High School Student Seoul Foreign School Jong-no, United States
Introduction: Organ-on-a-chip (OOC) devices are increasingly used to replicate human physiological conditions in vitro, providing valuable platforms for studying cellular interactions, drug responses, and disease mechanisms. A critical feature of these devices is the ability to cultivate endothelial cell monolayers, such as those formed by human umbilical vein endothelial cells (HUVECs), which are essential for modeling the vascular endothelium, particularly angiogenesis assays. Current methods for inducing monolayer formation typically involve placing the OOC devices at a 90-degree angle, allowing gravity to assist in the alignment and adhesion of cells along the channel walls. However, this method can be inconsistent and difficult to standardize across experiments, leading to variability in the results. To address these challenges, I developed a simple 3D-printed tool that enables controlled tilt-induced positioning of OOC devices (TIPOD). The TIPOD not only facilitates the reproducible formation of HUVEC monolayers by maintaining the optimal angle for cell attachment and growth but also has the capability to introduce a consistent unidirectional flow that can mimic the physiological conditions of blood vessels. By using this device, researchers can achieve more reliable and reproducible results, enhancing the utility of OOC systems in various biomedical applications.
Materials and
Methods: The tilting device was designed using computer-aided design (CAD) software and fabricated using the Creality K1 Max 3D printer. Polylactic acid (PLA) was chosen as the printing material due to its biocompatibility, ease of use, and structural integrity. The Creality K1 Max was selected for its high precision and simplicity, allowing for accurate reproduction of the design while minimizing the potential for errors. The printer’s large build volume also accommodated the creation of multiple devices simultaneously, enhancing the efficiency of the fabrication process. Human umbilical vein endothelial cells (HUVECs) were cultured in endothelial growth medium (EGM-2, Lonza) after OOCs were plasma treated at 70 W for 3 minutes to enhance surface hydrophilicity. The devices were then loaded with a fibrin hydrogel mixture to form the extracellular matrix and injected into the central channel of the OOC device. The chips were rotated to varying angles to facilitate gravity-induced cell settling along the channel walls.
Results, Conclusions, and Discussions: The TIPOD significantly influenced HUVEC monolayer formation. Figure 1a shows four OOCs inserted into the TIPOD and the notch system that allows precise angles to be set. Figure 1b depicts HUVEC adhesion within the chip, as well as the angle settings. As shown in Figure 1e, cell numbers were highest in the side channel at 0° (mean = 973.4, SEM = 29.5) and decreased sharply with increasing tilt, reaching the lowest at 90° (mean = 228.7, SEM = 22.3). Figure 1c and Figure 1d illustrate the decline in cell density in the side channel, meaning more HUVEC adhere to the hydrogel center channel, causing improved monolayer formation. These results indicate that optimal HUVEC alignment occurs at higher tilts, demonstrating the device's effectiveness in controlling cell patterning within organ-on-a-chip systems. The study demonstrates that the TIPOD is effective in controlling HUVEC monolayer formation within organ-on-a-chip systems. Optimal cell alignment and density are achieved at higher tilting angles, with significant declines in cells observed in the side channel as the tilt increases. These findings highlight the importance of tilt-induced flow in vascular model development and suggest that this device can enhance reproducibility in tissue engineering applications. Future studies should explore the long-term effects of tilt-induced flow on cellular behavior and its applicability to other cell types and organ systems.
Acknowledgements (Optional): Department of Mechanical Engineering, Seoul National University, Seoul, South Korea Sangmin Jung & Noo Li Jeon
References (Optional): Aazmi, A., Zhou, H., Li, Y., Xu, X., Wu, Y., Ma, L., & Yang, H. Engineering, 2022, 9, 131-147. (Engineered Vasculature for Organ-on-a-Chip Systems)
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Medina-Leyte, D.J., Domínguez-Pérez, M., Mercado, I., Villarreal-Molina, M.T., & Jacobo-Albavera, L. Appl. Sci., 2020, 10, 938. (Use of Human Umbilical Vein Endothelial Cells (HUVEC) as a Model to Study Cardiovascular Disease: A Review)
