He attended The Ohio State University where he received his B.S. in Mechanical Engineering (2003). He attended Stanford University as a National Science Foundation Graduate Research Fellow and obtained his M.S. (2005) and Ph.D. (2009) in Mechanical Engineering. Cullen's Ph.D. research, with Professor Juan Santiago, involved the study of microfluidic pumps to manage liquid water in proton exchange membrane fuel cells. Cullen spent a year at UC Berkeley working with Professor Liwei Lin and Professor John Coates as a UC President’s Postdoctoral Fellow. At MIT his laboratory explores flow physics at the microscale for applications in materials science and microbiology. Cullen is the recipient of numerous awards for his research and service including the National Science Foundation CAREER Award (2012), the DuPont Young Professor Award (2013), and the DARPA Young Faculty Award (2013).