Microfluidic devices have sparked a potential light in the point-of-care diagnostics revolution. These systems enable the integration with myriads of analytical detection strategies to establish rapid analysis and less-laborious operations using minute volumes of samples and reagents [1–3]. Besides, these devices offer versatility targeting a broad range of applications, such as sample preparation, sample delivery, sample waste, sample handling, and modeling organ-on-a-chip[4–8]. A prominent trajectory in microfluidics is the micro-total analysis system (µ-TAS) which holds the ultimate premises of comprehensive integration of a sensing element and sample handling system, including manipulations of small volumes in the microchannel and data processing module[9–12].
In microfluidic device production, the conventional fabrication techniques, for instance, soft lithography, remain a major shortcoming due to their long process, the requirement for masking, and operation by trained technicians. Moreover, despite other maskless methods, such as engraving mold using a laser and milling machine, which were reported to simplify the molding fabrication process[13, 14], the structure resolution is still hard to compete with the photolithography process using the mask. Meanwhile, polymer casting is noticed to be the most critical step for microfluidic fabrication [15, 16]. The casting method is the main challenge for the commercialization of microfluidic devices because of its low reproducibility and throughput of yields. These limitations inflict a significant gap between lab prototyping, scale-up production needs, and market standardization [17, 18].
3D printing is one of the disruptive technologies in the microfluidics field. It speeds up the molding fabrication and makes it feasible for direct microfluidic fabrication without polymer casting, owing to the high availability of the various resin types in the market[19–23]. Among the number of distinctive printing techniques, such as laser sintering, fused filament, and an inkjet-based 3D printer, resin stereolithography emanates as a potential fabrication pathway of 3D printing because of its high resolution, good surface finishing, and considerably low expenses per printed device. Stereolithography is a remarkable process of exposing photosensitive monomers layer by layer using a controlled ultraviolet light source to the resin. The master file of the 3D model can be designed by commercial or open-source software and loaded into the 3D printer machine. The curing methods include stereolithography with direct laser writing, digital light processing, continuous liquid interface production (CLIP), and continuous digital light manufacturing (CDLM), which varied approaches to the mechanism of exposing the resin to define each fabricated layer [24]. The structure is constructed by slice per slice pattern in the X-Y direction, which later moves on to the Z direction for forming subsequent layers until the 3D structure is completed. Curing the deposited liquid resin layer by layer gives an advantage of faster printing and an optimal observational view than filament-based 3D printing, which is generally intruded by the visible printing lines whenever each layer is formed.
There are critical features for functional microfluidics for bio-clinical applications: such as single-use application, biocompatibility, disposability, reliability, cost-effectiveness, modularity, and high reproducibility, especially for cohort studies. In particular, the last three features could be overcome by using 3D printed devices. For example, high-throughput yields significantly reduce production costs with a reasonable and scalable production time[19, 25, 26]. Furthermore, the reproducibility of 3D printed modular microfluidics is more controllable compared to conventional casted microfluidics[27, 28]. Nie et al. show the capillary-driven modular microfluidic inspired by Lego® [29]. The modular microfluidics were assembled from individual functional modules, which provide versatility and flexibility for reconfiguration and customization of microfluidic devices. Straightforward fabrication of complex structures with resolution under millimeter scale using an entry-level and open-source hardware 3D printing could be an alternative for the engineering of small dimension structures [30].
This article presents the fabrication of lock-and-key modular microfluidics for the production of connector and chamber modules. These two components would be the pivotal features for versatile microfluidics applications. The zig-zag connector for the mixer of liquid samples was fabricated and optimized to explore the potencies of the low-cost LCD-resin 3D printer. Next, the connector could be integrated into a single functional microfluidic device. We initially investigated the structural design evaluation and printing parameters. The next part entails the detailed strategy for the submillimeter fluid chamber module creation.