Imperforate bowl: centrifugal separators – Process
Reexamination Certificate
1999-09-10
2001-08-21
Cooley, Charles E. (Department: 1723)
Imperforate bowl: centrifugal separators
Process
C494S045000
Reexamination Certificate
active
06277060
ABSTRACT:
This invention relates to a centrifuge chamber for a cell separator, in particular for separating blood into several fractions.
DESCRIPTION OF THE RELATED ART
Cell separators having a centrifuge chamber are used for separating whole blood into its individual components.
The centrifuge chamber of known cell separators has a separation channel into which the cell suspension to be separated is sent. Under the influence of centrifugal force, the blood is separated in the separation channel into different fractions, such as platelets (PLT), erythrocytes (RBC), platelet-rich plasma (PRP) and platelet-poor plasma (PPP) which are discharged from the chamber.
The centrifuge chamber of known cell separators for separating blood into multiple fractions is generally intended for a single use. One-part and two-part centrifuge chambers are also known. In two-part centrifuge chambers, the separation channel is formed by a flexible film part inserted into a rigid receptacle unit. The separation channel of known one-part or two-part centrifuge chambers is designed with one or more steps.
Centrifuge chambers with a multi-step separation channel have the disadvantage that cells which have already been separated may be entrained into another fraction by turbulent eddies in the transition area between the individual sections of the channel. Thus, for example, there is the risk that platelets which have already been separated might become mixed completely or partially with the plasma, or that leukocytes may be entrained by flow eddies as impurities.
One-step separation chambers, however, have so far been characterized by unclean or inadequate separation of platelets. In particular, this occurs because platelets are obtained from the so-called buffy coat portion of the flow, which also contains a great many leukocytes.
German Patent A-28 21 055 describes a multi-step centrifuge chamber for separating blood into several fractions, whose separation channel consists of several arc-shaped sections with different radii, with a distinct separation between them formed by transitional areas or dams. Each section of the channel has a distinctly different slope, with the slope of the channel section having a discontinuity at the point of transition to the next section connected to it.
A centrifuge chamber whose separation channel is composed of several sections is known from U.S. Pat. No. 4,342,420. This separation channel has an inlet area extending outward, a middle area extending on a circular path around the axis of rotation and an end area extending toward the axis of rotation.
U.S. Pat. No. 4,342,420 discloses a one-step separation chamber with a spiral-shaped separation channel. The separation channel is designed so that it does not extend toward the axis of rotation, but instead it drains in the edge area of the chamber.
SUMMARY OF THE INVENTION
The present invention is directed to centrifuge chamber for a cell separator that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
The invention includes a centrifuge chamber for a cell separator with a separation channel, that includes at least one channel section bordered by an inner side wall and an outer side wall, the inner side wall being radially closer than the outer side wall to an axis of rotation of the centrifuge chamber, an inlet for introducing a cell suspension in the separation channel, and at least one outlet for withdrawing a fraction of the cell suspension. A path line defining a locus of midpoints between the inner and outer side walls describes each of the channel sections. The path line has a spiral shape extending from a radially outer end of the separation channel to a radially inner end of the separation channel, and has a progressive slope defined for each point of the path line as an angle between a first tangent to a circle about the axis of rotation intersecting the point, and a second tangent to the spiral at the point.
The invention also includes a method for separating a cell suspension into its desired component fractions, comprising the steps of introducing the cell suspension in a separation channel of a separation chamber, and rotating the separation chamber about an axis of rotation, thus forcing the cell suspension to distribute in the separation channel along a spiral shaped path extending from a radially outer end of the separation channel to a radially inner end of the separation channel. The spiral path has a progressively increasing slope defined for each point of the spiral path as an angle between a first tangent to a circle about the axis of rotation intersecting the point, and a second tangent to the spiral path at the point. The method includes also withdrawing the desired component fractions at corresponding outlets disposed on a radially outer surface of the separation channel.
It has been found that a relatively uniform and contamination-free separation of the cell suspension can be achieved with a channel design with a steady path, having a slope that is designed to be constant, or progressively increasing.
Because of the continuous spiral design of the individual sections of the separation channel, there are no discontinuities in the path, and turbulence is prevented so that a laminar flow can develop in the channel.
The separation channel may comprise one or more channel sections, and may have areas between the individual channel sections where fluid enters into the separation chamber or leaves from it. In these areas, the inside and outside walls of the separation channel may not form a steady path.
The centrifuge chamber according to the present invention may be used in particular for separating whole blood into several fractions, namely erythrocytes, platelets, and plasma.
In a preferred embodiment, the invention includes a separation channel that extends up to near the center of the axis of rotation of the centrifuge chamber.
In another preferred embodiment of the centrifuge chamber, the outlet for the erythrocyte fraction is arranged at the radially outer end of the channel, while the outlet for the plasma fraction is arranged at the radially inner end of the channel. The inlet for the cell suspension to be separated is preferably arranged between the outlet for the erythrocyte fraction and the outlet for the plasma fraction. The outlet for the platelet fraction is preferably arranged between the inlet for the blood and the outlet for the plasma fraction.
With this preferred embodiment, the advantages of the centrifuge chamber, whose separation channel has a progressive slope, are especially manifested. Because of the progressively varying slope of the channel, erythrocytes are not packed too compactly in the radially outer areas of the channel. Therefore, the hematocrit value of the erythrocytes in the radially outer areas does not exceed a maximum of 80% to 90%. This is an advantage inasmuch as high hematocrit values in the outer areas of the channel interfere with a radially inward flow of platelets into the plasma. In addition, this ensures that plasma can flow unhindered radially inward to the plasma outlet over the entire length of the channel.
Since the slope of the path increases progressively with a reduction in centrifugal force, platelets can fall back to the platelet outlet from inner areas of the channel, due to the centrifugal force.
In another preferred embodiment, the outlet for platelets is arranged in a recess which is located on the radially outside wall of the channel and extends over the entire height of the separation channel. The platelets can be removed from this recess with a high efficiency. Both of the platelets which are entrained by the plasma flow from the buffy coat layer on the erythrocytes to the plasma outlet, as well as the platelets that fall back from radially inner areas due to the progressive slope of the channel, may fall into this recess.
The outlet for platelets is advantageously located in the lower half of the recess, preferably in the radially outer part of the recess.
The separation channel with th
Cooley Charles E.
Fresenius AG
Kenyon & Kenyon
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