Microfluidic Cell Culture Devices for Gaseous Microenvironment Control

Abstract

The concentration of various gases plays an essential role for mammalian cells. For instance, oxygen is an important modulator of cellular function in both normal physiology and disease states. Cells respond to oxygen over a wide range of oxygen tensions, from hypoxia to hyperoxia. Oxygen affects cellular responses in various ways, including metabolic pathways and plasma membrane integrity. Oxygen gradients in physiologic systems also play a critical role in maintaining homeostasis and inducing acute cellular response. For example, angiogenesis in development, tissue repair, tumor growth, and vascular remodeling is potentiated by spatial oxygen gradients and the expression of oxygen-responsive genes. Due to the high diffusivity of gases in an aqueous solution, controlling gaseous microenvironments has been a challenging task for biologists. Studies of cellular responses to gases in cellular microenvironments would benefit from a reliable platform that is capable of robustly controlling the gaseous concentration in both spatial and temporal domains. However, existing microfluidic cell culture devices face several challenges that hinder their practical usage in biological labs. First, directly using gases for concentration and gradient generation requires precise flow control instruments, tedious interconnections, and bulky gas cylinders used to store compressed gases. Moreover, the gas can easily penetrate through the permeable membrane and may cause media evaporation and bubble generation inside the cell culture channel. As a result, the entire setup is unreliable for long-term studies, and cannot be directly implemented in conventional cell incubators. To overcome these challenges, my lab develops microfluidic cell culture platforms capable of controlling various gaseous microenvironments. The platforms take advantage of the spatially confined chemical reactions to generate or scavenge gases inside cell culture microfluidic channels or wells without direct chemical contact. The flow rates of chemicals can be precisely controlled by syringe pumps that are commonly used in biological labs. By confining the areas for chemical reactions, the device can control the gas concentrations and gradients, efficiently using minimal chemicals without altering the surrounding gaseous compositions. Furthermore, without tedious and unreliable gas interconnections, the entire microfluidic setup can be directly implemented into conventional cell incubators for optimized temperature and humidity control without additional instrumentation. Here, we demonstrate three different cell studies taking advantages of our microfluidic devices, including: study of cell proliferation and migration under oxygen gradients, study of cell migration and drug efficiency under combinations of chemical and oxygen gradients, and characterization of cell responses under nitric oxide gradients. With the demonstrated results, the developed microfluidic devices show great promise and advantages for various in vitro cell biology studies for biomedical applications.