Patterning collagen/poloxamine-methacrylate hydrogels for tissue-engineering-inspired microfluidic and laser lithography applications

The ability to pattern semi-synthetic collagen/poloxamine-methacrylate hydrogels into straight-channel flow circuits and sub-millimeter-sized rectangular blocks for tissue-engineering applications was evaluated. Endothelial cells, grown on the surface of flat collagen/poloxamine-methacrylate hydrogels, proliferated, expressed ICAM-1 (but not VCAM-1) and began to detach after 6 days. Seeding endothelial cells onto the lumen surface of straight collagen/poloxamine-methacrylate flow channels increased ICAM-1 and VCAM-1 expression, and exposure to laminar shear stress (0.3-10 dyn/cm(2)) was unable to attenuate activation on the relatively few cells that were able to withstand flow associated ablation. The enrichment of poloxamine-methacrylate at the lumen surface during fabrication likely caused the decrease in cell attachment and increased activation. To micropattern more complex structures, confocal microscopy UV laser lithography was used to selectively cross-link a HepG2-containing pre-polymer solution of collagen/poloxamine-methacrylate. Turbidity (caused by suspended cells and the incomplete miscibility of collagen and poloxamine-methacrylate) scattered the UV laser energy and necessitated the optimization of exposure times with respect to cross-linking extent and cell viability. Free radical diffusion beyond the bounds of the initial photopattern reduced the resolution of the structures and created a weakly cross-linked periphery around the original pattern. Over time, HepG2 cells migrated towards the less cross-linked periphery and proliferated, creating a non-uniform distribution of cells.