Rapid Prototyping Of Microfluidic Devices Research Articles

Rapid prototyping of PMMA-based microfluidic spheroid-on-a-chip models using micromilling and vapour-assisted thermal bonding

The application of microfluidic devices as next-generation cell and tissue culture systems has increased impressively in the last decades. With that, a plethora of materials as well as fabrication methods for these devices have emerged. Here, we describe the rapid prototyping of microfluidic devices, using micromilling and vapour-assisted thermal bonding of polymethyl methacrylate (PMMA), to create a spheroid-on-a-chip culture system. Surface roughness of the micromilled structures was assessed using scanning electron microscopy (SEM) and atomic force microscopy (AFM), showing that the fabrication procedure can impact the surface quality of micromilled substrates with milling tracks that can be readily observed in micromilled channels. A roughness of approximately 153 nm was created. Chloroform vapour-assisted bonding was used for simultaneous surface smoothing and bonding. A 30-s treatment with chloroform-vapour was able to reduce the surface roughness and smooth it to approximately 39 nm roughness. Subsequent bonding of multilayer PMMA-based microfluidic chips created a durable assembly, as shown by tensile testing. MDA-MB-231 breast cancer cells were cultured as multicellular tumour spheroids in the device and their characteristics evaluated using immunofluorescence staining. Spheroids could be successfully maintained for at least three weeks. They consisted of a characteristic hypoxic core, along with expression of the quiescence marker, p27kip1. This core was surrounded by a ring of Ki67-positive, proliferative cells. Overall, the method described represents a versatile approach to generate microfluidic devices compatible with biological applications.

Combined masked LCD-printing and microfabrication for bioimpedance-chips

Biomedical in vitro sensors use cell cultures grown on sensor chips for drug testing, toxicological screening, studying pathologic processes in tissue and for personalized medicine. Microfluidic systems and chips bridge the gap of the biological micro world to our accessible macro world, creating the interface between e.g., cells on a chip to reservoirs and pumps. Prototype and low volume lab scale microfluidic devices have traditionally been realized by soft lithography using polydimethylsiloxane (PDMS) technology. Recently, rapid prototyping of microfluidic devices using direct 3D printing has become widely available. Usually, the 3D printed parts are (i) either stand-alone systems requiring only fluidic connections, or (ii) they need to be carefully aligned and skilfully attached to the rigid micro fabricated chip. This post-fabrication attachment is time-consuming and a frequent source of error. In this work the fabrication of the microchip and the microfluidic system have been integrated into a multi technology fabrication process. For the first time we demonstrate the “on-chip 3D printing” of a microfluidic attachment directly onto an in-house fabricated multi electrode array chip. The process uses a desktop-sized LCD resin printer and eliminates the time-consuming post-deposition alignment and attachment. Biocompatibility of the used resin was confirmed for murine fibroblasts and validates this multi technology approach for biomedical cell chips. • Direct 3D printing of microfluidic structures on microchip demonstrated. • Electrophysiology measuring device fabricated by direct 3D printing. • No post-printing attachment and positioning step required. • Biocompatibility of used resin evaluated positively for short time culture.

Rapid Prototyping of Micropillars using Digital Light Process 3D Printing Technique

In this paper, we discuss a technique to fabricate a three-dimensional (3D) printed micropillars structure of microfluidic system. The developed system consists of microchannels, chambers, and micropillars. The creation of arrays of pillars were the focus of the study. The structure is fabricated using a 3D printing technique called Digital Light Process (DLP). In this paper, we examine the potential use of the 3D printing approaches for the fabrication of microfilter and micromixer devices integrated with microfluidic channels. Our 3D printing process shows that micropillars with diameters between 200 and 400 μm can be fabricated using a DLP 3D printer machine by optimizing the preparation process and post processing parameters. Later, SEM analysis shows that micropillars with high aspect ratio and straight side wall were achieved. The DLP 3D printer is the most suitable and reliable technique that can produce the smallest dimension compared to other types of 3D printer that shows a promising method for the rapid prototyping of microfluidic devices for biomedical application.

Aerosol-jet printing facilitates the rapid prototyping of microfluidic devices with versatile geometries and precise channel functionalization

Microfluidics has emerged as a powerful analytical tool for biology and biomedical research, with uses ranging from single-cell phenotyping to drug discovery and medical diagnostics, and only small sample volumes required for testing. The ability to rapidly prototype new designs is hugely beneficial in a research environment, but the high cost, slow turnaround, and wasteful nature of commonly used fabrication techniques, particularly for complex multi-layer geometries, severely impede the development process. In addition, microfluidic channels in most devices currently play a passive role and are typically used to direct flows. The ability to “functionalize” the channels with different materials in precise spatial locations would be a major advantage for a range of applications. This would involve incorporating functional materials directly within the channels that can partake in, guide or facilitate reactions in precisely controlled microenvironments. Here we demonstrate the use of Aerosol Jet Printing (AJP) to rapidly produce bespoke molds for microfluidic devices with a range of different geometries and precise “in-channel” functionalization. We show that such an advanced microscale additive manufacturing method can be used to rapidly design cost-efficient and customized microfluidic devices, with the ability to add functional coatings at specific locations within the microfluidic channels. We demonstrate the functionalization capabilities of our technique by specifically coating a section of a microfluidic channel with polyvinyl alcohol to render it hydrophilic. This versatile microfluidic device prototyping technique will be a powerful aid for biological and bio-medical research in both academic and industrial contexts.

Fabrication of integrated microfluidic devices by direct ink writing (DIW) 3D printing

This paper describes a simple method to apply 3D printing to fabricate microfluidic devices integrated with fluid handling and functional components. We used a direct ink writing (DIW) 3D printer to dispense a fast-curing flexible silicone resin on various substrates to form microchannels. The dispensed silicone was interfaced with another flat substrate to form microchannels with tunable dimensions. Using this method, we fabricated channels with dimensions as small as 32 μm in width and 30 μm height. We fabricated basic microfluidic modalities (e.g. straight and branched channels, mixers, chambers and droplet generators) as well as functional modalities (e.g. valves, variable flow resistors and gradient generators) on an optically transparent substrate. The method can be readily extended to fabricate microchannels on a diverse range of functional substrates. We showcased this capability by fabricating microchannels on an unmodified printed-circuit board (PCB) to form the interface between the fluid and the electric circuits, and microporous membranes to perform air-liquid human keratinocyte cell culture. Our approach has enabled rapid prototyping of microfluidic devices integrated with functional components required for lab-on-a-chip applications, complementing current approaches in 3D printed microfluidics that are restricted in attainable dimensions and available materials.

Reconfigurable Acrylic-tape Hybrid Microfluidics

There is a great interest in low-cost, versatile microfluidic platforms of which the fabrication processes are rapid, straightforward, and translatable to industrial mass productions. In addition, it is beneficial for microfluidic devices to be reconfigurable in the field, so that multiple functions can be realized by a minimum number of devices. Here, we present a versatile acrylic-tape platform which allows highly accessible rapid prototyping of microfluidic devices, as well as device reconfiguration to realize different functions. The clean-room-free fabrication and sealing process only requires a laser cutter, acrylic, and tapes and can be done by an untrained person in the field. We experimentally characterized the relationship between the capillary flow speed and the channel height, the latter of which can be well controlled by the fabrication process. Reconfiguration of microfluidic functions was demonstrated on a single acrylic-tape device, thanks to the reversible sealing enabled by functional tapes. Different pumping mechanisms, including on-chip pumps for better portability and syringe pumps for precise fluid control, have been employed for the demonstration of two-phase flow and droplet generation, respectively. The low-cost and versatile acrylic-tape microfluidic devices are promising tools for applications in a wide range of fields, especially for point-of-care biomedical and clinical applications.

Rapid fabrication and characterization of PDMS microfluidics device using printed conductive silver ink

Abstract Currently, new fabrication methods for rapid prototyping of microfluidic devices has bring attention among researchers from various fields. The main reason is the use of lithographic equipment in standard fabrication method for master fabrication require trained personnel and high cost disposable materials. In this paper, a new fabrication method via printed conductive silver ink is introduced in order to minimize the current fabrication process through elimination of the photolithography process. As a result, a usable, faster and cost effective prototyping process of a microfluidic based biosensor devices able to be produced. In this method, the conductive silver ink was used to create a master template contains microchannel onto glass-reinforced epoxy laminate sheets (FR-4). Then, Polydimethylsiloxane (PDMS) were used to replicate the structure. Next, the digital microscope was used to obtain images to demonstrate geometry fluidics structure with channel dimension up to 200 µm width. Moreover, a 3D profilometer was used to evaluate their thickness and roughness of the microfluidics structure. The stability test demonstrates the consistency of flow sequence inside the serpentine and separation channel.

Rapid prototyping of microfluidic devices by SL 3D printing and their biocompatibility study for cell culturing

Abstract In this work, we demonstrate the feasibility of creating biocompatible microfluidic devices using stereolithography (SL) 3D printing as a simple and low-cost methodology compared to conventional soft-lithography carried on at cleanroom facilities. SL printing has gained much interest for rapid prototyping of designs in the fields of jewelry, dentistry and materials engineering. Therefore, we exploit this potential in microfluidics for creating biocompatible devices using three different types of photocurable resins. The resins are: Clear standard, High Temp and Dental LT (Formlabs, USA). Special attention is dedicated to investigate the minimum feature size (MFS), roughness and design-orientation dependence of SL printed microchannels. To the best of our knowledge, cytotoxicity research of UV curable resins for SL printing has been done in literature for short incubation times (

Freeform Perfusable Microfluidics Embedded in Hydrogel Matrices.

We report a modification of the freeform reversible embedding of suspended hydrogels (FRESH) 3D printing method for the fabrication of freeform perfusable microfluidics inside a hydrogel matrix. Xanthan gum is deposited into a CaCl2 infused gelatine slurry to form filaments, which are consequently rinsed to produce hollow channels. This provides a simple method for rapid prototyping of microfluidic devices based on biopolymers and potentially a new approach to the construction of vascular grafts for tissue engineering.

Transparency of PDMS based microfluidic devices under temperature gradients

Polydimethylsiloxane (PDMS) is one the most popular materials for rapid prototyping of microfluidic devices. It is highly regarded for its optically transparency and chemical inertness in aqueous environments. Recently, we have observed a unique phenomenon that a PDMS microfluidic channel filled with water loses transparency upon exposure to a temperature gradient. This paper describes a characterization of this phenomenon and proposes a mechanism to explain its cause. Specifically, we have characterized the transparency loss over a variety of gradient magnitudes, absolute temperatures and exposure durations. Observing the low-transparency device with an optical microscope reveals droplets within the channel region (CH) but not within bulk PDMS. We hypothesize that the droplets form as a result of low molecular weight (LMW) PDMS chains entering the aqueous channel, driven by a thermophoretic response, and separating into a different phase from the aqueous medium. This hypothesis is supported by a strong correlation between the magnitude of temperature gradients and degree of transparency loss experienced by the device, while heating or cooling the device uniformly without a temperature gradient does not induce the transparency change. Additionally, we report an ability to restore the optical transparency by heating the device to evaporate water in the channel. The loss and recovery of optical transparency is repeatable. Substance extracted from the low-transparency channel demonstrates fingerprint features of PDMS, supporting our reasoning of the mechanism. To our knowledge, this is the first time such phenomenon is reported and systematically studied in the literature. This work provides some insight about thermophoresis of PDMS and the phenomenon could find applications in micro-sensors and micro-actuators.

Optofluidic Modular Blocks for On-Demand and Open-Source Prototyping of Microfluidic Systems.

Rapid prototyping of microfluidic devices has advanced greatly, along with the development of 3D printing and micromachining technologies. However, peripheral systems for microfluidics still rely on conventional equipment, such as bench-top microscopy and syringe pumps, which limit system modification and further improvements. Herein, optofluidic modular blocks are presented as discrete elements to modularize peripheral optical and fluidic systems and are used for on-demand and open-source prototyping of whole microfluidic systems. Each modular block is fabricated by embedding optical or fluidic devices into the corresponding 3D-printed housing. The self-interlocking structure of the modular blocks enables easy assembly and reconfiguration of the blocks in an intuitive manner, while also providing precise optical and fluidic alignment between the blocks. With the library of standardized modular blocks developed here, how the blocks can be easily assembled to build whole microfluidic systems for blood compatibility testing, droplet microfluidics, and cell migration assays is demonstrated. Based on the simplicity of assembling the optofluidic blocks, the prototyping platform can be easily used for open-source sharing of digital design files, assembly and operation instructions, and block specifications, thereby making it easy for nonexperts to implement microfluidic ideas as physical systems.

Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) Spectromicroscopy Using Synchrotron Radiation and Micromachined Silicon Wafers for Microfluidic Applications.

A custom-designed optical configuration compatible with the use of micromachined multigroove internal reflection elements (μ-groove IREs) for attenuated total reflectance Fourier transform infrared (ATR FT-IR) spectroscopy and imaging applications in microfluidic devices is described. The μ-groove IREs consist of several face-angled grooves etched into a single, monolithic silicon chip. The optical configuration permits individual grooves to be addressed by focusing synchrotron sourced IR light through a 150 µm pinhole aperture, restricting the beam spot size to a dimension smaller than that of the groove walls. The effective beam spot diameter at the ATR sampling plane is determined through deconvolution of the measured detector response and found to be 70 µm. The μ-groove IREs are highly compatible with standard photolithographic techniques as demonstrated by printing a 400 µm wide channel in an SU-8 film spin-coated on the IRE surface. Attenuated total reflection FT-IR mapping as a function of sample position across the channel illustrates the potential application of this approach for rapid prototyping of microfluidic devices.

Safe and cost-effective rapid-prototyping of multilayer PMMA microfluidic devices

The rapid translation of research from bench to bedside, as well as the generation of commercial impact, has never been more important for both academic and industrial researchers. It is therefore unsurprising that more and more microfluidic groups are investigating research using a wide range of thermoplastics which can be readily translated to large-scale manufacturing, if the technology is taken to commercialisation. While structuring, via additive or subtractive manufacturing, is becoming relatively easy through the use of commercial-grade devices, reliable and fast assembly remains a challenge. In this article, we propose an innocuous and cost-effective, under 2-min technique which enables the bonding of multiple poly(methyl methacrylate) layers. This bonding technique relies on the application of small amounts (10 µl/cm2) of ethanol, low temperatures (70 °C) and relatively low pressures (~1.6 MPa). Our characterisation analysis shows that using a bonding time of 2 min is enough to produce a strong bond able to withstand pressures always above 6.2 MPa (with mean of 8 MPa, highest reported in the literature), with minimal channel deformation (<5%). This technique, which we demonstrate on assembly comprising up to 19 layers, presents an exciting improvement in the field of rapid prototyping of microfluidic devices, enabling extremely fast design cycles in microfluidic research with a material compatible with mass manufacturing, thus allowing a smoother transition from the laboratory to the market. Beyond the research community, this robust prototyping technique has the potential to impact on the deliverability of other scientific endeavours including educational projects and will directly fuel the fluidic maker movement.

Inexpensive, rapid prototyping of microfluidic devices using overhead transparencies and a laser print, cut and laminate fabrication method.

We describe a technique for fabricating microfluidic devices with complex multilayer architectures using a laser printer, a CO2 laser cutter, an office laminator and common overhead transparencies as a printable substrate via a laser print, cut and laminate (PCL) methodology. The printer toner serves three functions: (i) it defines the microfluidic architecture, which is printed on the overhead transparencies; (ii) it acts as the adhesive agent for the bonding of multiple transparency layers; and (iii) it provides, in its unmodified state, printable, hydrophobic 'valves' for fluidic flow control. By using common graphics software, e.g., CorelDRAW or AutoCAD, the protocol produces microfluidic devices with a design-to-device time of ∼40 min. Devices of any shape can be generated for an array of multistep assays, with colorimetric detection of molecular species ranging from small molecules to proteins. Channels with varying depths can be formed using multiple transparency layers in which a CO2 laser is used to remove the polyester from the channel sections of the internal layers. The simplicity of the protocol, availability of the equipment and substrate and cost-effective nature of the process make microfluidic devices available to those who might benefit most from expedited, microscale chemistry.

Rapid prototyping of microfluidic devices with integrated wrinkled gold micro-/nano textured electrodes for electrochemical analysis.

Fully-integrated electro-fluidic systems with micro-/nano-scale features have a wide range of applications in lab-on-a-chip systems used for biosensing, biological sample processing, and environmental monitoring. Rapid prototyping of application-specific electro-fluidic systems is envisioned to facilitate the testing, validation, and market translation of several lab-on-a-chip systems. Towards this goal, we developed a rapid prototyping process for creating wrinkled micro-/nano-textured electrodes on shrink memory polymers, fabricating microfluidics using molds patterned by a craft-cutter, and bonding electrical and fluidic circuitries using a PDMS partial curing method optimized for creating void-free bonds at the side walls and surfaces of tall (>5 μm) micro-/nano-textured wrinkled electrodes. The resulting electro-fluidic devices, featuring closely spaced high topography electrodes for electrochemical analysis, can withstand flow-rates and burst pressures larger than 25 mL min(-1) and 125 kPa, respectively. In addition, the fully-integrated electrochemical flow-cell developed here demonstrates excellent electrochemical behaviour, with negligible scan to scan variation for over 100 cyclic voltammetry scans, and expected redox signatures measured under various voltage scan rates and fluidic flow rates.

Advances in three-dimensional rapid prototyping of microfluidic devices for biological applications.

The capability of 3D printing technologies for direct production of complex 3D structures in a single step has recently attracted an ever increasing interest within the field of microfluidics. Recently, ultrafast lasers have also allowed developing new methods for production of internal microfluidic channels within the bulk of glass and polymer materials by direct internal 3D laser writing. This review critically summarizes the latest advances in the production of microfluidic 3D structures by using 3D printing technologies and direct internal 3D laser writing fabrication methods. Current applications of these rapid prototyped microfluidic platforms in biology will be also discussed. These include imaging of cells and living organisms, electrochemical detection of viruses and neurotransmitters, and studies in drug transport and induced-release of adenosine triphosphate from erythrocytes.

Adhesive Transfer Soft Lithography: Low-Cost and Flexible Rapid Prototyping of Microfluidic Devices

A simple and low-cost approach was proposed for prototyping PDMS based microfluidic devices by transferringadhesive film microstructures onto a flexible substrate as a mould for PDMS replicas. The microstructures were engravedon an adhesive coated film using a commercial cutting plotter and then transferred (or laminated) onto a flexiblesubstrate, allowing for engraved isolated patterns. The proposed technique was demonstrated by a hydrodynamic focusingmicrofluidic device, having splitting and re-combining sheath channels. The whole processing could be finished within 1h in a normal laboratory environment. This approach offers an easy, flexible and rapid prototyping of microfluidic andlab-on-a-chip devices to users without expertise in microfabrication. In addition, by minimizing the use of chemicals, theprocess becomes more environmentally friendly than conventional photolithography based micro-fabrication techniques.

Stainless Steel Pinholes for Fast Fabrication of High-Performance Microchip Electrophoresis Devices by CO2 Laser Ablation

With the introduction of hobby laser engravers/cutters, the use of CO2 laser micromachining on poly(methyl methacrylate) (PMMA) has the potential for flexible, low cost, rapid prototyping of microfluidic devices. Unfortunately, the feature size created by most entry-level CO2 laser micromachining systems is too large to become a functional tool in analytical microfluidics. In this paper, we report a novel method to reduce the feature size of microchannels and the bulges formed at the rim of the channel during CO2 laser micromachining by passing the laser beam through a stainless steel pinhole. Without the pinhole, the channel width was typically 300 μm wide. However, when 50 or 35 μm diameter pinholes were used, channel widths of 60 and 25 μm, respectively, could be obtained. The height of the bulge deposited directly next to the channel was reduced to less than 0.8 μm with the pinhole during ablation. Separations of fluorescent dyes on devices ablated with and without the pinhole were compared. On devices fabricated with the pinhole, the number of theoretical plates/m was 2.2-fold higher compared to devices fabricated without the pinhole, and efficiencies comparable to embossed PMMA and laser ablated glass chips were obtained. A mass-produced commercial hobby laser (retailing at ∼$2500), when equipped with a $500 pinhole, represents a rapid and low-cost approach to the rapid fabrication of rigid plastic microchips including the narrow microchannels required for microchip electrophoresis.

A new UV-curing elastomeric substrate for rapid prototyping of microfluidic devices

Rapid prototyping in the design cycle of new microfluidic devices is very important for shortening time-to-market. Researchers are facing the challenge to explore new and suitable substrates with simple and efficient microfabrication techniques. In this paper, we introduce and characterize a UV-curing elastomeric polyurethane methacrylate (PUMA) for rapid prototyping of microfluidic devices. The swelling and solubility of PUMA in different chemicals is determined. Time-dependent measurements of water contact angle show that the native PUMA is hydrophilic without surface treatment. The current monitoring method is used for measurement of the electroosmotic flow mobility in the microchannels made from PUMA. The optical, physical, thermal and mechanical properties of PUMA are evaluated. The UV-lithography and molding process is used for making micropillars and deep channel microfluidic structures integrated to the supporting base layer. Spin coating is characterized for producing different layer thicknesses of PUMA resin. A device is fabricated and tested for examining the strength of different bonding techniques such as conformal, corona treating and semi-curing of two PUMA layers in microfluidic application and the results show that the bonding strengths are comparable to that of PDMS. We also report fabrication and testing of a three-layer multi inlet/outlet microfluidic device including a very effective fluidic interconnect for application demonstration of PUMA as a promising new substrate. A simple micro-device is developed and employed for observing the pressure deflection of membrane made from PUMA as a very effective elastomeric valve in microfluidic devices.

Beyond PDMS: off-stoichiometry thiol–ene (OSTE) based soft lithography for rapid prototyping of microfluidic devices

In this article we introduce a novel polymer platform based on off-stoichiometry thiol-enes (OSTEs), aiming to bridge the gap between research prototyping and commercial production of microfluidic devices. The polymers are based on the versatile UV-curable thiol-ene chemistry but takes advantage of off-stoichiometry ratios to enable important features for a prototyping system, such as one-step surface modifications, tuneable mechanical properties and leakage free sealing through direct UV-bonding. The platform exhibits many similarities with PDMS, such as rapid prototyping and uncomplicated processing but can at the same time mirror the mechanical and chemical properties of both PDMS as well as commercial grade thermoplastics. The OSTE-prepolymer can be cast using standard SU-8 on silicon masters and a table-top UV-lamp, the surface modifications are precisely grafted using a stencil mask and the bonding requires only a single UV-exposure. To illustrate the potential of the material we demonstrate key concepts important in microfluidic chip fabrication such as patterned surface modifications for hydrophobic stops, pneumatic valves using UV-lamination of stiff and rubbery materials as well as micromachining of chip-to-world connectors in the OSTE-materials.