Systems and methods for expression of breast milk

An apparatus for expression of breast milk from a breast, the apparatus comprising:

• a breast shield assembly comprising a breast interface and an actuatable assembly interface fluidly coupled with a tube, the breast interface configured to engage the breast and the actuatable assembly interface configured to removably couple to an actuatable assembly,
• wherein the breast shield assembly comprises an enclosed fluid reservoir extending between the breast interface and the actuatable assembly interface, the fluid reservoir physically separated from the breast milk expressed from the breast and filled with a driving fluid comprising a liquid, and
• wherein the breast shield assembly comprises a fill port configured to allow addition or removal of the driving fluid to or from the fluid reservoir,
• a fill port plug configured to removably couple to the fill port so as to form a fluid-tight seal between the fill port plug and the fill port, wherein the fill port plug comprises a cover portion and a plug portion, the cover portion configured to extend over the fill port along an outer surface of the breast interface or the actuatable assembly interface, and the plug portion configured to fit through the fill port, wherein the cover portion has an outer diameter that is greater than a diameter of the fill port, wherein the plug portion comprises an intermediate portion sized to fit snugly within the fill port and form a fluid-tight seal against an inner wall of the fill port, and an annular lip having an outer diameter that is greater than an outer diameter of the intermediate portion and greater than the diameter of the fill port, wherein an inner surface of the plug portion defines a recessed central region surrounded by the annular lip, the recessed central region configured to allow the annular lip to flex radially outwards in response to inward pull forces exerted on the fill port plug.