(102d) Spinning Desicurer: A Cost Effective and Generalizable Post Processing Method for Enhanced Optical Quality in 3D Printed Microfluidics

Microfluidics are miniaturized devices used for handling small amounts of fluids at the microscale and have been used for various applications, including environmental analysis, medical diagnostics, in vitro modeling of organs, and image-based screening. 3D printing, has paved the way to a new horizon for microfluidics by enabling rapid device prototyping, offering unprecedent flexibility in device design and minimal requirement of specialized equipment and expertise. Among various 3D printing approaches, stereolithography (SLA) 3D printing is the most popular to fabricate microfluidic devices due to the high spatial resolution it offers. SLA 3D printing uses patterned light to selectively crosslink photo-curable resin to achieve the device structure. Typically, post processing after printing is necessary, which includes a solvent wash step and an additional UV curing step to clean and strengthen the printed object. However, an often overlooked but critical aspect is that the porous nature of photo-crosslinked resin materials can result in the penetration and entrapment of these solvents in the print when alcohol-based washing solutions and resin-dissolving agents are used excessively. This results in a cloudy, translucent appearance of the printed device. Additionally, the lack of transparency can also be attributed to non-smooth printing surfaces of the build plate and the use of support structures. Lastly, the presence of oxygen during the post processing step can cause complication and contribute to the optical imperfection of the print surface since molecular oxygen is known to inhibit radical induced polymerizations due to its high reactivity toward radical species.

To address this challenge, we develop an integrated design to enable a simple, cost-effective, and generalizable post-processing method that removes the excess resin without using solvents and produces optically transparent microfluidic devices made by SLA 3D printing. Our equipment, termed “Spinning Desicurer” (short for “Spinning Desiccating Curer”), integrates a low-cost spinning motorized stage and a 395nm UV LED light in a vacuum desiccator. The Spinning Desicurer allows us to simultaneously expel the excess resin and create a smooth surface finish using centrifugal forces; At the same time, the device is UV-cured under a low-oxygen environment. Additionally, we introduce a simple build plate modification method using a flexible thin polyimide film to remove the need of supporting structure during printing and reduce surface imperfections. We quantify the transparency of the print using a Scale-Invariant Feature Transform algorithm on a reference image, which shows the print transparency made by our method is orders of magnitude higher than the traditional post processing method. We further demonstrated the optical quality of the microfluidic device made by our method with imaging of microflow and microparticles under different imaging modalities. The high-resolution images obtained via our device show high fidelity in both bright-field and fluorescence modes compared with the blurry and distorted images obtained from traditionally made devices. The optical property of our 3D-printed device is sufficient in most high-resolution image-based microfluidic applications such as phenotype-driven screening of cells and microorganisms. Our method can be executed using low-cost, easily accessible materials, circumventing expensive commercial apparatus, sophisticated printer modifications, and potential safety hazard of handling waste solvent. We hence envision that this novel method will be easily adopted in different labs and enable users to prototype microfluidic devices for high-resolution applications including but not limit to bioengineering, medical, and pharmaceutical fields, with minimal requirement in supplies and effort.