Rapid prototyping of glass-based microfluidic chips utilizing two-pass defocused CO2 laser beam method

A method is proposed for the scribing of glass substrates utilizing a commercial CO₂ laser system. In the proposed approach, the substrate is placed on a hotplate and the microchannel is then ablated using two passes of a defocused laser beam. The aspect ratio and surface quality of the microchannels formed after the first and second laser passes are examined using scanning electron microscopy and atomic force microscopy. The observation results show that the second laser pass yields an effective reduction in the surface roughness. The practicality of the proposed approach is demonstrated by fabricating a microfluidic chip for formaldehyde concentration detection. It is shown that the detection results obtained for five Chinese herbs with formaldehyde concentrations ranging from 5 to 55 ppm deviate by no more than 5.5 % from those obtained using a commercial macroscale device. In other words, the results confirm that the proposed defocused ablation technique represents a viable solution for the rapid and low-cost fabrication of a wide variety of glass-based microfluidic chips.     

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.     

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.

     

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.     

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.     

Fast and inexpensive method for the fabrication of transparent pressure-resistant microfluidic chips

The recent rise of high-pressure applications in microfluidics has led to the development of different types of pressure-resistant microfluidic chips. For the most part, however, the fabrication methods require clean room facilities, as well as specific equipment and expertise. Furthermore, the resulting microfluidic chips are not always well suited to flow visualization and optical measurements. Herein, we present a method that allows rapid and inexpensive prototyping of optically transparent microfluidic chips that resist pressures of at least 200 bar. The fabrication method is based on UV-curable off-stoichiometry thiol-ene epoxy (OSTE+) polymer, which is chemically bonded to glass. The reliability of the device was verified by pressure tests using CO₂, showing resistance without failure up to at least 200 bar at ambient temperature. The microchips also resisted operation at high pressure for several hours at a temperature of 40 °C. These results show that the polymer structure and the chemical bond with the glass are not affected by high-pressure CO₂. Opportunities for flow visualization are illustrated by high-pressure two-phase flow shadowgraphy experiments. These microfluidic chips are of specific interest for use with supercritical CO₂ and for optical characterization of phase transitions and multiphase flow under near-critical and critical CO₂ conditions.     

Development of two step carbon dioxide assisted thermal fusion PMMA bonding process

Poly-methyl methacrylate (PMMA) has been widely used for optical and microfluidic devices. This paper is devoted to the development of an effective low-temperature PMMA bonding technology. For bonding, Carbon dioxide (CO₂) has been used as gas solvent and pressuring agent. The bonding temperature thus is lowered and the pressing pressure becomes uniform. An innovative two-stage CO₂-assisted thermal fusion bonding process has been developed which takes the soaking and releasing times of CO₂ into account. The experimental results show that this new process significantly enhances the flatness after bonding process and increases bonding area and bonding strength. By coating a layer of PMMA solution on bonding surface, the diffusion number of chain increases, and thus further increases the bonding strength.     

On-chip CO<Subscript>2</Subscript> incubation for pocket-sized microfluidic cell culture

We have developed an on-chip CO₂ incubation system based on mass/heat transfer from aqueous solutions of bicarbonate source to cell culture media through a permeable poly(dimethylsiloxane) (PDMS) wall. Heating a carbonate-buffered bicarbonate solution successfully regulated CO₂ generation without any feedback control. Because a microfluidic cell culture chip with the incubation system does not require an external chamber or gas supply, the entire microfluidic cell culture setup becomes pocket sized. Using 5 ml of 0.8 M sodium bicarbonate with 65 mM sodium carbonate as the water jacket, the chip maintained the temperature, osmolality, and pH of 750 μl cell culture medium within physiological levels when the chip was placed on a 37°C surface. The osmolality shift and pCO₂ of the media reservoir stabilized within <5 mmol/kg and 5.0 ± 1.0% over at least 9 days. The incubation capabilities were demonstrated through microfluidic culture of COS-7 epithelial cells under an inverted microscope for 17 days.     

The manufacturing of packaged capillary action microfluidic systems by means of CO2 laser processing

In this article we demonstrate a simple yet robust rapid prototyping manufacturing technique for the construction of autonomous microfluidic capillary systems by means of CO₂ laser processing. The final packaging of the microfluidic device is demonstrated using thermal lamination bonding and allows for a turnaround time of approximately 30 min to 3 h from activation of the laser system to device use. The low-cost CO₂ laser system is capable of producing repeatable microfluidic structures with minimum feature sizes superior than 100–150 μm over channel depths of more than 100 μm. This system is utilised to create capillary pump and valve designs within poly (methyl methacrylate) (PMMA) substrates. Such components are part of advanced systems that can self initiate and maintain the flow of various volumes of fluids from an input to a collection reservoir, whilst also controlling the progression of the flow through the various demonstrated valve type structures. The resulting systems could prove a very useful alternative to traditional, non-integrated, fluidic actuation and flow control systems found on-chip, which generally require some form of energy input, have limited portable capabilities and require more complex fabrication procedures.     

A low temperature ultrasonic bonding method for PMMA microfluidic chips

Bonding is a bottleneck for mass-production of polymer microfluidic devices. A novel ultrasonic bonding method for rapid and deformation-free bonding of polymethyl methacrylate (PMMA) microfluidic chips is presented in this paper. Convex structures, usually named energy director in ultrasonic welding, were designed and fabricated around micro-channels and reservoirs on the substrates. Under low amplitude ultrasonic vibration, localized heating was generated only on the interface between energy director and cover plate, with peak temperature lower than T _g (glass transition temperature) of PMMA. With the increasing of temperature, solution of PMMA in isopropanol (IPA) increases and bonding was realized between the contacting surfaces of energy director and cover plate while no solution occurs on the surfaces of other part as their lower temperature. PMMA microfluidic chips with micro-channels of 80 μm × 80 μm were successfully bonded with high strength and low dimension loss using this method.     

Manufacture of microfluidic chips using a gap-control method based on traditional 3D printing technique

The solution to the commercialization of polymer microfluidic chips lies in the development of a low-cost and concise method. We present in this paper a gap-control method for obtaining low cost microfluidic chips on PMMA (polymethyl methacrylate) sheets based on traditional 3D printing technique—fused deposition modeling. The influence of 3D printing parameters such as printing temperature, printing speed, wire flow rate and initial layer thickness on printing quality is studied by experiments. The effect of O₂ plasma parameters such as chamber power and treatment time on the adhesion strength between printed PLA (polylactic acid) structures and PMMA substrate is investigated. The dye filling tests demonstrate that there is no blocking or leakage over the entire microchannels. With this newly developed technology, low-cost and large scale microfluidic chips can be fabricated, which allows commercial manufacturing of microchannels over large areas.

     

Remote measurement of chemical warfare agents by differential absorption CO<Subscript>2</Subscript> lidar

The possibilities of remote sensing of chemical warfare agents by the differential absorption method are analyzed. The CO₂ laser emission lines suitable for sensing chemical warfare agents with accounting for disturbing absorption by water vapor were chosen. The detection range of chemical warfare agents is obtained for a lidar based on CO₂ laser. Factors influencing upon the sensing range have been analyzed.     

Chitosan microfiber fabrication using a microfluidic chip and its application to cell cultures

In this study, a poly-methyl-methacrylate (PMMA) microfluidic chip with a 45° cross-junction microchannel is fabricated using a CO₂ laser machine to generate chitosan microfibers. Chitosan solution and sodium tripolyphosphate (STPP) solution were injected into the cross-junction microchannel of the microfluidic chip. The laminar flow of the chitosan solution was generated by hydrodynamic focusing. The diameter of laminar flow, which ranged from 30 to 50 μm, was controlled by changing the ratio between chitosan solution and STPP solution flow rates in the PMMA microfluidic chip. The laminar flow of the chitosan solution was converted into chitosan microfibers with STPP solution via the cross-linking reaction; the diameter of chitosan microfibers was in the range of 50–200 μm. The chitosan microfibers were then coated with collagen for cell cultivation. The results show that the chitosan microfibers provide good growth conditions for cells. They could be used as a scaffold for cell cultures in tissue engineering applications. This novel method has advantages of ease of fabrication, simple and low-cost process.     

Transparent thin thermoplastic biochip by injection-moulding and laser transmission welding

Recently microfluidic devices have emerged as a viable technology for the miniaturization of high throughput tools for analytical tasks related to structural biology such as screening of crystallization conditions and structural analysis. This work reports the manufacture of microfluidic chips in transparent thermoplastic polymers [poly(methylmethacrylate) (PMMA), and cyclic olefin copolymer (COC)] using two complementary technologies, injection moulding for the fabrication of the fluidic level and laser transmission welding for the sealing of the cover. A steel mould insert was produced by laser micro caving using a solid state laser radiation source (Nd:YAG, wavelength 1,064 nm). Fluidic chips of ~670 μm thickness comprising channels of 50 μm depth and width down to 50 μm were injection moulded in PMMA and COC. Joining of transparent thin cover film to the micro-injected fluidic level was performed by laser transmission welding using high power diode laser radiation (wavelength 940 nm) and an intermediate thin absorbing layer with a thickness of about several nanometers.     

Microfluidic analysis of CO<Subscript>2</Subscript> bubble dynamics using thermal lattice-Boltzmann method

By means of microfluidic analysis with a thermal lattice-Boltzmann method, we investigated the hydrophilic, thermal and geometric effects on the dynamics of CO₂ bubbles at anode microchannels (e.g., porous layers and flow channels) of a micro-direct methanol fuel cell. The simulation results show that a more hydrophilic wall provides an additional attractive force to the aqueous methanol in the flow direction and that moves the CO₂ bubble more easily. The bubble propagates quicker in the microchannel with a positive temperature gradient imposed from the inlet to the exit, mainly due to the Marangoni effect. Regarding the geometric effect of the microchannel, the bubble moves more rapidly in a divergent microchannel than in a straight or convergent channel. On the basis of the quantitative evaluation of hydrophilic, thermal and geometric effects, we are able to design the bubble-removal technique in micro fuel cells.     

Fabrication of flexible light guide plate using CO2 laser LIGA-like technology

The liquid crystal display (LCD) needs the back light module (BLM) for the light source. The light guide plate (LGP) is the main component of BLM to spread light source to the whole LCD surface and requires for the generation trend of lightweight, easy to carry, and bendable for LCD. In this article, we have demonstrated the fabrication of flexible LGP using CO₂ laser LIGA-like technology which includes the laser ablation of micro-groove polymethylmethacrylate (PMMA) master mold, pouring polydimethylsiloxane (PDMS) to the mold and casting the micro-groove microstructure for flexible LGP application. Different laser powers and micro-groove pitches were used to ablate the PMMA mold with varied groove depths and taper angles. Optical microscope was used to examine the morphology and profile of the final bendable LGP microstructure. Under the varied laser power of 1–12 W, the mean taper angles of PMMA micro-grooves ranged from 28° to 70° and the etching depths were from 44.5 to 281.8 μm. The flexible PDMS LGP had good microstructure duplication after casting. The optical uniformity and luminance of flexible LGP was concerned with structure of micro-grooves and measured using BM9 luminance meter. The maximal light uniformity and average luminance of LGP at some microstructure reaches 75 % and 119 cd/m², respectively.     

Thermal waveguide and fine-scale periodic relief on the semiconductor’s surface induced by TEA CO<Subscript>2</Subscript> laser radiation

The results of experimental study of linear CO₂ laser radiation interaction with semiconductor monocrystals (silicon, germanium, gallium arsenide,) are presented. It was shown that produced surface relief of micro- and nano-structures with spatial periods d ~ λ/n, d ~ λ/2n and d ~ λ/8n (for germanium) are well explained in the framework of universal polariton model of laser-induced condensed-matter damage.     

Influence of tool fabrication process on characteristics of hot embossed polymer microfluidic chips for electrospray

Fabrication techniques for mass manufacture of disposable polymer microfluidic chips are important for electrospray application used in mass spectrometry. Hot embossing offers advantages over traditional MEMS fabrication techniques and is the focus of this research. The aim of the paper is to evaluate hot embossed open channel polymer chips using two different hot embossing tools. One tool was fabricated in nickel using the electroforming process, and the other in high carbon bright steel by laser machining technique using a pulsed Nd:YAG laser that is normally used for conventional applications. Process parameters are determined and measurement of dimensions and surface roughness of tools and chips are presented. Depending on the fabrication method, each tool exhibits its own characteristic profile feature and surface roughness. Polystyrene and polycarbonate substrates embossed with the electroformed tool exhibited lowest surface roughness of 48 nm compared to 450 nm for the laser machined tool. The embossed microfluidic chips were tested for fluid flow and electrospray and showed good performance.     

Hydrophilicity modification of poly(methyl methacrylate) by excimer laser ablation and irradiation

Because of the micromachining characteristic of excimer laser ablation, the microchannels ablated with this technique on poly(methyl methacrylate) (PMMA) substrate have definite surface roughness. Utilizing this characteristic, the hydrophilicity of PMMA microchannels could be directly modified during fabrication process both by the mechanism of photochemical ablation and the effect of surface roughness. The contact angle is inversely proportional to the surface roughness under ablation with same fluence and could be reduced to 25° by choosing ablation parameters reasonably (7.38 J/cm², 20 Hz, 10 mm/min). Excimer laser irradiation of PMMA substrates for different irradiation times at fluence below the ablation threshold also results in the surfaces becoming more hydrophilic without any marked change in the surface topography. The contact angle decreases with the increase of irradiation times and finally reaches the saturated status after irradiation for 2,500 times. Under same irradiation times, higher fluence led to PMMA substrates more hydrophilic.     

Miniaturized DNA amplification platform with soft-lithographically fabricated continuous-flow PCR microfluidic device on a portable temperature controller

Fabrication of 3D microfluidic devices is normally quite expensive and tedious. A strategy was established to rapidly and effectively produce multilayer 3D microfluidic chips which are made of two layers of poly(methyl methacrylate) (PMMA) sheets and three layers of double-sided pressure sensitive adhesive (PSA) tapes. The channel structures were cut in each layer by cutting plotter before assembly. The structured channels were covered by a PMMA sheet on top and a PMMA carrier which contained threads to connect with tubing. A large variety of PMMA slides and PSA tapes can easily be designed and cut with the help of a cutting plotter. The microfluidic chip was manually assembled by a simple lamination process.The complete fabrication process from device design concept to working device can be completed in minutes without the need of expensive equipment such as laser, thermal lamination, and cleanroom. This rapid frabrication method was applied for design of a 3D hydrodynamic focusing device for synthesis of gold nanoparticles (AuNPs) as proof-of-concept. The fouling of AuNPs was prevented by means of a sheath flow. Different parameters such as flow rate and concentration of reagents were controlled to achieve AuNPs of various sizes. The sheet-based fabrication method offers a possibility to create complex microfluidic devices in a rapid, cheap and easy way.