Excessive expansion of adipose tissue and consequent obesity is a major risk factor for type 2 diabetes, which can further lead to stroke, hypertension and cardiovascular disease. In this poster, we describe a microfluidic reactor-based in vitro adipose tissue model. By including vascular endothelial cells, this system more closely mimics the heterogeneous nature of adipose tissue compared to conventional models that rely only on adipocytes. A key feature of the designed reactor is that it affords selective localization of micro-scale collagen gels, which serve as 3D scaffolds for cell culture. The selective localization is accomplished by fabricating regions of high (convective) transport resistance. This feature is used to partition the reactor's culture chamber into three regions, where a middle adipocyte region is flanked on either side by two tube-like structures lined with vascular endothelial cells, mimicking capillaries. This arrangement permits spatially controlled, direct cell to cell contact between adipocytes and endothelial cells without the use of intervening membrane structures and other artificial transport barriers. The optimal reactor dimensions and operating parameters were estimated using steady convection-diffusion models taking into account both nutrient transport, metabolism, and cell growth.