The pancreatic ductal adenocarcinoma (PDAC) stroma and its inherent biophysical barriers to drug delivery are central to therapeutic resistance. This makes PDAC the most prevalent pancreatic cancer with poor prognosis. The chemotherapeutic drug gemcitabine is used against various solid tumours, including pancreatic cancer, but with only a modest effect on patient survival. The growing PDAC tumour mass with high densities of cells and extracellular matrix (ECM) proteins, i.e., collagen, results in high interstitial pressure, leading to vasculature collapse and a dense, hypoxic, mechanically stiff stroma with reduced interstitial flow, critical to drug delivery to cells. Despite this, most drug studies are performed on cellular models that neglect these biophysical barriers to drug delivery. Microfluidic technology offers a promising platform to emulate tumour biophysical characteristics with appropriate flow conditions and transport dynamics. We present a microfluidic PDAC culture model, encompassing the disease's biophysical barriers to therapeutics, to evaluate the use of the angiotensin II receptor blocker losartan, which has been found to have matrix-depleting properties, on improving gemcitabine efficacy. PDAC cells were seeded into our 5-channel microfluidic device for a 21-day culture to mimic the rigid, collagenous PDAC stroma with reduced interstitial flow, which is critical to drug delivery to the cancer cells, and for assessment with gemcitabine and losartan treatment. With losartan, our culture matrix was more porous with less collagen, resulting in increased hydraulic conductivity of the culture interstitial space and improved gemcitabine effect. We demonstrate the importance of modelling tumour biophysical barriers to successfully assess new drugs and delivery methods.