Controlling Flow Rate and Shear Stress with Omi™ to Study Endothelial Cell Response

The protocol provides a straightforward model of vascular environments in vitro, demonstrating how organ-on-chip technology allows the study of cellular responses under dynamic flow conditions. 

Inside this application note: 

• A detailed step-by-step protocol for culturing human umbilical vein endothelial cells (HUVECs) in the BeFlow device 
• How to apply unidirectional, laminar flow onto the endothelial monolayer using the Omi™ perfusion platform 
• Insights into flow-induced responses including cell alignment, elongation, and proliferation  

Role of HUVECs in Organ-on-a-chip Models

Human umbilical vein endothelial cells (HUVECs) are an extensively used model in organ-on-chip applications. They exhibit key characteristics of vascular endothelial cells, including monolayer formation, extracellular matrix production, and response to angiogenic factors (1). They effectively mimic human vascular endothelium. Their in-vitro use provides a valuable tool for studying vascular endothelium interactions. Organ-on-chip (OoC) technology recreates complex human organ microenvironments in vitro, using microfluidic devices to precisely control and manipulate cellular and biochemical conditions.  

For discussion on key applications of HUVECs in OOAC models such as angiogenesis assays and shear stress response, download the full application note.

• Vascularized Kidney-on-Chip: create a vascular network within kidney-on-chip models. 
• Blood-Brain Barrier Models: form part of the endothelial layer in blood-brain barrier models on chips.  
• Lung-on-Chip: simulate the vascular compartment of lung-on-chip models. 

How do endothelial cells respond to shear stress? 

Shear stress, a force generated by fluid flow, plays a crucial role in the physiology of endothelial cells, which line the interior surface of blood vessels. When applied to endothelial cell cultures, it influences various cellular processes, including alignment, gene expression, and the production of nitric oxide. The dynamic nature of flow conditions simulates the natural environment of blood vessels, allowing researchers to better understand endothelial cell responses in physiological and pathological states (2).

Studies have shown that appropriate shear stress can promote healthy endothelial function, whereas abnormal patterns are linked to vascular diseases. Understanding these effects is vital for developing therapeutic strategies to address cardiovascular issues. 

We have written a review explaining why shear stress is an important parameter in the endothelial dynamic cell culture.

Endothelial cell culture under shear stress protocol 

In the application note, we outline the chip preparation, setup, and maintenance of microfluidic cell culture using the Omi™ device with Beonchip’s Be-Flow chip. Key steps include cartridge and adaptor installation, fluidic circuit priming (Loading step), and system sterilization using the built-in Sterilization protocol. Following medium loading, the confluent endothelial monolayer is connected for perfusion. 

Once Omi is connected, culture conditions are maintained at 37 °C with 5% CO₂, with medium exchanges performed on days 0*, 3, 5, and 7. Light-microscopy is used to monitor cell morphology, confluence, and alignment throughout the culture period. 

*Sampling and Loading steps in the Omi Protocol allow automated medium refreshing over the weekend. 

Figure 4: Omi Protocol 

Table 1: Set Flow Rate and Equivalent Shear Stress Values Calculated Using Fluigent Calculators 

References

1. The use of human umbilical vein endothelial cells (HUVECs) as an in vitro model to assess the toxicity of nanoparticles to endothelium: a review, Yi Cao et al, 2017 

2. Perfusion culture of endothelial cells under shear stress on microporous membrane in a pressure-driven microphysiological system, Shinji Sugiura et al, 2023.