Impact of Resin Reuse on Form Accuracy and Hydrodynamic Stability in 3D printed Microfluidic Channels

Acrylate and methacrylate resins are widely used in vat photopolymerization (VP) 3D printing techniques, such as Projection Micro-Stereolithography (PμSL), due to their rapid UV-curing behavior, high resolution, and low viscosity ideal for fabricating complex microfluidic devices (Wen et al., 2022). These resins enable the production of fine features like microchannels, while offering mechanical strength and optical transparency for micro-optofluidic (MoF) applications. However, their crosslinked structure formed during photopolymerization, i.e., not recyclable, poses significant recyclability challenges (Tosto et al., 2024). Conventional disposal methods, such as landfill and incineration, are not environmentally sustainable. As a practical alternative, reusing uncured resin has emerged as an effective green strategy. In VP 3D printing, leftover uncured resin from previous prints is typically filtered and stored for reuse, reducing material consumption and overall waste. This approach aligns with sustainable manufacturing goals by mitigating the environmental impact of non-recyclable thermoset materials. It also ensures a cost-effective and lower waste management through reduced fresh resin use and disposal (Nyika et al., 2022). But exploiting this practice may reduce VP 3D printing accuracy, especially for micrometric parts, due to contamination and resin aging (Sun et al., 2005). In this context, this study evaluates the effects of photocurable resin reuse on the form accuracy and hydrodynamic stability of microfluidic channels fabricated via PμSL. Three MoF devices were produced using fresh, once- and twice-reused acrylate-based resin batches. This represents a sustainable strategy to address recyclability limitations of crosslinked thermosets. Devices were tested using an air–water bi-phase flow to assess flow stability. Channel width consistency was evaluated through a Phase I distribution-free quality control approach using recursive sequential and permutation (RS/P) methods. Chemical alterations in reused resin batches were tracked by Fourier Transform Infrared Spectroscopy. A Design of Experiments (DoE) analysis showed that increasing the flow rate value improved hydrodynamic performance across all samples, mitigating flow constriction effects induced by resin reuse. These findings support resin reuse as a viable, eco-friendly option in MoF device manufacturing.