The first exposure of intravenously (IV) administered nanomedicines in vivo is to endothelial cells (ECs) lining blood vessels. While it is known that in vitro endothelium models to assess responses to circulating nanoparticles require shear stress, there is no consensus on when and how to include it in the experimental design. Our experimental workflow integrates shear stress by featuring a flow-induced mature endothelium (14 days) and a flow-mediated nanoparticle treatment. The mature endothelium model exhibited distinct features that indicated a structurally stable and quiescent monolayer. Upon treatment with iron sucrose under dynamic conditions, there was a lower nanoparticle uptake, lower cytotoxicity, and decreased expression of activation markers compared to the static control. This response was attributed to glycocalyx expression, predominantly observed on the mature endothelium. In conclusion, our proposed in vitro endothelium model can be leveraged to understand the dynamics of IV injectable nanomedicines at the initial nano-bio interface in veins immediately post-injection.