Machining technologies and structural models of microfluidic devices

In the past decades, microfluidic chips have been one of the hottest research topics in the “lab-on-a-chip” field. However, it is still a challenge for design the perfect microchannels with high functional integration, complex geometry, and high production efficiency. This review paper provides a comprehensive overview of microfluidic structural models and designs, manufacturing techniques, and bonding methods. The effect of three types of microfluidic channel structure models and their configuration parameters on the fluid behaviors of microfluidics was investigated. Surface-to-volume ratio of the flow channel is a critical parameter for determining the mixing and diffusion capabilities of the microfluidic devices (MDs). Thereafter, the main manufacturing techniques for microstructures were discussed, including etching, photolithography, soft lithography, molding, mechanical micro-machining, laser beam micromachining, printing, and 3D printing. We performed a statistical analysis to discuss the relative advantages and disadvantages of these manufacturing methods. In addition, the current bonding methods for MDs were also summarized, including thermal bonding, solution adhesive bonding, dry adhesive bonding, plasma bonding, and anodic bonding. a comparison of different bonding methods was presented to provide a reference to select a suitable bonding method for the assembly of microfluidic device. Finally, the tendencies and challenges of microchannel manufacturing were discussed, and the prospects were also provided.