This PhD thesis aimed to develop an in vitro microfluidic system to investigate the influence of red blood cell (RBC) mechanical properties, particularly deformability, on endothelial cell behaviour under shear stress, simulating the in vivo microvascular environment. The study comprised three key components. First, a PDMS-based microfluidic device with a 100 µm inner diameter was created and functionalised with fibronectin to facilitate endothelial cell attachment. Successful endothelialisation of the device was achieved, serving as a strong foundation for the subsequent work. Next, RBC samples were treated with varying glutaraldehyde concentrations to induce deformability changes. The deformability of these RBCs was assessed using Mizar, a high-throughput light transmittance-based blood analyser, which produced a Deformability Index showing a strong negative correlation with glutaraldehyde concentration. Additionally, a pressure-based perfusion system was developed to ensure controlled flow of RBCs through the microfluidic channel, allowing for the study of shear-mediated endothelial response. This system enabled the simultaneous perfusion of multiple microfluidic devices under different conditions. The study primarily focused on shear-mediated endothelial responses. Immunofluorescence staining was used to visualise and analyse the effects of different flow conditions and fluids on three specific endothelial proteins involved in the vasodilation response. The methods developed to analyse the data acquired successfully demonstrated the ability to detect differences in protein expressions under different flow conditions. In summary, this work has successfully developed an in vitro microfluidic platform for studying the interaction between RBC deformability and endothelial cells under shear stress. It offers potential applications beyond the immediate scope to contribute to the broader understanding of blood-related phenomena and serves as a versatile research platform.