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This invention relates to a unique element that floats in a physiological fluid undergoing centrifugation and assumes a location encompassing the boundary region between two components of different densities, and facilitates the isolation of a desired component found in the boundary region. Specifically, the floating element greatly facilitates the isolation and separation of the buffy coat from plasma and red blood cells.
Another aspect of the invention is the provision of a device for use both as a syringe for withdrawing physiological fluids and as a chamber for separating the components of the fluids. In its preferred embodiments, the invention is a syringe configured to withdraw fluids from a patient in known fashion and subsequently to be placed directly in the rotor of a centrifuge for separating components of different densities. The syringe is thereafter operated to express the components in serial fashion, for example, into separate cups.
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Processing physiological fluids by centrifugation for separating the fluids into components of different densities is known. Physiological fluids include, for example, peripheral blood, umbilical cord blood, and bone marrow aspirate and ordinarily include cellular components. The physiological fluids subjected to the processes described herein may be obtained directly from a patient being treated, in which case the fluids are autologous, obtained from a donor, or obtained from a plurality of donors, in which case the fluids are homologous. While the objects of the invention are primarily concerned with the treatment of human fluids, it will be appreciated that the methods and apparatus described herein are equally applicable to fluids from other species.
A primary objective of the invention is to isolate and obtain a layer of cells that forms during centrifugation and includes, among other components, platelets, white cells, stem cells, and nucleated cells. This layer is known as the buffy coat, and its density is between that of the red blood cells (1.08-1.09) and that of plasma (1.017-1.026). Plasma with most of the cellular components removed is known as platelet poor plasma (PPP), while plasma with its cellular components is known as platelet rich plasma (PRP). Platelet rich plasma has been found to produce several beneficial effects, such as a more rapid healing of wounds. Thus, another objective of the invention is to provide plasma with an increased level of platelets. This is known as a platelet concentrate (PC) or more broadly as a cell concentrate (CC). A typical concentration is four or more times the native concentration, and a typical ratio of input volume to cell concentrate volume is 6:1. Platelet or cell concentrates obtained by the invention comprises the buffy coat and plasma and may include a small amount of red blood cells.
One of the problems addressed by the present invention is that the specific proportion of the various components and, even, the density of the cells themselves are unique to the particular donor, which precludes an exact a priori determination of the location of any given component in the fluid after centrifugation. For example, the proportion of red blood cells in blood, the hematocrit, varies with each patient, and the average density of the red blood cell component varies with its proportion of neocytes, young red blood cells, whose density is less than 1.08.
Furthermore, the particular technique used to collect the fluids impacts the density of the cells. An anticoagulant is typically added to blood as it is collected, and the amount of anticoagulant and the particular anticoagulant used affects the density, particularly, of red blood cells. This is termed the lesion of collection and results from the effect of the anticoagulant on the osmolarity of the cells. For example, when the anticoagulant is acid citrate dextrose, ACD, red cells become hypo-osmolar and the cells draw water through the dell membrane, which decreases the density of the cells. Other anticoagulants, such as tri-sodium citrate at a concentration of 3.8%, are somewhat hyper-osmolar, which results in shrinkage of the red blood cells and an increase in their density. CPD is iso-osmolar and has much less effect on the density of the cells. CPD and tri-sodium phosphate are preferred and have produced superior results in separations of the kind contemplated herein.
A further factor is that the layers of components form along the radius of centrifugation and are thus cylindrical, which complicates the design of structural elements for separating or collecting the layers.
A system for separating blood into components for producing a platelet concentrate is described in U.S. Pat. No. 6,398,972. The system described in that patent uses a disposable processing unit having two chambers. Blood is drawn into a known syringe and expressed from the syringe into a first chamber of the processing unit. The processing unit is then placed in a centrifuge designed to automatically transfer supernatant fluids from one chamber to another. After a first centrifugation, platelet rich plasma is transferred into the second chamber, and the centrifuge is operated a second time to separate platelets from platelet poor plasma. While this system has many advantages, it has the disadvantage that the blood must be transferred from the syringe to the processing unit, and the centrifuge and the orientation of the processing unit must be controlled to decant the platelet rich plasma to the second chamber.
The first chamber of the system described in the '972 patent includes a disk that is positioned generally at the intersection of the red blood cells and the plasma to prevent decanting of red blood cells into the second chamber.
U.S. Pat. No. 5,456,885 shows a system wherein a collection tube is placed directly in a centrifuge to allow separation of the components. A floating element assumes a position between the plasma and the red blood cells and also acts as a check valve when the lighter phase is expressed from the tube. Systems of this type are, however, not generally capable of separating the buffy coat from the platelet-poor plasma and the red blood cells.
The known centrifuges operate according to a particular protocol when it is desired to obtain a component of intermediate density. For example, when the object is to obtain platelets, it is known to subject blood to a first centrifugation to separate heavier components, such as red blood cells, from plasma, transferring the plasma to a second container or chamber by decanting and then subjecting the plasma to a second centrifugation to separate the plasma from the platelets. The platelets are then separated from the plasma in a second decanting step.
Known techniques for obtaining the desired component of intermediate density are complicated because they require multiple centrifugations and multiple decant or centrifugal transfer steps. Also, the separation of a single component is often complicated because the physical, fluid properties of the desired component may tend to cause it to mix with the other components.
The buffy coat layer is easily disrupted, and when one attempts to express platelet poor plasma through the tip of a syringe, the buffy coat often mixes with the plasma or with the red blood cells. This effectively prevents the expressing of the buffy coat layer either by itself or with only a negligible amount of the other components.
As well, known tubes or syringes designed to be supplied directly to a centrifuge are difficult to use effectively.
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OF THE INVENTION
In accordance with the invention, an improved device is provided for separating components having differing densities in a centrifuge and isolating and dispensing a desired one of these components. The device may take the form of a syringe in the sense that it can be provided with a plunger and operated to draw a fluid, such as blood, bone marrow aspirate, or other physiological fluids, into a chamber through one end and to express the components through that end after separation. The device may, however, be a container of other configurations capable of being placed in a centrifuge and not necessarily designed to operate as a syringe.
A particular objective of the invention is to obtain a cell concentrate from whole blood (including umbilical cord blood), bone marrow aspirate, or other physiological fluid in an efficient fashion through centrifugation and the expressing of the several components. The cell concentrate preferably includes the buffy coat, some red cells, and plasma in desired ratio. The buffy coat is a thin layer that forms during centrifugation and includes mostly all of the cells other than the red blood cells. The buffy coat is known to include platelets, white cells, nucleated cells, and stem sells cells and may include other components as well. Because the buffy coat is a somewhat diffuse layer that is easily disrupted and mixed with the other components, which reduces the effectiveness of the procedure, an object of the invention is to provide a container that can be operated to dispense the cell concentrate without significant mixing of the desired cells with the plasma or the red blood cells. This is accomplished in the preferred embodiments primarily by providing a flow path for the cell concentrate that reduces mixing between the components. In the preferred embodiments, a disk assembly floats in a region containing an interface between plasma and the buffy coat and a diffuse interface between the buffy coat and the red cells, and assists in separating those components. As well, the disk assembly is shaped so that it forms a flow path for the components and reduces turbulence during separation of the components to prevent mixing the components during their expression.
In its preferred embodiment, a disk assembly that is allowed to float in the fluid presents a vertical gradient in the buoyant forces that cause it to assume a position in the region having the desired component, e.g., the buffy coat. This gradient is provided either by the shape of the assembly, by the use of materials of different densities, or by a combination of both. In the preferred embodiment, the disk assembly provides a conical upper surface, and an upper portion of the assembly is made of a material that is less dense than red blood cells but more dense that plasma. A lower portion of the assembly is made of a material that is denser than the red blood cells. Because of the conical shape, the buoyant force provided by the upper element at the boundary between the plasma and the red blood cells and in the region of the buffy coat is a non-linear function of the distance by which the upper element extends into the plasma. The density gradient of the fluids in the boundary region is large, and the use of a floating element with a density gradient also has been found to be beneficial.
The disk assembly according to the invention is designed to encompass both a desired component and a predetermined volume of fluid surrounding the desired component. In the preferred embodiment, the disk assembly comprises two floating parts that are movable relative to each other whereby the entire assembly is caused to assume a desired position after centrifugation, and one part moves toward the other during expression of the fluids to express a desired component or components, e.g., the buffy coat and a predetermined volume of plasma. This structure allows the user to obtain a cell concentrate comprising the buffy coat mixed with plasma at a desired increased concentration.
The invention also relates to perfecting mechanical features, such as a handle for a plunger that accommodates placing the syringe in a centrifuge, and a stand for holding the syringe after centrifugation for facilitating expression of the components. The handle may be detachable or flexible whereby the distance by which it extends from the end of the barrel when the syringe is full is greatly reduced.
It is an object of this invention to provide a device for use in separating the various components of a fluid by placing the fluid in the device, subjecting the device and fluid to centrifugation, and then expressing the components.
It is a further object of this invention to provide a syringe for withdrawing fluids from a container or from the patient, for being placed directly into a centrifuge, and for expressing the separated components in serial fashion with minimal mixing.
BRIEF DESCRIPTION OF THE DRAWINGS
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FIG. 1 is a vertical cross section of a first embodiment of a syringe according to the invention.
FIG. 2 is a vertical cross section of a second embodiment of a syringe according to the invention.
FIGS. 3a and 3b are vertical cross sections of a third embodiment of a syringe according to the invention.
FIGS. 4a and 4b are vertical cross sections of a fourth embodiment of a syringe according to the invention.
FIG. 5 is a side view of a stand, or holder for engaging a syringe of the invention.
FIGS. 6a and 6b are side views of a syringe according to the invention showing a first embodiment of plunger handles that can be detached.
FIGS. 7a and 7b are side views of a syringe according to the invention showing a second embodiment of plunger handles that can be detached.
FIGS. 8a and 8b illustrate a further embodiment of a detachable plunger.
FIG. 9 shows yet another embodiment of a detachable handle.
FIG. 10a illustrates a syringe having a ring that retains a piston, and