 Popa eventually followed Rainer to the University of Bucharest's medical faculty in 1920, and was appointed assistant professor.With Rainer as his doctoral advisor, Popa completed his docent degree, describing the functional structure of the dura mater.Over the course of his career, his students included some twenty-two university professors and Romanian Academy members, among them George Emil Palade and Constantin Bălăceanu-Stolnici.