In this thesis, microfluidic systems which mimic blood vessels and tumour areas are developed to bridge the gap between conventional cell culture assays and animal models. The interactions of polymeric nanocarriers with different physicochemical properties and cells presented in the vessel wall and tumour tissue under exposure to the flow are examined. Our findings indicate critical roles of not only particle properties (size and surface chemistry), but also biological properties (flow conditions or leaky nature of tumour vessels) in nano-bio interactions. Therefore, these microfluidic systems are shown to be promising models for preclinical screening of potential drug delivery carriers.