We provide a facile and low-cost method (F-L) to fabricate a two-dimensional positive master using a milling technique for polydimethylsiloxane (PDMS)-based microchannel molding. This method comprises the following steps: (1) a positive microscale master of the geometry is milled on to an acrylic block; (2) pre-cured PDMS is used to mold the microscale positive master; (3) the PDMS plate is peeled off from the master and punctured with a blunt needle; and (4) the PDMS plate is O₂ plasma bonded to a glass slide. Using this technique, we can fabricate microchannels with very simple protocols quickly and inexpensively. This method also avoids breakage of the end mill (ϕ = 0.4 mm) of the computerized numerical control (CNC) system when fabricating the narrow channels (width < 50 µm). The prominent surface roughness of the milled bottom-layer could be overcomed by pre-cured PDMS with size trade-off in design. Finally, emulsion formation successfully demonstrates the validity of the proposed fabrication protocol. This work represents an important step toward the use of a milling technique for PDMS-based microfabrication.

In this study, we introduce a novel hybrid technique for fabricating two-dimensional paper-based microfluidic analytical devices (μPADs) that combines capillary-driven wax patterning with embossing. The method utilizes capillary action to guide molten wax through a sealed polydimethylsiloxane microfluidic chip onto a glass substrate, where it forms high-resolution wax stamps upon demolding. The wax-glass assembly is then heated to facilitate wax penetration through the paper matrix, creating well-defined hydrophobic-hydrophilic barriers. This process allows precise control over stamp dimensions, offering considerable design flexibility. We systematically examined the relationship between flow time and channel length, with experimental results showing strong consistency with a modified Lucas-Washburn model developed in this study. Furthermore, the technique supports seamless integration of biological and chemical sensors into patterned μPADs, enabling the fabrication of fully functional devices. Our results highlight the robustness and scalability of this combined approach, achieving a remarkably reduction of cost. Combined with its operational simplicity, this method is particularly suitable for large-scale applications in resource-limited environments.

This study proposes a simple yet versatile microfluidic strategy for fabricating monodisperse alginate hydrogel microspheres using a symmetric flow-focusing device. The system integrates three key innovations: (1) Cost-effective mold fabrication: A paper-based positive master replaces conventional SU-8 photoresist, significantly simplifying device prototyping; (2) Surfactant-free droplet generation: Alginate hydrogel droplets are formed at the first flow-focusing junction without requiring interfacial stabilizers; (3) In situ solidification with coalescence suppression: Acetic acid-infused corn oil is introduced at the adjacent junction, simultaneously triggering ionic crosslinking of alginate via pH reduction while preventing droplet aggregation. Notably, the hydrogel microspheres can be efficiently harvested through oscillatory aqueous phase separation, removing post-fabrication washing steps (typically 6-8 cycles for surfactant and oil removal). This integrated approach demonstrates exceptional advantages in fabrication simplicity, process scalability, and operational robustness for high-throughput hydrogel microsphere production.

In this study, we present a two-stage method for fabricating monodisperse alginate hydrogel microspheres using a symmetrically designed flow-focusing microfluidic device. One of the flow-focusing junctions generates alginate hydrogel droplets without the addition of surfactants, while the other junction introduces corn oil with acetic acid, which facilitates the solidification of the homogeneous alginate hydrogel droplets and prevents coalescence. These hydrogel microspheres can be easily separated from the oil phase using an oscillation state, eliminating the need for a demulsifier. This microfluidic system for hydrogel microsphere formation is notable for its simplicity, ease of fabrication, and user-friendliness.