Spatially defined oxygen gradients and vascular endothelial growth factor expression in an engineered 3D cell model

Tissue hypoxia results in rapid angiogenesis in vivo, triggered by angiogenic proteins, including vascular endothelial growth factor (VEGF). Current views of tissue viability are founded on whether 'deeper-lying' cells receive sufficient nutrients and oxygen for normal activity and ultimately survival. For intact tissues, levels of such essential nutrients are governed by micro-vascular perfusion. However, there have been few effective quantitatively defined 3D models, which enable testing of the interplay or interdependence of matrix and cell density, and path diffusion on oxygen consumption in vitro. As a result, concepts on cell vulnerability to low oxygen levels, together with the nature of cellular responses are ill defined. The present study has adapted a novel, optical fibre-based system for in situ, real-time oxygen monitoring within three-dimensionally-spiralled cellular collagen constructs, which were then unfurled to enable quantitative, spatial measurements of VEGF production in different parts of the same construct exposed to different oxygen levels. A VEGF response was elicited by cells exposed to low oxygen levels (20 mmHg), primarily within the construct core.