Patient interface for supplying a flow of pressurized gas to a subject, with: an interfacing portion that gets in contact with the subject, and a gas supply system (10, 12, 14, 16, 18, 20, 22, 24), wherein the gas supply system comprises: at least one pump device (55, 72, 88, 110, 112, 170, 172, 258, 276, 278, 280, 282, 302, 304, 306), comprising: - at least two membranes (58, 59, 76, 92, 93, 116, 240, 242, 244, 269, 308), each membrane comprising at least one electro-active polymer material (60, 61, 78, 94, 95, 118, 246, 268, 310), and - at least one valve (64, 65, 150, 152, 202, 214, 226, 250, 267, 314); and a controller (130, 154), for controlling the at least one pump device, wherein the pump device comprises at least one closed volume (140, 162), and wherein the membranes are arranged on opposite sides of the closed volume such that they are in operative communication with the at least one closed volume and are further designed for altering the size of the at least one closed volume based on actuation by the electro-active polymer material in a periodic way resulting in a flow of pressurized gas, wherein the controller is designed to receive electric signals from the at least one electro-active polymer material for detecting forces that act on the at least one electro-active polymer material. an interfacing portion that gets in contact with the subject, and a gas supply system (10, 12, 14, 16, 18, 20, 22, 24), wherein the gas supply system comprises: at least one pump device (55, 72, 88, 110, 112, 170, 172, 258, 276, 278, 280, 282, 302, 304, 306), comprising: - at least two membranes (58, 59, 76, 92, 93, 116, 240, 242, 244, 269, 308), each membrane comprising at least one electro-active polymer material (60, 61, 78, 94, 95, 118, 246, 268, 310), and - at least one valve (64, 65, 150, 152, 202, 214, 226, 250, 267, 314); and a controller (130, 154), for controlling the at least one pump device, wherein the pump device comprises at least one closed volume (140, 162), and wherein the membranes are arranged on opposite sides of the closed volume such that they are in operative communication with the at least one closed volume and are further designed for altering the size of the at least one closed volume based on actuation by the electro-active polymer material in a periodic way resulting in a flow of pressurized gas, wherein the controller is designed to receive electric signals from the at least one electro-active polymer material for detecting forces that act on the at least one electro-active polymer material. at least one pump device (55, 72, 88, 110, 112, 170, 172, 258, 276, 278, 280, 282, 302, 304, 306), comprising: - at least two membranes (58, 59, 76, 92, 93, 116, 240, 242, 244, 269, 308), each membrane comprising at least one electro-active polymer material (60, 61, 78, 94, 95, 118, 246, 268, 310), and - at least one valve (64, 65, 150, 152, 202, 214, 226, 250, 267, 314); and - at least two membranes (58, 59, 76, 92, 93, 116, 240, 242, 244, 269, 308), each membrane comprising at least one electro-active polymer material (60, 61, 78, 94, 95, 118, 246, 268, 310), and - at least one valve (64, 65, 150, 152, 202, 214, 226, 250, 267, 314); and a controller (130, 154), for controlling the at least one pump device, wherein the pump device comprises at least one closed volume (140, 162), and wherein the membranes are arranged on opposite sides of the closed volume such that they are in operative communication with the at least one closed volume and are further designed for altering the size of the at least one closed volume based on actuation by the electro-active polymer material in a periodic way resulting in a flow of pressurized gas, wherein the controller is designed to receive electric signals from the at least one electro-active polymer material for detecting forces that act on the at least one electro-active polymer material.