With the advantages of rapid prototyping and complex structure formation demonstrated by 3D printing technology in microfluidic chip manufacturing, new development momentum has been injected into fields such as biomedical and chemical analysisHowever, the high manufacturing costs and serious waste of resin materials caused by the photopolymerization printing process have gradually become key bottlenecks restricting the large-scale application and promotion of this technology in scientific research and industrial fields. The data shows that after a single printing task is completed, the proportion of residual resin can reach up to about 90%. The methyl methacrylate monomers contained in these residues not only have complex processing procedures and high disposal costs, but may also pose potential environmental risks.Recently, fromItalyThe University of Cataniaresearch teampasssystemExperimental results have shown that,The photo cured resin that has undergone regeneration treatment can be reused more than three times, and the optical performance of the resulting microfluidic devices is almost unaffected.This breakthrough discovery provides key technological support for the 3D printing industry to achieve sustainable development goals. This study aims to“Micro‑optofluidic Devices via Projection Micro‑Stereolithography: Impact of Resin Reuse on Optical Sensing Performance”Title, published in an international journal《The International Journal of Advanced Manufacturing TechnologyHow to translateUp there.The research team has developed a complete set ofResin regeneration technology，It includes five key steps: resin recovery, primary filtration (100-200 μ m metal mesh sieve), secondary filtration (0.45-1 μ m PTFE membrane vacuum filtration), uniform mixing (3000rpm/5min), and dark storage.This process can effectively remove impurities and partially cured particles from residual resin, ensuring the chemical stability of regenerated resin.Figure 1. Micro optofluidic (MoF) for gas-liquid slug flow detection
）The working principle of the equipment.Three resin batches were used in the experiment: brand new resin, primary regenerated resin, and secondary regenerated resin, which were used to manufacture three identical T-junction microfluidic devices. These microfluidic devices are designed specifically for absorption optical detection,The research team adopted Mofang Precision Surface Projection Micro Stereoscopic Lithography (P μ SL) technology (nanoArch)®
S140， Precision: 10 μ m) integrally formed and printed
No additional assembly is required.Figure 2. 3D printed organic framework (MoF) devices manufactured using P µ SL technology (labeled as Dev-1, Dev-2, and Dev-3, respectively).Through Fourier transform infrared attenuated total reflection spectroscopy (FTIR-ATR) analysis, researchers found that the chemical structure of the regenerated resin only undergoes minor changes. The absorption peak intensity slightly decreased at 1635cm ⁻¹ (C=C stretching vibration) and 810cm ⁻¹ (C-H out of plane bending vibration), indicating a slight decrease in the content of methacrylate monomer. This change is mainly due to the dark curing phenomenon during the printing process and the pre polymerization caused by trace light scattering, while the overall chemical structure of the resin remains stable.Figure 3. Comparison of FTIR spectra collected along the range of 1800-650 cm ⁻¹ from four different quadrants Qki of different batches of resin: fresh photo cured resin (Dev-1, blue curve); One time resin recycling (Dev-2, light blue curve); Secondary recycling resin (Dev-3, yellow curve). The peaks identified by 1 and 2 are 1635 cm ⁻¹ and 810 cm ⁻¹, respectively.Optical performance is the core indicator of microfluidic devices. The research team measured the transmittance of the device at a wavelength of 589nm (sodium D-line) using a spectrophotometer and calculated the refractive index using a dedicated regression model. The experiment conducted five repeated measurements in four different regions of each device to ensure data reliability.Figure 4. Spatial layout of the studied quadrant Qki (i=1,..., 4) for each considered k-th microfluidic device (k=1, 2, 3).The results showed that the refractive indices of the devices made from the three resins were 1.7044 (new resin), 1.7043 (primary regeneration), and 1.7042 (secondary regeneration), with a difference of only 0.012%. Two factor analysis of variance showed that the number of repeated resin uses and measurement area had no significant effect on the refractive index (p-value>0.05).Figure 5. Process diagram for obtaining the estimated refractive index value (¹) of 3D printed resin.Figure 6. Comparison of transmission spectra obtained on four different quadrants Qki (n=1): fresh photo cured resin (Dev-1, blue curve); One time resin recycling (Dev-2, light blue curve); Secondary recycling resin (Dev-3, yellow curve).During the functional verification phase, researchersA gas water slug flow detection platform was built, and the device performance was systematically evaluated through experimental design (DoE) method. The experiment investigated the effects of three factors, laser power (1mW and 5mW), flow rate (0.1-0.3mL/min), and resin type, on the optical detection capability.The results show that all devices can clearly distinguish the gas phase and liquid phase in the slug flow, and the signal waveform maintains a stable square wave characteristic. Statistical analysis confirms that there is no significant difference in the detection performance of devices from different resin batches, proving that the regenerated resin meets the functional requirements of microfluidic devices.Figure 7. Three dimensional effect diagram of the studied response variable A, where the column height represents the average response value for each research scenario, and the circular markers represent separately collected observations.Summary: This study demonstrates the feasibility of recycling and reusing photocurable resin in the manufacturing of microfluidic devices.Through rigorous experimental design and system performance evaluation, researchers have confirmedEven after two cycles of recycling, the optical properties of the resin remain stableThe optical detection capability of the device is not affected. This achievement not only provides a sustainable solution for the 3D printing industry, but also contributes to the application of microfluidic technology in biomedical research and clinical diagnosis
