Directly Printed Hollow Connectors for Microfluidic Interconnection with UV-Assisted Coaxial 3D Printing

Abstract

Effective and reliable interconnections are crucial for microfluidics to connect with the macro world. Current microfluidic interfaces are still bulky, expensive, or with issues of clogging and material limitation. In this study, a novel ultraviolet (UV)-assisted coaxial three-dimensional (3D) printing approach was proposed to fabricate hollow microfluidic connectors with advantages of rapid prototyping, fixture-free, and materials compatible. An assembled coaxial nozzle was designed to enable co-flow extrusion, where the inner flow (water) served as the sacrificial layer and the outer flow (adhesive) was cured for shell formation. Furthermore, a converged UV-LED light source was attached to the coaxial nozzle for UV curing of adhesives. UV rheological characterizations were performed to study the UV curing kinematics, and the gelation time was employed to describe the state transition behaviors of UV curable adhesives used in the study. To explore requirements for successful hollow connectors direct printing, processing criteria such as co-flow regime and pre-cure time were investigated. The hollow connectors with an inner channel diameter of ~150 μ m and a height of 5 mm were successfully printed on polymethyl methacrylate (PMMA) and glass substrate. The integration feasibility of the proposed method was also demonstrated by the presented microfluidic device with printed hollow connectors.

Characterization and Evaluation of 3D-Printed Connectors for Microfluidics

“…To summarize, the obtained process window helped choose the appropriate combinations of flow rates to manufacture 3D-printed connectors. On the other hand, by comparing the coaxial flow behavior region under non-UV exposure in previous works [22] and the process window of connector printing under UV exposure, we found UV exposure conditions impacted the coaxial flow status. The reason is that the material viscosity of UV adhesives dynamically changes under UV exposure.…”

“…A 28 G (ID 0.17 mm, OD 0.35 mm) inner steel nozzle was chosen for water extrusion, and an 18 G (ID 0.91 mm, OD 1.26 mm) outer steel nozzle was employed for UV adhesive (LOCTITE 3491, Henkel AG & Company, Düsseldorf, Germany) extrusion. As discussed in previous works [ 22 ], it takes at least 6 s for LOCTITE 3491 to stabilize its structure under the shine of a converged UV–LED light source. Thus, we introduced a transparent jacket (ID 1 mm, OD 2 mm, length 25 mm) to assist the pre-curing step for UV adhesive before its deposition.…”

“…A general interconnection solution for most existing microfluidic devices is necessary to ease microfluidic fabrication. Thus, coaxial 3D-printed connectors without any additional components or adhesives have been reported by us before [ 22 ]. Previous works have successfully demonstrated the feasibility of coaxial 3D-printed connectors for microfluidic applications.…”

Thermal Annealing Effects on the Mechanical Properties of Bio-based 3D Printed Thermosets

“…Additionally, comparing the spectra of the resin vs the polymers, the disappearance of the C=C (~810, 1405 and 1640 cm -1 ) signals and increase in the C-H (2868 and 2952 cm -1 ) signals indicated complete polymerization. 46 These characteristic peaks of the polymerization were highly noticeable when comparing the resin spectrum to the as printed spectrum. However, when comparing the as printed spectrum to the annealed spectrum, not much change was observed.…”

A Review of Microfluidic Experimental Designs for Nanoparticle Synthesis

“…3D printing can also be used not only for developing whole microfluidic platforms but also for fabricating auxiliary components for such systems. For instance, Xu et al [ 104 ] have employed a UV-assisted coaxial printing method for manufacturing microfluidic connectors. In more detail, the researchers fabricated hollow microscale connectors using water as a sacrificial layer and a UV-curable adhesive for shell formation under UV irradiation.…”