Photolamination bonding for PMMA microfluidic chips

Finding out a rapid and reliable bonding method for plastic microfluidic chips with PCR functions is challenging for analytical chemistry and biochemistry. A rapid, reliable covalent bonding method is introduced for fabricating PMMA PCR biochips with long channels and thin walls. The bonding strength of ~5 MPa was obtained and bulk cohesive failure occurred during tensiling tests. Preliminary leaking tests indicate that photolamination bonding can be implemented readily in the fabrication of PMMA PCR biochips.     

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.     

Plasma assisted thermal bonding for PMMA microfluidic chips with integrated metal microelectrodes

Fracture of integrated metal microelectrodes likely happens during the thermal bonding process of PMMA [poly (methylmethacrylate)] microfluidic chips. In this paper, the fracture behaviors are studied. The fracture is mainly caused by the plastic deformation of the electrode plate (the PMMA plate with microelectrodes) and the thermal stress of microelectrodes, which is due to the high bonding temperature. To decrease the bonding temperature, a plasma assisted thermal bonding method is evaluated and first used to eliminate the fracture of microelectrodes. In this process, the surface of the cover plate (the PMMA plate with microchannels) is modified using oxygen plasma before the electrode plate is thermally bonded to the cover plate. The parameters of the oxygen plasma treatment are optimized, and the contact angle is decreased from 71.7° to 43.6°. The thermal bonding temperature is optimized, which decreases the temperature from 100 °C to 85 °C. Testing of bonding strength shows an average failure pressure of 1.75 MPa, which is comparable to the bonding strength of 1.46 MPa for chips bonded at 100 °C without plasma modification. In order to demonstrate this bonding method, a PMMA microfluidic chip with integrated copper interdigitated microelectrode arrays for AC electroosmotic pump is fabricated.     

Replication and bonding techniques for integrated microfluidic systems

From the technical and economic points of view, systems integration, and packaging represent a crucial step in the production of microsystems. Compared to purely silicon- or glass-based systems, the variety of materials and geometries available for purely polymer microfluidic systems is much larger, due to the outstanding material properties. Moreover, polymers may be shaped and joined by comparably simple methods. Examples are polymer microreplication as well as various bonding methods. With them, complete polymer microsystems can be integrated. In addition, a number of established, compatible processes are available for the integration of functional elements that may also be made of other materials.     

Replication and bonding techniques for integrated microfluidic systems

From the technical and economic points of view, systems integration, and packaging represent a crucial step in the production of microsystems. Compared to purely silicon- or glass-based systems, the variety of materials and geometries available for purely polymer microfluidic systems is much larger, due to the outstanding material properties. Moreover, polymers may be shaped and joined by comparably simple methods. Examples are polymer microreplication as well as various bonding methods. With them, complete polymer microsystems can be integrated. In addition, a number of established, compatible processes are available for the integration of functional elements that may also be made of other materials.

     

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 method of water pretreatment to improve the thermal bonding rate of PMMA microfluidic chip

A new method of water pretreatment for thermal bonding polymethylmethacrylate microfluidic chip was proposed in this paper. The bonding rate (effective bonding area) of microfluidic chip under different pretreatment time was studied and the mechanism of this method was discussed. The main thermal bonding parameters were as follows: bonding pressure 1.4 ~ 1.9 Mpa, temperature 91 ~ 93°C, time 360 s. The experimental result shows that this method can increase the effective bonding area, improve the bonding quality of the microfluidic chip compared to the conventional thermal bonding method. The optimal water pretreatment time is 1 h with the bonding rate increased by 34% compared with the conventional thermal bonding method. The pollution to the micro-channels is avoided and the performance of the microfluidic system will be reserved with this water pretreatment method. This method is available for the biochemical analysis of the chip, and holds the benefits of easy-operation, high-efficiency and low-cost properties.     

Electroactive polymer based microfluidic pump

A planar, valveless, microfluidic pump using electrostrictive poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] based polymer as the actuator material is presented. P(VDF-TrFE) thick films having a large electrostrictive strain ∼5–7% and high elastic energy density of 1 J/cm³ have been used in a unimorph diaphragm actuator configuration. The microfluidic pump was realized by integrating a nozzle/diffuser type fluidic mechanical-diode structure with the polymer microactuator. The P(VDF-TrFE) unimorph diaphragm actuator, 80 μm thick and 2.2 mm × 2.2 mm in lateral dimensions, showed an actuation deflection of 80 μm for an applied electric field of 90 MV/m. The microfluidic pump could pump methanol at a flow rate of 25 μl/min at 63 Hz with a backpressure of 350 Pa. The flow rate of this pump could be easily controlled by external electrical field. Two different sizes of nozzle/diffuser elements were studied and the pumping efficiency of these structures is 11 and 16%, respectively.     

Thermal bonding of PMMA: effect of polymer molecular weight

Microfluidics devices have attracted increasing interest over the last decade. Glass was initially the materials of choice for these devices but polymers such as polymethylmethacrylate (PMMA) have a great potential to be used for these devices because of their low cost, ease of fabrication and chemical properties. A key step in fabrication of these microfluidic devices is the enclosing of microchannels by cover plate, i.e., layer to layer bonding. This investigation focused on the thermal bonding of PMMA layers of different molecular weights. The bond strength and the effect of temperature and pressure on bond strength between various PMMA pairs of different molecular weights were studied. Thermal bonding was realized using a hot embossing system. PMMA strips made from predefined parameters were prepared and a customized CNC machine mold was used to determine the optimized parameters of the thermal bonding. The PMMA pairs investigated are of molecular weights 96.7, 120, 350 and 996 kDa using Instron machine; the shear strength of the thermally bonded specimens was determined. For the PMMA pairs investigated, the greatest shear strength of 1.589 ± 0.286 MPa was observed between molecular weights of 350 and 996 kDa.     

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...     

Thin-film electrode based droplet detection for microfluidic systems

We report on a droplet-producing microfluidic system with electrical impedance-based detection. The microfluidic devices are made of polydimethylsiloxane (PDMS) and glass with thin film electrodes connected to an impedance-monitoring circuit. Immiscible fluids containing the hydrophobic and hydrophilic phases are injected with syringe pumps and spontaneously break into water-in-oil droplet trains. When a droplet passes between a pair of electrodes in a medium having different electrical conductivity, the resulting impedance change signals the presence of the particle for closed-loop feedback during processing. The circuit produces a digital pulse for input into a computer control system. The droplet detector allows estimation of a droplet's arrival time at the microfluidic chip outlet for dispensing applications. Droplet detection is required in applications that count, sort, and direct microfluidic droplets. Because of their low cost and simplicity, microelectrode-based droplet detection techniques should find applications in digital microfluidics and in three-dimensional printing technology for rapid prototyping and biotechnology.     

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.

     

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.     

Study of PMMA thermal bonding

The bond strength dependence on bonding temperature and bonding pressure in traditional thermal bonding and surface modification bonding of PMMA is investigated. The results show that the bond strength of the latter bonding method is larger than the former. The effects of post-annealing and aging on bond strength are also demonstrated. Then the bonding parameters of temperature and pressure are optimized, and typical bond strength of 1 MPa is obtained at bonding temperature of 95°C, bonding pressure at 2 MPa, bonding time for 3 min and 50°C post-annealing for 2 h. The successful bonded microfluidic device was obtained through this optimized thermal bonding method.     

Bench scale glass-to-glass bonding for microfluidic prototyping

Microfluidics, an increasingly ubiquitous technology platform, has been extensively utilized in assorted research areas. Commonly, microfluidic devices are fabricated using cheap and convenient elastomers such as poly(dimethylsiloxane) (PDMS). However, despite the popularity of these materials, their disadvantages such like deformation under moderate pressure, chemical incompatibility, and surface heterogeneity have been widely recognized as impediments to expanding the utility of microfluidics. Glass-based microfluidic devices, on the other hand, exhibit desirable properties including rigidity, chemically inertness, and surface chemistry homogeneity. That the universal adoption of glass-based microfluidics has not yet been achieved is largely attributable to the difficulties in device fabrication and bonding, which usually require large capital investment. Therefore, in this work, we have developed a bench-scale glass-to-glass bonding protocol that allows the automated bonding of glass microfluidic devices within 6 h via a commercially available furnace. The quality of the bonds was inspected comprehensively in terms of bonding strength, channel deformation and reliability. Additionally, femtosecond pulsed laser micromachining was employed to rapidly engrave channels on a glass substrate with arbitrary-triangular in this case-cross-section. Bonded glass microfluidic devices with machined channels have been used to verify calculated capillary entry pressures. This combination of fast laser micromachining that produces arbitrary cross-sectioned microstructures and convenient bench-scale glass bonding protocol will facilitate a broad range of micro-scale applications.

     

The effect of injection molding PMMA microfluidic chips thickness uniformity on the thermal bonding ratio of chips

Injection molding PMMA microfluidic chips can significantly improve the efficiency of chips forming. However, due to the coexistence of macro and micro effects in the injection molding process, the thickness uniformity of molding substrates is poor, which will seriously affect the thermal bonding quality of chips. In this paper, the effect of injection molding PMMA microfluidic chips thickness uniformity on the thermal bonding ratio and the quality of micro-channels was studied by experiments and simulations. The results show that when the following three conditions were satisfied during injection molding process, chips bonding ratio reaches to 93.9?% and the distortions of micro-channels caused by thermal bonding were acceptable. Firstly, the cover plates flatness error is smaller than 50–60?μm and substrates flatness error is smaller than 80–90?μm. Secondly, the maximum thickness difference of stack chips (cover plate stack with substrate) is smaller than 70–80?μm. Thirdly, chips thickness of the middle is larger than that of the two ends along their length direction and chips thickness distribute evenly along their width direction. These conclusions can be used for the parameters selection and moulds design during injection molding process of PMMA microfluidic chips.     

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.     

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...