A microfluidic device to produce polymersomes having three coaxial passageways of increasing size with fluid flowing in one direction. The first and smallest passageway contains the content of the polymersome, the middle passageway contains a block copolymer, and the largest and outer passageway contains an aqueous medium or water. The device can produce polymersomes with control of size and membrane thickness. The device will allow quantitative loading of the polymersomes in high quantities. The device is robust and easily assembled and has the ability to independently control the three streams involved in making the polymersomes.