Fluidic Chip Research Articles

Process for integrating multiple porous silicon membranes with variable characteristics into planar microfluidics

We present a fabrication process based on selective ion implantation to monolithically integrate several porous silicon membranes with different morphologies in the same planar fluidic chip through a single anodization step. By manipulating the dopant concentration of specific zones of a silicon on insulator wafer, the porous silicon elements formed through electrochemical anodization present different characteristics in terms of pore size and porosity. Using this technique, we are able to fabricate both lateral porous silicon membranes and standard porous silicon membranes with vertical pores that can be used in flow-through and flow-over configurations. Achieved mean pore sizes and porosities for the various membranes integrated in the same chip range from 25 nm to 50 nm, and 65–90 %, respectively. Because porous silicon membranes have been used for biosensing and for sample preparation in microfluidics devices, this method is foreseen to enable the use of porous silicon membranes to achieve all the functions involved in the analytical process on a single chip.

Terahertz SWNT-based fluidic chip for sensing enantioselectivity

Enantioselectivity sensing is crucial in biological systems due to the impact of the selective behaviors of chiral compounds on their targets. Conventional approaches for detecting enantioselectivity are restricted by the presence of high phonon energy, complex device manufacturing processes, low sensitivity, and the need for large sample sizes. Here, we propose a single-walled carbon nanotube (SWNT)-based fluidic chip that uses terahertz (THz) optical rotatory dispersion (ORD) spectroscopy to detect tartaric acids with high selectivity in very small amounts of liquid. The chip is composed of tailored U-shaped metasurfaces that show significant amplification of the near-field around the typical peaks of tartaric acids in the ORD spectrum. Additionally, it includes subwavelength gratings made of SWNTs, allowing for accurate detection of polarization angles. The limit of detection (LOD) for d-tartaric acid and l-tartaric acid are 17.9 mg/L and 11.0 mg/L, respectively. The sensitivities are superior to those of UV ORD or CD spectrometers. Furthermore, the presence of tartaric acid in wine is effectively identified, with a LOD of 25.60 mg/L. This technological development provides a significant improvement in chiral analysis by allowing for quick, highly sensitive, and precise detection of enantiomers.

Multifunctional Spirulina-hybrid helical microswimmers: Imaging and photothermal efficacy enabled by intracellular gold deposition

Helical micro-/nanoswimmers have been extensively explored as a miniaturized robotic tool for advanced biomedicine in the past two decades. However, the integration of biomedical functions on the existing swimmers remains insufficient to allow further in vivo developments. We propose a chemically engineered Spirulina microalgae with biogenic gold nanoparticles deposited in its cells and magnetite nanoparticles assembled on its surface. This biohybrid helical microswimmer is naturally of many desired functions and can be easily functionalized through surface modification and/or intracellular loading. The gold-enabled digital subtraction angiography of multimodal imaging function is highlighted herein. Such imaging modality makes real-time tracking possible in deep anatomical regions, guaranteeing precise in vivo navigation of our swimmers to specific lesions. Meanwhile, the gold-enhanced photothermal efficacy is also noteworthy. It regulates swimmer degradation via controlling photothermal heat and can be harnessed to implement targeted therapy, for which the targeting process and therapeutic effect are successfully demonstrated in a fluidic chip. Furthermore, the fabrication method is straightforward and cost-effective, suitable for mass production. All these results clarify the functionalization strategy enabled by biogenic intracellular deposition and provide a multifunctional biohybrid microswimmer.

Flow Behavior Characterization of DNA Molecules in Passive Nanofluidic Devices†

This work aims to develop a method for analyzing the dynamic flow of single DNA molecules through nanochannels in fluidic chip which work passively. For this purpose, a two‐laser system was used, which is coupled into a fluorescence microscope and can detect labeled DNA molecules using a single photon counter for signal read‐out in real‐time. The two laser spots are focused at different points of the nanochannel, and can be used to obtain the speed and molecular extension of the DNA. For example, a velocity of 1.82 μm/ms and a spatial extension of 0.9 μm were determined for pUC18/19 DNA (2686 bp) in a nanochannel with a width and depth of 200 nm × 100 nm and a length of 10 μm. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Optical knife-edge detection for micropillar-based microfluidic viscometer

We demonstrate the use of an optical knife-edge technique in micropillar-based microfluidic chips, which are intended for viscosity measurements. Our demonstrations rely on the use of a single photodiode, offering a significant cost, form factor and computational efficiency advantage over CMOS camera detection. Our readout methodology involves the utilization of pillars as waveguides, such that a laser is coupled from the backside of the fluidic chip, while the output light is monitored with a photodiode using knife-edge detection. The bending of the pillars due to applied flow alters the observed light intensity, from which the bending angle could be deduced. We present ray-tracing simulations and conduct proof-of-concept experiments on a micropillar-based microfluidic chip. The bending of the pillar observed with the knife-edge technique matches well with that observed with a camera. With further development, the proposed methodology can be employed as a compact and low-cost point-of-care instrument for real-time viscosity measurements.

B-031 Digital Elisatotal 25-Hydroxyvitamin D

Abstract Evaluation of digital ELISA using a high-resolution computational optical system for measurement of total 25-hydroxyvitamin D Background Biomarkers such as vitamin D occur at very low concentrations in blood, and sensitive detection methods are required in order to measure them. It is difficult to accurately measure low-concentration biomarkers using conventional enzyme-linked immunosorbent assays (ELISA) with fluorescence staining. By developing a digital ELISA (DELISA, Small Machines, Seoul, Korea) platform, a low concentration substance was realized by analyzing the digitalized signal through a high-resolution computational optical system in a microfluidic chip. We evaluated DELISA for measurement of total 25-hydroxyvitamin D (25OHD) in a fluidic chip. Methods The sample with monoclonal antibody bead conjugates mixture was incubated for 20 min at 37°C, then 30 uL sample mixture was applied to inlet of the chip. After additional incubation for 2 min at room temperature and 2 min after sample application, 120 uL of washing buffer was applied onto the washing hole and the chip was incubated for 10 min. 25OHD molecules in the sample bond to magnetic beads coupled with anti-25OHD at the end of the membrane. Chips were inserted into DELISA, and 25OHD results were derived by analysis of the computational method of microscopic imaging, proportional to the concentration of 25OHD. Assay performance characteristics of the limit of detection (LoD), precision and analytical measurement interval (AMI) using Vitamin D Depleted, Low and High Serum (Molecular Depot, San Diego, CA) were determined according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. 87 Samples for method comparison studies were obtained from routine clinical samples submitted for 2 OHD determination or from apparently healthy normal volunteers. The study was approved by the Institutional Review Board of Dongguk University Ilsan Hospital (202207024). Results LoD was 10.3 ng/mL and within-laboratory precision was 11, 12, and 10% coefficient of variation at 14.1, 56.6, and 113.2 ng/mL, respectively. The best fit polynomial was a cubic equation from 14.1 to 113.2 ng/mL and the difference between the third-order equation and the first-order equation at Level 3 and 4 concentrations was outside the non-linearity limit. Comparison with chemiluminescent assay (Elecsys Vitamin D total II, Roche Diagnostics, Mannheim, Germany) yielded a 0.904 of correlation coefficient and 0.921 slope in the range from 7.0 to 57.9 ng/mL. Conclusions The DELISA 25OHD assay has a suitable LoD and precision, however, it is necessary to improve the AMI at high concentration values and correlation with the automated analyzer.

Blood and liver telomere length, mitochondrial DNA copy number, and hepatic gene expression of mitochondrial dynamics in mid-lactation cows supplemented with l-carnitine under systemic inflammation

The current study was conducted to examine the effect of l-carnitine (LC) supplementation on telomere length and mitochondrial DNA copy number (mtDNAcn) per cell in mid-lactation cows challenged by lipopolysaccharide (LPS) in blood and liver. The mRNA abundance of 31 genes related to inflammation, oxidative stress, and the corresponding stress response mechanisms, the mitochondrial quality control and the protein import system, as well as the phosphatidylinositol 3-kinase/protein kinase B pathway, were assessed using microfluidics integrated fluidic circuit chips (96.96 dynamic arrays). In addition to comparing the responses in cows with or without LC, our objectives were to characterize the oxidative and inflammatory status by assessing the circulating concentration of lactoferrin (Lf), haptoglobin (Hp), fibrinogen, derivates of reactive oxygen metabolites (dROM), and arylesterase activity (AEA), and to extend the measurement of Lf and Hp to milk. Pluriparous Holstein cows were assigned to either a control group (CON, n = 26) or an LC-supplemented group (CAR; 25 g LC/cow per day; d 42 ante partum to d 126 postpartum (PP), n = 27). On d 111 PP, each cow was injected intravenously with LPS (Escherichia coli O111:B4, 0.5 µg/kg). The mRNA abundance was examined in liver biopsies of d -11 and +1 relative to LPS administration. Plasma and milk samples were frequently collected before and after the challenge. After LPS administration, circulating plasma fibrinogen and serum dROM concentrations increased, whereas AEA decreased. Moreover, serum P4 initially increased by 3 h after LPS administration and declined thereafter irrespective of grouping. The Lf concentrations increased in both groups after LPS administration, with the CAR group showing greater concentrations in serum and milk than the CON group. After LPS administration, telomere length in blood increased, whereas mtDNAcn per cell decreased; however, both remained unaffected in liver. For mitochondrial protein import genes, the hepatic mRNA abundance of the translocase of the mitochondrial inner membrane (TIM)-17B was increased in CAR cows. Moreover, TIM23 increased in both groups after LPS administration. Regarding the mRNA abundance of genes related to stress response mechanisms, 7 out of 14 genes showed group × time interactions, indicating a (local) protective effect due to the dietary LC supplementation against oxidative stress in mid-lactating dairy cows. For mtDNAcn and telomere length, the effects of the LPS-induced inflammation were more pronounced than the dietary supplementation of LC. Dietary LC supplementation affected the response to LPS primarily by altering mitochondrial dynamics. Regarding mRNA abundance of genes related to the mitochondrial protein import system, the inner mitochondrial membrane translocase (TIM complex) seemed to be more sensitive to dietary LC than the outer mitochondrial membrane translocase (TOM complex).

In-Situ Young’s Modulus Characterization of Elastomeric Microfluidic Chips With Micropillars

This study presents a novel in-situ Young’s modulus measurement technique of polydimethylsiloxane (PDMS) microfluidic chips that are designed to measure fluid viscosities. In such chips, viscosity can be accurately determined once the Young’s modulus of PDMS is also known. Yet, the Young’s modulus values of elastomers are highly dependent on their chemical composition and curing temperature. The presented approach involves integrating a piezoelectric sheet underneath the chip, oscillating the chip through sweeping the drive frequency, and monitoring the blur and speckle contrast of the pillar via an external camera. A local maximum in the blur and speckle contrast is achieved at the fundamental resonance of the pillars, from which its Young’s modulus is predicted. The experimental results validate the relationship between the Young’s modulus of PDMS and base polymer:curing agent ratio, curing time, and temperature, demonstrating that it could be measured optically. Six different PDMS microfluidic chips prepared by curing elastomer at different temperatures and using different base polymer to curing agent ratios, 5:1, 10:1, and 20:1, were utilized. The Young’s modulus of the prepared sample microfluidic chips varied within the range of 0.72 to 3.64 MPa. The successful measurement of the Young’s modulus of PDMS using the proposed techniques demonstrates its potential in determining the mechanical properties of fluidic chips in-situ, with a low-cost and simple setup.

A Facile and Green Microwave‐Assisted Strategy to Induce Surface Properties on Complex‐Shape Polymeric 3D Printed Structures

AbstractLight‐ induced polymeric 3D printing is becoming a well‐established fabrication method, showing manifold advantages such as control of the local chemistry of the manufactured devices. It can be considered a green technology, since the parts are produced when needed and with minimum amount of materials. In this work 3D printing is combined with another green technology, microwave‐assisted reaction, to fabricate objects of complex geometry with controllable surface properties, exploiting the presence of remaining functional groups on the surface of 3D printed specimens. In this context, surface functionalization with different amines is studied, optimizing formulations, reaction times, and avoiding surface deterioration. Then, two different applications are investigated. MW‐functionalized filter‐type structures have been tested against Staphylococcus aureus bacteria, showing high bactericidal activity on the surface along all areas of the complex‐shaped structure. Second, a fluidic chip composed of three separated channels is 3D printed, filled with different amine‐reactive dyes (dansyl and eosine derivatives), and made to react simultaneously. Complete and independent functionalization of the surface of the three channels is achieved only after 2 min of irradiation. This study demonstrates that light induced 3D printing and microwave‐induced chemistry can be used together effectively, and used to produce functional devices.

Prediction and mechanism of surface evolution in high-pressure slurry jet micro-machining of channels

Recent advances in abrasive water jet (AWJ) processes have enabled controlled-depth micro milling for a variety of applications, such as micro fluidic chip manufacturing. However, AWJ micro milling can be difficult to control and its successful application requires judicious selection of the process parameters. Since the mechanics of the process have not been fully understood, prediction of the machined topography arising from a set of process parameters is difficult. The present work combines computational fluid dynamics, Lagrangian particle tracking, and a deformed geometry surface evolution technique into a comprehensive model that predicts the evolving shape of micro-channels milled on 6061-T6 aluminum plates using high-pressure abrasive slurry jet machining (HASJM). Requiring calibration using only a single channel centerline depth, the model could predict the machined profiles of micro-channels milled using multiple nozzle passes with less than a 2% error. The model was also used to investigate the underlying physics of the machining process. This allowed experimental observations to be explained in terms of the changes that occur, due to the evolving eroded shape, in stagnation zone size, particle ricochet behavior, secondary slurry flow, and local particle impact angles and velocities. Overall, the work shows that such models can not only very accurately predict evolving machined topography, but also be very useful tools to understand abrasive jet machining mechanisms which occur on time scales which are too brief to be directly observed experimentally.

Gradient Nanoconfinement Facilitates Binding of Transcriptional Factor NF-κB to Histone- and Protamine-DNA Complexes.

Mechanically induced chromosome reorganization plays important roles in transcriptional regulation. However, the interplay between chromosome reorganization and transcription activities is complicated, such that it is difficult to decipher the regulatory effects of intranuclear geometrical cues. Here, we simplify the system by introducing DNA, packaging proteins (i.e., histone and protamine), and transcription factor NF-κB into a well-defined fluidic chip with changing spatical confinement ranging from 100 to 500 nm. It is uncovered that strong nanoconfinement suppresses higher-order folding of histone- and protamine-DNA complexes, the fracture of which exposes buried DNA segments and causes increased quantities of NF-κB binding to the DNA chain. Overall, these results reveal a pathway of how intranuclear geometrical cues alter the open/closed state of a DNA-protein complex and therefore affect transcription activities: i.e., NF-κB binding.

Ultralow and Dynamic Flow Field Generator Composed of Microfluidic Peristaltic Pump

Precise control over flow rate and flow pattern is critical for investigating the contribution of shear force in cellular responses, biofluidic transport, and living matter in a flowing environment. Generation and control over the ultralow flow fields at microscale are, however, difficult, due to thermal agitation and fluctuations in the surrounding environment. Herein, pa novel microfluidic flow field generator is proposed, capable of generating stable flow field down to the limit of thermal noise. Integrated with a customized MATLAB program controlling timely open–close of 18 monolithic PDMS valves, the flow generator outperforms the existing methods by both achievable low flow rate, that is, 0.01 nL s−1, temporal resolution of flow rate fluctuation down to 100 ms, and provides complex flow patterns. Moreover, unlike external devices (e.g., the syringe pump), the design can be easily integrated into any fluidic chip and sealed from the disturbance of experimental conditions, for example, the airflow and the movement of connected pipelines. The methodology is, therefore, suitable for biological and biophysical studies requiring a well‐defined flowing environment.

Integrated slip valve-assisted fluidic chip coupling with CRISPR/Cas12a system for nucleic acid analysis

Currently, some on-site nucleic acid detection platforms have been developed. However, these platforms still need to be improved in device integration and multiple detection capability. In this work, an integrated dual nucleic acid analysis platform was developed by slip valve-assisted fluidic chip coupled with CRISPR/Cas12a system. All the reagents, including nucleic acid extraction, air-dried loop-mediated isothermal amplification (LAMP) and CRISPR/Cas12a detection reagents, were preloaded on the fluidic chip. Liquids transfer and stirring could be controlled by a slip valve and a syringe. By combining duplex LAMP reaction with two CRISPR detection units, CRISPR/Cas12a-based dual nucleic acid analysis was successfully constructed. Benefiting from high-quality nucleic acid extraction on the chip, as low as 30 copies/reaction of Vibrio parahaemolyticus (V. parahaemolyticus) and 20 copies/reaction of Salmonella typhimurium (S. typhimurium) could be simultaneously detected. Detection results could be observed by the naked eye under a portable ultraviolet lamp. The whole detection procedure was finished within 60 min. This method with integrated nucleic acid analysis, dual detection capability and fluorescence visualized results provides a new solution for on-site nucleic acid analysis.

Organ-on-a-chip: A new tool for in vitro research

Organ-on-a-chip (OOC, organ chip) technology can closely simulate the human microenvironment, synthesize organ-like functional units on a fluidic chip substrate, and simulate the physiology of tissues and organs. It will become an increasingly important platform for in vitro drug development and screening. Most importantly, organ-on-a-chip technology, incorporating 3D cell cultures, overcomes the traditional drawbacks of 2D (flat) cell-culture technology in vitro and in vivo animal trials, neither of which generate completely reliable results when it comes to the actual human subject. It is expected that organ chips will allow huge reductions in the incidence of failure in late-stage human trials, thus slashing the cost of drug development and speeding up the introduction of drugs that are effective. There have been three key enabling technologies that have made organ chip technology possible: 3D bioprinting, fluidic chips, and 3D cell culture, of which the last has allowed cells to be cultivated under more physiologically realistic growth conditions than 2D culture. The fusion of these advanced technologies and the addition of new research methods and algorithms has enabled the construction of chip types with different structures and different uses, providing a wide range of controllable microenvironments, both for research at the cellular level and for more reliable analysis of the action of drugs on the human body. This paper summarizes some research progress of organ-on-a-chip in recent years, outlines the key technologies used and the achievements in drug screening, and makes some suggestions concerning the current challenges and future development of organ-on-a-chip technology.

Environmentally Friendly Method of Assembly of Cardanol and Cholesterol into Nanostructures Using a Continuous Flow Microfluidic Device

This study shows a viable and straightforward microfluidic method of assembly of cardanol (CA) and cholesterol (CH) into amphiphile nanostructures obtained through a hydrodynamic focusing approach according to which an alcoholic solution of CA and CH is constrained within a two-dimensional lamina shape by two lateral streams of borate buffer solution. The process is performed within glass-made cross-shaped micro-sized fluidic chips specially designed to achieve a laminar regime. CA, distilled from the cashew nut shell liquid, is demonstrated as a surface-active molecule in borate buffer basic medium and when mixed with CH it produces versatile nanovesicles through an in-batch solvent-free process. Compared to this conventional method, the microfluidic route allows operating under continuous flows, with a reduced amount of reagents and at lower experimental temperatures, ensuring no waste formation and the achievement of size-monodisperse amphiphile nanostructures that do not need further steps of purification. Electron microscopy analyses demonstrate that upon increasing CH in the lipid mixture, a switchover from spherical CA micelles to CA/CH mixed closed vesicles occurs. Differential scanning microcalorimetry confirms the formation of vesicular structures and evidences the primary role of CH, which increasingly lowers the temperature of transition depending on its concentration.

3D bioprinted, vascularized neuroblastoma tumor environment in fluidic chip devices for precision medicine drug testing

Neuroblastoma is an extracranial solid tumor which develops in early childhood and still has a poor prognosis. One strategy to increase cure rates is the identification of patient-specific drug responses in tissue models that mimic the interaction between patient cancer cells and tumor environment. We therefore developed a perfused and micro-vascularized tumor-environment model that is directly bioprinted into custom-manufactured fluidic chips. A gelatin-methacrylate/fibrin-based matrix containing multiple cell types mimics the tumor-microenvironment that promotes spontaneous micro-vessel formation by embedded endothelial cells. We demonstrate that both, adipocyte- and iPSC-derived mesenchymal stem cells can guide this process. Bioprinted channels are coated with endothelial cells post printing to form a dense vessel—tissue barrier. The tissue model thereby mimics structure and function of human soft tissue with endothelial cell-coated larger vessels for perfusion and micro-vessel networks within the hydrogel-matrix. Patient-derived neuroblastoma spheroids are added to the matrix during the printing process and grown for more than two weeks. We demonstrate that micro-vessels are attracted by and grow into tumor spheroids and that neuroblastoma cells invade the tumor-environment as soon as the spheroids disrupt. In summary, we describe the first bioprinted, micro-vascularized neuroblastoma—tumor-environment model directly printed into fluidic chips and a novel medium-throughput biofabrication platform suitable for studying tumor angiogenesis and metastasis in precision medicine approaches in future.

Rapid label-free detection of Pseudomonas aeruginosa using a fluidic grating chip with a reflective laser system

Stripe arrays of poly(methacrylic acid) (PMAA) brushes were grafted using a photoresist template to fabricate one-dimensional photonic crystal (OPCs). The as-prepared samples were first bound with protein G to immobilize and orient tails of the antibody of Pa (abY). A fluidic diffraction chip based on the abY-tailed PMMA OPC was fabricated to examine the ability of Pa detection from whole blood specimen. Pa was attached to the abY-tailed PMMA OPC after flowing through the fluidic chip, which changed the diffraction intensity. A laser beam was employed to analyze the reflective signals of OPCs at an incident angle of 45°. The abY-tailed PMAA OPC possessed an optical feature with a characteristic diffraction effect such that the projection of the laser beam on the plane of the OPC chip was parallel to the strips in SII configurations, whereas they were perpendicular in ST configurations. The degree of the diffraction intensity exhibited a linear response to Pa at concentrations from 102 to 107 CFU mL−1, and the limit of detection was 100 CFU mL−1, indicating the excellent sensitivity in Pa-spiked whole blood samples. The proposed platform provides a rapid, label-free method for Pa detection to improve the administration of antibiotics in a timely manner.

Reducing the channel diameter of polydimethylsiloxane fluidic chips made by a 3D-printed sacrificial template and their application for flow-injection analysis

Fluidic chips have attracted considerable interest in recent years for their potential applications in analytical devices. Previously, we developed a method to fabricate polydimethylsiloxane (PDMS) fluidic chips via templates made using a low-priced commercial Fused Deposition Modeling (FDM) type 3D printer and polymer coatings. However, in general, methods using a template cannot form a flow channel thinner than the template thickness and the width. In this study, the inner wall of a PDMS fluidic chip was coated with PDMS to create a chip with a channel inner diameter smaller than a template. Then, by measuring the flow signal of methyl orange with a single line, the basic properties of the non-coated and coated chip were investigated. As a result, almost the same flow profile was obtained in non-coated and coated chips at the same linear velocity and the same sample injection length. By coating and narrowing the channel width, it is possible to save the amount of sample and carrier solution. Measuring hydrazine in water using a coated chip was also tried. The calibration curve indicated good linearity in the range of 1–6 ppm. However, a concentration point of 7 ppm deviated. The reason for this deviation was presumably due to inadequate mixing of the sample and reagent. By decreasing the flow rate, the calibration curve indicated good linearity in the range of 1–7 ppm.Graphical abstract

Isolation and label-free detection of circulating tumour cells by fluidic diffraction chips with a reflective laser beam system

A photonic crystal (PC) based line array of poly(methacrylic acid) (PMAA) brushes was grafted from a photoresist template using a trench array. The array was functionalised with anti-epithelial cell adhesion molecule antibodies (EpY). A laser beam was employed to analyse the two-dimensional (2D) and three-dimensional (3D) reflective signals of PCs at an incidence angle of 45°. The EpY-tailed PMAA PC possessed an optical feature with a characteristic diffraction effect along two laser input configurations including the SII configuration, in which the projection of the laser beam on the plane of the SPM chip was parallel to the strips, and the ST configuration, in which they were perpendicular. A fluidic diffraction chip based on the EpY-tailed PMAA PC with 1-μm resolution was fabricated to examine the ability to detect circulating tumour cells (CTCs) along the ST configuration. The CTCs attached on the EpY-tailed PMAA PC, resulting in the change in the diffraction intensity. Dependence of change degree of the diffraction intensity exhibited a linear range of concentration of CTC from 0 to 64 cells and a limit of detection of 5 cells in 3 mL. CTC detection using both fluidic diffraction chips and a commercial IsoFlux system was carried out in clinical trials, including three healthy donors and 12 patients at various stages of colorectal cancer for comparison. Our platform provides a simple label-free method with high accuracy for rapid CTC counting, which has great potential in clinical treatment applications.

An electric-pulse-assisted stamping process towards springback suppression and precision fabrication of micro channels

Micro channel features have been widely used in miniaturized products, such as micro reactor, micro heat exchanger, micro fluidic chip. For example, the metallic bipolar plate (BPP) characterized by dense submillimeter channels is a key component of the proton exchange membrane fuel cell (PEMFC). Since several hundreds of BPPs are assembled in a PEMFC stack, a high precision and uniformity of the formed micro channels is required. The micro/meso stamping process has been attracting tremendous attention due to its unique advantages in efficiency and cost. However, the uneven springback of ultra-thin metallic sheet results in evident nonuniformity in the micro channels arrays. In that regard, an electric-pulse-assisted (EPA) stamping method is developed in this research, in which sheet metals are first stamped and electric pulses are subsequently introduced to reduce the springback of formed micro channels. During a series of 7-channel EPA stamping tests, an evident springback suppression is revealed. In the case of 1 Hz electric pulses with the effective current density of 26.56 A/mm2, 83% of the channel height loss due to the springback is suppressed. Micro hardness tests reveal that the hardening of specimens in the deformation zone is significantly reduced with the introduction of electric pulses. The hardness decreases from 230 to 188 HV due to the accelerated stress relaxation, and the softening effect further leads to lower springback. Based on the analytical calculation and finite element analysis, a combined model is developed to capture the springback suppression effect of electric pulses, which is characterized by the accelerated stress relaxation. The applicability of the EPA stamping is verified and discussed.