"To cross the membrane" refers to the process of moving from one side of a barrier in a cell or organism to the other side. It can apply to various substances such as molecules, ions, or even larger particles. Full definition
All animal viruses have to cross membranes for cell entry and exit. (sciencedaily.com)
They're hard to get into the body, and they have difficulty crossing membranes in the body. (sciencedaily.com)
Gold nanowires may cross a membrane passively, but thanks to their rod - or wirelike asymmetric shape, active motion can be triggered by ultrasound. (phys.org)