Microfluidic supported liquid membrane extraction is a promising technique for microliter-scale radionuclide separations because it requires very small reagent volumes and combines extraction and stripping in a single unit operation. Flat sheet supported liquid membrane (FS-SLM) modules with 100, 200, 300, and 400 pm deep channels were fabricated at a cost of less than 5 USD in material using a commercially available resin three-dimensional (3D) printer. The performance of these modules was characterized by quantifying uranium transport across a 15 v/v % tributyl phosphate (TBP) liquid membrane at flow rates between 5 and 60 mu L min(-1) and developing a two-dimensional (2D) numerical transport model for the system. The extent of uranium extraction was found to increase with increasing residence time and decreasing channel depth, with quantitative extraction occurring at the slowest flow rates and shallowest channel depths. The numerical model agreed well with the experimental extraction results. Time-dependent calculations showed that the modules reach steady state in fewer than 9 min and that there is a considerable buildup of uranium in the membrane during that time.