Microfluidic platforms for cell culture and microenvironment control
Microfluidic systems have the ability to tailor cell microenvironment in a con-trollable and reproducible fashion that cannot be easily achieved by conventional me-thods. This research aimed to develop microfluidic platforms for manipulation of cel-lular microenvironment and communication, which enabled new assays for biological studies to advance our understanding of various biological systems. These simple and compact platforms were compatible with conventional cell culture practice, which would lead to potential widespread acceptance by the biological community. To control the interactions between two cell populations, a mechanical valve was integrated into the microfluidic platform containing two cell culture chambers. In the natural state, the two microfluidic chambers were connected, and the two cell pop-ulations cultured side by side communicated with each other. Once the valve was ac-tivated, the two cell populations were isolated and distinct cell types could be treated individually without affecting the other. To differentiate cell-cell interactions through either direct cell contacts or soluble factors alone, an agarose-coupled valve barrier was constructed. This barrier blocked cell migration but permitted exchange of signaling molecules. We further modified the permeable barrier by embedding ligand traps, which had the ability to bind selectively to certain soluble molecules with high affinity. As a result, the barrier became semi-permeable and could block the transport of a specific type of molecule, which provided a new way to probe the cellular signaling pathway. To study chemotaxis, a pressure balance fluidic circuit was designed and fabri-cated which had the ability to generate automatically two streams with equivalent pressure and flow rate from two individual passive pumps. By feeding a pyramidal microfluidic circuit with these two streams, an approximately linear concentration gradient was created and maintained. The pressure balance fluidic circuit was also integrated into the traditional Dunn chamber to generate a concentration gradient on a two-dimensional surface or in a three-dimensional matrix. We believe that these platforms would have extensive applications for neuro-biology and cancer biology, as demonstrated by the studies of dynamic imaging of synapse formation, neuron-glia co-culture, tumor cell – endothelial cell cross-migration, and fibrosarcoma cell migration.