Leaching behaviour of stereolithography 3D-printed microfluidics

Stereolithography (SLA) 3D printing has become a standard tool to produce microfluidic structures, thanks to advancements in both 3D printer technology and resin materials. Used across many applications, SLA-printed microfluidics are often exposed to a variety of solvents, giving rise to potential leaching from the printed structure (in the form of unreacted resin components) that can potentially interfere with device functionality. In this study, we investigated the leaching behavior of SLA-printed structures from both external surfaces (under static conditions) and microfluidic surfaces (under flowing conditions). We focused on how leaching is affected by factors such as resin and solvent type, post-processing, fluidic architecture, and internal flow rates. Using a combination of gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC) analysis, we identified 15 chemical species consistently found in leachate samples from 4 commercial resins, in the form of monomers and photoinitiators. We found that increased post-processing led to an overall reduction in leaching, with monomers being more affected than photoinitiators. In no case was leaching eliminated. For leaching from microfluidic channels, we found that light treatment did not result in any reduction in leachate levels, which can be attributed to the absorption of light in the external regions of the structure. These findings highlight the importance of thorough post-processing, careful solvent selection, and optimal fluid flow conditions to improve the chemical stability and biocompatibility of SLA-printed devices in fluidic applications.