Microfluidic patterning of cellular biopolymer matrices for biomimetic 3-D structures

Microtechnology has found exciting potential applications in recreating in vivo tissue architecture due to its ability to create complex structures with size scales spanning from the micron to millimeter range. However, most microscale systems are 2-dimensional, and few 3-dimensional systems are being explored. We have developed a versatile technique to create a 3-dimensional microscale hierarchical system for cells and biopolymers. By taking advantage of the contraction of hydrogel matrix biopolymers, one can achieve multiple layers of cells within biopolymers using microchannels, and eventually form a hierarchical layered microstructure of cells and biopolymer. Pressure-driven microfluidics was applied in order to transport cells within matrix biopolymers through the channels with controled flow rates. Flow imaging was used to estimate the shear stress and examine the useful range of flow rates for biopolymer fluids to form the layered structure. Activated glass chips were used to effectively immobilize cell-matrix assemblies. For our model system, a vascular structure was set up using endothelial cells, smooth muscle cells and fibroblasts to mimic the three layers found in vivo (intima, media and adventitia). Collagen or collagen-chitosan matrix biopolymers were used as constructs throughout all layers. The final structure was characterized using confocal microscopy for reconstructed 3-dimensional cell distribution. Using this approach, a "neotissue" can be formed with cellular and biopolymer components engineered to model in vivo systems.