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Polyformaldehyde (POM) is one of the most commonly used engineering thermoplastics that has been widely used in the industry as well as in our daily life. Compared with other thermoplastics, POM has a relatively high thermal resistance and self-lubricating properties. In this study, the POM was used as the bulk material for microfluidic devices, with the microchannels directly laser ablated on the surface of POM plates. The profile of the microchannels with various CO2 laser energy and scan speed was also studied in detail. To enclose the channel, a layer of adhesive polyester film was attached to the surface of the POM plate to seal the fabricated microchannels, and the bonding strength was enhanced with a further compression procedure and then tested with a burst opening method. With the help of the high thermal resistance of POM, an enhanced oil recovery (EOR) test under high temperature was conducted in this study based on the POM-based microfluidic device to mimic the underground oil recovery process in the porous sandstone structure.

This study proposed a novel method for the rapid fabrication of paper-based microfluidic devices using a roll-to-roll wax transfer method. In this approach, a custom-made device was designed and fabricated for the direct roll-to-roll wax transfer from commercially available wax ribbon to the surface of paper substrate. After wax transfer, a thermal reflow process was conducted to enable the melt wax penetration through the whole thickness of the hydrophilic paper substrate to form hydrophobic wax barriers. Compared with the conventional approaches for paper-based microfluidics (wax printing, photolithography, and inkjet printing), the proposed fabrication technique for paper-based microfluidic devices is suitable for the batch fabrication of paper-based microfluidic chips at high production speed. Additional advantages including simple fabrication process, low material and fabrication cost, low-energy consumption, and without the requirement of cleanroom environment or facilities. The paper-based microfluidics fabricated with the proposed roll-to-roll wax transfer method is widely adaptable for microfluidic applications in biological and chemical fields.

Paper-based microfluidics has been widely used in chemical and medical analysis applications. In the conventional paper-based microfluidic approach, fluid is propagating inside the porous structure, and the flow direction of the fluid propagation is usually controlled with the pre-defined hydrophobic barrier (e.g. wax). However, the fluid propagation velocity inside the paper-based microfluidic devices largely depends on the material properties of paper and fluid, the relative control method is rarely reported. In this study, a fluid propagation velocity control method is proposed for paper-based microfluidics: hydrophobic pillar arrays with different configurations were deposited in the microchannels in paper-based microfluidics for flow speed control, the result indicates the deposited hydrophobic pillar arrays can effectively slow down the fluid propagation at different levels and can be used to passively control the fluid propagation inside microchannels for paper-based microfluidics. For the demonstration of the proposed fluid control methods, a paper-based microfluidic device for nitrite test in water was also fabricated. The proposed fluid control method for paper-based microfluidics may have significant importance for applications that involve sequenced reactions and more actuate fluid manipulation.

In this work, a diode laser ablation approach was used for the fabrication of PMMA-based microfluidic devices. Compared with the conventional CO2 or femtosecond laser fabrication method, the proposed laser ablation method based on diode laser significantly lowered the cost in the fabrication of polymer-based microfluidic devices with comparable resolution and surface quality. PMMA substrate was used for the laser ablation process, due to the transparency of PMMA in the diode laser's working wavelength, a layer of Kraft tape was applied on the surface of PMMA for the absorption of laser energy, and microchannels were then achieved on the surface of PMMA with the proposed low-cost diode laser system. The comparison between the proposed method and the CO2 laser ablation method was also conducted in this study. The profile of the fabricated microchannels was carefully characterized, several microfluidic devices were also fabricated for the demonstration of the proposed fabrication method using a diode laser.

This study proposes a novel method for the fabrication of paper-based microfluidic devices using laser-induced selective thermal reflow for wax penetration. A layer of wax was evenly deposited on the front side of a filter paper; then a low-cost diode laser was used to scan the designed area from the back side of the filter paper. At the laser irradiated spot, the wax was heated, melted down and penetrated through the whole thickness of the filter paper, and formed hydrophobic barriers on the hydrophilic cellulose fibers. The patterned hydrophobic wax barriers on the filter paper defined the flow path of the fluid for the paper-based microfluidic device. Compared with conventional two-step (deposit and reflow) approaches for paper-based microfluidics using wax barriers, e.g. wax printing, stamping or photolithography, the proposed fabrication protocol achieved wax patterning and reflow simultaneously, conducted during the laser scan process, and without the requirement for any sophisticated instruments or a cleanroom environment. A series of tests were also conducted for the characterization of the proposed paper-based microfluidic device fabrication technique. The fabrication technique used in this approach could have broad application potential in point-of-care diagnosis and testing, especially for applications in the developing world.

Biaxially oriented polystyrene (BOPS) is a commercialized packaging material, which has the advantages of biocompatibility, non-toxic, transparency, light-weight and cost-effective. Due to the stress accumulated from both directions in plane during the fabrication process, when BOPS was reheated above the glass transition temperature, an isotropic shrinkage will occur. This study proposed a low-cost and rapid prototyping method for the fabrication of BOPS-based microfluidics device. Both laser ablation and micro-milling were used for the fabrication of microchannels on the surface of the BOPS sheet, after thermal induced shrinkage, microchannels with finer microstructure could be achieved. For the sealing of fabricated microchannels on BOPS, two approaches were made using a layer of BOPS or a layer of polyester adhesive film. The thermal induced shrinkage and bonding strength were carefully studied in this study. Several microfluidic devices, including a droplet generator and a diffusion mixer were also fabricated for demonstration. The proposed fabrication method for BOPS-based microfluidics is simple, rapid, cost-effective and without the requirement of cleanroom facility, with help of thermal induced shrinkage, finer structure with high resolution could be achieved with conventional lab tools.