Design and evaluation of flow distributors for microfabricated pillar array columns

Capillary Underfill Flow Simulation as a Design Tool for Flow-Optimized Encapsulation in Heterogenous Integration

As the power electronics landscape evolves, pushing for greater vertical integration, capillary underfilling is considered a versatile encapsulation technique suited for iterative development cycles of innovative integration concepts. Since a defect-free application is critical, this study proposes a capillary two-phase flow simulation, predicting both the flow pattern and velocity with remarkable precision and efficiency. In a preliminary performance evaluation, Volume of Fluid (VOF) outperforms the Level-Set method in terms of accuracy and computation time. Strategies like HRIC blending, artificial viscosity, and implicit Multi-Stepping prove effective in optimizing the numerical VOF scheme. Digital mapping using physical experiments and virtual simulations validates transient flow predictions, achieving excellent agreement with deviations as low as 1.48-3.34%. The accuracy of flow predictions is thereby greatly influenced by non-Newtonian viscosity characteristics in the low shear range and time-dependent contact angle variations. The study further explores flow manipulation concepts, focusing on local flow speed adjustment, gap segmentation, and the use of arcuate shapes to influence interface confluence near the chip. Experimental validation corroborates the effectiveness of each design intervention. In conclusion, this research highlights the potential of predictive engineering to develop flow-optimized package designs that enhance reliability while supporting high manufacturing yields.

ZnO NRs/rGO Photocatalyst in a Polymer-Based Microfluidic Platform

This paper reports the development of ZnO NRs/rGO-based photocatalysts integrated into a tree-branched polymer-based microfluidic reactor for efficient photodegradation of water contaminants. The reactor system includes a photocatalytic reactor, tree-branched microfluidic channels, and ZnO nanorods (NRs) coated with reduced graphene oxide (rGO) on a glass substrate within an area of 0.6 × 0.6 cm2. The ZnO NRs/rGO acts as a photocatalyst layer grown hydrothermally and then spray-coated with rGO. The microfluidic system is made of PDMS and fabricated using soft lithography (micro molding using SU-8 master mold patterned on a silicon wafer). The device geometry is designed using AutoCAD software and the flow properties of the microfluidics are simulated using COMSOL Multiphysics. The microfluidic platform’s photocatalytic process aims to bring the nanostructured photocatalyst into very close proximity to the water flow channel, reducing the interaction time and providing effective purification performance. Our functionality test showed that a degradation efficiency of 23.12 %, within the effective residence time of less than 3 s was obtained.

Reversed-Phase Liquid Chromatography of Peptides for Bottom-Up Proteomics: A Tutorial

The performance of the current bottom-up liquid chromatography hyphenated with mass spectrometry (LC-MS) analyses has undoubtedly been fueled by spectacular progress in mass spectrometry. It is thus not surprising that the MS instrument attracts the most attention during LC-MS method development, whereas optimizing conditions for peptide separation using reversed-phase liquid chromatography (RPLC) remains somewhat in its shadow. Consequently, the wisdom of the fundaments of chromatography is slowly vanishing from some laboratories. However, the full potential of advanced MS instruments cannot be achieved without highly efficient RPLC. This is impossible to attain without understanding fundamental processes in the chromatographic system and the properties of peptides important for their chromatographic behavior. We wrote this tutorial intending to give practitioners an overview of critical aspects of peptide separation using RPLC to facilitate setting the LC parameters so that they can leverage the full capabilities of their MS instruments. After briefly introducing the gradient separation of peptides, we discuss their properties that affect the quality of LC-MS chromatograms the most. Next, we address the in-column and extra-column broadening. The last section is devoted to key parameters of LC-MS methods. We also extracted trends in practice from recent bottom-up proteomics studies and correlated them with the current knowledge on peptide RPLC separation.

PolyJet printed high aspect ratio three-dimensional bifurcating microfluidic flow distributor and its application in solid-phase extraction

Microfluidic distributors that can uniformly distribute fluid from a single channel to multiple channels and into, or across, 3D spaces and vice versa has always represented a challenge. Recently, significant interest has been observed in 3D printing three-dimensional flow distributors. However, they either lack their use at low flow rates or in high aspect ratio environments, which are usually encountered in various applications, such as generating organs-on-a-chip, chromatographic columns, solid-phase extractors, etc. Hence, herein, a three-dimensional bifurcating microfluidic distributor that can be used in both low flow rate and high aspect ratio environments has been designed and developed using PolyJet printing. A 1:4 aspect ratio distributor has been developed with 64 exit channels (array of 16 X 4), however, it can be easily customised to modulate both the aspect ratio and the number of exit channels (in the order of 2). Computational fluid dynamic (CFD) simulation of 0.2 and 0.1 mL min^-1 flow through the distributor recorded a maldistribution factor of only 2.29% and 1.72%, respectively. The distributor has resulted in low-dispersion divergence and convergence of flow to and from 64 parallel channels while operating at flow rates ranging from 0.25 mL min^-1 to 2 mL min^-1. It has been further used to develop a high-performance online solid-phase extractor. The extractor was designed with the three-dimensional bifurcating distributor based inlet and outlet and a packed bed of 15 × 20 × 8 mm (length × breadth × height), which resulted in extraction efficiency of 88.8% ± 0.3. In comparison, the extraction efficiency of 81.1% ± 1.1 and 70.4% ± 0.8 was obtained with its two-dimensional distributor and single-channel inlet and outlet based counterparts, respectively.

[Recent advances in microchip liquid chromatography]

微型化是现代分析仪器发展的重要趋势。微型化液相色谱仪器在提供与常规尺度液相色谱相同甚至更高分离效率的同时,可以有效减少溶剂和样品的消耗;在液相色谱-质谱联用中,低流速进样可以有效提高质谱离子源的离子化效率,提高质谱检测效率;对于极微量样品的分离,微型化的液相色谱可以有效减少样品稀释;液相色谱的微型化还有利于液相色谱仪器整体的模块化和集成化设计。芯片液相色谱是在微流控芯片上制备色谱柱并集成相应的流体控制系统和检测系统。芯片液相色谱是色谱仪器微型化的一种重要方式,受到学术界和产业界的普遍关注,但是这一方式也充满挑战。液相色谱微流控芯片需要在芯片基底材料、芯片色谱柱的结构设计、微流体控制技术、检测器技术等方面做出创新,使微流控芯片系统适配液相色谱分离技术的需要。目前芯片液相色谱领域面临的主要问题在于芯片基底材料的性质难以满足芯片液相色谱进一步微型化和集成化的需求;因此芯片液相色谱在未来的发展中需要着重关注新型微流控芯片基底材料的开发以及微流控芯片通道结构的统一设计。该文着重介绍了芯片液相色谱技术近年来的研究进展,并简要展示了商品化芯片色谱当前的发展情况。

A New Direction in Microfluidics: Printed Porous Materials

In this work, the feasibility of a novel direction for microfluidics is studied by demonstrating a set of new methods to fabricate microfluidic systems. Similarly to microfluidic paper-based analytical devices, porous materials are being used. However, alternative porous materials and different printing methods are used here to give the material the necessary pattern to act as a microfluidic system. In this work, microfluidic systems were produced by the following three separate methods: (1) by curing a porous monolithic polymer sheet into a necessary pattern with photolithography, (2) by screen printing silica gel particles with gypsum, and (3) by dispensing silica gel particles with polyvinyl acetate binder using a modified 3D printer. Different parameters of the printed chips were determined (strength of the printed material, printing accuracy, printed material height, wetting characteristics, repeatability) to evaluate whether the printed chips were suitable for use in microfluidics. All three approaches were found to be suitable, and therefore the novel approach to microfluidics was successfully demonstrated.

Clogging sensitivity of flow distributors designed for radially elongated hexagonal pillar array columns: a computational modelling

Flow distributor located at the beginning of the micromachined pillar array column (PAC) has significant roles in uniform distribution of flow through separation channels and thus separation efficiency. Chip manufacturing artifacts, contaminated solvents, and complex matrix of samples may contribute to clogging of the microfabricated channels, affect the distribution of the sample, and alter the performance of both natural and engineered systems. An even fluid distribution must be achieved cross-sectionally through careful design of flow distributors and minimizing the sensitivity to clogging in order to reach satisfactory separation efficiency. Given the difficulty to investigate experimentally a high number of clogging conditions and geometries, this work exploits a computational fluid dynamic model to investigate the effect of various design parameters on the performance of flow distributors in equally spreading the flow along the separation channels in the presence of different degrees of clogging. An array of radially elongated hexagonal pillars was selected for the separation channel (column). The design parameters include channel width, distributor width, aspect ratio of the pillars, and number of contact zone rows. The performance of known flow distributors, including bifurcating (BF), radially interconnected (RI), and recently introduced mixed-mode (MMI) in addition to two new distributors designed in this work (MMII and MMIII) were investigated in terms of mean elution time, volumetric variance, asymmetry factors, and pressure drop between the inlet and the monitor line for each design. The results show that except for pressure drop, the channel width and aspect ratio of the pillars has no significant influence on flow distribution pattern in non-clogged distributors. However, the behavior of flow distributors in response to clogging was found to be dependent on width of the channels. Also increasing the distributor width and number of contact zone rows after the first splitting stage showed no improvement in the ability to alleviate the clogging. MMI distributor with the channel width of 3 µm, aspect ratio of the pillars equal to 20, number of exits of 8, and number of contact zones of 3 exhibited the highest stability and minimum sensitivity to different degrees of clogging.

Fabrication of immobilized enzyme reactors with pillar arrays into polydimethylsiloxane microchip

This paper demonstrates the design, efficiency and applicability of a simple and inexpensive microfluidic immobilized enzymatic reactor (IMER) for rapid protein digestion. The high surface-to-volume ratio (S/V) of the reactor was achieved by forming pillars in the channel. It was found that pillar arrays including dimensions of 40 μm × 40 μm as pillar diameter and interpillar distance can provide both relatively high S/V and flow rate in the PDMS chip, the fabrication of which was performed by means of soft lithography using average research laboratory infrastructure. CZE peptide maps of IMER-based digestions were compared to peptide maps obtained from standard in-solution digestion of proteins. The peak patterns of the electropherograms and the identified proteins were similar, however, digestion with the IMER requires less than 10 min, while in-solution digestion takes 16 h.

Effect of the Length-to-Width Aspect Ratio of a Cuboid Packed-Bed Device on Efficiency of Chromatographic Separation

In recent papers we have discussed the use of cuboid packed-bed devices as alternative to columns for chromatographic separations. These devices address some of the major flow distribution challenges faced by preparative columns used for process-scale purification of biologicals. Our previous studies showed that significant improvements in separation metrics such as the number of theoretical plates, peak shape, and peak resolution in multi-protein separation could be achieved. However, the length-to-width aspect ratio of a cuboid packed-bed device could potentially affect its performance. A systematic comparison of six cuboid packed-bed devices having different length-to-width aspect ratios showed that it had a significant effect on separation performance. The number of theoretical plates per meter in the best-performing cuboid packed-bed device was about 4.5 times higher than that in its equivalent commercial column. On the other hand, the corresponding number in the worst-performing cuboid-packed bed was lower than that in the column. A head-to-head comparison of the best-performing cuboid packed bed and its equivalent column was carried out. Performance metrics compared included the widths and dispersion indices of flow-through and eluted protein peaks. The optimized cuboid packed-bed device significantly outperformed its equivalent column with regards to all these attributes.

Frit-free PDMS microfluidic device for chromatographic separation and on-chip detection

A simple frit-free PDMS (polydimethylsiloxane) microfluidic chromatographic separation and detection device, packed with diatomaceous earth (DE) microparticles as a normal phase stationary material using iron oxide magnetic nanoparticles is described.

Design and implementation of injector/distributor structures for microfabricated non-porous pillar columns for capillary electrochromatography

A previously proposed foil definition is applied in the design of injector/distributor structures for solid microfabricated column structures for capillary electrochromatography. In addition to a typical bifurcated distributor, an optimized design alternative with two different configurations is experimentally evaluated. Optimized designs yielded a flat profile for the injected sample with a maximum of 3% variation from the mean width, while it went up to 18% for the typical bifurcated distributor. The implemented electrokinetic injection approach enabled controlling the volume of the injected sample accurately without sacrificing the compactness of the device design. The width of the injected sample was directly proportional to the injection time, namely 165 and 218 μm base widths were obtained for 0.6 and 0.8s of feeding, respectively. Reducing the external porosity of the distributor by 85% compared to the typical design, optimized distributors caused a decrease in the mean flow velocity of up to 70%. However, having a flat initial plug shape enabled the separation of a mixture of Coumarin 440, 460, 480 and 540 at 1 mm downstream of the injection point in 80s, while it was even not possible to detect the C440 signal for a typical bifurcated design.

Microscale liquid dynamics and the effect on macroscale propagation in pillar arrays

Liquid dynamics in micropillar arrays have received significant fundamental interest and have offered opportunities for the development of advanced microfluidic, thermal management, and energy-harvesting devices. However, a comprehensive understanding of complex liquid behavior and the effect on macroscopic propagation rates in micropillar arrays is needed. In this work, we investigated the microscopic sweeping behavior of the liquid front along the spreading direction in micropillar arrays where the sweeping distance scales with the one-fifth power of time. We explain the scaling with a simplified model that captures the capillary pressure gradient at the liquid front. Furthermore, we show that such microscopic dynamics is the mechanism that decreases the macroscopic propagation rate. This effect is a result of the reduction in the interfacial energy difference used to generate the capillary pressure, which is explained with an energy-based model and corroborated with experiments. The results indicate the importance of accounting for the microscopic dynamics of the liquid on microstructured surfaces, particularly in sparse geometries.

Fabrication and chromatographic performance of porous-shell pillar-array columns

We report on a new approach to obtain highly homogeneous silica-monolithic columns, applying a sol-gel fabrication process inside a rectangular pillar-array column (1 mm in width, 29 microm in height and 33.75 mm in length) having a cross-sectional area comparable to that of a 200 microm diameter circular capillary. Starting from a silicon-based pillar array and working under high phase-separation-tendency conditions (low poly(ethylene glycol) (PEG)-concentration), highly regular silica-based chromatographic systems with an external porosity in the order of 66-68% were obtained. The pillars, 2.4 microm in diameter, were typically clad with a 0.5 microm shell layer of silica, thus creating a 3.4 microm total outer pillar diameter and leaving a minimal through-pore size of 2.2 microm. After mesopore creation by hydrothermal treatment and column derivatization with octyldimethylchlorosilane, the monolithic column was used for chip-based liquid-chromatographic separations of coumarin dyes. Minimal plate heights ranging between 3.9 microm (nonretaining conditions) and 6 mum (for a retention factor of 6.5) were obtained, corresponding to domain-size-reduced plate heights ranging between 0.7 and 1.2. The column permeability was in the order of 1.3 x 10(13) m(2), lower than theoretically expected, but this is probably due to obstructions induced by the sol-gel process in the supply channels.