Patent Description:
Conventionally, centrifuging of whole blood samples has been used for plasma extraction from the whole blood sample. However, recent developments in diagnostics, particularly in near patient care or point-of-care (POC) testing has presented many challenges for this conventional technique. Near patient blood testing often requires rapidly obtained test results with small volume collection samples, for example, a blood sample collected using a capillary draw. Therefore, other techniques including filtering, hydrodynamic branch flow extraction, dielectrophoresis separation, acoustic focusing, and magnetic separation have been developed. However, all of these methods have various limitations. For example, many of these methods have one or more drawbacks including the need for high fold dilution, reliance on external hardware, lower plasma yield, long separation times, high cellular contamination, and significant sample hemolysis.

Specifically, track etched membranes have been used to separate a plasma portion from whole blood. The advantage of track etched membranes is the uniform pore size and relatively small surface area as compared to other filtration membranes. The potential low non-specific binding characteristics of track etched membranes is very attractive for detecting low concentration analytes such as troponin in a cardiac patient. While direct filtration using track etched membranes is limited due to clotting, a tangential flow process has shown much better performance. A multi-pass reciprocating process using a track etched membrane to extract plasma from whole blood outperforms other cross flow hydrodynamic based technologies in plasma yield, cellular contamination, and separation time. However, the system requires a complicated power mechanism and control system including optical sensors.

Therefore, a need exists for a simplified system that can easily be used for near patient care or point-of-care (POC) testing
<CIT> discloses a device for processing and producing autologous platelet-rich plasma.

The present invention is directed to a filtration cell for a biological sample having an outer housing having a first end, a second end, and a sidewall extending therebetween and defining a first chamber and an inner housing having a first end, a second end, and a sidewall extending therebetween and defining a second chamber. The inner housing is disposed within the first chamber and rotatable with respect to the outer housing and at least a portion of the inner housing includes a filtration membrane. Upon rotation of the inner housing with respect to the outer housing, the filtration membrane is adapted to allow a first portion of the biological sample to pass from the first chamber into the second chamber and to restrain a second portion of the biological sample in the first chamber. The filtration cell may further include a closure sealing the first end of the outer housing and the first end of the inner housing.

Rotation of the inner housing with respect to the outer housing causes a tangential flow of the biological sample contained in the first chamber over the filtration membrane of the inner housing. The rotation axis of the inner housing may be coaxial with a central axis of the outer housing or the rotation axis of the inner housing may be offset from a central axis of the outer housing. The rotation may be provided by a biasing member acting on the inner housing. The biasing member may be a spring. In certain embodiments, the inner housing may be movable in a direction parallel to a central axis of the outer housing.

In certain embodiments, a pressure differential may be created across the filtration membrane by introducing a positive pressure into the first chamber or by creating a vacuum in the second chamber.

In certain embodiments, an inner surface of the outer housing sidewall may include grooves and/or include a port for receiving the biological sample.

The filtration cell may further include an air-permeable liquid seal between an interior surface of the sidewall of the outer housing and an exterior surface of the sidewall of the inner housing.

In some embodiments, the distance from the first end of the outer housing to the second end of the outer housing may be larger than the diameter of the outer housing and the distance from the first end of the inner housing to the second end of the inner housing may be larger than a diameter of the inner housing. In other embodiments, the distance from the first end of the outer housing to the second end of the outer housing may be smaller than the diameter of the outer housing and the distance from the first end of the inner housing to the second end of the inner housing may be smaller than the diameter of the inner housing.

In certain embodiments, the filtration membrane may be a track-etched membrane. In other embodiments, the filtration membrane may be a fibrous membrane.

The present invention is also directed to a method of filtering a biological sample. A biological sample is placed in the first chamber of a filtration cell as described above. The inner housing of the filtration cell is rotated with respect to the outer housing, and a filtrate is collected in the second chamber.

In certain embodiments, a pressure differential may be created across the filtration membrane by introducing a positive pressure into the first chamber or by creating a vacuum in the second chamber. In other embodiments, the inner housing may be moved in a direction parallel to a central axis of the outer housing while it is being rotated.

A biasing member may rotationally bias the inner housing with respect to the outer housing. The biasing member may be a compression spring or a torsional spring. An engagement element may hold the biasing member in a biased position and release of the engagement element and the biasing member may provide the rotational force to the inner housing.

The present invention is also directed to a filtration cell for a biological sample including an outer housing having a first end, a second end, and a sidewall extending therebetween and defining a first chamber, an inner housing having a first end, a second end, and a sidewall extending therebetween and defining a second chamber, and a rotation element rotatable with respect to the outer housing and the inner housing. The inner housing is disposed within the first chamber and the rotation element is disposed within the second chamber. At least a portion of the inner housing is a filtration membrane. Upon rotation of the inner housing with respect to the outer housing, the filtration membrane is adapted to allow a first portion of a biological sample to pass from the second chamber into the first chamber and to restrain a second portion of the biological sample in the second chamber. The filtration cell may further include a closure sealing the first end of the outer housing and the first end of the inner housing.

Rotation of the rotation element with respect to the inner housing causes a tangential flow of the biological sample contained in the second chamber over the filtration membrane of the inner housing. The rotation axis of the rotation element may be coaxial with a central axis of the inner housing or the rotation axis of the rotation element may be offset from a central axis of the inner housing. The rotation may be provided by a biasing member acting on the rotation element. The biasing member may be a compression spring or a torsional spring. In certain embodiments, the rotation element may be movable in a direction parallel to a central axis of the outer housing.

In certain embodiments, a pressure differential may be created across the filtration membrane by introducing a positive pressure into the second chamber or by creating a vacuum in the first chamber.

In certain embodiments, the outer housing sidewall may include a port for extracting the filtered portion of the biological sample. In other embodiments, the rotation element may include grooves.

The present invention is also directed to a method of filtering a biological sample. A biological sample is placed in the second chamber of a filtration cell as described above. The rotation element of the filtration cell is rotated with respect to the inner housing, and a filtrate is collected in the first chamber.

In certain embodiments, a pressure differential may be created across the filtration membrane by introducing a positive pressure into the second chamber or by creating a vacuum in the first chamber. In other embodiments, the rotation element may be moved in a direction parallel to a central axis of the inner housing while it is being rotated.

A biasing member may provide the rotational force to the rotation element. The biasing member may be a compression spring or a torsional spring. An engagement element may hold the biasing member in a biased position and release of the engagement element and the biasing member may provide the rotational force to the rotation element.

The present invention is directed to a filtration cell for a biological sample and a method of filtering a biological sample for the purpose of isolating one component or fraction of a biological sample from another component or fraction of the sample. In one configuration, the biological sample may include whole blood from which a plasma portion is to be separated.

As shown in <FIG>, the filtration cell <NUM> includes an outer housing <NUM>, an inner housing <NUM>, and a closure <NUM>.

The outer housing <NUM> may have an open first end <NUM>, a closed second end <NUM>, and a sidewall <NUM> extending therebetween. The sidewall <NUM> defines a first chamber <NUM>. The outer housing may take any suitable shape but is preferably substantially cylindrical.

The inner housing <NUM> may have a first end <NUM>, a second end <NUM>, and a sidewall <NUM> extending therebetween. The sidewall <NUM> defines a second chamber <NUM>. The inner housing <NUM> may take any suitable shape but is preferably shaped to complimentarily be received within the interior of the outer housing <NUM>. The inner housing <NUM> may have three portions, a filtering portion <NUM>, a shaft portion <NUM>, and an extension portion <NUM>. The filtering portion <NUM> and at least a part of the shaft portion <NUM> of the inner housing <NUM> may be disposed within the first chamber <NUM> of the outer housing <NUM>.

The closure <NUM> comprises a flange portion <NUM> and a central passageway <NUM> passing through the flange portion <NUM> and having a first end <NUM> and a second end <NUM>. The flange portion <NUM> is adapted to be removably connected to the first open end <NUM> of the outer housing <NUM>. The connection between the closure <NUM> and the outer housing <NUM> may take any suitable form including, but not limited to, a threaded connection and a snap-fit connection.

When the closure <NUM> is connected to the outer housing <NUM>, the first end <NUM> of the central passageway <NUM> extends above the flange portion <NUM> of the closure <NUM> and outside of the first chamber <NUM> of the outer housing <NUM> and the second end <NUM> of the central passageway <NUM> extends below the flange portion <NUM> and inside of the first chamber <NUM> of the outer housing <NUM>. The shaft portion <NUM> of the inner housing <NUM> extends through the central passageway <NUM> of the closure <NUM>. At least the extension portion <NUM> of the inner housing <NUM> and, optionally, a part of the shaft portion <NUM> of the inner housing <NUM> extend beyond the first end <NUM> of the central passageway <NUM>. In this manner, the closure <NUM> closes the first open end <NUM> of the outer housing <NUM> and the first end <NUM> of the inner housing <NUM> and holds them in a fixed position relative to one another, with the inner housing <NUM> at least partially received within the outer housing <NUM>.

As shown in <FIG> and <FIG>, an annular seal <NUM> may be provided on the second end <NUM> of the central passageway <NUM> of the closure <NUM> to provide a seal between the inner surface <NUM> of the sidewall <NUM> of the outer housing <NUM> and the closure <NUM>. Alternatively, the annular seal <NUM> may be provided adjacent the inner surface <NUM> of the sidewall <NUM> of the outer housing <NUM> to provide a seal between the inner surface <NUM> of the sidewall <NUM> of the outer housing <NUM> and the closure <NUM>. The annular seal <NUM> may also provide a seal around the shaft portion <NUM> of the inner housing <NUM>. The seal <NUM> may be air permeable and may be a hydrophobic porous material or simply a hydrophobic surface with a minimum gap which acts as a liquid barrier.

The filtering portion <NUM> of the inner housing <NUM> includes in the sidewall <NUM> at least one filtration membrane <NUM>. In use, a biological specimen intended for separation into at least two components can be provided within the first chamber <NUM> in an initial sample receiving space defined between an inner surface <NUM> of the sidewall <NUM> of the outer housing <NUM> and an outer surface <NUM> of the inner housing <NUM>. Upon application of rotation to at least a portion of the filtration cell <NUM>, as will be discussed herein, a portion of the biological specimen held within the first chamber <NUM> can pass from the first chamber <NUM> into the second chamber <NUM>, defined within the interior of the inner housing <NUM>, through the filtration membrane <NUM>. A plurality of filtration membranes <NUM> may be provided as shown in <FIG>, <FIG>, <FIG> and <FIG>.

The filtration membrane <NUM> may be made from any suitable material capable of filtering the biological sample including, but not limited to fibrous membranes and track etched membranes. For example, the filtration membrane <NUM> may be made from a track-etched membrane comprising a thin film including discrete pores. In certain embodiments, the film may be formed through a combination of charged particle bombardment or irradiation and chemical etching providing increased control over the pore size and density. More specifically, the filtration membrane <NUM> may be a polycarbonate track-etched membrane (PCTE membrane). In certain configurations, a track-etched membrane may have a thickness of about <NUM>-<NUM>. In other configurations, a fibrous membrane may have a thickness of > <NUM>. In many sample separation procedures, a thinner membrane requires smaller initial sample collection volumes.

It is contemplated herein that the inner housing <NUM>, specifically the filtering portion <NUM>, may have many different configurations in which the filtration membrane <NUM> is supported by a housing element. The inner housing <NUM> may include different openings supporting a filtration membrane <NUM> across which a component of the biological specimen may pass while restraining at least another component of the biological sample. In one configuration, the filtration membrane <NUM> allows a plasma portion of a whole blood specimen to pass through the filtration membrane <NUM>, while restraining the remaining portions of the whole blood specimen. As shown specifically in <FIG>, the inner housing <NUM> includes a plurality of vertically disposed indentations <NUM> or non-cut through channels disposed within the sidewall <NUM> of the filtering portion <NUM>. The filtration membrane <NUM> is supported across the indentations <NUM> by adjacent support regions <NUM>. In one embodiment, an aperture <NUM> is provided at the bottom end <NUM> of at least one indentation <NUM>. In one configuration, an aperture <NUM> is provided at the bottom end <NUM> of each indentation <NUM>. As a first component of the biological sample, such as plasma, is separated across the filtration membrane <NUM>, the separated component, such as plasma, flows along the indentations <NUM>, which act like channels, and is directed into the apertures <NUM>. The separated plasma passes through the apertures <NUM> and is collected within the second chamber <NUM> disposed within the interior of the inner housing <NUM>. In one configuration, the filtration membrane <NUM> is disposed over both the indentations <NUM> and the apertures <NUM>. In a further configuration, the filtration membrane <NUM> is wrapped around a substantial portion, such as the entirety of, the filtering portion <NUM>, and is supported by the support regions <NUM>.

Alternatively, the indentations <NUM> may be provided with a slit or vertical opening which extends along a portion of, or the entirety of, the indentation <NUM>. The slit functions in the same manner as the aperture <NUM> in order to allow passage of the plasma into the second chamber <NUM> disposed within the interior of the inner housing <NUM> after it is separated by the filtration membrane <NUM>.

In a further configuration, as shown in <FIG>, the inner housing <NUM> includes a filtering portion <NUM> including a plurality of horizontally disposed indentations <NUM> or non-cut through channels disposed within the sidewall <NUM>. A plurality of vertically disposed apertures <NUM> or cut-through channels are also disposed adjacent the horizontally disposed indentations <NUM>. In one configuration, the inner housing <NUM> includes one vertically disposed aperture <NUM>. In a further configuration, the inner housing <NUM> includes two vertically disposed apertures <NUM>. In yet a further configuration, the inner housing <NUM> includes a plurality of vertically disposed apertures <NUM>. The vertically disposed apertures <NUM> function similarly to the apertures <NUM>, as described above, and allow plasma separated by the filtration membrane <NUM> to pass therethrough into the second chamber <NUM> within the interior of the inner housing <NUM>. The horizontally disposed indentations <NUM> are intended to terminate into the vertically disposed indentation <NUM>, such that plasma may freely flow through the horizontally disposed indentation <NUM> and into the vertically disposed aperture <NUM>. In one configuration, the horizontally disposed indentations <NUM> are defined adjacent horizontally disposed support elements <NUM>. These support elements <NUM> support the filtration membrane <NUM> along most of the circumference of the filtering portion <NUM>, such as along almost the entirety of the perimeter of the filtering portion <NUM>.

The outer housing <NUM> may include a port <NUM> in the sidewall <NUM> or a port 56A the closed second end <NUM> to allow a biological specimen intended for separation to be placed in first chamber <NUM> between an inner surface <NUM> of the sidewall <NUM> of the outer housing <NUM> and an outer surface <NUM> of the inner housing <NUM>. The port <NUM> may be closed by a removable closure such including, but not limited to a plug. The outer housing <NUM> may also include grooves on the inner surface <NUM> of the sidewall <NUM> of the outer housing in order to promote mixing of the biological specimen, such as with a sample stabilizer.

In order to effect separation across the filtration membrane <NUM>, at least one of the inner housing <NUM> and the outer housing <NUM> is rotatable with respect to the other of the inner housing <NUM> and the outer housing <NUM>. Rotation of one of the inner housing <NUM> and the outer housing <NUM> with respect to the other of the inner housing <NUM> and the outer housing <NUM>, creates a rotational fluid force which allows the specimen received within the first chamber <NUM> to contact the filtration membrane <NUM> and to allow a component or the specimen, such as plasma, be forced through the filtration membrane <NUM>.

Rotation of the inner housing <NUM> with respect to the outer housing <NUM> may occur by rotating either the inner housing <NUM> or the outer housing <NUM>. Rotation of the inner housing <NUM> or the outer housing <NUM> may be accomplished using any suitable means including, but not limited to, an air-powered motor, an electric motor, a pneumatic motor, and a mechanical motor. Optionally, such motors may be battery powered. A compressed spring <NUM>, as shown in <FIG>, or a torsional spring <NUM>, as shown in <FIG>, may be used. Alternatively, the inner housing <NUM> or the outer housing <NUM> may be rotated manually. If the inner housing <NUM> is being rotated, the rotation device may be attached to the extension portion <NUM> of the inner housing <NUM> while the outer housing <NUM> is held in a stationary position. Alternatively, if the outer housing <NUM> is being rotated, the rotation device may be attached to the outer housing <NUM> while the inner housing <NUM> is held in a stationary position. Rotation of the inner housing <NUM> with respect to the outer housing <NUM> may be coaxial as shown in <FIG> and <FIG> or may be non-coaxial.

Optionally, the inner housing <NUM> may be moved in an up and down motion in a direction parallel to its longitudinal axis <NUM>.

An opening <NUM> to which a pressure unit <NUM> may be connected may be provided in the outer housing <NUM> or through the closure <NUM> into the first chamber <NUM> or the second chamber <NUM> in order to provide and regulate trans-membrane pressure by introducing a positive pressure in the first chamber <NUM> or by creating a vacuum in the second chamber <NUM>.

In use, a sample, for example, whole blood, in placed in the first chamber <NUM> between an inner surface <NUM> of the sidewall <NUM> of the outer housing <NUM> and an outer surface <NUM> of the inner housing <NUM>. Either the inner housing <NUM> is rotated with respect to the outer housing <NUM> or the outer housing <NUM> is rotated with respect to the inner housing <NUM> causing a tangential flow of the sample over the filtration membrane <NUM>. During rotation and movement of the sample over the filtration membrane <NUM> of the inner housing <NUM>, a portion of the sample, for example, the plasma portion of a whole blood sample, passes through the filtration membrane <NUM> into the second chamber <NUM>.

In another embodiment, the filtration cell may have a distance from the first open end of the outer housing to the second closed end of the outer housing is smaller than a diameter of the outer housing and the distance from the first end of the inner housing to the second end of the inner housing is smaller than a diameter of the inner housing such that the outer housing and the inner housing have a disc shape. In this embodiment, the filtration membrane is included on the second end of the inner housing which includes a filtration portion and an extension portion. The extension portion extends from the first end of the inner housing.

In another embodiment, the filtration cell is very similar to the filtration cell <NUM> shown <FIG>. The filtration cell includes an outer housing, an inner housing, a closure, and a rotation element. All elements identified herein with respect to this second embodiment are identical to those described above.

The outer housing may have an open first end, a closed second end, and a sidewall extending therebetween. The sidewall defines a first chamber. The outer housing may take any suitable shape but is preferably cylindrical.

The inner housing may have a first end, a second end, and a sidewall extending therebetween. The sidewall defines a second chamber. The inner housing may take any suitable shape but is preferably cylindrical. The inner housing is disposed within the first chamber of the outer housing.

The closure comprises a flange portion and a central passageway passing through the flange portion and having a first end and a second end. The flange portion is adapted to be removably connected to the first open end of the outer housing. The connection between the closure and the outer housing may take any suitable form including, but not limited to, a threaded connection and a snap-fit connection.

The rotation element may have a first end and a second end and may take any suitable shape including, but not limited to, cylindrical.

When the closure is connected to the first housing, the first end of the central passageway extends above the flange portion of the closure and outside of the first chamber of the outer housing and the second end of the central passageway extends below the flange portion and inside of the first chamber of the outer housing. The first end of the rotation element extends through the central passageway of the closure and the second end of the rotation element is located in the second chamber.

The inner housing includes at least one filtration membrane in the sidewall such that at least a portion of a biological sample placed in the second chamber can pass from the second chamber to the first chamber through the filtration membrane. A plurality of filtration membranes may be provided.

The outer housing may include a port in the sidewall or the closed second end to allow the filtrate to be removed from the first chamber. The port may be closed by a removable closure such including, but not limited to a plug.

The rotation element is rotatable with respect to the outer housing, the inner housing, and the closure. Rotation of the rotation element with respect to the inner housing may be accomplished using any suitable means including, but not limited to, an electric motor, a pneumatic motor, and a mechanical motor. Such motors may be battery powered. A compressed spring or a torsional spring may be used. Alternatively, the rotation element may be rotated manually.

Optionally, the rotation element may be moved in an up and down motion in a direction parallel to its longitudinal axis.

An opening to which a pressure unit may be connected may be provided in the outer housing or through the closure into the first chamber or the second chamber in order to provide and regulate trans-membrane pressure by introducing a positive pressure in the second chamber or by creating a vacuum in the first chamber.

In use, a sample, for example, whole blood, in placed in the second chamber. The rotation element is rotated with respect to the inner housing causing a tangential flow of the sample over the filtration membrane. During rotation and movement of the sample over the filtration membrane of the inner housing, a portion of the sample, for example, the plasma portion of a whole blood sample, passes through the filtration membrane into the first chamber.

Claim 1:
A filtration cell (<NUM>) for a biological sample comprising:
an outer housing (<NUM>) having a first end (<NUM>), a second end (<NUM>), and a sidewall (<NUM>) extending therebetween, the sidewall defining a first chamber (<NUM>);
an inner housing (<NUM>) having a first end (<NUM>), a second end (<NUM>), at least one aperture (<NUM>), at least one vertical or horizontal indentation (<NUM>) terminating into the at least one aperture (<NUM>) and disposed within a sidewall (<NUM>) of the inner housing (<NUM>), the sidewall (<NUM>) of the inner housing (<NUM>), defining a second chamber (<NUM>), the inner housing (<NUM>) being disposed within the first chamber (<NUM>) and rotatable with respect to the outer housing (<NUM>) and the at least one aperture (<NUM>) providing an opening into the second chamber (<NUM>);
wherein at least a portion of the inner housing (<NUM>) comprises a filtration membrane (<NUM>) wherein the filtration membrane (<NUM>) is disposed over the at least one aperture (<NUM>); and
an opening into the first chamber (<NUM>) or the second chamber (<NUM>) connected to a pressure unit (<NUM>) wherein the pressure unit (<NUM>) regulates a trans-membrane pressure across the filtration membrane (<NUM>);
the filtration cell further comprising at least one support region (<NUM>) adjacent the at least one vertical or horizontal indentation (<NUM>) for supporting at least a portion of the filtration membrane (<NUM>);
wherein upon rotation of the inner housing (<NUM>) with respect to the outer housing (<NUM>), the filtration membrane (<NUM>) is adapted to allow a first portion of the biological sample to pass from the first chamber (<NUM>) into the second chamber (<NUM>) wherein the first portion is directed along the at least one vertical or horizontal indentation (<NUM>) to the at least one aperture (<NUM>) and directly into the second chamber defined by the inner housing through the at least one aperture (<NUM>) and to restrain a second portion of the biological sample in the first chamber (<NUM>).