Fabrication of large-volume microfluidic chamber embedded in glass using three-dimensional femtosecond laser micromachining

We report on fabrication of large-volume, square-shaped microfluidic chamber embedded in glass by scanning a tightly focused femtosecond laser beam inside a porous glass immersed in water. After the hollow structure is created in the porous glass substrate, the fabricated glass sample is post-annealed at 1,050°C during which it can be sintered into a compact glass. By the use of this technique, a 1 mm × 1 mm × 100 μm microchamber connected to four microfluidic channels is created inside the transparent glass substrate, showing that our technique allows for fabrication of not only thin channel structures with arbitrary lengths and configurations, but also hollow structures with infinitely large sizes.     

Fabrication of microfluidic channels based on melt-electrospinning direct writing

Microfluidics is a flourishing field, enabling a wide range of applications. However, the current fabrication methods for creating the microchannel structures of microfluidic devices, such as photolithography and 3D printing, mostly have the problems of time-consuming, high cost or low resolution. In this work, we developed a simple and flexible method to fabricate PDMS microfluidic channels, based on poly(ε-caprolactone) (PCL) master mold additive manufactured by a technique termed melt-electrospinning direct writing (MEDW). It relies on the following steps: (1) direct writing of micrometric PCL 2D or 3D pattern by MEDW. (2) Casting PDMS on the printed PCL pattern. (3) Peeling off of patterned PDMS from the embedded sacrificial PCL layer. (4) Bonding the PDMS with microchannel to another PDMS layer by hot pressing. The process parameters during MEDW such as collector speed, nozzle dimension and temperature were studied and optimized for the quality and dimension of the printed micropatterns. Multilayer fiber deposition was developed and applied to achieve microscale architectures with high aspect ratio. Thus, the microchannels fabricated by the proposed approach could possess tunable width and depth. Finally, T-shape and cross-channel devices were fabricated to create either laminar flow or microdroplets to illustrate the applicability and potential of this method for microfluidic device manufacture.     

Fabrication of circular microfluidic channels through grayscale dual-projection lithography

Circular microfluidic channels are in great demand since they are more realistic in mimicking physiological flow systems, generating axis-symmetrical flow, and achieving uniform shear stress. A typical microchannel with rectangular cross section can induce non-physiological gradients of shear rate, pressure, and velocity. This paper presents a novel method of fabricating microfluidic channels with circular and elliptical cross sections through grayscale dual-projection lithography. Our method utilizes two projecting systems to expose grayscale image face-to-face and simultaneously polymerize the photocurable material. The cross-sectional profiles of the fabricated microchannels are consistent with mathematical predictions and, therefore, demonstrate the capability of controlling the channel shapes precisely. Customized circular microchannels can be generated with complex features such as junctions, bifurcations, hierarchies, and gradually changed diameters. This method is capable of fabricating circular channels with a wide range of diameters (39 μm–2 mm) as well as elliptical channels with a major-to-minor axis ratio up to 600%. Microfluidic devices with circular cross sections suitable for particle analysis were made as a demonstrative application in nanoparticle binding and distribution within a mimetic blood vessel. A ready-to-use microfluidic device with customized circular channels can be fabricated within 1 h without the need of clean room or expensive photolithography devices.     

Fabrication and characterization of a polymethyl methacrylate continuous-flow PCR microfluidic chip using CO2 laser ablation

An improved microfabrication method was used to fabricate a continuous-flow PCR (polymerase chain reaction) microfluidic chip on the PMMA substrate using the low-power CO₂ laser ablation technique. The use of the low-power CO₂ laser and the PMMA material could reduce the cost and the time of the fabrication process, especially at the step of laboratory research because of the high flexibility of the laser fabrication technique and the low cost of PMMA. A CO₂ laser output power of 4.5 W and a laser scanning velocity of 76.2 mm/s were chosen to fabricate the chip in this work. The micromachining quality could satisfy the microfluidic requirement of the PCR mixture within the microchannel. Good temperature distribution and gradient were obtained on the PMMA chip with a home-built integrated heating system. An amplification of DNA template with a 990 base pair fragment of Pseudomonas was successfully performed with this chip to characterize its availability and performance with various flow rates.     

Fabrication of three-dimensional microfluidic channels in a single layer of cellulose paper

Three-dimensional microfluidic paper-based analytical devices (3D-μPADs) represent a promising platform technology that permits complex fluid manipulation, parallel sample distribution, high throughput, and multiplexed analytical tests. Conventional fabrication techniques of 3D-μPADs always involve stacking and assembling layers of patterned paper using adhesives, which are tedious and time-consuming. This paper reports a novel technique for fabricating 3D microfluidic channels in a single layer of cellulose paper, which greatly simplifies the fabrication process of 3D-μPADs. This technique, evolved from the popular wax-printing technique for paper channel patterning, is capable of controlling the penetration depth of melted wax, printed on both sides of a paper substrate, and thus forming multilayers of patterned channels in the substrate. We control two fabrication parameters, the density of printed wax (i.e., grayscale level of printing) and the heating time, to adjust the penetration depth of wax upon heating. Through double-sided printing of patterns at different grayscale levels and proper selection of the heating time, we construct up to four layers of channels in a 315.4-μm-thick sheet of paper. As a proof-of-concept demonstration, we fabricate a 3D-μPAD with three layers of channels from a paper substrate and demonstrate multiplexed enzymatic detection of three biomarkers (glucose, lactate, and uric acid). This technique is also compatible with the conventional fabrication techniques of 3D-μPADs, and can decrease the number of paper layers required for forming a 3D-μPAD and therefore make the device quality control easier. This technique holds a great potential to further popularize the use of 3D-μPADs and enhance the mass-production quality of these devices.     

CO2激光直写结合湿法刻蚀加工玻璃基微流控芯片

玻璃是制作微流控芯片的重要材料,其加工工艺主要基于光刻后湿法腐蚀,对设备和实验室要求较高.本文提出以普通指甲油和指甲油/金/铬为牺牲层,利用CO2激光烧蚀开窗口,辅以湿法腐蚀加工玻璃基微流控芯片的方法,并考察了激光加工参数,腐蚀液组成,牺牲层等因素对芯片质量的影响.该方法简便易行,不需要光刻的昂贵设备和繁杂步骤.     

Fabrication of polyimide microfluidic devices by laser ablation based additive manufacturing

Polyimide microfluidic devices (MFDs) have been attached enormous significance because of its excellent organic-solvent inertness, biocompatibility, and thermal stability. In this paper, a novel fabrication method based on the thought of additive manufacturing, which is adding materials layer by layer from bottom to top, was used to construct a multilayer polyimide MFD. The MFD has sophisticated three-dimensional (3D) microchannels with adjustable cross-sectional geometries and high bonding strength, which leads to good reagent mixing performance, large surface-to-volume ratio, and great durability. Starting from a single polyimide film, ultraviolet (UV) laser was utilized to ablate microchannels on the film. Due to the studies over the influence of UV laser on the channel width, the microchannel edge shape is under control, varying from trapezoid to rectangle. From monolayer to multilayer MFDs, thermal bonding with fluorinated ethylene propylene (FEP) nanoparticle dispersion as the adhesive was adopted to stack polyimide films tightly with precise alignment. In this way, microchannels can be connected vertically between layers to form 3D structures. Besides, a homogeneous adhesive interlayer and polyimide-FEP mixing regime were formed, which can provide high bonding strength. Results of computational fluid dynamics simulation of 3D microchannel structures and organic synthesis experiment revealed that our device has great reagent mixing efficiency and promising application prospects in diverse research fields, especially organic chemical and biological studies.

     

Surface polishing of quartz-based microfluidic channels using CO<Subscript>2</Subscript> laser

Recently, microgrinding using a polycrystalline diamond tool has been introduced to fabricate microchannels and structures from quartz (fused silica). Compared to wet or dry etching processes, the grinding process is very simple and time-efficient for prototyping. However, the roughness of the machined surface remains an issue, because the surface is covered with many small cracks. Poor surface roughness can affect fluid flow in the microfluidic channels. To reduce the surface roughness of microchannels generated by a grinding process, this study presents the laser polishing of quartz and investigates the effects of the translational speed and pitch of a laser spot on the surface roughness and shape accuracy of microchannels.     

Fabrication of microfluidic networks with integrated electrodes

In this paper a method is presented for the fabrication of micro-channel networks in glass with integrated and insulated gate electrodes to control the zeta-potential at the insulator surface and therewith the electro-osmotic flow (EOF). The fabrication of the electrodes is a sequence of photolithography, etching and thin film deposition steps on a glass substrate, followed by chemical mechanical polishing (CMP) and subsequently direct thermal bonding to a second glass plate to form closed micro-channels. Plasma enhanced chemical vapor deposition (PECVD) SiO₂-layers as insulating material between the electrodes and micro-channels and different electrode materials are examined with respect to a high bonding temperature to obtain an optimal insulating result. A CMP process for the reduction of the SiO₂ topography and roughness is studied and optimized in order to obtain a surface that is smooth enough to be directly bondable to a second glass plate.     

Fabrication of polystyrene microfluidic devices using a pulsed CO<Subscript>2</Subscript> laser system

In this article, we described a simple and rapid method for fabrication of droplet microfluidic devices on polystyrene substrate using a CO₂ laser system. The effects of the laser power and the cutting speed on the depth, width and aspect ratio of the microchannels fabricated on polystyrene were investigated. The polystyrene microfluidic channels were encapsulated using a hot press bonding technique. The experimental results showed that both discrete droplets and laminar flows could be obtained in the device.     

Manufacture of microfluidic glass chips by deep plasma etching, femtosecond laser ablation, and anodic bonding

Two dry subtractive techniques for the fabrication of microchannels in borosilicate glass were investigated, plasma etching and laser ablation. Inductively coupled plasma reactive ion etching was carried out in a fluorine plasma (C₄F₈/O₂) using an electroplated Ni mask. Depth up to 100 μm with a profile angle of 83°–88° and a smooth bottom of the etched structure (Ra below 3 nm) were achieved at an etch rate of 0.9 μm/min. An ultrashort pulse Ti:sapphire laser operating at the wavelength of 800 nm and 5 kHz repetition rate was used for micromachining. Channels of 100 μm width and 140 μm height with a profile angle of 80–85° were obtained in 3 min using an average power of 160 mW and a pulse duration of 120 fs. A novel process for glass–glass anodic bonding using a conductive interlayer of Si/Al/Si has been developed to seal microfluidic components with good optical transparency using a relatively low temperature (350°C).     

Capillarity in microfluidic channels with hydrophilic and hydrophobic walls

The authors investigate the spontaneous filling of microchannels with mixed hydrophilic and hydrophobic walls. We show that in these channels, unlike that case when all the walls are either hydrophilic or hydrophobic, the local distribution of capillary drive can make partial filling of the channel the most favorable filling type. A strategy for finding the most favorable filling type is presented and tested against capillary filling experiments made on oxygen plasma treated SU-8 microchannels. Good agreement is found between the theory and the experiments.     

Fabrication of microfluidic device channel using a photopolymer for colloidal particle separation

We have developed a method of fabricating microfluidic device channels for bio-nanoelectronics system by using high performance epoxy based dry photopolymer films or dry film resists (DFRs). The DFR used was with a trademark name Ordyl SY355 from Elga Europe. The developing and exposing processes as well as the time taken in making the channels are recorded. Finally from those recorded methods, the accurate procedures and time taken for DFR development and exposure have been found and ultimately been consistently used in fabricating our channels. These channels were patterned and sandwiched in between two glass substrates. In our advance, the channel was formed for the colloidal particle separation system. They can be used for handling continuous fluid flow and particle repositioning maneuver using dielectrophoresis that have showed successful results in the separation.     

Fabrication of microfluidic channel utilizing silicone rubber with vacuum casting

Microfluidic patterns of 100 μm in width and 50 μm height were replicated from a master using vacuum casting with silicone rubber. These silicone copies are subjected to thorough analysis for dimensional accuracy against the master pattern. Analysis of experimental results shows repeatability of the silicone rubber molds. To test the limits of vacuum casting with silicone rubber, an attempt was undertaken to replicate 8 μm microchannel and submicron features. The results show that casting of microfluidic channel via vacuum casting has high repeatability.     

PMMA microfluidic chip fabrication using laser ablation and low temperature bonding with OCA film and LOCA

A new PMMA microfluidic chip fabrication method by combining laser ablation technology with low-temperature bonding using optically clear adhesive (OCA) film and liquid optically clear adhesive (LOCA) was presented in this paper. The deformation and clogging issues of the microfluidic channel were well solved. The effective bonding area ratio of microfluidic chips could be greatly improved by adjusting bonding temperature and bonding time. The crevices around the microchannels were effectively eliminated by coating treatment of LOCA. The bonding strength and waterproof of PMMA microfluidic chips coating with/without LOCA were also evaluated in this paper.

     

Fabricated polycarbonate microchannel with different films using CO2 laser beam of two-pass for microfluidic chip

Microsystem Technologies - This paper demonstrates a novel and low-cost method for fabricating microchannel on polycarbonate (PC) sheet using CO2 laser. In the work, many microchannels are...     

Fabrication and testing of embedded microvalves within PMMA microfluidic devices

The integration of a PDMS membrane within orthogonally placed PMMA microfluidic channels enables the pneumatic actuation of valves within bonded PMMA–PDMS–PMMA multilayer devices. Here, surface functionalization of PMMA substrates via acid catalyzed hydrolysis and air plasma corona treatment were investigated as possible techniques to permanently bond PMMA microfluidic channels to PDMS surfaces. FTIR and water contact angle analysis of functionalized PMMA substrates showed that air plasma corona treatment was most effective in inducing PMMA hydrophilicity. Subsequent fluidic tests showed that air plasma modified and bonded PMMA multilayer devices could withstand fluid leakage at an operational flow rate of 9 μl/min. The pneumatic actuation of the embedded PDMS membrane was observed through optical microscopy and an electrical resistance based technique. PDMS membrane actuation occurred at pneumatic pressures of as low as 10 kPa and complete valving occurred at 14 kPa for ~100 μm by 100 μm channel cross-sections.     

Fabrication of layered polydimethylsiloxane/perfluoropolyether microfluidic devices with solvent compatibility and valve functionality

The development of multilayer soft lithography methodology has seen polydimethysiloxane (PDMS) as the preferred material for the fabrication of microfluidic devices. However, the functionality of these PDMS microfluidic chips is often limited by the poor chemical resistance of PDMS to certain solvents. Here, we propose the use of a photocurable perfluoropolyether (PFPE), specifically FOMBLIN^® MD40 PFPE, as a candidate material to provide a solvent-resistant buffer layer to make the device substantially impervious to chemically induced swelling. We first carried out a systematic study of the solvent resistance properties of FOMBLIN^® MD40 PFPE as compared with PDMS. The comparison presented here demonstrates the superiority of FOMBLIN^® MD40 PFPE over PDMS in this regard; moreover, the results permitted to categorize solvents in four different groups depending on their swelling ratio. We then present a step-by-step recipe for a novel fabrication process that uses multilayer lithography to construct a comprehensive solvent-resistant device with fluid and control channels integrated with a valve structure and also permitting easy establishment of outside connections.     

Fabrication of silicon microstructure for cell separation using ultrashort laser ablation

Many decades have seen the exploration of a novel methodology for developing microstructure in Microfluidic devices. Despite many methodologies, femtosecond laser technique has been a rising method in the conspicuous way of developing microstructures through direct write method which provides an ease of fabrication. For fabrication precise microstructure in semiconductor devices such as silicon, the femtosecond laser is preferred. An array of micro-holes has been created in monocrystalline silicon (100) using femtosecond laser ablation with multiple pulses. An investigation is carried out for obtaining the minimum diameter holes by varying the power for multiple pulses. The fabricated microhole array find its application in cancer cell separation from human blood.

     

Application of metal film protection to microfluidic chip fabrication using CO2 laser ablation

The CO₂ laser ablation is a common technique for patterning the microchannels and holes used in microfluidic devices. However, the ablation process frequently results in an accumulation of resolidified material around the rims of the ablated features and a clogging of the base of the microchannel. In the article, these problems are resolved by means of a proposed metal-film-protected CO₂ laser ablation technique. In the approach, the substrate is patterned with a thin metallic mask prior to the ablation process and the mask is then stripped away once the ablation process is complete. The feasibility of the proposed approach is demonstrated by fabricating two micromixers with Y-shaped and T-shaped microchannels, respectively. It shows that for a designed channel width of 100 μm, the metallic mask reduces the ablated channel width from 268 to 103 μm. Moreover, the bulge height around the rims of the channel is reduced from 8.3 to <0.2 μm. Finally, the metallic mask also prevents clogging in the intersection regions of the two devices. The experimental mixing results obtained using red and green pigment dyes confirm the practical feasibility of the proposed approach.