Serum/plasma separator - piston with red-cell trapping surfaces

Claim 1

A self-contained fluid separator assembly capable of separating blood into its component parts of plasma or serum and cellular portion comprising: a. a container having at least one open end which is adapted to receive blood for subsequent separation into a light phase and a heavy phase; b. a closure sealing the open end of the container, the closure being formed of a self-sealing elastomeric material which is penetrable by a cannula through which blood to be separated is conducted into the container; c. a piston having a specific gravity relatively greater than the cellular portion of the blood and slidably mounted in the upper portion of the container and having means on its lateral outer surface in sealing engagement with the inner surfaces of the container; d. pressure responsive valve means associated with said piston, said valve means being normally closed when there is a pressure differential on different portions of the valve means below a predetermined value and which automatically opens in response to a pressure differential which is greater than said value so that when said container is subjected to moderate centrifugal force the blood separates into its light phase and heavy phase but the piston stays in the upper portion of the container, and subsequently when increased centrifugal force is used the valve means automatically opens with the light phase passing up through the valve means enabling the piston to move down through the light phase while retaining sealing engagement with the inner surfaces of the container; e. a throat within said piston leading from the lower surface thereof to said valve means, said throat having walls which are serrated with a series of ridges for trapping unwanted cellular material; and f. mechanical stop means on the container whereby the piston when moving through the light phase will stop a predetermined distance from one of the ends of the container followed by termination of the differential pressure which permits the valve means to automatically shift from an open position to a closed position to provide an impervious barrier between the separated light phase and heavy phase of the blood.