Abstract The ability to trap and deposit particles from flowing suspensions onto solid substrates underpins a wide range of technological applications, from coatings and sensors to biomedical devices and filtration systems. Entrapping particles from non-colloidal suspensions onto cylindrical substrates is governed by a competition between transport/impaction and adhesion/retention. We quantify “dispersion energy” (agitation intensity) via a normalized parameter and evaluate its effect on microparticle capture for low (Al) and high (Ni) density non-Brownian polydisperse particle suspensions. Image-based metrics (surface coverage, particle-transfer efficiency, size distributions) and spatial statistics (SOM, Voronoi tessellation and Delaunay triangulation) reveal a non-monotonic response: capture is maximized at intermediate dispersion energy where Stokes-number driven transport is sufficient for impaction, but impact energy and shear remain low enough for binder-mediated adhesion to arrest particles. At the range between Ψ ≈ 0.04 ×10-6-0.15×10-6 m5kg-1s-2, Al (lower specific density) reaches coverage 17.82 ± 17.40, while Ni (higher specific density) attains coverage 11.29 ±3.77. Size distributions are lognormal, narrowing with increasing as large-particle capture is suppressed. Spatial descriptors corroborate the mechanistic picture: near-optimal Ψ yields the most isotropic local packing; at higher Ψ, rebound and shear-induced sliding/rolling reduce adhesion; at lower Ψ, insufficient impaction limits capture. The framework-linking Ψ, impaction (via Stokes number), and adhesion thresholds-provides actionable guidance for tuning agitation to maximize entrapment in binder-assisted coatings, filtration preforms, and surface functionalization.
Abstract Chip evacuation is a critical aspect of the micro-drilling process, as the confined nature of the chips between the hole wall and flute can lead to clogging, increased thrust and torque, tool wear, and potential failure. This paper presents a physics-based analytical model for predicting chip evacuation force using principles of granular chip particle kinetics and energy transfer. The model incorporates material properties, tool geometry, and cutting conditions, while also accounting for the adhesion and drag effects due to scaling of drilling process geometry. Validation through micro-drilling experiments on hardened steel demonstrates strong agreement between predicted and measured chip evacuation forces. The model offers a generalized approach applicable to various work materials eliminating the need for costly calibration experiments.
A geometry-based chip thickness model is proposed to enhance the understanding of chip behavior in the microdrilling of Stavax hardened steel under dry condition. Chip formation at specific cutting regions, including the primary cutting blade, secondary cutting blade, and chisel indentation zone, is evaluated in the model. The cutting size effect is incorporated into the model to address the unique plowing and shearing phenomena. The model is experimentally validated over a range of chiploads. The progression of chip morphology is observed. Overall chip thickness is shown to be thicker as compared to the theoretical chip thickness. Both experimental and analytical models show a strong dependence of chip thickness, chip thickening rate, and morphology on the size effect that dictates the effectiveness of the chip removal process.
Micro-force sensors are of utmost importance for a variety of state-of-the-art biomedical devices that require micro-manipulative operations with high precision and accuracy. Unfortunately, the measurement accuracy of miniaturized sensors decreases as they become smaller. Conventional sensing systems such as piezoelectric sensors are also inadequate for numerous sensing applications because they exhibit a decrease in detection output when scaled down. In contrast, a micro-force sensor equipped with a hydraulic drive mechanism can obtain a large output even when the size is significantly reduced. By observing the pressure change in the water feeder, the external force applied to the end effector can be measured. In this study, we measure the mechanical properties of cancer tumors, which are a leading cause of death, by using a peeling motion, as cancer tumors tend to be harder than benign tumors and the tensile reaction force increases as the neovascularization of the tumor expands. First, a simulated tumor model was created to measure the change in reaction force with hardness, and viscoelasticity was then measured and evaluated by a peeling motion using a hydraulic drive mechanism.
Micro-electrical discharge machining (micro-EDM) has the advantage of being a noncontact machining technique that allows it to machine high-aspect-ratio microfeatures in difficult-to-cut materials. The objective of this study was to explore the machining of highest possible aspect ratio micro-electrodes using micro-EDM and determine the most suitable techniques, materials, and machining parameters to produce consistent, high-quality micro-electrodes with smallest possible diameter and largest possible aspect ratios. Micro-electrodes were fabricated using the self-drilled holes technique in which a hole is drilled in a piece of plate metal under conventional polarity (workpiece positive, tool negative), and then, the polarity is reversed to make the tool positive, thereby making it the "workpiece" and allowing the micro-EDM process to remove material from it. The electrode is then moved slightly off-center relative to the previously drilled hole, and the edge being fed into the plate is removed. This reduces the diameter of the electrode, and the process can be repeated until the electrode has reached the desired diameter and length. It was found that the self-drilled hole technique is capable of repeatedly producing electrodes with less than 50-mu m diameter at the base, less than 20-mu m diameter at the tip, and over 5 mm length which constitutes aspect ratios of over 100. Using this method, it was possible to produce an electrode with tip diameter of 7.054 mu m, base diameter of 73.64 mu m, average diameter of 40.35 mu m, length of 5.265 mm, and aspect ratio of 130, making it one of the highest aspect ratio electrodes reported in the literature using the micro-EDM-based in situ electrode fabrication techniques. Finally, the application of the fabricated high-aspect-ratio micro-electrodes was demonstrated by successfully machining high-aspect-ratio microholes in a silicon wafer.
Large-area nanopillar fabrication on polystyrene surface has been reported. Nanopillars are fabricated with reusable AAO mold with an ordered pore size of 80 nm. Honeycomb-ordered domain nanopores were made with different anodization parameters which further improved by pore widening. A single-step approach of hot embossing is used to make different aspect ratio nanopillars of polystyrene. Hot embossing process parameters such as embossing pressure, temperature, and holding time are optimized for contact angle as a response parameter. The moth-eye type textured nanopillars have the maximum water contact angle. The water contact angle obtained increased from 66.2° to 143° for for moth-eye type nanopillars.
Cancer is the second leading cause of mortality worldwide, making early detection essential for improving patient outcomes and enabling early treatment. Microfluidic systems can provide promising methods for cancer cell sorting due to their minimal sample requirements, rapid processing times, and cell isolation capabilities. However, current microfluidic systems heavily depend on complex techniques, such as magnetic or electric fields and/or size-based channels, constraining the separation efficiency. In this study, a secondary-flow-enabled microfluidic chip is designed and fabricated by digital light processing (DLP) three-dimensional (3D) printing to achieve high-precision, rapid fabrication of specific microfluidic channels. DLP 3D printing enables customizable and cost-effective microfluidic device production. By utilizing secondary flow in the microfluidic chip system, it is technically feasible to separate cancer cells from normal blood cells due to their size difference. A representative application demonstrated in this work is to sort mimicries of red blood cells and circulating tumor cells (CTCs) with relatively high efficiency. This approach offers a streamlined and scalable alternative for particle separation, providing a robust platform for liquid biopsies in cancer monitoring. Additionally, the proposed approach is expandable to other industrial fields, such as mining, in which precise particle separation is essential.
Aerosol jet printing (AJP) is an ink-depositing additive manufacturing method used in the production of small-scale electronic devices, utilizing a gas flow to aerodynamically print conductive lines. Although the process shows promise, its potential is limited by quality-limiting phenomena. Predicting their occurrence can be a time-consuming and complex process due to the strong sensitivity of the process to individual operating conditions, limiting reproducibility. This oftentimes can render experimental setups uneconomical. Numerical methods, such as computational fluid dynamics, are appealing due to their ability to easily change process parameters, enabling cost-effective analysis of several process setups. As we consider turbulence to be one of the primary causes of quality limitations, it is crucial to predict turbulent properties accurately when numerically modeling the flow. Traditional turbulence modeling within a Reynolds-averaged Navier-Stokes (RANS) approach has been found to be inadequate for accurately predicting turbulent quantities of low Reynolds number free jets, rendering it unsuitable as a tool for investigations of aerosol jet printing. In the study presented, a first step toward three-dimensional investigation of a free jet under aerosol jet printing operating conditions using large eddy simulation (LES) is proposed. The accuracy of the model regarding predictability of turbulent quantities is assessed in a first manner by comparing turbulent transition points to experimental findings and found to be in overall satisfactory agreement.
Digital microfluidics can be used to reliably automate repeated ligation steps to create accurate DNA products. This investigation demonstrates assembly of single-stranded and double-stranded DNA products on digital microfluidics devices. It also presents simple, low-cost methods to integrate on-chip incubation on a commonly used digital microfluidic platform. This work presents the ligation of single-stranded and double-stranded DNA products in droplets surrounded in oil and air with on-chip and off-chip incubations. Successful assembly of DNA products was determined by verifying that the size of on-chip DNA products was equal to benchtop controls. This suggests that digital microfluidic devices are a suitable platform for automated assembly of DNA products in a variety of biomedical applications.
Nanowire-based microfluidic devices combine the strengths of microfluidics and nanostructures for applications in cell biology and chemical sensing. However, their use has been limited by the complexity of the fabrication methods. In this study, we present a simple approach for fabricating and integrating metallic glass nanowires into microfluidic channels. Metallic glass nanowires were formed by thermoplastic drawing on a silicon substrate. The silicon-anchored nanowire array was sealed with a polydimethylsiloxane (PDMS) channel to create a nanowire-integrated microfluidic device. The effect of nanowire geometry on the flowrate was characterized. The experimental results were compared with computational fluid dynamics (CFD) simulations to understand the fluid-nanowire interaction. The potential of surface modification to functionalize the metallic glass nanowires was evaluated.
Nickel coatings have demonstrated significant benefits in protecting copper from oxidation and fouling, thereby enhancing the longevity of copper-based components. This study employed an electroplating apparatus featuring a Watts bath and copper electrode to investigate the impact of flowing electrolyte, both with and without an applied magnetic field, on the interfacial characteristics of nickel-coated copper surfaces. The findings reveal the relationship between current density and deposition thickness. The application of a perpendicular magnetic field and increase in current density generally increased coating thickness to 0.2 mu m from 0.05 mu m, with the most pronounced effects at moderate flow rates and narrower gaps; however, at the highest flowrate and widest gap, deposition thickness diminished due to the divergence of magnetic field lines. Design of experiments (DOE) analysis revealed that the magnetic field homogeneously improved surface roughness uniformity compared to other variables. Lower current densities produced smoother surfaces, while magnetically assisted electroplating yielded consistent roughness values even at higher current densities. Exposure to the magnetic field improved wettability, evidenced by decreased contact angles. This enhancement is attributed to the alignment of nickel particles during deposition, facilitating a transition from the Cassie-Baxter to the Wenzel wetting state. Notably, thicker deposits were observed at lower flow rates and narrower electrode gaps, suggesting significant influence of gas bubble dynamics on the deposition process. These findings provide insights into the complex interplay between electrochemical reactions, hydrodynamics, and magnetic fields in nickel electrodeposition, with implications for optimizing coating.
Industrial surface modification techniques are commonly employed to enhance the adhesion between polymer matrices and aramid fibers (AFs) in composite materials. However, these techniques are often associated with high costs, operational complexity, and environmental drawbacks. This study presents the development of a cost-effective, eco-friendly, and efficient microwave-assisted surface treatment for aramid fibers. The technique utilizes microwave irradiation to increase surface roughness, disrupt crystalline bonding, and introduce oxygen-containing functional groups, thereby enhancing surface energy and fiber reactivity. Moreover, the microwave-induced electromagnetic fields promote microstructural changes within the aramid fabric, strengthening intermolecular interactions and improving interfibrillar bond integrity. The process was optimized using the Taguchi design of experiments (DOE) methodology, ensuring that the mechanical properties of the fibers remained intact while achieving precise adhesion control with thermoplastic matrices. The study also incorporates advanced additive manufacturing techniques—fused deposition modeling (FDM) and direct ink writing (DIW)—to fabricate aramid fiber-reinforced sandwich composites. These techniques were selected to enhance the composite's mechanical strength, interfacial adhesion, and resistance to environmental degradation. Experimental results demonstrate a significant enhancement in surface wettability, with the water contact angle reduced from 120 deg to 11.2 deg. Additionally, interlaminar shear strength increased substantially from 35 MPa to 96 MPa. Tensile tests revealed a modulus of 516 MPa, and Izod impact tests showed an impact resistance of 599 J/m, validating the effectiveness of the microwave-assisted surface treatment in significantly improving the performance metrics of aramid fiber-reinforced composites.
Aerosol jet printing (AJP) is a direct-write additive manufacturing technique used to fabricate electronics, such as sensors, capacitors, and optoelectronic devices. It has gained significant attention in being able to utilize aerodynamic principles to deposit conductive inks (such as silver nanoparticle-based inks) onto rigid and flexible substrates. The aerosol jet printing system consists of three main components to execute the printing process: (i) the pneumatic atomizer, (ii) the virtual impactor, and (iii) the deposition head. The virtual impactor (VI) lies between the pneumatic atomizer and the deposition head, accepting the accelerated flow of differently sized aerosol particles from the pneumatic atomizer while acting as an "aerodynamic separator." With the challenges associated with efficiency as well as resulting quality of the AJP process, the virtual impactor presents a unique opportunity to gain a deeper understanding of the component itself, aerosol particle flow behavior, and how it contributes to overall printing inefficiencies, poor repeatability, and resulting print quality. Broadly, this effort enables the expedited adoption of AJP in the electronics industry and beyond large scales. The challenges mentioned are addressed in this work by conducting a computational fluid dynamics (CFD) study of the virtual impactor to visualize fluid transportation and deposition under specific conditions. The objective of this study is to observe and characterize a single-phase, compressible, turbulent flow through the virtual impactor in AJP. The virtual impactor geometry is modeled in the ANSYS FLUENT environment based on the design by Optomec. The virtual impactor is assembled using a housing, collector, jet, stem, O-rings, and a retaining nut. Subsequently, a mesh structure is generated to discretize the flow domain. In addition, material properties, boundary conditions, and the relevant governing equations (based on the Navier-Stokes equations) are utilized to, ultimately, generate an accurate steady-state solution. The fluid flow is examined with respect to mass flow rates set at boundary conditions. The aerosol particles' interactions with the inner walls of the virtual impactor are observed. Particularly, an insight into the characteristics of aerosol particles entering the virtual impactor and their transition into a smoother flow before entering the deposition head is gained. Furthermore, the analysis provides an opportunity to observe fluid flow separation based on the design of the virtual impactor, one of its main functions in the AJP process. This exposes probable causes for inaccurate print quality, flow blockages, inconsistent outputs, process instability, and other material transport inefficiencies. Overall, this research work lays the foundation for improvements in the knowledge and performance of aerosol jet printing's virtual impactor toward optimal fabrication of printed electronics.
This study investigates the evolution of surface integrity of a strategically important niobium-based cermet with nickel binder (NbC-Ni), while processing it with electrochemical machining (ECM) and hybrid laser-ECM (LECM) processes for shaping toward molds and cutting tools applications. The results indicate that, while the ECM process can preserve material properties due to its athermal and noncontact nature, it suffers from selective phase dissolution, particle breakout, and passivation issues when processing the cermet. LECM synergistically applies laser and EC process energies to address these challenges, particularly by homogenizing multiphase dissolution and facilitating passivation weakening while using pH-neutral aqueous electrolyte. A combination of metallography techniques were employed to study the surface integrity and correlate it with process mechanisms. Results indicate that ECM selectively dissolves the Ni phase and induces passivation, while LECM mitigates these surface integrity compromising effects by virtue of passivation weakening (lowest O wt % of 33.2) through enhanced transpassive dissolution and escalated reaction kinetics, leading to surface integrity improvement by lowering the roughness (Sa) by 30%, feature slopes (Sdq) by 32%, and increasing the hardness (HV5 738.7) by 55% as compared to ECM. Thus, LECM presents a promising technique for shaping advanced passivating and multiphase materials.
This study proposes a novel approach for synthesizing and etching bicontinuous FeCrAl-Al2O3 composites as a means for replacing FeCrAl foams as catalyst scaffolds in biodriven alcohol reactors for jet-fuel production. Conventional FeCrAl foams suffer from poor availability and consequent high costs. New additive manufacturing techniques provide an opportunity to produce tailored foams at reasonable times and at acceptable costs. This research aimed to generate a porous FeCrAl structure by etching a bicontinuous FeCrAl-Al2O3 composite produced by laser powder bed fusion of amalgamated FeCrAl and Al2O3 powders. The composite powder for laser powder bed fusion is created by ball-milling FeCrAl and Al2O3 powders. This research focuses on achieving a bi-continuous FeCrAl-Al2O3 structure, essential for the selective removal of the ceramic phase. The influence of laser processing parameters on the microstructure was examined across a range of laser powers (60-120 W) and scan speeds (100-400 mm/s), showing that higher powers and speeds produce finer metal struts. A bi-continuous microstructure was consistently obtained, marking a key achievement. The Al2O3 removal process involved a two-step etching method using hydrochloric and phosphoric acids, tested across various etching times. The alumina phase was reduced from 36 vol% to 17 vol% (corresponding to an increase in porosity from 24 vol% to 43 vol%), showing the potential for use as a porous catalyst scaffold. This research demonstrates the potential for using additive manufacturing to produce porous FeCrAl structures capable of replacing hard-to-source FeCrAl foams.
Three-dimensional (3D) microneedle arrays (MAs) have shown remarkable performances for a wide range of biomedical applications. Achieving advanced customizable 3D MAs for personalized research and treatment remains a formidable challenge. In this paper, we have developed a high-resolution Electrohydrodynamic (EHD) 3D printing process for fabricating customizable 3D MAs with economical and biocompatible molten alloy. The critical printing parameters (i.e., voltage and pressure) on the printing process for both 2D and 3D features are characterized, and an optimal set of printing parameters was obtained for printing 3D MAs. We have also studied the effect of the tip-nozzle separation speed on the final tip dimension, which will directly influence MAs' insertion performance and functions. With the optimal process parameters, we successfully EHD printed customizable 3D MAs with varying spacing distances and shank heights. A 3=3 customized 3D MAs configuration with various heights ranging from 0.8mm to 1mm and a spacing distance as small as 350 um were successfully fabricated, in which the diameter of each individual microneedle was as small as 100 um. A series of tests were conducted to evaluate the printed 3D MAs. The experimental results demonstrated that the printed 3D MAs exhibit good mechanical strength for implanting and good electrical properties for electrophysiological sensing and stimulation. All results showed the potential applications of the EHD printing technique in fabricating cost-effective customizable high-performance MAs for biomedical applications.
Multimaterial design with a combination of solid and foam structures offers a promising avenue for reducing component weight while enhancing their functionalities. However, the complexity of multistage manufacturing processes poses significant challenges to adopting such approaches. To address these challenges, this paper introduces an innovative concept known as Electromagnetic Forming Injection Foaming (EFIF), which integrates injection molding, forming, and foaming processes into a single hybrid process. This process begins with a simultaneous filling-forming phase, followed by supercritical fluid (SCF) assisted foaming controlled by electromagnetic forming. Through a series of experimental and analytical studies, this work investigates the feasibility and effectiveness of EFIF. First, the impact of pressure drop rate and pressure drop on cell size and density is examined through a specialized experimental setup enabling performing injection, forming, and foaming processes in a single operation. The potential influence of electromagnetic forming on foam injection molding is explored through experiments focusing on the effects of a polymer layer between sheet metal blank and the electromagnetic coils. Additionally, an analytical study evaluates the EFIF process by calculating expected pressure drop rates under different processing conditions and their influence on cell nucleation rates. The results showed the possibility of achieving pressure drop rates up to 1.5 & times; 105 bar/sec, resulting in nucleation rates up to 1.77 & times; 109 nuclei/cm3sec. Overall, this paper highlights the potential of EFIF to merge existing technologies into a scalable solution for manufacturing multimaterial components with micro- to nanocellular polymer foams.
Two-photon lithography (TPL) is an attractive technique for nanoscale additive manufacturing of functional three-dimensional (3D) structures due to its ability to print subdiffraction features with light. Despite its advantages, it has not been widely adopted due to its slow point-by-point writing mechanism. Projection TPL (P-TPL) is a high-throughput variant that overcomes this limitation by enabling the printing of entire two-dimensional (2D) layers at once. However, printing the desired 3D structures is challenging due to the lack of fast and accurate process models. Here, we present a fast and accurate physics-based model of P-TPL to predict the printed geometry and the degree of curing. Our model implements a finite difference method (FDM) enabled by operator splitting to solve the reaction-diffusion rate equations that govern photopolymerization. When compared with finite element simulations, our model is at least a hundred times faster and its predictions lie within 5% of the predictions of the finite element simulations. This rapid modeling capability enabled performing high-fidelity simulations of printing of arbitrarily complex 3D structures for the first time. We demonstrate how these 3D simulations can predict those aspects of the 3D printing behavior that cannot be captured by simulating the printing of individual 2D layers. Thus, our models provide a resource-efficient and knowledge-based predictive capability that can significantly reduce the need for guesswork-based iterations during process planning and optimization.
