PMMA to Polystyrene bonding for polymer based microfluidic systems

A thermal bonding technique for Poly (methylmethacrylate) (PMMA) to Polystyrene (PS) is presented in this paper. The PMMA to PS bonding was achieved using a thermocompression method, and the bonding strength was carefully characterized. The bonding temperature ranged from 110 to 125 °C with a varying compression force, from 700 to 1,000 N (0.36–0.51 MPa). After the bonding process, two kinds of adhesion quantification methods were used to measure the bonding strength: the double cantilever beam method and the tensile stress method. The results show that the bonding strength increases with a rising bonding temperature and bonding force. The results also indicate that the bonding strength is independent of bonding time. A deep-UV surface treatment method was also provided in this paper to lower the bonding temperature and compression force. Finally, a PMMA to PS bonded microfluidic device was fabricated successfully.     

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.     

Micro-injection moulding of polymer microfluidic devices

Microfluidic devices have several applications in different fields, such as chemistry, medicine and biotechnology. Many research activities are currently investigating the manufacturing of integrated microfluidic devices on a mass-production scale with relatively low costs. This is especially important for applications where disposable devices are used for medical analysis. Micromoulding of thermoplastic polymers is a developing process with great potential for producing low-cost microfluidic devices. Among different micromoulding techniques, micro-injection moulding is one of the most promising processes suitable for manufacturing polymeric disposable microfluidic devices. This review paper aims at presenting the main significant developments that have been achieved in different aspects of micro-injection moulding of microfluidic devices. Aspects covered include device design, machine capabilities, mould manufacturing, material selection and process parameters. Problems, challenges and potential areas for research are highlighted.     

Pre-programmable polymer transformers as on-chip microfluidic vacuum generators

This paper develops novel polymer transformers using thermally actuated shape memory polymer (SMP) materials. This paper applies SMPs with thermally induced shape memory effect to the proposed novel polymer transformers as on-chip microfluidic vacuum generators. In this type of SMPs, the morphology of the materials changes when the temperature of materials reaches its glass transition temperature (T _g). The structure of the polymer transformer can be pre-programmed to define its functions, which the structure is reset to the temporary shape, using shape memory effects. When subjected to heat, the polymer transformer returns to its pre-memory morphology. The morphological change can produce a vacuum generation function in microfluidic channels. Vacuum pressure is generated to suck liquids into the microfluidic chip from fluidic inlets and drive liquids in the microchannel due to the morphological change of the polymer transformer. This study adopts a new smart polymer with high shape memory effects to achieve fluid movement using an on-chip vacuum generation source. Experimental measurements show that the polymer transformer, which uses SMP with a T _g of 40°C, can deform 310 μm (recover to the permanent shape from the temporary shape) within 40 s at 65°C. The polymer transformer with an effective cavity volume of 155 μl achieved negative pressures of −0.98 psi. The maximum negative up to −1.8 psi can be achieved with an effective cavity volume of 268 μl. A maximum flow rate of 24 μl/min was produced in the microfluidic chip with a 180 mm long channel using this technique. The response times of the polymer transformers presented here are within 36 s for driving liquids to the end of the detection chamber. The proposed design has the advantages of compact size, ease of fabrication and integration, ease of actuation, and on-demand negative pressure generation. Thus, this design is suitable for disposable biochips that need two liquid samples control. The polymer transformer presented in this study is applicable to numerous disposable microfluidic biochips.     

低成本聚合物微流控芯片加工技术综述

针对传统微流控芯片加工方法成本高昂、耗时长的问题,近年来出现了多种低成本的微流控芯片加工方法,在聚合物、纸等材料上加工、完成了能够满足其应用需求的微流控芯片。对当前各类基于聚合材料的低成本微流控芯片加工技术进行了梳理和总结,并对未来低成本微流控芯片的发展进行了展望。     

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.     

A positive pressure-driven PDMS pump for fluid handling in microfluidic chips

By utilizing the high gas permeability of polydimethylsiloxane (PDMS), a simple positive pressure-driven pumping method was introduced. The pump was an aerated PDMS with a central channel in it and packing with a transfusion bottle. It could be attached to the inlet of microfluidic chip using a Teflon tube to release the air into the microfluidic system and then to create a positive pressure for driving fluid. In comparison with the degas-based PDMS pump, positive pressure-driven PDMS pump offered increased system flexibility and reduced individual device fabrication complexity due to its independence and versatility. More importantly, it offered the advantages that the PDMS pump could be wrapped in transfusion bottles to meet the readily available requirements, and it also easily assembled, which only required the user use a Teflon tube to connect a PDMS pump and a microfluidic chip. This assembly provided great freedom to meet different pumping requirements. Furthermore, this PDMS pump could offer many possible configures of pumping power by adjusting the geometries of the pump or by combining different pump modules, the adjustment of pumping capacity was investigated. To help design pumps with a suitable pumping performance, the sealing effect, pumping pressure and flow rate were also investigated. The results indicated that the performance of the positive pressure-driven PDMS pump was reliable. Finally, we demonstrated the utility of this pumping method by applying it to a PDMS-based viscometer microfluidic chip.     

Magnetically controlled valve for flow manipulation in polymer microfluidic devices

A simple, external in-line valve for use in microfluidic devices constructed of polydimethylsiloxane (PDMS) is described. The actuation of the valve is based on the principle that flexible polymer walls of a liquid channel can be pressed together by the aid of a permanent magnet and a small metal bar. In the presence of a small NdFeB magnet lying below the channel of interest, the metal bar is pulled downward simultaneously pushing the thin layer of PDMS down thereby closing the channel stopping any flow of fluid. The operation of the valve is dependent on the thickness of the PDMS layer, the height of the channel, the gap between the chip and the magnet and the strength of the magnet. The microfluidic channels are completely closed to fluid flows ranging from 0.1 to 1.0 μL/min commonly used in microfluidic applications.     

Low-cost polymer microfluidic device for on-chip extraction of bacterial DNA

A polymer microfluidic device for on-chip extraction of bacterial DNA has been developed for molecular diagnostics. In order to manufacture a low-cost, disposable microchip, micropillar arrays of high surface-to-volume ratio (0.152 μm⁻¹) were constructed on polymethyl methacrylate (PMMA) by hot embossing with an electroformed Ni mold, and their surface was modified with SiO₂ and an organosilane compound in subsequent steps. To seal open microchannels, the organosilane layer on top plane of the micropillars was selectively removed through photocatalytic oxidation via TiO₂/UV treatment at room temperature. As a result, the underlying SiO₂ surface was exposed without deteriorating the organosilane layer coated on lateral surface of the micropillars that could serve as bacterial cell adhesion moiety. Afterwards, a plasma-treated PDMS substrate was bonded to the exposed SiO₂ surface, completing the device fabrication. To optimize manufacturing throughput and process integration, the whole fabrication process was performed at 6 inch wafer-level including polymer imprinting, organosilane coating, and bonding. Preparation of bacterial DNA was carried out with the fabricated PDMS/PMMA chip according to the following procedure: bacterial cell capture, washing, in situ lysis, and DNA elution. The polymer-based microchip presented here demonstrated similar performance to Glass/Si chip in terms of bacterial cell capture efficiency and polymerase chain reaction (PCR) compatibility.     

A vapor based microfluidic flow regulator

We introduce a flow regulating technology that uses trapped air bubbles in a hydrophobic microfluidic channel. We present basic designs for flow regulators and flow valves using trapped air. Experiments have successfully demonstrated the capability of this technique for delivering constant and varying flow rate, and for on-off valving. This approach to valving provides a simple, yet effective way to monolithically integrate flow and valve control on polymer Lab-on-Chip devices.     

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.     

高聚物微流控芯片上集成化气动微阀的研制

报道了一种新型的聚甲基丙烯酸甲酯(PMMA)/聚二甲基硅氧烷(PDMS)复合芯片。该芯片采用PMMA-PDMS…PDMS-PMMA的四层构型,以在芯片上集成气动微阀。具有液路和控制通道网路的PMMA基片与PDMS弹性膜间采用不可逆封接,分别形成液路半芯片和控制半芯片,而2个半芯片则依靠PDMS膜间的粘性实现可逆封接,组成带有微阀的全芯片。这种制备方法解决了制备PMMA-PDMS-PMMA三层结构芯片的封接难题,封接过程简单可靠。其控制部分和液路部分可以单独更换,可进一步降低使用成本,尤其适合一次性应用场合。初步实验表明:该微阀具有良好的开关性能和耐用性。     

单泵控制聚焦流形态的微流控芯片的研制

研究一种单动力源、聚焦流形态可控的用于细胞排队的微流控芯片。建立了样品沟道与鞘流沟道不同长度比例、不同夹角的模型并进行了不同负压条件下聚焦流形态仿真,运用SPSS软件进行了回归分析并进行了模型优化。在芯片的微加工过程中,利用印刷电路板(PCB)制作了母板,以聚二甲基硅氧烷(PDMS)为芯片主要材料,制作了PDMS—PDMS,PDMS—玻璃及PCB—PDMS三种芯片。制作的芯片能够在单个动力源条件下控制聚焦流宽度,使不同大小的微粒及细胞呈单个排列流动。研究结果为分析不同尺寸的细胞而选择合适的样品流沟道与鞘流沟道长度、夹角等条件提供了依据,所制作的芯片也达到了廉价且实用的目的。     

A microfluidic based differential plasmon resonance sensor

A new type of differential surface plasmon (SPR) sensor integrated with a microfluidic system is presented. The working principle of the microfluidic device is based on hydrodynamic modulation of two laminar streams inside a microchannel to provide periodic changes of the environment on the SPR sensor. The modulated reflectance is then demodulated using a lock-in amplifier. The presented sensor provides sensitivities of index of refraction about 4 × 10⁻⁸ RIU together with a 4 orders of magnitude dynamic range. This method demonstrates a sensitive detection scheme which could be used for label-free detection.     

Direct bonding of polymer/glass-based microfluidic chips with dry film photoresist

Microsystem Technologies - Dry film has been widely used as a low-cost photoresist in the print circuit board industry which consists of a thin layer of photoresist sandwiched between two...     

A multilevel polymer process for direct encapsulation of fluids in microfluidic systems

This paper describes a polymer manufacturing technique for the realization of sealed liquid tanks with a high filling ratio. It is based on a lithographic process combined with lamination and can be performed on any type of substrate: Si, glass or polymer films. We demonstrated the encapsulation of solvents or inks in multilevel tanks on large surface area (>118 cm²) without any damage of the stored liquid. This micro-fabrication technology proposes a significant breakthrough for micro-fluidic applications. We propose a one step process for the filling and sealing of tanks which are performed simultaneously. Tanks can be integrated at any level in the micro-fluidic system with a perfect filling rate and an excellent tightness.