Fabrication of cyclic olefin polymer and polydimethylsiloxane co-bonded microfluidic device and its appliactions in terahertz biological effects on intestinal cells
Authors: Wang Cheng-Yao , Li Xu , Lu Xiao-Yun ,   National Center for International Research on Transient Electromagnetics & Applications (TEA), Xi’an Jiaotong University, Xi’an 710049, China,   Key Laboratory of Biomedical Information Engineering of Ministry of Education, Institute of Mitochondrial Biology and Medicine, School of Life Science and Technology, Xi’an Jiaotong University, Xi’an 710049, China
Published: November 2021

<sec>The current research on the terahertz biological effects at a cellular level is limited by the conventional petri dishes used for cell culture, which cannot be directly used for confocal laser microscopy. In this research, the cycloolefin polymer (COP), a material that possesses low terahertz absorption rate but excellent optical property for microscopy, is bonded to polydimethylsiloxane (PDMS), thereby developing a novel COP-PDMS microfluidic device by using the techniques of soft etching, photolithography, plasma cleaning, high-temperature and high-pressure incubation. The bonding strength of resulting device is tested by using a push-tension meter. The results indicate that the developed device shows a bonding strength as strong as the device fabricated by quartz and PDMS, which is thought as the tightest binding in the multiple types of microfluidic device. In addition, by perfusing the device chamber at a high flow rate (200 μL/s) and long-term time-course (2 weeks), which simulates the dynamic shearing stress occurring in <i>in-vivo</i> organs and tissues, this COP-PDMS microfluidic device can still maintain the original shape and sealing property, indicating that this device qualifies the requirements of the following dynamic cell culture.</sec><sec>The biological effects of terahertz on the cells are explored by using this COP-PDMS microfluidic device mentioned above. In this device, we develop the dynamic culture of intestinal epithelial cells Caco-2 with a perfusion rate of 0.05 μL/s, which meets the findings of the <i>in-vivo</i> gastrointestinal lumen shearing stress. The Caco-2 cells are then irradiated with 0.1 THz wave with the power of 15 mW/cm<sup>2</sup> for 3 days, and the irradiation duration is 10 min per day. The biological effects of terahertz irradiation on the intercellular tight junction protein ZO-1, the Paxillin relating to the cell adhesion and migration, and the cytoskeletal microfilament protein F-actin of Caco-2 cells are detected in the device directly using the technique of immunofluorescence staining.</sec><sec>The results show that the morphology of cell adhesion as well as the level and distribution of ZO-1 and Paxillin are changed. In brief, the protein expression of ZO-1 and Paxillin are induced more by the terahertz irradiation, while the F-actin is not influenced by the irradiation. As can be seen from the F-actin results, the cells without terahertz irradiation show a spread and outward shape with regular smooth cell edge while a contraction and burr shape of cell edge are shown after irradiation, suggesting that the cell adhesion is weakened after irradiation. Even though the expression level of F-actin is consistent, the changed morphology indicates that terahertz may regulate the interaction and aggregation among actin proteins in cells. Interestingly, the ZO-1 presents diffuse distribution in the cells and its location on the cell membrane is not obvious, that is, a large amount of ZO-1 expresses not only on the cell membrane but also in the intracellular matrix after the irradiation. The expression of Paxillin is enhanced after terahertz irradiation, and some cells show local aggregation and distribution of Paxillin. These indicate that the terahertz irradiation might affect the biomolecular mechanism of synthesis and distribution of protein. The COP-PDMS co-bonded microfluidic device developed in this study provides a convenient and effective platform for exploring the biological effects of terahertz irradiation on cells, and is expected to be further used for real-time research on the effects of terahertz on cells and molecules in the future.</sec>