Oxygen gradients correlate with cell density and cell viability in engineered cardiac tissue

TLDR

Cardiac grafts must be thick, compact, and contain physiologic densities of active cells, requiring precise control of nutrient and oxygen levels to avoid detrimental gradients of oxygen, cell density, viability, and function. This study aimed to quantify diffusional oxygen gradients in statically cultured cardiac constructs and relate them to spatial patterns of cell number and viability. Oxygen distribution was measured with microelectrodes in 3.6 mm × 1.8 mm disc‑shaped neonatal rat cardiomyocyte constructs, and a mathematical model linked oxygen levels to cell density, viability, and position. Oxygen and viability declined linearly with depth, live cell density fell exponentially, physiological live‑cell density existed only within the first 128 µm, and medium flow markedly raised oxygen and improved tissue properties. © 2005 Wiley Periodicals, Inc.

Abstract

Abstract For clinical utility, cardiac grafts should be thick and compact, and contain physiologic density of metabolically active, differentiated cells. This involves the need to control the levels of nutrients, and most critically oxygen, throughout the construct volume. Most culture systems involve diffusional transport within the constructs, a situation associated with gradients of oxygen concentration, cell density, cell viability, and function. The goal of our study was to measure diffusional gradients of oxygen in statically cultured cardiac constructs, and to correlate oxygen gradients to the spatial distributions of cell number and cell viability. Using microelectrodes, we measured oxygen distribution in a disc‐shaped constructs (3.6 mm diameter, 1.8 mm thickness) based on neonatal rat cardiomyocytes cultured on collagen scaffolds for 16 days in static dishes. To rationalize experimental data, a mathematical model of oxygen distribution was derived as a function of cell density, viability, and spatial position within the construct. Oxygen concentration and cell viability decreased linearly and the live cell density decreased exponentially with the distance from the construct surface. Physiological density of live cells was present only within the first 128 µm of the construct thickness. Medium flow significantly increased oxygen concentration within the construct, correlating with the improved tissue properties observed for constructs cultured in convectively mixed bioreactors. © 2005 Wiley Periodicals, Inc.