Microfluidic platforms for studying cell behavior in complex microenvironments

For better translation from basic science to everyday clinical practice, biomedical research must attempt to understand cellular behavior that occurs in vivo. This is assuredly a daunting task as cells receive many cues from the surrounding microenvironment. Cues such as changes in the extracellular matrix, gradients of soluble molecules, or reduced oxygen tensions will cause cells to alter their behavior. To more thoroughly understand how these cues alter cellular processes, advanced platforms capable of mimicking these microenvironments are necessary. Microfluidic platforms have the potential to enable systematic studies of cell behavior in these complex microenvironments. Microfluidic platforms provide control over the chemical microenvironment. This inherent control enables generation of linear chemical concentration gradients, control over diffusion of soluble molecules, and regulation of gaseous conditions. This work aims at developing and applying microfluidic platforms to study (1) neutrophil chemotaxis, (2) intercellular communication, and (3) cell behavior under controlled oxygen conditions. In chapter 1, conventional methods and emerging techniques using microfluidic platforms to study cell behavior in complex microenvironments are discussed. In chapter 2, the study of neutrophil chemotaxis in competing chemical concentration gradients using a microfluidic platform is discussed. Neutrophils were observed to oscillate between the maxima of the two intermediary chemoattractants LTB4 and IL-8. Chapter 3 discusses the design and characterization of a microfluidic platform with barriers that act as bifurcations in the path of neutrophil migration. Neutrophils were found to efficiently migrate around 40-μm and 100-μm wide barriers. However, when the barrier width was increased to 200 μm neutrophils took an inefficient, tortuous path. In chapter 4, the design, operation, and application of a microfluidic platform that enables the study of intercellular communication is discussed. A model system was used to experimentally measure and computationally simulate intercellular communication within the device. The agreement of these two techniques enabled the complete description of spatiotemporal distribution of signaling molecules in the microfluidic platform. In chapter 5, methods to study the tumor microenvironment under controlled oxygen conditions were discussed. This chapter details characteristics of the tumor microenvironment. Further, the advantages and limitations of conventional methods and recently developed microfluidic platforms were discussed in detail. Chapter 6 discusses the design, fabrication, operation, and validation of an open-welled microfluidic platform that enables control over oxygen concentration during cell studies. The oxygen concentration within the microfluidic platform was experimentally measured and computationally simulated as different parameters of the platform were varied. Overall, this dissertation discusses the design and use of microfluidic platforms to study cell behavior in complex microenvironments