Liquid purification or separation – Processes – Separating
Reexamination Certificate
1996-12-09
2001-05-29
Kim, John (Department: 1723)
Liquid purification or separation
Processes
Separating
C210S513000, C210S516000, C210S789000, C427S236000
Reexamination Certificate
active
06238578
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the method and apparatus for separating blood components in a blood collection device. Specifically, the invention relates to a method for the separation of the light serum portion of blood from the heavy cellular portion of blood, the blood collection device used to collect and separate the blood, and the method of manufacturing the blood collection device. More particularly, the invention relates to a method of dispensing separator gel in a blood collection tube for improving gel barrier stability and adhesion of the gel to the tube wall during the separation process.
PRIOR ART
Blood collection devices for separating the lighter serum portion of a blood sample from the heavier cellular portion thereof are well known. These devices usually comprise a collection tube containing a thixotropic gel and a contact activated clotting agent. The gel has a specific gravity intermediate the specific gravity of the serum and the cellular phases of the blood sample.
After a sample of blood has been deposited into the collection tube, the contact-activated clotting agents begin to clot the blood sample by activating clotting factors within the blood. The agent facilitates the clotting process until the blood is completely coagulated. It is essential that the agent coagulate substantially all of the blood sample in order for the subsequent serum separation process to be complete. Once the blood has coagulated, the collection tube is placed in a centrifuge to separate the lighter serum from the heavier coagulum portion. Coagulum is defined as the cellular portion and fibrin clot of the blood as opposed to the lighter serum portion of the blood. During centrifugation, the gel on the bottom of the collection tube is displaced upwardly through the blood sample until it reaches its equilibrium position at the interface between the serum and the coagulum. In this position, the gel forms a barrier between the serum and the coagulum which permits the lighter serum to be either decanted directly from the collection tube, or sampled using automated blood analyzing equipment, without interference from the coagulum.
It has long been known in the art that human blood can be readily centrifuged to effect a separation of the blood into its lighter serum and heavier coagulum portions. The specific gravity of the serum portion of human blood is between approximately 1.026 and 1.031, while the specific gravity of the coagulum portion of human blood is between approximately 1.092 and 1.095. The specific gravity of the gel is therefore chosen to be approximately between 1.032 and 1.091, so that once a blood sample is centrifuged, the gel will form an effective barrier between the serum and the coagulum. A preferred gel to be used with the method of the present invention is a thixotropic composition described in U.S. Pat. No. 4,140,631 to Okuda et al, entitled “Sealant for Separation of Serum or Plasma, and It's Use”, the entire disclosure of which is hereby incorporated by reference. As described in Okuda et al., the preferred thixotropic gel is a polymer essentially consisting of at least one compound from the group of alkyl acrylates and alkyl methacrylates, which has a specific gravity of 1.03 to 1.08 and a viscosity of about 5,000 to 1,000,000 cps at a shear rate of 1 second−
1
when measured at 25° C. However, any suitable gel-like composition which can be used as a barrier between blood portions separated in a centrifuge is felt to fall within the spirit and scope of the present invention.
This type of gel is adapted to migrate or flow from the bottom of the tube under the influence of centrifugation to the interface position between the serum and the coagulum portions of the blood and adhere to the inside surface of the collection tube wall to form a barrier between the blood portions to maintain a separation therebetween. However, this migration causes an attendant loss of gel along the tube wall, thereby requiring initial placements of larger amounts of gel in the tube in order to insure the formation of a strong enough mechanical barrier to properly separate the two portions of blood during centrifugation.
Weak adhesion of the gel to the collection tube's inner surface during centrifugation of the blood sample is a problem with prior art blood collection devices. Such weak adhesion of the gel is due to the blood sample wetting the inner surface of the blood collection device prior to the migration of the gel. This wetted inner surface inhibits the natural adhesive properties of the gel, thereby preventing the gel from forming a strong adhesive bond thereto. U.S. Pat. No. 4,257,886 seeks to overcome this deficiency by disclosing a blood separation assembly that coats the bottom portion of the collection tube with a hydrophobic material that resists wetting of the collection tube's inner surface and allows the gel to form a strong adhesive bond to the inner surface during centrifugation.
Another method of addressing the gel migration problem with its attendant loss of adhesion is found in U.S. Pat. No. 4,417,981 (hereinafter the '981 patent) which attempts to overcome the problems associated with gel migration by dispensing the gel in a separator assembly located in the central portion of the collection tube near the eventual formation of the gel barrier. The pre-placement and dispensation of the gel in a separator assembly permits the gel to quickly adhere to the tube wall during centrifugation without migration and attendant loss of gel. However, the above method of dispensing gel using a device incurs further expense in manufacturing an additional element to attain proper separation of the blood sample.
Referring to
FIGS. 1-4
, the prior art method of dispensing separator gel
3
and separating a blood sample into two portions is shown. The method involves utilizing a commonly known gel dispensing apparatus (not shown) to dispense a predetermined amount of gel
3
into the bottom
5
of a collection tube
2
. Contact-activated clotting powder or particles
6
are then deposited inside the collection tube
2
for eventual activation of clotting factors within blood
7
after blood
7
is added to the tube
2
.
As shown in
FIG. 2
, a predetermined amount
4
of blood
7
is added to the collection tube
2
and the contact clot-activating material
6
within tube
2
begins to coagulate the blood
7
before the tube
2
is placed in a centrifuge (not shown) for centrifugation of the blood
7
. The contact clot-activating material
6
promotes clot formation and includes but is not limited to glass and silica. Referring now to
FIG. 3
, during centrifugation of the blood
7
in the collection tube
2
, the gel
3
becomes less viscous and begins to migrate upward along the tube's
2
inner surface
8
until it reaches an interface point
9
where the lighter serum portion
10
of the blood
7
begins to separate from the heavier coagulum portion
11
. The interface point
9
is a result of the two portions of blood, serum
10
and coagulum
11
, being physically separated due to the effect of their different specific gravities during centrifugation. As shown in
FIG. 4
, the separation gel
3
, having a specific gravity intermediate that of the serum
10
and coagulum
11
, has migrated to the interface point
9
between the two blood portions. At the interface point
9
, the gel
3
forms a mechanical barrier
12
inside the collection tube
2
that physically separates the two blood portions and prevents the serum
10
from being contaminated by coagulum
11
.
As of yet, nothing in the prior art has addressed the problem of developing an efficient means of dispensing gel that does not suffer from either attendant loss of gel caused by migration or weak adhesive properties when the gel barrier
12
is formed.
Therefore, there exists a need in the blood collection art for an improved means of dispensing gel into a collection tube in an inexpensive and efficient manner which promotes both quick formation of the
Brown Rudnick Freed & Gesmer
Kim John
Leonardo Mark S.
Sherwood Services AG
Sorell Peter B.
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