Capacity and limitations of microfluidic flow to increase solute transport in three-dimensional cell cultures

Culturing living cells in three-dimensional (3D) environments increases the biological relevance of laboratory experiments, but has the caveat of requiring solutes to overcome a diffusion barrier to reach the center of cellular constructs. We present a theoretical and numerical investigation that brings a mechanistic understanding of how microfluidicculture conditions, including chamber size, inlet fluid velocity, and spatial confinement, affect solute distribution within 3D cellular constructs. Contact with the culture chamber reduces the maximally achievable construct radius by 15%. In practice, finite diffusion and convection kinetics in the microfluidic chamber further lower that limit. The benefits of external convection are greater if transport rates across diffusion-dominated areas are high. Those are omnipresent and include the diffusive boundary layer growing from the fluid-construct interface and regions near corners where fluid is recirculating. Less convection is required to approach an ideal maximally-supplied state when diffusion within the constructs is slow. Our results contribute to defining the conditions where complete solute transport into an avascular 3D cell construct is achievable and demonstrate how flow velocity must evolve with construct radius in order to maintain a given solute penetration depth.