Reversible bonding for microfluidic devices with UV release tape

Microfluidics and Nanofluidics - A microfluidic paper-based analytical device (µPAD) is a new technology platform for extremely low-cost sensing applications. This study aimed to explore for...     

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.     

Adhesive bonding by SU-8 transfer for assembling microfluidic devices

SU-8 is largely used to make microfluidic molds or components, but mainly for producing high-precision and thermally stable structures. We present a versatile method that employs SU-8 as glue to perform an adhesive bonding between micro-patterned structures. More in general, this technique enables an easy assembly of microfluidic devices, which can also be made by different materials, where selective bonding is required. The adhesive bonding is achieved by transferring a thin layer of SU-8 5 (thickness ≤15?μm) on a substrate by means of a polyimide foil. The method is described in detail and an example of its application is given. Finally, a shear test is carried out to prove sufficient adhesion strength for microfluidic applications.     

Gas-assisted thermal bonding of thermoplastics for the fabrication of microfluidic devices

Microsystem Technologies - The challenges for high-strength adhesive-free sealing of thermoplastic microfluidics have impeded commercialization. We present the technique of gas-assisted thermal...     

Corona discharge assisted thermal bonding of polymer microfluidic devices

We present a study on the use of corona discharge surface treatment to achieve a fast thermal diffusion bonding process for the creation of microfluidic chips. Wafer scale bonding at 100 mm diameter was attempted. Polymethyl methacrylate (PMMA) wafers were hot embossed to create microchannels before bonding to another blank PMMA wafer. Corona discharge treatment of the PMMA resulted in a more hydrophilic surface. The average water contact angle on PMMA surface decreased from 74.5° before treatment to 35.5° after the treatment. The optimized bonding condition was found to be: 108°C for 4 min at a contact pressure of 3.1 MPa. The bonded chips could withstand an internal gauge pressure in the microchannels of at least seven bars. The rectangular shape of the cross section of the microchannels was conserved with some contraction in the dimensions of 3.7% on the mean widths and 2.1% on the mean depths. Bonding strength was found to increase with the bonding temperature and time while the effect of bonding pressure is evident at lower pressures. At higher pressures, the effect of bonding pressure seemed to have reduced. These effects could be explained by the diffusion mechanisms of the process.     

MCU based real-time temperature control system for universal microfluidic PCR chip

The analysis of genetic materials in the post-human genome project era has become an ever-expanding branch of research and thus routinely employed in majority of biochemical laboratories. Most of the diagnostic research area emphasizes on polymerase chain reaction for detecting pathogenic organisms. However, the conventional polymerase chain reaction requires expensive and sophisticated thermal cycler and is not handy owing to its large dimensions. Therefore, we fabricated a continuous-flow polymerase chain reaction chip on a PDMS based microfluidic platform to ease the hardship of the conventional system. Temperature being the most crucial factor in polymerase chain reaction, was monitored and regulated by thermostatic action using an on-line computer system. Indium tin oxide coated glass platform was used for heating as it is transparent and has good thermal conductivity under the influence of DC bias. The heating circuit used an ATMega 128 MCU to control the temperature. As a result, a precise and quick heating environment was maintained on the microfluidic chip to amplify the target DNA. We successfully amplified Lambda phage and Escherichia coli DNA on our chip to prove the practicality of the device.     

微流控PCR装置中温度控制技术评述

在微流控PCR装置中,温度直接影响PCR扩增结果,精确控制温度是微流控PCR的一个关键问题。温度控制包括系统加热方式和冷却方式,温度的测量和控制算法。加热和冷却有多种不同的实现方式,控制算法基本采用PID算法。总结了微流控PCR温度控制系统的加热方式、冷却方式和测量方式,并比较了各种方法的优缺点。     

A fluidic interconnection system for polymer-based microfluidic devices

A microfabricated fluidic interconnection system for polymer-based microfluidic nebulizer chips is presented and discussed. The new interconnection mechanism can be used to make fluidic connection between external capillary and the polymer microfluidic chip. The connector mechanism was fabricated using a combination of mechanical milling and laser micromachining. Preliminary leakage tests were performed to demonstrate that the interconnection system is leak-free and pressure tests were performed to evaluate the burst pressure (maximum working pressure). The interconnection system has several advantages over commercially available Nanoport™ interconnection system. The new fluidic interconnection system implemented onto a microfluidic nebulizer chip was successfully tested for desorption electrospray ionization mass spectrometry applications. The performance of the chip using the new connector mechanism was excellent demonstrating the usability of the new connector mechanism.     

Two-stage polymer embossing of co-planar microfluidic features for microfluidic devices

A two-stage embossing technique for fabricating microchannels for microfluidic devices is presented. A micromachined aluminum mold is used to emboss a polyetherimide (PEI) substrate with a relatively high glass transition temperature (T_g). The embossed PEI is then used as a mold for embossing an amorphous polyethylene terephthalate (APET) substrate with a lower T_g. The resulting APET substrate has the same features as those of the aluminum mold. Successful transfer of features from the aluminum mold to the APET substrate was verified by profilometry, and an application of this method in production of a microfluidic device is presented.     

A post-bonding-free fabrication of integrated microfluidic devices for mass spectrometry applications

This paper presents a novel process for fabricating integrated microfluidic devices with embedded electrodes which utilizes low-cost UV curable resins. Commercial UV glue is sandwiched between two substrates and is used for both the structural material and the bonding adhesive. During the exposure procedure, the pattern of micro-fluidic channels is defined using a standard lithography process while the two substrates are bonded. The un-cured UV glue is then removed by vacuum suction to form the sealed microfluidic channel. With this simple approach, conventional high-temperature bonding processes can be excluded in the fabrication of sealed microfluidic structures such that the developed method is highly advantageous for fabricating microchip devices with embedded electrodes. The overall time required to fabricate the sealed microchip device is less than 10 min since no time-consuming etching and bonding process is necessary. An innovative micro-reactor integrated with an in-channel micro-plasma generator for real-time chemical reaction analysis is fabricated using the developed process. On-line mass-spectrum (MS) detection of an esterification reaction is successfully demonstrated, which results in a fast, label-free, preparation-free analysis of chemical samples. The developed process can thus show its potential for rapid and low-cost microdevice manufacturing.     

A simple approach to fabricate multi-layer glass microfluidic chips based on laser processing and thermocompression bonding

Microfluidics and Nanofluidics - We study the influence of variations of cross-section on the drying dynamics by pervaporation in microfluidic channels surrounded by water-permeable...     

A clip-on electroosmotic pump for oscillating flow in microfluidic cell culture devices

Recent advances in microfluidic devices put a high demand on small, robust and reliable pumps suitable for high-throughput applications. Here we demonstrate a compact, low-cost, directly attachable (clip-on) electroosmotic pump that couples with standard Luer connectors on a microfluidic device. The pump is easy to make and consists of a porous polycarbonate membrane and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) electrodes. The soft electrode and membrane materials make it possible to incorporate the pump into a standard syringe filter holder, which in turn can be attached to commercial chips. The pump is less than half the size of the microscope slide used for many commercial lab-on-a-chip devices, meaning that these pumps can be used to control fluid flow in individual reactors in highly parallelized chemistry and biology experiments. Flow rates at various electric current and device dimensions are reported. We demonstrate the feasibility and safety of the pump for biological experiments by exposing endothelial cells to oscillating shear stress (up to 5 dyn/cm²) and by controlling the movement of both micro- and macroparticles, generating steady or oscillatory flow rates up to ± 400 μL/min.     

Large-strain thermo-mechanical behavior of cyclic olefin copolymers: Application to hot embossing and thermal bonding for the fabrication of microfluidic devices

Amorphous cyclic olefin copolymers (COCs) are beginning to be used for making microfluidic devices for life science applications. Typically, both micro-scale and nano-scale channels are imprinted onto the copolymer by hot embossing. However, optimal manufacturing process conditions will only be possible if the COCs thermo-mechanical behavior is experimentally well characterized, mathematically modeled, and implemented in a numerical simulation. We have conducted large-strain compression experiments on two commercial grades of COCs: TOPAS-8007, and TOPAS-6015 in a wide temperature, and strain rate range. A constitutive theory and numerical implementation developed by Srivastava et al. [1] was applied to model the behavior of TOPAS. We have employed that numerical implementation, together with the material parameters for TOPAS determined here, to predict the response of TOPAS in the following microfluidic fabrication operations: (i) micro-scale hot embossing on TOPAS-8007 to replicate a micro-chip; and (ii) for sealing the channels in the micro-chip: (a) thermal bonding of an embossed chip of TOPAS-8007 with a cover plate of TOPAS-8007; and (b) thermal bonding of an embossed chip of TOPAS-6015 with a cover plate of TOPAS-8007. We show that the model can provide a simulation capability for estimation of the processing parameters for hot embossing and thermal bonding.     

Enhancement of bonding strength of packaging based on BCB bonding for RF devices

This paper presents a Si cap zero-level packaging technique based on a double-layer BCB sealing ring. The BCB ring is defined before the housing cavity etching to achieve high BCB bonding strength. It is found that the non-uniformity of the BCB ring defined on a Si cap with housing cavity prevents the package having high bonding strength. Three different packages have been prepared for shear test; a Si cap without cavity, a recessed Si cap with a conventional BCB ring and a recessed Si cap with pre-defined BCB ring. The three samples for each type of package are measured. The average measured bonding strengths of the test samples are 71, 16 and 42?MPa, respectively, and hence the proposed BCB sealing ring process provides 60?% of bonding strength of Si cap package without cavity for Si cap package with cavity. In addition, the insertion loss change of the packaged CPW is less than 0.1?dB up to 67?GHz while the return loss better than 15?dB at the measured frequency range.     

A way to develop devices for image fusion under rigid hardware restrictions

The algorithms and devices for image digital fusion are examined. The main steps for developing digital devices for image fusion are described, and the problems solved at each step are presented. The conclusions are illustrated by examples of development of such devices.     

Functionalization of microfluidic devices for investigation of liquid crystal flows

Systematic studies of thermotropic liquid crystals in confinement, such as liquid crystals in microfluidic channels, require control of the anchoring conditions on the surfaces. Especially for the case of uniform planar anchoring, the standard method involves a mechanical treatment (rubbing) of the surface that is not applicable to microfluidic devices. In the present study, we report methods for the achievement of well-defined anchoring conditions for liquid crystals in microfluidic channels consisting of polydimethylsiloxane and glass. Various physico-chemical techniques enable to establish homeotropic, degenerate planar, uniform planar, and hybrid anchoring conditions on the surface of the channel walls. We characterize the treated surfaces in terms of wettability and liquid crystal anchoring and determine the director field in the microchannels for the different anchoring configurations using polarizing optical microscopy and fluorescence confocal polarization microscopy. The relevance of the surface anchoring for the flow behavior of the liquid crystal in the microchannel is demonstrated by studying the onset of defect-mediated chaotic-like flow at high Ericksen numbers for the different anchoring cases.     

A one-step microfluidic approach for controllable preparation of nanoparticle-coated patchy microparticles

In this work, we describe a one-step microfluidic method for fabricating nanoparticle-coated patchy particles. Janus droplets composed of curable phase and non-curable phase were produced via a co-axial microfluidic device first. Nanoparticles were dispersed into the continuous phase or the non-curable phase to realize the surface coating of the curable phase. The curable phase was then polymerized by UV light and nanoparticle-coated patchy particles were obtained. The SEM characterization shows that the particles are monodispersed with nanoparticle selectively distributed on the convex or concave surface. The dispersity, size and shape of the particles could be easily controlled by changing the microfluidic flow parameters. Three different types of nanoparticles were successfully used to synthesize the patchy particles to demonstrate the validity of the method.     

Fabrication of microfluidic devices for packaging CMOS MEMS impedance sensors

This work presents a polydimethylsiloxane (PDMS) microfluidic device for packaging CMOS MEMS impedance sensors. The wrinkle electrodes are fabricated on PDMS substrates to ensure a connection between the pads of the sensor and the impedance instrument. The PDMS device can tolerate an injection speed of 27.12 ml/h supplied by a pump. The corresponding pressure is 643.35 Pa. The bonding strength of the device is 32.44 g/mm². In order to demonstrate the feasibility of the device, the short circuit test and impedance measurements for air, de-ionized water, phosphate buffered saline (PBS) at four concentrations (1, 2 × 10⁻⁴, 1 × 10⁻⁴, and 6.7 × 10⁻⁵ M) were performed. The experimental results show that the developed device integrated with a sensor can differentiate various samples.