Hi Rebecca, thanks for your question. The buoyancy media composition was developed to replace the presence of red blood cells in the vasculature which provide buoyancy, pushing immune cells to the blood vessel walls to roll along the endothelial surface. We use Percoll (colloidal silica) to create this buoyancy in the channel during flow so that the immune cells interact with the membrane. We also add gellan gum (polysaccharide) to homogeneously suspend the immune cells when not under flow (i.e. in the Pod media reservoir).
This buoyancy media solution is based on standard RPMI-1640 media and provides necessary nutrients for immune cell culture. We do not see any effect in immune cell viability or activation through flow cytometry analysis of immune cells in buoyancy media up to 72hrs, including after flow through the chip.