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Open AccessEditorial

Editorial for the Special Issue on Micro/Nano-Chip Electrokinetics

by Xiangchun Xuan and Shizhi Qian

Micromachines 2017, 8(5), 145; https://doi.org/10.3390/mi8050145 - 4 May 2017

Cited by 2 | Viewed by 3714

Abstract

Micro/nanofluidics-based lab-on-a-chip devices have found extensive applications in the analysis of chemical and biological samples over the past two decades. Electrokinetics is the method of choice in these micro/nano-chips for transporting, manipulating and sensing various analyte species (e.g., ions, molecules, fluids and particles, [...] Read more.

Micro/nanofluidics-based lab-on-a-chip devices have found extensive applications in the analysis of chemical and biological samples over the past two decades. Electrokinetics is the method of choice in these micro/nano-chips for transporting, manipulating and sensing various analyte species (e.g., ions, molecules, fluids and particles, etc.) [1,2].[...] Full article

(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics)

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4472 KiB

Open AccessArticle

Microfluidic Techniques for Analytes Concentration

by Cunlu Zhao, Zhengwei Ge and Chun Yang

Micromachines 2017, 8(1), 28; https://doi.org/10.3390/mi8010028 - 22 Jan 2017

Cited by 44 | Viewed by 8147

Abstract

Microfluidics has been undergoing fast development in the past two decades due to its promising applications in biotechnology, medicine, and chemistry. Towards these applications, enhancing concentration sensitivity and detection resolution are indispensable to meet the detection limits because of the dilute sample concentrations, [...] Read more.

Microfluidics has been undergoing fast development in the past two decades due to its promising applications in biotechnology, medicine, and chemistry. Towards these applications, enhancing concentration sensitivity and detection resolution are indispensable to meet the detection limits because of the dilute sample concentrations, ultra-small sample volumes and short detection lengths in microfluidic devices. A variety of microfluidic techniques for concentrating analytes have been developed. This article presents an overview of analyte concentration techniques in microfluidics. We focus on discussing the physical mechanism of each concentration technique with its representative advancements and applications. Finally, the article is concluded by highlighting and discussing advantages and disadvantages of the reviewed techniques. Full article

(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics)

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14151 KiB

Open AccessArticle

Frequency-Dependent Electroformation of Giant Unilamellar Vesicles in 3D and 2D Microelectrode Systems

by Qiong Wang, Xiaoling Zhang, Ting Fan, Zhong Yang, Xi Chen, Zhenyu Wang, Jie Xu, Yuanyi Li, Ning Hu and Jun Yang

Micromachines 2017, 8(1), 24; https://doi.org/10.3390/mi8010024 - 16 Jan 2017

Cited by 7 | Viewed by 5520

Abstract

A giant unilamellar vesicle (GUV), with similar properties to cellular membrane, has been widely studied. Electroformation with its simplicity and accessibility has become the most common method for GUV production. In this work, GUV electroformation in devices with traditional 3D and new 2D [...] Read more.

A giant unilamellar vesicle (GUV), with similar properties to cellular membrane, has been widely studied. Electroformation with its simplicity and accessibility has become the most common method for GUV production. In this work, GUV electroformation in devices with traditional 3D and new 2D electrode structures were studied with respect to the applied electric field. An optimal frequency (10 kHz in the 3D and 1 kHz in the 2D systems) was found in each system. A positive correlation was found between GUV formation and applied voltage in the 3D electrode system from 1 to 10 V. In the 2D electrode system, the yield of the generated GUV increased first but decreased later as voltage increased. These phenomena were further confirmed by numerically calculating the load that the lipid film experienced from the generated electroosmotic flow (EOF). The discrepancy between the experimental and numerical results of the 3D electrode system may be because the parameters that were adopted in the simulations are quite different from those of the lipid film in experiments. The lipid film was not involved in the simulation of the 2D system, and the numerical results matched well with the experiments. Full article

(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics)

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7193 KiB

Open AccessArticle

Electrokinetic Phenomena in Pencil Lead-Based Microfluidics

by Yashar Bashirzadeh, Venkat Maruthamuthu and Shizhi Qian

Micromachines 2016, 7(12), 235; https://doi.org/10.3390/mi7120235 - 15 Dec 2016

Cited by 12 | Viewed by 5763

Abstract

Fabrication of microchannels and associated electrodes to generate electrokinetic phenomena often involves costly materials and considerable effort. In this study, we used graphite pencil-leads as low cost, disposable 3D electrodes to investigate various electrokinetic phenomena in straight cylindrical microchannels, which were themselves fabricated [...] Read more.

Fabrication of microchannels and associated electrodes to generate electrokinetic phenomena often involves costly materials and considerable effort. In this study, we used graphite pencil-leads as low cost, disposable 3D electrodes to investigate various electrokinetic phenomena in straight cylindrical microchannels, which were themselves fabricated by using a graphite rod as the microchannel mold. Individual pencil-leads were employed as the micro-electrodes arranged along the side walls of the microchannel. Efficient electrokinetic phenomena provided by the 3D electrodes, including alternating current electroosmosis (ACEO), induced-charge electroosmosis (ICEO), and dielectrophoresis (DEP), were demonstrated by the introduced pencil-lead based microfluidic devices. The electrokinetic phenomena were characterized by micro-particle image velocimetry (micro-PIV) measurements and microscopy imaging. Highly efficient electrokinetic phenomena using 3D pencil-lead electrodes showed the affordability and ease of this technique to fabricate microfluidic devices embedded with electrodes for electrokinetic fluid and particle manipulations. Full article

(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics)

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2266 KiB

Open AccessArticle

An Enhanced Electroosmotic Micromixer with an Efficient Asymmetric Lateral Structure

by Teng Zhou, Hanlin Wang, Liuyong Shi, Zhenyu Liu and Sang Woo Joo

Micromachines 2016, 7(12), 218; https://doi.org/10.3390/mi7120218 - 1 Dec 2016

Cited by 51 | Viewed by 5817

Abstract

Homogeneous and rapid mixing in microfluidic devices is difficult to accomplish, owing to the low Reynolds number associated with most flows in microfluidic channels. Here, an efficient electroosmotic micromixer based on a carefully designed lateral structure is demonstrated. The electroosmotic flow in this [...] Read more.

Homogeneous and rapid mixing in microfluidic devices is difficult to accomplish, owing to the low Reynolds number associated with most flows in microfluidic channels. Here, an efficient electroosmotic micromixer based on a carefully designed lateral structure is demonstrated. The electroosmotic flow in this mixer with an asymmetrical structure induces enhanced disturbance in the micro channel, helping the fluid streams’ folding and stretching, thereby enabling appreciable mixing. Quantitative analysis of the mixing efficiency with respect to the potential applied and the flow rate suggests that the electroosmotic microfluidic mixer developed in the present work can achieve efficient mixing with low applied potential. Full article

(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics)

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1939 KiB

Open AccessArticle

Numerical Model of Streaming DEP for Stem Cell Sorting

by Rucha Natu and Rodrigo Martinez-Duarte

Micromachines 2016, 7(12), 217; https://doi.org/10.3390/mi7120217 - 30 Nov 2016

Cited by 16 | Viewed by 5591

Abstract

Neural stem cells are of special interest due to their potential in neurogenesis to treat spinal cord injuries and other nervous disorders. Flow cytometry, a common technique used for cell sorting, is limited due to the lack of antigens and labels that are [...] Read more.

Neural stem cells are of special interest due to their potential in neurogenesis to treat spinal cord injuries and other nervous disorders. Flow cytometry, a common technique used for cell sorting, is limited due to the lack of antigens and labels that are specific enough to stem cells of interest. Dielectrophoresis (DEP) is a label-free separation technique that has been recently demonstrated for the enrichment of neural stem/progenitor cells. Here we use numerical simulation to investigate the use of streaming DEP for the continuous sorting of neural stem/progenitor cells. Streaming DEP refers to the focusing of cells into streams by equilibrating the dielectrophoresis and drag forces acting on them. The width of the stream should be maximized to increase throughput while the separation between streams must be widened to increase efficiency during retrieval. The aim is to understand how device geometry and experimental variables affect the throughput and efficiency of continuous sorting of SC27 stem cells, a neurogenic progenitor, from SC23 cells, an astrogenic progenitor. We define efficiency as the ratio between the number of SC27 cells over total number of cells retrieved in the streams, and throughput as the number of SC27 cells retrieved in the streams compared to their total number introduced to the device. The use of cylindrical electrodes as tall as the channel yields streams featuring >98% of SC27 cells and width up to 80 µm when using a flow rate of 10 µL/min and sample cell concentration up to 10⁵ cells/mL. Full article

(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics)

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8099 KiB

Open AccessFeature PaperArticle

Microfluidic Mixing and Analog On-Chip Concentration Control Using Fluidic Dielectrophoresis

by Nicholas Mavrogiannis, Mitchell Desmond, Kenny Ling, Xiaotong Fu and Zachary Gagnon

Micromachines 2016, 7(11), 214; https://doi.org/10.3390/mi7110214 - 23 Nov 2016

Cited by 17 | Viewed by 5377

Abstract

Microfluidic platforms capable of complex on-chip processing and liquid handling enable a wide variety of sensing, cellular, and material-related applications across a spectrum of disciplines in engineering and biology. However, there is a general lack of available active microscale mixing methods capable of [...] Read more.

Microfluidic platforms capable of complex on-chip processing and liquid handling enable a wide variety of sensing, cellular, and material-related applications across a spectrum of disciplines in engineering and biology. However, there is a general lack of available active microscale mixing methods capable of dynamically controlling on-chip solute concentrations in real-time. Hence, multiple microfluidic fluid handling steps are often needed for applications that require buffers at varying on-chip concentrations. Here, we present a novel electrokinetic method for actively mixing laminar fluids and controlling on-chip concentrations in microfluidic channels using fluidic dielectrophoresis. Using a microfluidic channel junction, we co-flow three electrolyte streams side-by-side so that two outer conductive streams enclose a low conductive central stream. The tri-laminar flow is driven through an array of electrodes where the outer streams are electrokinetically deflected and forced to mix with the central flow field. This newly mixed central flow is then sent continuously downstream to serve as a concentration boundary condition for a microfluidic gradient chamber. We demonstrate that by actively mixing the upstream fluids, a variable concentration gradient can be formed dynamically downstream with single a fixed inlet concentration. This novel mixing approach offers a useful method for producing variable on-chip concentrations from a single inlet source. Full article

(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics)

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2121 KiB

Open AccessArticle

Power Generation by Reverse Electrodialysis in a Microfluidic Device with a Nafion Ion-Selective Membrane

by Tsung-Chen Tsai, Chia-Wei Liu and Ruey-Jen Yang

Micromachines 2016, 7(11), 205; https://doi.org/10.3390/mi7110205 - 10 Nov 2016

Cited by 29 | Viewed by 6267

Abstract

An energy conversion microchip consisting of two circular microchambers and a Nafion-filled microchannel is fabricated using standard micro-electro-mechanical systems (MEMS) techniques. When the chambers are filled with KCl solutions with different concentrations, the Nafion microchannel acts as a cation-selective membrane and results in [...] Read more.

An energy conversion microchip consisting of two circular microchambers and a Nafion-filled microchannel is fabricated using standard micro-electro-mechanical systems (MEMS) techniques. When the chambers are filled with KCl solutions with different concentrations, the Nafion microchannel acts as a cation-selective membrane and results in the generation of electrical power through a reverse electrodialysis (RED) process. The current-potential characteristics of the Nafion membrane are investigated for devices with various microchannel lengths and electrolyte concentration ratios. It is shown that for a given voltage, the current and generated power increase with a reducing channel length due to a lower resistance. In addition, a maximum power density of 755 mW/m² is obtained given an electrolyte concentration ratio of 2000:1 (unit is mM). The optimal device efficiency is found to be 36% given a channel length of 1 mm and a concentration ratio of 1000:1 (mM). Finally, no enhancement of the short circuit current is observed at higher concentration ratios. Full article

(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics)

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5236 KiB

Open AccessArticle

Electro-Deformation of Fused Cells in a Microfluidic Array Device

by Yan Liu, Xiaoling Zhang, Mengdi Chen, Danfen Yin, Zhong Yang, Xi Chen, Zhenyu Wang, Jie Xu, Yuanyi Li, Jun Qiu, Ning Hu and Jun Yang

Micromachines 2016, 7(11), 204; https://doi.org/10.3390/mi7110204 - 9 Nov 2016

Cited by 5 | Viewed by 4825

Abstract

We present a new method of analyzing the deformability of fused cells in a microfluidic array device. Electrical stresses—generated by applying voltages (4–20 V) across discrete co-planar microelectrodes along the side walls of a microfluidic channel—have been used to electro-deform fused and unfused [...] Read more.

We present a new method of analyzing the deformability of fused cells in a microfluidic array device. Electrical stresses—generated by applying voltages (4–20 V) across discrete co-planar microelectrodes along the side walls of a microfluidic channel—have been used to electro-deform fused and unfused stem cells. Under an electro-deformation force induced by applying an alternating current (AC) signal, we observed significant electro-deformation phenomena. The experimental results show that the fused stem cells were stiffer than the unfused stem cells at a relatively low voltage (<16 V). However, at a relatively high voltage, the fused stem cells were more easily deformed than were the unfused stem cells. In addition, the electro-deformation process is modeled based on the Maxwell stress tensor and structural mechanics of cells. The theoretical results show that a positive correlation is found between the deformation of the cell and the applied voltage, which is consistent with the experimental results. Combined with a numerical analysis and experimental study, the results showed that the significant difference of the deformation ratio of the fused and unfused cells is not due to their size difference. This demonstrates that some other properties of cell membranes (such as the membrane structure) were also changed in the electrofusion process, in addition to the size modification of that process. Full article

(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics)

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1580 KiB

Open AccessArticle

UV Light–Induced Aggregation of Titania Submicron Particles

by Can Zhou, Yashar Bashirzadeh, Timothy A. Bernadowski and Xiaoyu Zhang

Micromachines 2016, 7(11), 203; https://doi.org/10.3390/mi7110203 - 8 Nov 2016

Cited by 11 | Viewed by 5340

Abstract

In this study, aggregation of TiO₂ (rutile and anatase) submicron particles in deionized (DI) water under ultra-violet (UV) light irradiation was investigated. While no aggregation was observed in the dark, rutile and anatase submicron particles started aggregating upon application of UV light [...] Read more.

In this study, aggregation of TiO₂ (rutile and anatase) submicron particles in deionized (DI) water under ultra-violet (UV) light irradiation was investigated. While no aggregation was observed in the dark, rutile and anatase submicron particles started aggregating upon application of UV light and ceased aggregation in about 2 and 8.4 h, respectively. It has been demonstrated that UV light directly mitigated the particle mobility of TiO₂, resulting in a neutralization effect of the Zeta potential. It was also observed that rutile particles aggregated much faster than anatase particles under UV radiation, indicating that the Zeta potential of as-prepared rutile is less than that of anatase in deionized (DI) water. In addition, the interaction energy of rutile and anatase particles was simulated using the Derjaguin–Landau–Verwey–Overbeek (DLVO) model. The results showed a significant reduction of barrier energy from 118.2 k_BT to 33.6 k_BT for rutile and from 333.5 k_BT to 46.1 k_BT for anatase, respectively, which further validated the remarkable influence of UV irradiation on the aggregation kinetics of rutile and anatase submicron particles. This work presents a further understanding of the aggregation mechanism of light-controlled submicron particles and has a promising potential application in environmental remediation. Full article

(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics)

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3316 KiB

Open AccessArticle

Microfluidic Paper-Based Sample Concentration Using Ion Concentration Polarization with Smartphone Detection

by Xue Li, Yanan Niu, Yunyi Chen, Di Wu, Long Yi and Xianbo Qiu

Micromachines 2016, 7(11), 199; https://doi.org/10.3390/mi7110199 - 4 Nov 2016

Cited by 22 | Viewed by 7190

Abstract

A simple method for microfluidic paper-based sample concentration using ion concentration polarization (ICP) with smartphone detection is developed. The concise and low-cost microfluidic paper-based ICP analytical device, which consists of a black backing layer, a nitrocellulose membrane, and two absorbent pads, is fabricated [...] Read more.

A simple method for microfluidic paper-based sample concentration using ion concentration polarization (ICP) with smartphone detection is developed. The concise and low-cost microfluidic paper-based ICP analytical device, which consists of a black backing layer, a nitrocellulose membrane, and two absorbent pads, is fabricated with the simple lamination method which is widely used for lateral flow strips. Sample concentration on the nitrocellulose membrane is monitored in real time by a smartphone whose camera is used to collect the fluorescence images from the ICP device. A custom image processing algorithm running on the smartphone is used to track the concentrated sample and obtain its fluorescence signal intensity for quantitative analysis. Two different methods for Nafion coating are evaluated and their performances are compared. The characteristics of the ICP analytical device especially with intentionally adjusted physical properties are fully evaluated to optimize its performance as well as to extend its potential applications. Experimental results show that significant concentration enhancement with fluorescence dye sample is obtained with the developed ICP device when a fast depletion of fluorescent dye is observed. The platform based on the simply laminated ICP device with smartphone detection is desired for point-of-care testing in settings with poor resources. Full article

(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics)

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2166 KiB

Open AccessArticle

A New Microfluidic Device for Classification of Microalgae Cells Based on Simultaneous Analysis of Chlorophyll Fluorescence, Side Light Scattering, Resistance Pulse Sensing

by Junsheng Wang, Jinsong Zhao, Yanjuan Wang, Wei Wang, Yushu Gao, Runze Xu and Wenshuang Zhao

Micromachines 2016, 7(11), 198; https://doi.org/10.3390/mi7110198 - 2 Nov 2016

Cited by 17 | Viewed by 4930

Abstract

Fast on-site monitoring of foreign microalgae species carried by ship ballast water has drawn more and more attention. In this paper, we presented a new method and a compact device of classification of microalgae cells by simultaneous detection of three kinds of signals [...] Read more.

Fast on-site monitoring of foreign microalgae species carried by ship ballast water has drawn more and more attention. In this paper, we presented a new method and a compact device of classification of microalgae cells by simultaneous detection of three kinds of signals of single microalgae cells in a disposable microfluidic chip. The microfluidic classification device has advantages of fast detection, low cost, and portability. The species of a single microalgae cell can be identified by simultaneous detection of three signals of chlorophyll fluorescence (CF), side light scattering (SLS), and resistance pulse sensing (RPS) of the microalgae cell. These three signals represent the different characteristics of a microalgae cell. A compact device was designed to detect these three signals of a microalgae cell simultaneously. In order to demonstrate the performance of the developed system, the comparison experiments of the mixed samples of three different species of microalgae cells between the developed system and a commercial flow cytometer were conducted. The results show that three kinds of microalgae cells can be distinguished clearly by our developed system and the commercial flow cytometer and both results have good agreement. Full article

(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics)

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3425 KiB

Open AccessFeature PaperArticle

Tunable Particle Focusing in a Straight Channel with Symmetric Semicircle Obstacle Arrays Using Electrophoresis-Modified Inertial Effects

by Dan Yuan, Chao Pan, Jun Zhang, Sheng Yan, Qianbin Zhao, Gursel Alici and Weihua Li

Micromachines 2016, 7(11), 195; https://doi.org/10.3390/mi7110195 - 1 Nov 2016

Cited by 22 | Viewed by 4864

Abstract

In this work, a novel microfluidic platform for tunable particle focusing in a straight channel with symmetric semicircle obstacle arrays using electrophoresis (EP)-modified inertial effects was presented. By exerting an EP force on the charged microparticles, a relative velocity gap between microspheres and [...] Read more.

In this work, a novel microfluidic platform for tunable particle focusing in a straight channel with symmetric semicircle obstacle arrays using electrophoresis (EP)-modified inertial effects was presented. By exerting an EP force on the charged microparticles, a relative velocity gap between microspheres and fluid in a straight channel with symmetric semicircle obstacle arrays was implemented. The relative velocity and fluid shear will induce shear-slip lift force (Saffman lift force) perpendicular to the mainstream direction. Therefore, the focusing pattern can be altered using the electrophoresis-induced Saffman force. The effects of electric field direction, flow rate, electric field magnitude, and particle size were also studied. This demonstrates the possibility of adjusting the particle inertial focusing pattern in a straight channel with with symmetric semicircle obstacle arrays using electrophoresis. Manipulation of the lateral migration of focusing streaks increases controllability in applications such as blood cell filtration and the separation of cells by size. Full article

(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics)

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3675 KiB

Open AccessArticle

Deformability-Based Electrokinetic Particle Separation

by Teng Zhou, Li-Hsien Yeh, Feng-Chen Li, Benjamin Mauroy and Sang Woo Joo

Micromachines 2016, 7(9), 170; https://doi.org/10.3390/mi7090170 - 20 Sep 2016

Cited by 20 | Viewed by 5783

Abstract

Deformability is an effective property that can be used in the separation of colloidal particles and cells. In this study, a microfluidic device is proposed and tested numerically for the sorting of deformable particles of various degrees. The separation process is numerically investigated [...] Read more.

Deformability is an effective property that can be used in the separation of colloidal particles and cells. In this study, a microfluidic device is proposed and tested numerically for the sorting of deformable particles of various degrees. The separation process is numerically investigated by a direct numerical simulation of the fluid–particle–electric field interactions with an arbitrary Lagrangian–Eulerian finite-element method. The separation performance is investigated with the shear modulus of particles, the strength of the applied electric field, and the design of the contracted microfluidic devices as the main parameters. The results show that the particles with different shear moduli take different shapes and trajectories when passing through a microchannel contraction, enabling the separation of particles based on their difference in deformability. Full article

(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics)

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3927 KiB

Open AccessArticle

Enhanced Throughput for Electrokinetic Manipulation of Particles and Cells in a Stacked Microfluidic Device

by Lin Zhu, Saurin H. Patel, Mark Johnson, Akshay Kale, Yash Raval, Tzuen-Rong Tzeng and Xiangchun Xuan

Micromachines 2016, 7(9), 156; https://doi.org/10.3390/mi7090156 - 1 Sep 2016

Cited by 6 | Viewed by 5193

Abstract

Electrokinetic manipulation refers to the control of particle and cell motions using an electric field. It is an efficient technique for microfluidic applications with the ease of operation and integration. It, however, suffers from an intrinsic drawback of low throughput due to the [...] Read more.

Electrokinetic manipulation refers to the control of particle and cell motions using an electric field. It is an efficient technique for microfluidic applications with the ease of operation and integration. It, however, suffers from an intrinsic drawback of low throughput due to the linear dependence of the typically very low fluid permittivity. We demonstrate in this work a significantly enhanced throughput for electrokinetic manipulation of particles and cells by the use of multiple parallel microchannels in a two-layer stacked microfluidic device. The fabrication of this device is simple without the need of a precise alignment of the two layers. The number of layers and the number of microchannels in each layer can thus be further increased for a potentially high throughput electrokinetic particle and cell manipulations. Full article

(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics)

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2677 KiB

Open AccessArticle

Fabrication of High-Aspect-Ratio 3D Hydrogel Microstructures Using Optically Induced Electrokinetics

by Yi Li, Sam H. S. Lai, Na Liu, Guanglie Zhang, Lianqing Liu, Gwo-Bin Lee and Wen Jung Li

Micromachines 2016, 7(4), 65; https://doi.org/10.3390/mi7040065 - 12 Apr 2016

Cited by 9 | Viewed by 7020

Abstract

We present a rapid hydrogel polymerization and prototyping microfabrication technique using an optically induced electrokinetics (OEK) chip, which is based on a non-UV hydrogel curing principle. Using this technique, micro-scale high-aspect-ratio three-dimensional polymer features with different geometric sizes can be fabricated within 1–10 [...] Read more.

We present a rapid hydrogel polymerization and prototyping microfabrication technique using an optically induced electrokinetics (OEK) chip, which is based on a non-UV hydrogel curing principle. Using this technique, micro-scale high-aspect-ratio three-dimensional polymer features with different geometric sizes can be fabricated within 1–10 min by projecting pre-defined visible light image patterns onto the OEK chip. This method eliminates the need for traditional photolithography masks used for patterning and fabricating polymer microstructures and simplifies the fabrication processes. This technique uses cross-link hydrogels, such as poly(ethylene glycol) (PEG)-diacrylate (PEGDA), as fabrication materials. We demonstrated that hydrogel micropillar arrays rapidly fabricated using this technique can be used as molds to create micron-scale cavities in PDMS (polydimethylsiloxane) substrates. Furthermore, hollow, circular tubes with controllable wall thicknesses and high-aspect ratios can also be fabricated. These results show the potential of this technique to become a rapid prototyping technology for producing microfluidic devices. In addition, we show that rapid prototyping of three-dimensional suspended polymer structures is possible without any sacrificial etching process. Full article

(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics)

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