Nutrient depletion thresholds in 3D printed cell assemblies

Energy consumption is an essential part of active matter; in biological systems energy consumption is often limited by the delivery of oxygen and glucose. Within tissues, these molecules are delivered to cells by a combination of flow through vasculature and intra-tissue diffusion. For dense tissues, the rates of oxygen and glucose diffusion compete with the rates at which they are metabolized, creating a threshold distance from a blood vessel, beyond which cells will become starved. It is almost universally accepted that in tissues of living organisms and in engineered tissues, all cells must be within 200 microns of vasculature because of this competition between diffusion and consumption. However, this rule cannot apply generally to all tissues because cellular metabolic rates are highly variable across cell types and cell densities. In this talk, we will describe experiments that test the 200 micron rule in which we 3D print controlled distributions of hepatocytes into 3D culture medium made from jammed granular microgels. By monitoring cell viability and the consumption of oxygen and glucose, we identify the diffusion-limited crossover to nutrient or oxygen deprived conditions. We vary the size of 3D printed structures and the cell density within them.