Directed oxygen gradients initiate a robust early remodeling response in engineered vascular grafts

Whereas functionally different, both organogenesis and wound-healing processes create zones or regions of hypoxia that persist until capillary networks are formed to facilitate oxygen and nutrient delivery. Similarly, regenerative processes within in vitro engineered tissues experience the same hypoxic regions, but without the capacity to form functional capillaries resulting in a major limitation in developing full-thickness organs and tissues. Due to the importance of oxygen in wound healing and tissue regeneration, we hypothesize that directed oxygen gradients can be used to modulate cell function and promote more effective tissue regeneration. The effect of controlled oxygen gradients on human smooth muscle cells (SMCs) was assessed using dual chambered perfusion bioreactors to regulate transport conditions occurring in a model vascular construct. SMCs were seeded onto the ablumenal surface of the scaffold and cultured for 21 days under 3 independent gas environments: (1) 21% oxygen, (2) 11% oxygen, or (3) an ablumen to lumen oxygen gradient from 11% to 21%. When compared to 21% oxygen and 11% oxygen conditions, the directed 11%-21% oxygen gradient resulted in a raised metabolic activity and significantly improved cell migration. After 21 days from seeding, cells were shown to migrate entirely across the scaffold to the vessel lumen (>450 μm). Concomitant with a more uniform cell dispersion, scaffold mechanics were significantly enhanced with increased stiffness and tensile strength. Native oxygen gradients are known to play a pivotal role during organ development; these results show that directed oxygen gradients within in vitro systems can be used to facilitate early remodeling leading to significantly enhanced cell migration and scaffold biomechanics.