Tissue expanders having integrated drainage and moveable barrier membranes

A tissue expander having an integrated drain includes a shell having an opening and one or more drainage holes, and an injection port disposed in the opening of the shell and forming a fluid-tight seal with the shell. The injection port includes a needle guard having a needle guard base with a top surface. The injection port includes a moveable barrier membrane overlying the top surface of the needle guard base. The moveable barrier membrane is moveable between a first position for inflating and deflating the shell with a first fluid and a second position for draining a second fluid from outside the shell. A magnet is coupled with the moveable barrier membrane, and a compressible spring is connected with the magnet. The compressible spring is compressed for storing energy as the moveable barrier membrane moves from the first position to the second position.