid metal is first injected into a micro‐mold. The micro‐mold is made by polydimethylsiloxane (PDMS) and porous polycarbonate track‐etched (PCTE) membranes. The mold is then treated with ethanol and deionized water to release the inner injected 2D micro metal components. The effect of each parameter on the generated metal structures is experimentally validated and a LM line with a minimum width of 10 µm is also obtained. For making more functional components, the 2D structures are assembled into 3D. To demonstrate the potential of the technique, reconfigurable micro‐antennas and 3D flow sensors are fabricated and tested at the end of this work, demonstrating potential applications for the micro casting/assembly technology.

Early detection of hypo/hyperglycemia using a microneedle electrode array-based biosensor for glucose ultrasensitive monitoring in interstitial fluid.

Diabetes is a common chronic metabolic disease with a wide range of clinical symptoms and consequences and one of the main causes of death. For the management of diabetes, painless and continuous interstitial fluid (ISF) glucose monitoring is ideal. Here, we demonstrate continuous diabetes monitoring using an integrated microneedle (MN) biosensor with an emergency alert system. MNs are a novel technique in the field of biomedical engineering because of their ability to analyze bioinformation with minimal invasion. In this work we developed a poly(methyl methacrylate) (PMMA) based MN glucose sensor. The device was produced by the 3D printing technique, microfabrication, electrodeposition, and enzyme immobilization step. The in vitro test for the glucose MN sensor showed a linear range from 1.5 to 14 mM with a sensitivity of 1.51 μA mM-1, limit of detection (LOD) of 0.35 mM and good selectivity. Highly repeatable sensing is observed with good reproducibility. The interference-free detection of glucose in the presence of physiologically relevant concentrations of ascorbic acid, uric acid, and mannose is demonstrated, along with the operational stability of the array. After resolving the biofouling consequences linked to on-body sensing, this MN platform would be appealing for minimally invasive electrochemical glucose monitoring. An alert is sent to confidants via email or SMS when the values are abnormal. The application is also able to display the recorded values in the form of a graph to help determine the state of health of the user over a period of time. It can be concluded that continuous monitoring and an emergency alert system are important for keeping an eye on diabetic patients and can send alert in case of an abnormal situation of the patient.

Biomaterials for Artificial Organs and Organoids- A Comprehensive review

The technological development of biomaterials used in forming artificial organs and organoids indicates a revolutionary area within biomedical engineering and the field of regenerative medicine. This study provides an in-depth review of recent progress in biomaterials, emphasizing their design and use for fabricating artificial organs and organoids. The analysis proceeds with examining the necessary parameters for biomaterials in simulating the biological and biomechanical qualities of local tissues. The next effort turns towards synthesizing and characterizing innovative biomaterials, including biocompatible polymers, hydrogels, and bioactive scaffolds that can be tailored to suit specific organ systems. The paper provides an in-depth take on the developments in 3D biological printing and microfabrication techniques, emphasizing how they facilitate the synthesis of complicated, multicellular structures. The research also examines the integration of biomaterials when combined with stem cell technologies, focusing on their role in forming organs and the prospects for customized medical treatments. This review highlights the significant developments achieved in this area and the potential of these technologies in addressing the limited supply of organs, performing drug testing, and improving knowledge of the growth of organs and diseases.

Effect of substituents on the performance of N-carbazolyl double benzylidene ketones in visible/NIR light one/two-photon polymerization

Developing high-performance photoinitiation systems with high sensitivity is of great significance in one/two-photon polymerization. Especially, photoinitiators with rapid photobleaching effects, deep curing abilities and potential for two-photon lithography have great commercial prospects. However, such photoinitiators often require complex organic synthesis, thus having relatively limited varieties. Double benzylidene ketone is widely used as a high-performance dye and can be constructed through a one-step classical aldol condensation reaction. The optimization of its structure often involves introducing extended conjugated structures or different terminal substituents. However, the synergistic impacts of side substituents with different electron effects are rarely studied. Here, six novel carbazolyl double benzylidene ketones with tert-butyl on the terminal position and F atom or N, N-dimethylamino groups substituted at the side position on conjugated structures are designed and prepared to explore the structure–activity relationships. Notably, results show that introducing electron-donating groups at both positions can effectively induce a redshift in the absorption spectra of molecules, and the introduction of an electron-withdrawing F atom on the side position induces impressive photobleaching during photopolymerization under visible LED irradiation. Moreover, CZs/MDEA with PETA exhibit fast writing speed and excellent nano-patterning capability under 780 nm laser in two-photon polymerization (TPP) and have potential applications in 3D microfabrication technologies.

Modeling and Simulation of a Massively Parallelized Multiphoton Polymerization 3D Microfabrication Process

While additive manufacturing based on multiphoton polymerization is currently considered to be a very promising technique for the fabrication of 3D micro‐ and nanostructures, long fabrication times are a major limitation of this approach. Parallelization of the fabrication process is an important technique to overcome this issue. The fabrication process is parallelized by imaging a 1920 × 1080 pixel spatial light modulator into an ultrasensitive triplet–triplet annihilation resist. However, proximity effects between close pixels generate uncontrolled polymerization and make the controlled fabrication of 3D structures difficult. This work models light propagation and chemical interactions in the system to predict fabricated structures with a view to precompensating plot data and improving 3D resolution by performing optical and chemical proximity correction. A simple model gives reasonable predictions of fabricated structures helping us fabricate fully 3D structures in parallel.

Ultra‐Low Threshold Single‐Mode Upconversion Lasing in a Strong Coupled Microcavity via Four‐Photon Absorption

AbstractWith the development of ultra‐fast optical technology, the nonlinear interaction between light and matter has attracted great attention. Upconversion laser generation through multiphoton absorption (MPA) enables numerous critical applications such as quantum signal processing, biophotonics, and 3D microfabrication. Herein, an ultra‐low threshold single‐mode four‐photon absorption (4PA) upconversion lasing at room‐temperature (RT) by constructing a strong‐coupling microcavity is demonstrated. The planar microcavity significantly enhances the 4PA nonlinear interaction, which facilitates the obtainment of low‐threshold upconversion lasing with an excellent output divergence angle and beam quality. In addition, the temporal dynamic mechanism and polarization characteristics of single‐mode upconversion lasing are also comprehensively discussed. The work provides a feasible approach to fabricate a low‐threshold single‐mode upconversion laser through high‐order nonlinear MPA processes.

Thermal Reflow Simulation for PMMA Structures with Nonuniform Viscosity Profile.

This paper presents a new approach to the simulation of the thermal reflow of e-beam-exposed polymethyl methacrylate (PMMA) taking into account its nonuniform viscosity profile. This approach is based on numerical "soapfilm" modeling of the surface evolution, processed by the free software "Surface Evolver" in area normalization mode. The PMMA viscosity profile is calculated via the simulation of the exposed PMMA number average molecular weight distribution using the Monte-Carlo method and empirical formulas. The relation between the PMMA viscosity and the mobility of PMMA surface vertices was determined via the thermal reflow simulation for uniform PMMA gratings using analytical and numerical approaches in a wide viscosity range. The agreement between reflowed profiles simulated with these two approaches emphasizes the applicability of "soapfilm" modeling in the simulation of polymer thermal reflow. The inverse mobility of PMMA surface vertices appeared to be proportional to the PMMA viscosity with a high precision. The developed approach enables thermal reflow simulations for complex nonuniform structures, which allows the use of predictable reflow as a stage of 3D microfabrication.

Optical Waveguides Fabricated via Femtosecond Direct Laser Writing: Processes, Materials, and Devices

AbstractAs the most fundamental unit of photonic integration, optical waveguides offer the possibility of developing efficient and practical photonic chips by facilitating the on‐chip integration of devices with different functions. Femtosecond direct laser writing (FsDLW), as a burgeoning 3D microfabrication technology, can realize the rapid formation of arbitrary optical waveguides without any mask inside versatile materials, such as crystalline dielectric crystals, glasses, polymers, and photoresists. This significant material‐independence allows FsDLW to combine different materials and manufacturing processes to implement a cross‐platform solution. This review first describes the different optical loss types and suitable measurement methods for different applicable scenes, then summarizes the two fabrication mechanisms and points out the general direction for adjusting the waveguide properties by fabrication processes. Finally, the application fields and development prospects of different materials are discussed by overviewing the characteristics of different materials and the material selection preferences of different devices. With a panoramic view of the development, it is concluded with insights and perspectives of the future development of optical waveguides and processing technology via FsDLW.

Digital LIGA: exploitation of droplet-on-demand inkjet printing to fabricate complex mechanical structures by electroforming

A novel 3D fabrication technique called digital LIGA is proposed, integrating functional digital printing with 3D microfabrication via electrodeposition. This allows for the realization of complex multilevel metallic structures without problems associated with merging growth fronts. To achieve this, we developed a gold nanoparticle ink, compatible with a SU-8 photoresist, for printing the digitally-defined seed layers. Using this ink, selective printing of a conductive seed layer on a multi-level photoresist was used along with subsequent electrodeposition. Defect-free complex multilevel metallic 3D structures were successfully prepared via this method.

Ultra-short laser structuring of 3D-microfabricated non-resorbable polystyrene polymer to anchor cellular adhesion

Tissue engineering is emerging as a preferred choice for regeneration of irreversible bone tissue defects. It’s main “weapons” are the artificially created biocompatible three-dimensional cellular matrices that mimic the extracellular matrix’s structure and provide a mechanically stable inert substrate for the natural growth of cells. These porous scaffolds provide sufficient inner surface for cell adhesion, migration, proliferation and protrusion “inside” the temporal implant, facilitating in that way the natural bone ingrowth and vascularization. This leads, eventually, to overgrowing the outer and inner surface of the biomimetic implant with recipient self-formed bone tissue, thus avoiding a possible immune response.In the current study 3D Polystyrene (PS) non-resorbable synthetic cellular bone scaffolds, produced by 3D microfabrication technology, were additionally structured by applying femtosecond (fs) laser radiation with variable parameters thus achieving optimal laser processing conditions, for creation of 3D matrix with enhanced fiber surface properties. The main aim is the establishment of surface structured microporous biomimetic scaffolds, providing improved cell adhesion, infiltration and formation of extracellular matrix. The 3D laser functionalized PS samples were investigated by Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray analysis (EDX), confocal (optical profilometer) and roughness analyses for evaluation of their morphological and chemical properties before and after fs structuring was performed. Water contact angle (WCA) evaluation was also conducted. Future experimental work will include in vitro cellular studies for determining the optimal structuring laser parameters, providing osteoconductive and osteoinductive qualities of the 3D fs-microstructured PS scaffolds.

3D Micropatterned Functional Surface Inspired by Salvinia Molesta via Direct Laser Lithography for Air Retention and Drag Reduction

AbstractBioinspired functional surfaces are attracting increasing interest in surface engineering, mostly in the field of wettability. The Salvinia‐effect is a remarkable example of superficial air retention and drag force reduction caused by selective chemical coating (super‐hydrophobic wax and hydrophilic dead cells) and peculiar 3D hierarchical morphological structures. The replication of Salvinia‐like patterns at the microscale has always been prevented by limitations in microfabrication techniques, thus hindering relevant technological applications at this dimensional scale. Integrating 3D laser lithography and traditional microfabrication techniques, dimensionally downscaled, 3D micropatterned surfaces inspired for the first time by both morphology and chemical coating of the hairs present on the Salvinia Molesta leaves are reproduced. The effect of design and different surface energies (bare hydrophilic, hydrophobic, selective hydrophilic/hydrophobic coating) on the wettability are modeled and investigated. Bioinspired surfaces demonstrated to be super‐hydrophobic in terms of apparent static contact angle (up to 170°) and provide tunable adhesion with roll‐off angle from less than 10° to 90°. They successfully proved remarkable underwater air retention capability, sustained by stable Cassie‐Baxter state under external hydrostatic pressure up to 4 atm. The proposed surfaces are tested in hydrodynamic conditions: drag force reduction is successfully demonstrated with up to 40% of energy saved.

Capillary-driven microfluidics: impacts of 3D manufacturing on bioanalytical devices.

Over decades, decentralized diagnostics continues to move towards rapid and cost-effective testing at the point-of-care (POC). Although microfluidics has become a key enabling technology for POC testing, the need for robust peripheral equipment has been a key limiting factor in reaching an ideal device. Manufacturing technologies are now reaching a level of maturity that allows the definition of 3D features down to the sub-millimeter scale. Employing three-dimensional (3D) features and surface chemistry allows the possibility to pre-program sophisticated control of the capillary flow avoiding bulky peripheral equipment. By designing a sequence of steps, like elution of reagents, washing, mixing, and sensing, capillary valves have become a powerful tool for POC applications. These valves use capillary force to stop and then release flows within pre-programmed capillary circuits without any moving part. Without their 3D structure, the feasibility of creating pre-programmed bioanalytical devices would be nearly impossible. Besides, the advent of smart materials and their variety of surface properties permitted the unprecedented ability to fabricate reliable flow control with a range of capillary driving forces. The classification of such capillary elements is presented in two functional steps - stop and actuation. This review includes the advances in 3D microfabrication, design, and surface chemistry for manufacturing bioanalytical devices. These developments are critically reviewed, focusing on the process and considering phenomena such as timing, reproducibility, unwanted diffusion, and cross-contaminations.

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.

Sapphire Selective Laser Etching Dependence on Radiation Wavelength and Etchant

Transparent and high-hardness materials have become the object of wide interest due to their optical and mechanical properties; most notably, concerning technical glasses and crystals. A notable example is sapphire-one of the most rigid materials having impressive mechanical stability, high melting point and a wide transparency window reaching into the UV range, together with impressive laser-induced damage thresholds. Nonetheless, using this material for 3D micro-fabrication is not straightforward due to its brittle nature. On the microscale, selective laser etching (SLE) technology is an appropriate approach for such media. Therefore, we present our research on C-cut crystalline sapphire microprocessing by using femtosecond radiation-induced SLE. Here, we demonstrate a comparison between different wavelength radiation (1030 nm, 515 nm, 343 nm) usage for material modification and various etchants (hydrofluoric acid, sodium hydroxide, potassium hydroxide and sulphuric and phosphoric acid mixture) comparison. Due to the inability to etch crystalline sapphire, regular SLE etchants, such as hydrofluoric acid or potassium hydroxide, have limited adoption in sapphire selective laser etching. Meanwhile, a 78% sulphuric and 22% phosphoric acid mixture at 270 °C temperature is a good alternative for this process. We present the changes in the material after the separate processing steps. After comparing different processing protocols, the perspective is demonstrated for sapphire structure formation.

3D microfabrication by applying the laser-induced bubble method to the thermoset polymer PDMS using a conventional nanosecond laser.

We recently developed a microfabrication technique [microfabrication using laser-induced bubble (microFLIB)] and applied it to polydimethylsiloxane (PDMS), a thermoset polymer. The technique enabled the rapid fabrication of a microchannel on a PDMS substrate and selective metallization of the channel via subsequent plating; however, the technique was limited to surface microfabrication. Therefore, we explored the feasibility of three-dimensional (3D) microFLIB of PDMS using a nanosecond laser. In the experiment, a laser beam was focused inside pre-curing liquid PDMS and was scanned both perpendicular and parallel to the laser-beam axis to generate a 3D line of laser-induced bubbles. In the microFLIB processing, the shape of the created bubbles was retained in the pre-curing PDMS for more than 24 h; thus, the line of bubbles generated by the perpendicular laser scanning successfully produced a 3D hollow transverse microchannel inside the PDMS substrate after subsequent thermal curing. In addition, a through-hole with an aspect ratio greater than ∼200 was easily fabricated in the PDMS substrate by parallel laser scanning. The fabrication of a 3D microfluidic device comprising two open reservoirs in a PDMS substrate was also demonstrated for biochip applications.

Two-photon polymerization for 3D biomedical scaffolds: Overview and updates.

The needs for high-resolution, well-defined and complex 3D microstructures in diverse fields call for the rapid development of novel 3D microfabrication techniques. Among those, two-photon polymerization (TPP) attracted extensive attention owing to its unique and useful characteristics. As an approach to implementing additive manufacturing, TPP has truly 3D writing ability to fabricate artificially designed constructs with arbitrary geometry. The spatial resolution of the manufactured structures via TPP can exceed the diffraction limit. The 3D structures fabricated by TPP could properly mimic the microenvironment of natural extracellular matrix, providing powerful tools for the study of cell behavior. TPP can meet the requirements of manufacturing technique for 3D scaffolds (engineering cell culture matrices) used in cytobiology, tissue engineering and regenerative medicine. In this review, we demonstrated the development in 3D microfabrication techniques and we presented an overview of the applications of TPP as an advanced manufacturing technique in complex 3D biomedical scaffolds fabrication. Given this multidisciplinary field, we discussed the perspectives of physics, materials science, chemistry, biomedicine and mechanical engineering. Additionally, we dived into the principles of tow-photon absorption (TPA) and TPP, requirements of 3D biomedical scaffolders, developed-to-date materials and chemical approaches used by TPP and manufacturing strategies based on mechanical engineering. In the end, we draw out the limitations of TPP on 3D manufacturing for now along with some prospects of its future outlook towards the fabrication of 3D biomedical scaffolds.