Microfabrication Methods Research Articles

Microfabrication of Highly Robust Superhydrophobic Glass Surfaces Via Combined Thermal Poling and HF Gas Etching

Superhydrophobic glass affords a clear view by preventing the adhesion of raindrops and dirt. This type of glass can be used in automotive windows, sensor covers for automatic driving, solar panels, and building windows. A superhydrophobic surface has a water contact angle greater than 150° and is fabricated by combining micro- to nanoscale structures with low-surface energy coating materials. In the previous study [1], we demonstrated that the transparent superhydrophobic glass can be efficiently produced through HF gas etching. The robustness of its superhydrophobic surface is the most challenging issue in the practical application of the superhydrophobic glass. The recent breakthrough, namely, the development of superhydrophobic surfaces with “armor structures” [2], addresses this issue for conventional superhydrophobic surfaces containing nanostructures that would be easily destroyed by abrasion. The armor structures protect the fragile superhydrophobic nanostructures, resulting in highly robust abrasion resistance. In the previous study, the armor structures were fabricated using molding methods that impose strict limitations on the shapes that can be formed. A common microfabrication technique, which combines photolithography and reactive ion etching (RIE), can be applied to glass surfaces. This method allows for the formation of any desired shape on the glass surface. However, this method involves vacuum processes that require masks, resulting in extremely low productivity. Compared to electronic components, for which this technique is typically used, glass has a larger area and lower unit cost. The low production efficiency of the technique would therefore hinder its applicability.In this study, we developed a unique microfabrication method that combines thermal poling and HF gas etching. In thermal poling, heated glass is sandwiched between electrodes, and a high voltage is applied to transfer alkali metal ions from the anode-side surface of the glass [3]. Microstructures formed on the surface of the anode used for thermal poling are transferred onto the glass surface as alkali metal-deficient regions. Subsequently, etching the glass facilitates the formation of these shapes on the glass surface owing to the difference in etching rates. At this stage, traditional solution-etching fabricated steps on the nanometer scale; larger steps on the microscale remain to be formed. We fabricated the steps on the micrometer scale via HF gas etching, which presents a large difference in the etching rate between the alkali-metal-deficient layer and the normal surface. Figure 1 presents the results of glass microfabrication using thermal poling and HF gas etching. Circular shapes with diameters of 2.5, 5, 10, 20, and 40 µm were created for the proof of concept. A glassy carbon microfabricated via RIE was used as the anode. For thermal poling, a voltage of 300 V was applied to the glass heated to 450 °C for 5 min. HF gas etching was performed at 500 °C with a small amount of HF gas for a few seconds. A highly robust superhydrophobic glass surface was thus fabricated. The surface produced using the proposed method successfully endured 1000 abrasion cycles, while that produced using the conventional method lost its superhydrophobicity after ten abrasion cycles.[1] K. Yasuda, Y. Hayashi, and T. Homma, ACS Omega, 9, 12204–12210 (2024).[2] D. Wang et al., Nature, 582, 55–59 (2020).[3] S. Ikeda, K. Uraji, T. Suzuki, K. Yamamoto, and J. Nishii, J. Non-Cryst. Solids, 453, 103–107 (2016). Figure 1

3D Printed Metallic Pillar Nanomechanical Resonators Decorated with TiO2 Nanotubes for Highly Sensitive Environmental Applications

AbstractMicro and nanomechanical devices offer enhanced sensing capabilities for detecting biological and chemical small molecules. However, miniaturization necessitates advanced fabrication processes and complex measurement systems, hindering routine sensor analysis. While alternative methods like 3D printing show promise, challenges such as low device resolution persist due to intrinsic damping of polymer inks. In this study, an array of micrometric pillar resonators is fabricated in Ti6Al4 V alloy using additive manufacturing based on laser powder bed fusion technology. These metallic nanomechanical resonators exhibit a very high quality factor with minimal difference between air and vacuum measurements due to low intrinsic damping. Furthermore, titania nanotubes grown on the pillars via anodic oxidation heighten sensitivity for molecular dye degradation evaluation. Leveraging the weak coupling phenomenon among the pillars in the array, these devices facilitate large‐scale parallelized measurements, here demonstrated with real‐time analysis of dye degradation process. This approach to creating mass sensing devices via metallic additive manufacturing can usher in a new generation of highly performing resonating sensor arrays, offering a cost‐effective and efficient alternative to traditional silicon microfabrication methods.

Limitations and characteristics of converted industrial acrylic sheet into an in vitro platform using CO2 laser

The recent US FDA Modernization Act 2.0 has intensified interest in microfluidic-based in vitro systems for preclinical research. However, the high costs of conventional microfabrication methods and commercial devices present significant barriers, particularly in developing countries. This study addresses these challenges by exploring the use of industrial-grade acrylic sheets and a conventional CO2 laser for cost-effective microfabrication. The research investigates the effects of laser parameters—specifically nozzle speed and power—on the dimensions and quality of microchannels, surface roughness, and bonding strength. Results indicate that increased nozzle speed reduces kerf width and enhances microchannel quality, whereas high laser power (∼52 watts) induces bubbling at the edges. A simple acetone and ethanol mixture was found to provide optimal bonding strength without altering the acrylic’s molecular structure. UV spectrophotometry revealed minimal changes (∼6 %) in visible light transmittance due to bonding conditions, while FTIR analysis showed no residuals that could potentially cause cytotoxicity. Despite variations in surface roughness resulting from the etching process, cell viability remained unaffected. The surfaces supported effective cell culture for lung (A549), neuron (SH-SY5Y), and liver (HepG2) cell lines. This approach presents a practical and cost-effective solution for developing in vitro platforms, making it an accessible option for research and academic applications.

Optimization of W-band interaction structure developed using three different micro-fabrication techniques.

In this paper, an experimental investigation has been performed for the three different micro-fabrication techniques for optimization in the development process of the W-band planar beam-wave interaction structure. The W-band planar beam-wave interaction structure has been developed using three different micro-fabrication methods, namely micro-EDM (electric discharge milling), wire-EDM, and micro-milling. The effect of each fabrication method on the developed structure is analyzed using scanning electron microscopy and ZETA 3D optical microscopy for their optimization. The experimental analysis has been performed for the developed W-band planar beam-wave interaction structure with an optimized process to achieve a dimensional deviation of less than 10μm and surface roughness of less than 50nm.

Replicating biological 3D root and hyphal networks in transparent glass chips

Replicating the complex 3D microvascular architectures found in biological systems is a critical challenge in tissue engineering and other fields requiring efficient mass transport. Conventional microfabrication techniques often face limitations in creating extensive hierarchical networks, especially within bulk materials. Here, we report a versatile bioinspired approach to generate optimized 3D microvascular networks within transparent glass matrix by transcribing the natural growth patterns of plants and fungi. Plant seeds or fungal spores are first cultivated on nanoparticle-based culture media. Subsequent heat treatment removes the biological species while sintering the surrounding compound into a solidified chip with replica root/hyphal architectures as open microchannels. A diverse range of architectures, including the hierarchical branching of plant roots and the intricate networks formed by fungal hyphae, can be faithfully replicated. The resultant glass microvascular networks exhibit high chemical and thermal stability, enabling applications under harsh conditions. Fluid flow experiments validate the functionalities of the fabricated channels. By co-cultivating plants and fungi, hierarchical multi-scale architectures mimicking natural vascular systems are achieved. This bioinspired manufacturing technique leverages autonomous biological growth for architectural optimization, offering a complementary approach to existing microfabrication methods. The transparent nature of the glass chips allows for direct optical inspection, potentially facilitating integration with imaging components. This versatile platform holds promise for various engineering applications, such as microreactors, heat exchangers, and advanced filtration systems.

Development of a Highly Sensitive Electrochemical Detection of Salivary Glucose and pH Sensors Based on Glucose Oxidase Using Interdigitated Microelectrodes

The use of electrochemical nanosensors has seen a significant uptick in recent years, largely due to the improved chemical and physical properties that result from the modification of nano or microelectrode devices with nanomaterials.[1] These electrodes play a crucial role in enhancing electrochemical-based nanosensors, offering benefits such as a higher signal-to-noise ratio, lower detection limits, cost-effectiveness, ease of fabrication, and the ability to achieve steady-state currents. The interest in electrochemical nanosensors is considerable, given their broad application spectrum, which includes areas like animal health, human health, environmental monitoring, and bioprocess monitoring.[2] The focus of this research is the development of on-chip salivary glucose and pH sensors that are integrated on silicon wafers. These sensors are specifically designed to identify two frequently occurring bovine diseases: bovine respiratory disease (BRD) and scour. Both of these diseases are highly contagious, often resulting in fatal outcomes for calves, and cause economic losses amounting to millions of euros across Europe. Therefore, early detection of BRD and scour is essential to prevent, oversee, or delay the progression of the disease and its related complications. However, the current methods of blood glucose testing for calves have a significant disadvantage, as they require regular invasive blood sampling. Encouragingly, the analysis of saliva has surfaced as a non-invasive and convenient alternative for monitoring glucose levels in calves with above-mentioned disease.[3] Thus, it is necessary to develop a highly sensitive electrochemical nanosensor for early detection of BRD and scour by using biomarkers (glucose, pH) in a calf's saliva. The proposed electrochemical nanosensor is based on a micro fabricated device that integrates a silicon microelectrode, reference electrode, and counter electrode with six individual sensor that can be used for the detection of six different biomarkers i.e. glucose, pH, lactate, electrolytes, etc. The sensing mechanism is based on the measurement of changes in current that occur because of glucose and pH interactions with the modified silicon surface. The sensors are designed to detect small changes in glucose and pH concentrations that can be indicative of the onset of BRD and scour. The main advantage of the proposed electrochemical nanosensor is its ability to provide rapid and accurate detection of BRD and scour in calves. Early detection of these diseases can significantly improve treatment outcomes and reduce the risk of transmission to other animals. In addition, the low cost and ease of fabrication of these sensors make them an attractive option for large-scale deployment in agricultural settings. In conclusion, the development of on-chip electrochemical nanosensors for the early detection of bovine respiratory disease and scour by using saliva as a medium is a promising approach for improving animal health and reducing economic losses. The proposed sensors offer high sensitivity, low cost, and easy fabrication, making them an attractive option for widespread deployment in agricultural settings. Future research can focus on optimizing the sensor design for improved performance and expanding the range of biomarkers that can be detected.This work represents the microfabrication and characterization of gold interdigitated electrodes (IDE) on silicon using standard microfabrication methods i.e., lithography and etching techniques. The sensor have six individual working electrodes (WEs) along with on-chip gold counter and platinum reference electrodes and can be modified individually for glucose and pH sensor. A two-step electrodeposition process was carried out for platinum platting thus incorporating glucose oxidase (GOx) onto a platinum-modified gold IDE with an o-phenylenediamine (o-PD). The enzymatic based nanosensor demonstrated a linear reduction response to wider range of glucose from 0.02-7mM using chronoamperometric measurements in artificial saliva (Figure 1a,b). In addition, real calf samples have been used to detect the glucose level in calf saliva and compared with commercial glucometer (Figure 1c). Furthermore, at gold IDE, the sensor exhibits linear responses for pH ranging from pH 5-8 using cyclic voltammetric analysis (Figure 1d,f).

Evaluation of industrial and consumer 3-D resin printer fabrication of microdevices for quality management of genetic resources in aquatic species

Aquatic germplasm repositories can play a pivotal role in securing the genetic diversity of natural populations and agriculturally important aquatic species. However, existing technologies for repository development and operation face challenges in terms of accuracy, precision, efficiency, and cost-effectiveness, especially for microdevices used in gamete quality evaluation. Quality management is critical throughout genetic resource protection processes from sample collection to final usage. In this study, we examined the potential of using three-dimensional (3-D) stereolithography resin printing to address these challenges and evaluated the overall capabilities and limitations of a representative industrial 3-D resin printer with a price of US$18,000, a consumer-level printer with a price <US$700, and soft lithography, a conventional microfabrication method. A standardized test object, the Integrated Geometry Sampler (IGS), and a device with application in repository quality management, the Single-piece Sperm Counting Chamber (SSCC), were printed to determine capabilities and evaluate differences in targeted versus printed depths and heights. The IGS design had an array of negative and positive features with dimensions ranging from 1 mm to 0.02 mm in width and depth. The SSCC consisted of grid and wall features to facilitate cell counting. The SSCC was evaluated with polydimethylsiloxane (PDMS) devices cast from a typical photoresist and silicon mold. Fabrication quality was evaluated by optical profilometry for parameters such as dimensional accuracy, precision, and visual morphology. Fabrication time and cost were also evaluated. The precision, reliability, and surface quality of industrial-grade 3-D resin printing were satisfactory for operations requiring depths or heights larger than 0.1 mm due to a low discrepancy between targeted and measured dimensions across a range of 1 mm to 0.1 mm. Meanwhile, consumer-grade printers were suitable for microdevices with depths or heights larger than 0.2 mm. While the performance of either of these printers could be further optimized, their current capabilities, broad availability, low cost of operation, high throughput, and simplicity offer great promise for rapid development and widespread use of standardized microdevices for numerous applications, including gamete quality evaluation and “laboratory-on-a-chip” applications in support of aquatic germplasm repositories.

Integration of Sm2Co17 Micromagnets in a Ferromagnetic Multipolar Microrotor to Enhance MEMS and Micromotor Performance.

MEMS and micromotors may benefit from the increasing complexity of rotors by integrating a larger number of magnetic dipoles. In this article, a new microassembly and bonding process to integrate multiple Sm2Co17 micromagnets in a ferromagnetic core is presented. We experimentally demonstrate the feasibility of a multipolar micrometric magnetic rotor with 11 magnetic dipoles made of N35 Sm2Co17 micromagnets (length below 250 μm and thickness of 65 μm), integrated on a ferromagnetic core. We explain the micromanufacturing methods and the multistep microassembly process. The core is manufactured on ferromagnetic alloy Fe49Co49V2 and has an external diameter of 800 μm and a thickness of 200 μm. Magnetic and geometric measurements show good geometric fitting and planarity. The manufactured microrotor also shows good agreement among the magnetic measurements and the magnetic simulations which means that there is no magnetic degradation of the permanent magnet during the manufacturing and assembly process. This technique enables new design possibilities to significantly increase the performance of micromotors or MEMS.

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.

Nuclear deformation and cell division of single cell on elongated micropatterned substrates fabricated by DMD lithography

Cells sense mechanical signals from the surrounding environment and transmit them to the nucleus through mechanotransduction to regulate cellular behavior. Microcontact printing, which utilizes elastomer stamps, is an effective method for simulating the cellular microenvironment and manipulating cell morphology. However, the conventional fabrication process of silicon masters and elastomer stamps requires complex procedures and specialized equipment, which restricts the widespread application of micropatterning in cell biology and hinders the investigation of the role of cell geometry in regulating cell behavior. In this study, we present an innovative method for convenient resin stamp microfabrication based on digital micromirror device planar lithography. Using this method, we generated a series of patterns ranging from millimeter to micrometer scales and validated their effectiveness in controlling adhesion at both collective and individual cell levels. Additionally, we investigated mechanotransduction and cell behavior on elongated micropatterned substrates. We then examined the effects of cell elongation on cytoskeleton organization, nuclear deformation, focal adhesion formation, traction force generation, nuclear mechanics, and the growth of HeLa cells. Our findings reveal a positive correlation between cell length and mechanotransduction. Interestingly, HeLa cells with moderate length exhibit the highest cell division and proliferation rates. These results highlight the regulatory role of cell elongation in mechanotransduction and its significant impact on cancer cell growth. Furthermore, our methodology for controlling cell adhesion holds the potential for addressing fundamental questions in both cell biology and biomedical engineering.

A Versatile Microchannel Array Device for Portable and Parallel Droplet Generation

The efficient generation of monodispersed droplets holds great promise for micro‐/nanoparticle synthesis and biochemical analysis. However, it remains a challenge to achieve high‐throughput generation of monodispersed droplets in a portable and/or parallel manner in nonexpert biomedical laboratories. Herein, a versatile microchannel array (μCA) device is reported that is portable, multifaceted, reliable, and mass‐manufacturable, supporting the high‐throughput generation of monodispersed droplets in different ways. This device consists of a silicon‐based μCA chip based on the step emulsification principle, as well as two matching plastic containers, both of which can be mass‐manufactured by traditional microfabrication methods at low material costs. With the μCA device, aqueous solution can be dispersed into emulsion droplets by various modes, such as mechanical pump‐based large‐scale, handheld syringe‐based portable, and gas pump‐based highly parallel droplet generation. Furthermore, it is demonstrated that our cost‐effective device can be applied for digital polymerase chain reaction analysis, supporting the need for more accessible microfluidic systems. Thus, the present device is expected to have a significant impact on both benchside and bedside applications.

Batch Fabrication of Microelectrode Arrays with Glassy Carbon Microelectrodes and Interconnections for Neurochemical Sensing: Promises and Challenges.

Flexible multielectrode arrays with glassy carbon (GC) electrodes and metal interconnection (hybrid MEAs) have shown promising performance in multi-channel neurochemical sensing. A primary challenge faced by hybrid MEAs fabrication is the adhesion of the metal traces with the GC electrodes, as prolonged electrical and mechanical stimulation can lead to adhesion failure. Previous devices with GC electrodes and interconnects made of a homogeneous material (all GC) demonstrated exceptional electrochemical stability but required miniaturization for enhanced tissue integration and chronic electrochemical sensing. In this study, we used two different methods for the fabrication of all GC-MEAs on thin flexible substrates with miniaturized features. The first method, like that previously reported, involves a double pattern-transfer photolithographic process, including transfer-bonding on temporary polymeric support. The second method requires a double-etching process, which uses a 2 µm-thick low stress silicon nitride coating of the Si wafer as the bottom insulator layer for the MEAs, bypassing the pattern-transfer and demonstrating a novel technique with potential advantages. We confirmed the feasibility of the two fabrication processes by verifying the practical conductivity of 3 µm-wide 2 µm-thick GC traces, the GC microelectrode functionality, and their sensing capability for the detection of serotonin using fast scan cyclic voltammetry. Through the exchange and discussion of insights regarding the strengths and limitations of these microfabrication methods, our goal is to propel the advancement of GC-based MEAs for the next generation of neural interface devices.

Laser constructed vacancy-rich TiO2-x/Ti microfiber via enhanced interfacial charge transfer for operando extraction-SERS sensing

Semiconductor-molecule surface-enhanced Raman scattering (SERS), especially the stronger interfacial charge transfer process (ICTP), represents a frontier in the field of SERS with spectral reproducibility and unparalleled selectivity. Herein, through a laser microfabrication method in situ, the free-standing, super hydrophilic and vacancy-rich TiO2-x/Ti is successfully synthesized. Using blue TiOx/Ti (B-TiOx/Ti) as pre-concentrated substrate, a nanomolar-level limit of detection of 12 nmol/L at 1385 cm–1, is confirmed using crystal violet (CV) bacteriostat as a model under 532 nm excitation. Furthermore, the results demonstrate that the SERS enhancement mechanism is via the moderate adulteration of oxygen vacancy, which leads to a narrow value of band gap and increases the ICTP of substrate to molecules. Using a hand-held extractor assembled with B-TiOx/Ti microfiber, the operando analysis of mixtures distributed information excited in different parts of Asian carp is facilely achieved. This work guides the controlled synthesis of vacancy-rich TiO2-x/Ti nanostructure and its application in ultrasensitive extraction-SERS detection. It also provides the direction for the rapid and operando transmission of biological information with temporal and spatial concentration distribution in human tissues by highly sensitized materials.

Thermal Conductivity Gas Sensors for High-Temperature Applications.

This paper describes a fast and flexible microfabrication method for thermal conductivity gas sensors useful in high-temperature applications. The key parts of the sensor, the microheater and the package, were fabricated from glass-coated platinum wire and the combination of laser micromilling (ablation) of already-sintered monolithic ceramic materials and thick-film screen-printing technologies. The final thermal conductivity gas sensor was fabricated in the form of a complete MEMS device in a metal ceramic package, which could be used as a compact miniaturized surface-mounted device for soldering to standard PCB. Functional test results of the manufactured sensor are presented, demonstrating their full suitability for gas sensing applications and indicating that the obtained parameters are at a level comparable to those of standard industrially produced sensors. The results of the design and optimization principles of applied methods are discussed with regard to possible wider applications in thermal gas sensor prototyping in the future. The advantage of the developed sensors is their ability to operate in air environments under high temperatures of 900 °C and above. The sensor element material and package metallization were insensitive to oxidation compared with classical sensor-solution-based metal-glass packages and silicone MEMS membranes, which exhibit mechanical stress at temperatures above 700 °C.

Design, fabrication, and optimization of superbiphilic-pillar structures for extreme efficient boiling

Boiling enhancement of engineering surfaces has important applications in energy systems and effective thermal management. This study developed the superbiphilic-pillar structures to maximize boiling efficiency. By utilizing micro-manufacturing methods and subsequent chemical modifications, superbiphilic-pillar specimen possesses both superhydrophobic pyramid-pillar and superhydrophilic channel were successfully fabricated. The developed superbiphilic-pillar structures can enhance the bubble nucleation through superhydrophobic pyramid-pillar, and achieve rapid detachment and effective coolant supply using superhydrophilic channel. The innovative structure and wettability design makes the superbiphilic-pillar specimen show an ultra-high heat transfer coefficient of 123.3 kW/m2K in the pool boiling test, and reach an excellent critical heat flux of 201.6 W/cm2, which is 216.2% and 97.1% higher than the flat specimen. To optimize the regional configuration, the effect of the proportion of superhydrophobic pyramid-pillar on boiling enhancement was studied. Combined with bubble dynamics analysis, it is shown that superhydrophobicity and pyramid-pillar structures have a competitive mechanism for the bubble coalescence and detachment. Thus, which leads to a non-monotonic relationship between boiling enhancement and the proportion of superhydrophobic pyramid-pillar, and the specimen with 56% superhydrophobic pyramid-pillar has the most efficient boiling performance.

Discharge Characteristics and Mechanisms of Electrolytic Discharge Processing by Jet Mask

As a novel microfabrication method, electrochemical discharge machining has remarkable effects on the forming and processing of brittle and hard materials and non-conductive materials, but little research has been done on the electrochemical discharge mode in the jet state. To fulfil the potential of this technology, innovative research on the discharge characteristics and mechanism of electrochemical discharge machining in the jet mask is proposed. A high-speed camera observation experiment was set up to record the process of the jet flow column discharge formation and penetration. Changes in the electric field of the electrolytic jet channel were analysed by simulation software, and the morphology of the machined micro-pits was observed using a microscope. A mathematical derivation of the dielectric electric field in the gas–liquid two-phase jet column reveals the mechanism of discharge channel formation in the jet state. The experiments show that when the processing voltage is 400 V, a stable continuous spark appears, realizing the unique characteristics of a large-gap long-distance discharge and a flat small circle-shaped discharge mark produced at the bottom of the crater. The actual field strength within the bubble of this model obtained by mathematical derivation is approximately 61.5 kV/cm greater than the critical field strength for air bubble breakdown in the standard state, where bubble breakdown occurs in the discharge.

Microfluidic Devices for Precision Nanoparticle Production

In recent years, the field of drug delivery has seen a significant shift towards the exploration and utilization of nanoparticles (NPs) as versatile carriers for therapeutic agents. With its ability to provide exact control over NPs’ characteristics, microfluidics has emerged as a potent platform for the efficient and controlled synthesis of NPs. Microfluidic devices designed for precise fluid manipulation at the micro-scale offer a unique platform for tailoring NP properties, enabling enhanced control over NP properties such as size, morphology, and size distribution while ensuring high batch-to-batch reproducibility. Microfluidics can be used to produce liposomes, solid lipid nanoparticles, polymer-based NPs, and lipid-polymer hybrid NPs, as well as a variety of inorganic NPs such as silica, metal, metal oxide, quantum dots, and carbon-based NPs, offering precise control over composition and surface properties. Its unique precision in tailoring NP properties holds great promise for advancing NP-based drug delivery systems in both clinical and industrial settings. Although challenges with large-scale production still remain, microfluidics offers a transformative approach to NP synthesis. In this review, starting from the historical development of microfluidic systems, the materials used to create the systems, microfabrication methods, and system components will be discussed in order to provide the reader with an overview of microfluidic systems. In the following, studies on the fabrication of nanoparticles such as lipid NPs, polymeric NPs, and inorganic NPs in microfluidic devices are included.

Etching-Free Wafer-Level Fabrication of Suspended Mesh-Type Nanoheaters

Recently, various strategies have been demonstrated to reduce the operating power of electrothermal devices by implementing a miniaturized Joule-heating-based heater. To operate the heaters with low power, the miniaturized heating element must be well-insulated by spacing it apart from the substrate. The conventional microfabrication methods for implementing small-size (e.g., sub-micrometer to micrometer scales) and suspended heater architecture have relied on the etching process [1], which requires accurate and delicate process control. Moreover, the etching process becomes more complicated to prevent damage to the delicate heater structures, hindering yield and reliability. Therefore, a trade-off has occurred between the reduction in power consumption (i.e., heater size reduction) and production cost (e.g., cost, time, and high-tech development).Prior to this research, we demonstrated the fabrication of suspended 1D nanoheaters by depositing a thin Au layer selectively on top of a suspended carbon nanowire and their applications as ultralow-power gas sensors [2, 3]. Although the suspended nano-sized carbon heater body was patterned without an etching process, the Si substrate had to be etched in an isotropic manner to form a built-in shadow mask to facilitate batch nanofabrication.Here, we present a novel wafer-level fabrication method of a suspended sub-micrometer-sized mesh-type heater without using any conventional etching process. The mesh structure is separated from the substrate by 7–8 μm through two-step UV exposure on a negative photoresist layer: the first exposure is executed with large energy for post-forming, and the second exposure forms a suspended structure at the surface of the photoresist with small UV energy. This monolithic polymer structure is then pyrolyzed and converted to a suspended glassy carbon mesh. The suspended mesh consists of sub-micrometer-sized grid-shaped lines (width 200~500 nm, grid size ~ 10 μm). A thin (~ 50 nm) metal film is deposited on the top of the mesh for use as a heater layer by a directional evaporation method. During the directional deposition, the metal deposited on the substrate in the shape of the suspended mesh. Therefore, as long as the photomask size of the metal coating is smaller than the entire mesh size, the metal layer on the substrate is disconnected. Consequently, suspended mesh-type heaters can be facilitated without the etching process. Furthermore, various heater shapes can be engraved according to the photomask patterns of the mesh structure and metal layer, enabling customized mass production. At this conference, the fabrication of the various types of mesh-type nanoheaters and their applications as gas sensors will be presented. Reference [1] Choi, K. W.; Lee, J. S.; Seo, M. H.; Jo, M. S.; Yoo, J. Y.; Sim, G. S.; Yoon, J. B. Batch-fabricated CO gas sensor in large-area (8-inch) with sub-10 mW power operation. Sens. Actuators, B Chem. 2019, 289, 153–159.[2] Kim, T.; Cho, W.; Kim, B.; Yeom, J.; Kwon, Y. M.; Baik, J. M.; Kim, J. J.; Shin, H. Batch Nanofabrication of Suspended Single 1D Nanoheaters for Ultralow‐Power Metal Oxide Semiconductor‐Based Gas Sensors. Small 2022, 2204078.[3] Cho, W.; Kim, T.; Shin, H. Thermal conductivity detector (TCD)-type gas sensor based on a batch-fabricated 1D nanoheater for ultra-low power consumption. Sens. Actuators, B Chem. 2022, 371, 132541.

Industrial perspectives for personalized microneedles.

Microneedles and, subsequently, microneedle arrays are emerging miniaturized medical devices for painless transdermal drug delivery. New and improved additive manufacturing methods enable novel microneedle designs to be realized for preclinical and clinical trial assessments. However, current literature reviews suggest that industrial manufacturers and researchers have focused their efforts on one-size-fits-all designs for transdermal drug delivery, regardless of patient demographic and injection site. In this perspective article, we briefly review current microneedle designs, microfabrication methods, and industrialization strategies. We also provide an outlook where microneedles may become personalized according to a patient's demographic in order to increase drug delivery efficiency and reduce healing times for patient-centric care.

Laser-induced forward transfer (LIFT) based bioprinting of the collagen I with retina photoreceptor cells

This study focuses on the 3D bioprinting of retina photoreceptor cells using a laser-induced forward transfer (LIFT) based bioprinting system. Bioprinting has a great potential to mimic and regenerate the human organoid system, and the LIFT technique has emerged as an efficient method for high-resolution micropatterning and microfabrication of biomaterials and cells due to its capability of creating precise, controlled microdroplets. In this study, the parameters for an effective femtosecond laser-based LIFT process for 3D bioprinting of collagen biomaterial were studied. Different concentrations of collagen I solutions were tested and 0.75 mg/ml to 1 mg/ml collagen Ⅰ was identified as the right concentration that can be transferred through the LIFT system. Then, retinal cone cells were mixed with collagen I and Dulbecco's Modified Eagle's Medium (DMEM) and printed drop-by-drop lines. Some important laser parameters such as pulse energy and pulse pick divider were experimented with to form a successful, smooth, high-resolution deposition. The cell viability in the bioink and printed droplet was measured at different time horizons. A general full factorial design of the experiment was used to analyze and observe the relationship between the droplet quality and the LIFT process parameters. Using 15 µJ and 16 µJ pulse energy, the cell-laden bioink was printed successfully. This research study will help to print other retinal neuron cells with collagen Ⅰ in the LIFT system and show the way of constructing layer-by-layer different cell lines that will help to fabricate the retina ultimately.