a semipermeable ultrathin polymer membrane is a microfluidic device that comprises a substantially optically transparent polymer film having a surface area to thickness ratio of at least 1 , 000 , 000 : 1 , and an array of precisely spatially ordered pores of a user - selected diameter defined therethrough . such membranes can be fabricated by providing a mold having a patterned array of nanoholes femtosecond laser ablated in a surface thereof ; applying a first polymer solution onto the mold surface so that the first polymer solution infiltrates the nanoholes ; allowing the first polymer solution to dry and form a replica of the mold having a plurality of freestanding nanoneedles extending from a surface of the replica ; removing the replica from the mold ; coating the replica surface with a second polymer solution ; drying the second polymer solution to form a porous polymer film ; and dissolving the replica in a solvent to release the film from the replica as a semipermeable ultrathin polymer membrane . also disclosed are multi - chambered microfluidic devices for studying cell biology in vitro that incorporate one or more such semipermeable ultrathin polymer membranes .