A method and apparatus for selectively expressing one or more selected fluid materials out of a fluid container, including a centrifuge rotor having a round centrifuge chamber of selected volume, a round expandable enclosure disposed within the centrifuge chamber having a rotation axis coincident with the central rotation axis and a flexible wall, a pump for controllably pumping a selected volume of expressor fluid into and out of the expandable enclosure wherein the fluid container is receivable with the centrifuge chamber, and a retaining mechanism for holding the fluid container within the centrifuge chamber in a coaxial position. The flexible wall of the fluid container is in contact with the flexible wall of the expandable enclosure.