Abstract:
A method and apparatus for continuous removal of sub-micron sized particles and other materials attached thereto such as cancer cells and bacteria from blood and other liquids. A centrifuge rotor having a curved shape is offset on a spinning rotor base and creates contiguous areas of low to high centrifugal force depending on the distances from the axis of the rotor base. This creates a density gradient field that separates materials of different densities input to the centrifuge that exit via different outputs. A monitor detects components of the fluid that are mixed with the particles before they exit the centrifuge. If there are any unwanted components detected with the particles logic circuitry changes the speed of rotation of the rotor, and the flow rate of pumps inputting and removing separated fluid and particles to and from the centrifuge until there are no unwanted components in the fluid exiting with the particles from the centrifuge.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation-in-Part of U.S. patent application Ser. No. 13/322,790, entitled “Method and Apparatus for Continuous Removal of Submicron Sized Particles in a Closed Loop Liquid Flow System”, filed on Nov. 28, 2011, which is a National Stage Entry of International Patent Application PCT/US10/46421, entitled “Method and Apparatus for Continuous Removal of Submicron Sized Particles in a Closed Loop Liquid Flow System, filed on Aug. 24, 2010, which claims priority to and the benefit of U.S. Provisional Patent Application Serial No. 61/236,810, entitled “Synthesis of Oxygen Carrying, Turbulence Resistant High Density Submicron Particulates and Method for Their Continuous Retrieval from the Blood Including Submicron Size Perfluorocarbon Emulsion and PolyHb Dual-Cored Oxygen Carries (DCOC)”, filed on Aug. 25, 2009. The specification and claims thereof are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a method and apparatus for continuous removal of sub-micron sized particles from the blood or other liquids. 
       BACKGROUND OF THE INVENTION 
       [0003]    The blood consists of wide ranges of cells, molecules, ions and water. But, their abnormal degradation or proliferation, their functional changes, and invasion of foreign matters or toxins into the blood call for immediate intervention. Removing unwanted materials from the blood is a solution. Embodiments of the present invention provides for a system and method to specifically remove unwanted targets in the blood by attaching the unwanted target to a high density sub-micron particle and separating the high density sub-micron particle from the blood with density dependent centrifugation. An embodiment of a device as disclosed herein will also be capable of removing specific targets from other liquids and solvents after the targets have been attached to a high density sub-micron particle functionalized to bind to the specific target. 
         [0004]    A high density sub-micron particle as referenced herein may have intrinsic biological function, such as use as a perfluorocabon based artificial oxygen carrier (AOC). After some time, the AOC may have to be centrifugally collected from the blood and removed, by taking advantage of their density being higher than that of the blood components. 
         [0005]    The benefits of other types of high density sub-micron particles may be found in their ability to capture the desired targets after the sub-micron high density particles are functionalized to conjugate with the specific cells, molecules and ions in the blood. The sub-micron high density particles may be able to capture the circulating tumor cells (CTC), sickle cell hemoglobin (HbS), toxins, irons etc. in the blood and then be retrieved from the circulation using the specialized centrifuge rotor described herein, after the targets bind to the binding partner located on a sub-micron high density particles. 
         [0006]    Removing the sub-micron high density particles as described herein will be possible with aphaeresis instruments of various types already available. However, the instruments already available are tuned for separating molecules and cells found in blood which span a limited range of densities. The densities of sub-micron particles of interest are 1.9 gm/ml or higher and are significantly higher than those of the highest density component found in blood, namely 1.2 g/ml of RBC, and most synthetic organic and polymeric materials. Separating materials with such large differences in density is carried out with a rotor as described herein rather than those described for use in conventional clinical aphaeresis instruments. 
         [0007]    An embodiment of a rotor as described herein will continuously or intermittently isolate high density sub-micron particles from blood components (for example whole blood or subfraction thereof) continuously and quickly. In one embodiment, since the separation is continuous, there will be no limits in the volume of materials to be centrifuged. In one embodiment of the rotor, the volume of rotor is no more than about 15 mls and counting the volumes of the tubes that provide flow to the rotor and the tubes that direct the liquid from the rotor through the treatment process the volume will be less than 70 mls. Thus, the volume of exo-corporeal treatment will be about 85-100 mls. In another embodiment the rotor can be used to continuously or intermittently isolate high density sub-micron particles from other biological fluids, cell lysates, macromolecule or polymer solutions etc. 
       SUMMARY OF THE INVENTION 
       [0008]    One embodiment of the present invention provides for a rotor for a centrifuge used to separate a mixture of components in a fluid having different densities, the rotor comprising a rotor base having a central axis and the rotor base is rotated about the central axis when the centrifuge is in use. A first rotor element that is curved and is attached to and has an orientation extending away from the rotor base, the first rotor element having a first end and a second end; and a second rotor element that is curved and is attached to and has an orientation extending away from the rotor base, the second rotor element having a first end and a second end, the second end of the first rotor element being connected to the first end of the second rotor element to form a composite rotor element; wherein the composite rotor element is positioned on the rotor base so that the first end of the first rotor element and the second end of the second end of the second rotor element are at different distances from the central axis wherein the composite rotor element traverses 180° or less around the axis of rotation of the rotor base. The rotor base with composite rotor element mounted thereon is rotated the orientation of the composite rotor element on the rotor base and creates a density gradient that separates two components of the mixture of components that is input to the composite rotor element, where the two components have different densities, and a first of the two components moves in a first direction inside composite rotor element and is removed from the composite rotor element at the first output port while a second of the two components moves in a second, opposite direction inside the composite rotor element and is removed from the composite rotor element at the second output port. 
         [0009]    Optionally a monitor port through the sidewall of composite rotor element can be included, the monitor port being closer to the second output port at the second end of the second rotor element than the input port is, the monitor port being used to extract a sample of the second of the two components moving toward the second output port, the sample being used to determine if the first of the two components has been separated from the second component. In addition an outwardly extending end at the first end of the first rotor segment and at the second end of the second rotor segment can be included, wherein as the rotor these two ends create a pressure pushing the first component of the mixture of components toward the first output port and pushing the second component of the mixture of components toward the second output port. A sensor can be connected to the monitor output port to monitor the sample of the second of the two components moving toward the second output port and extracted at the monitor port for the presence of any of the first of the two components, the sensor generating an output signal if any of the first of the two components is present; and electronics receiving the output signal from the sensor, the electronics causing a change in the rate at which the first of the two components is removed from the centrifuge at the first output port, and changing the rate at which the second of the two components is removed from the centrifuge at the second output port to eliminate the presence of any of the first of the two components in the sample taken at the monitor output port, thus assuring there is none of the first of the two components present with the second of the two components exiting the centrifuge at the second output port. The electronics can also cause a change in the rate at which the mixture of components is input to the composite rotor element to assure there is none of the first of the two components present with the second of the two components exiting the composite rotor element at the second output port. 
         [0010]    Additionally, a monitor port through the sidewall of the composite rotor element, the monitor port being closer to the second output port at the second end of the second rotor element than the input port is, the monitor port being used to extract a sample of the second of the two components moving toward the second output port, the sample being used to determine if the first of the two components has been separated from the second component. Further still, an outwardly extending end at the first end of the first rotor segment and at the second end of the second rotor segment is included, wherein as the rotor turns these two ends create a pressure pushing the first component of the mixture of components toward the first output port and the second component of the mixture of components toward the second output port. The rotor base with composite rotor element mounted thereon is rotated the orientation of the composite rotor element on the rotor base creates a density gradient that separates two components of the mixture of components that is input to the centrifuge housing, where the two components have different densities, and a first of the two components moves in a first direction inside the centrifuge housing and is removed from the centrifuge housing at the first output port while a second of the two components moves in a second, opposite direction inside the centrifuge housing and is removed from the centrifuge housing at the second output port. In addition, a sensor connected to the monitor output port to monitor the sample of the second of the two components moving toward the second output port and extracted at the monitor port for the presence of any of the first of the two components, the sensor generating an output signal if any of the first of the two components is present; and electronics receiving the output signal from the sensor, the electronics causing a change in the rate at which the first of the two components is removed from the centrifuge at the first output port, and changing the rate at which the second of the two components is removed from the centrifuge at the second output port to eliminate the presence of any of the first of the two components in the sample taken at the monitor output port, thus assuring there is none of the first of the two components present with the second of the two components exiting the component rotor element at the second output port. The electronics can also causes a change in the rate at which the mixture of components is input to the component rotor element to assure there is none of the first of the two components present with the second of the two components exiting the component rotor element at the second output port. 
         [0011]    Another embodiment provides a rotor for a centrifuge used to separate whole blood from other artificial blood having a density higher than any of the components of the whole blood, the rotor comprising a rotor base having a central axis and the rotor base is rotated about the central axis when the centrifuge is in use; a first rotor element that is curved and is attached to and has an orientation extending away from the rotor base, the first rotor element having a first end and a second end; and a second rotor element that is curved and is attached to and has an orientation extending away from the rotor base, the second rotor element having a first end and a second end, the second end of the first rotor element being connected to the first end of the second rotor element to form a composite rotor element; wherein the composite rotor element is positioned on the rotor base so that the first end of the first rotor element and the second end of the second end of the second rotor element are at different distances from the central axis wherein the composite rotor traverses about 180° around the axis of rotation of the rotor base and contains a chamber therein. 
         [0012]    The rotor base with composite rotor element mounted thereon is rotated, and the orientation of the composite rotor element on the rotor base creates a density gradient that separates the whole blood from the artificial blood where the components of the whole blood have a lower density than the artificial blood, and a first of the whole blood moves inside the composite rotor element toward and is removed from the composite rotor element at the first output port while the artificial blood moves inside the composite rotor element and is removed from the composite rotor element at the second output port. Additionally, a monitor port through the sidewall of the component rotor element is added, the monitor port being closer to the second output port at the second end of the second rotor element than the input port is, the monitor port being used to extract a sample of the artificial blood moving toward the second output port, the sample being used to determine if the whole blood has been completely separated from the artificial blood. Further, an outwardly extending end at the first end of the first rotor segment and at the second end of the second rotor segment can be included, wherein as the rotor turns, these two ends create a pressure pushing the whole blood toward the first output port and the artificial blood toward the second output port. Further still, a sensor connected to the monitor output port to monitor the sample of the artificial blood moving toward the second output port and extracted at the monitor port to test for the presence of any whole blood components, the sensor generating an output signal if any of the whole is present; and electronics receiving the output signal from the sensor, the electronics causing a change in the rate at which the whole blood is removed from the centrifuge at the first output port, and changing the rate at which the artificial blood is removed from the centrifuge at the second output port to eliminate the presence of any of the whole blood in the sample taken at the monitor output port, thus assuring there is none of the first of the two components present with the second of the two components exiting the centrifuge at the second output port. The electronics can also causes a change in the rate at which the mixture of whole blood and artificial blood is input to the composite rotor element to assure there is none of the whole blood components present with the artificial blood exiting the composite rotor element at the second output port. 
         [0013]    In another embodiment a method of separating components in a fluid based upon a difference in density of the components in the fluid when the components are mixed together comprising the steps of providing to a rotor as described herein the fluid containing the mixed together components to be separated based upon the difference in density of the mixed together components and continuously flowing the components in the fluid to the rotor while the rotor is spinning. The components in the fluid are separated based upon the difference in density of the mixed together components with the use of centrifugal force when the rotor is spinning. The components having a first density are collected via a first tube located at a first position on the rotor and the components having a second density are collected via a second tube located at a second position on the rotor and a the components having a third density are collected via a third tube at a third position on the rotor. The components having a first density comprise high density sub-micron particles that have a density different than the components with a second density or a third density and wherein the high density sub-micron particles are functionalized to capture a first component from the components mixed together in the fluid. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention will be better understood upon reading the following Detailed Description in conjunction with the drawings in which: 
           [0015]      FIG. 1  is a perspective view of the novel centrifuge that utilizes density gradient separation to efficiently remove particulate artificial oxygen carriers from blood or other biofluids; 
           [0016]      FIG. 2  is a top view of the novel centrifuge that better shows the novel rotor used in the centrifuge; and 
           [0017]      FIG. 3  is a linear graphical representation of the novel rotor of the centrifuge. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    As used herein “a” and “the” means one or more unless otherwise specified. 
         [0019]    The term “about” as used herein is a flexible word with a meaning similar to “approximately” or “nearly”. The term “about” indicates that exactitude is not claimed, but rather a contemplated variation. Thus, as used herein, the term “about” means within 1 or 2 standard deviations from the specifically recited value, or±a range of up to 20%, up to 15%, up to 10%, up to 5%, or up to 4%, 3%, 2%, or 1% compared to the specifically recited value. 
         [0020]    The term “comprising” as used in a claim herein is open-ended, and means that the claim must have all the features specifically recited therein, but that there is no bar on additional features that are not recited being present as well. The term “comprising” leaves the claim open for the inclusion of unspecified ingredients even in major amounts. The term “consisting essentially of” in a claim means that the invention necessarily includes the listed ingredients, and is open to unlisted ingredients that do not materially affect the basic and novel properties of the invention. A “consisting essentially of” claim occupies a middle ground between closed claims that are written in a closed “consisting of” format and fully open claims that are drafted in a “comprising&#39; format”. These terms can be used interchangeably herein if, and when, this may become necessary. Furthermore, the use of the term “including”, as well as other related forms, such as “includes” and “included”, is not limiting. 
         [0021]    During the continuous flow of liquid, a rotor as described herein is spinning and designed to separate the components of the liquid according to the densities of components located within the fluid and collect the components of highest, lowest and other defined densities via tubes. The blood or other fluid or solution having components to be separated will enter through a port (for example near in the middle of the rotor) and the components will be separated to high density on one end of the rotor and low density on the other end. Components with densities between the two limits will concentrate at a position between the two ends for example near in the middle of the rotor. The three different density fractions will leave through their own ports. The entering flow rate of blood or other fluid solution will often be determined by an external requirement such as the status of a patient and the desired purity of separation. The flow rate can be adjusted by a dedicated pump. In one embodiment to adjust the exit flow rates through all three exit ports only two pumps are used. The rate of each outward flow rate will be defined by the type of high-density sub-micron particles used (i.e whether or not it is surface activated to capture a target substance), the amounts of target expected to be captured by the sub-micron particles, and the source fluid. Typically, the rate of flow of a fluid such as blood entering the rotor should be in compatible with the rates of blood flows in the blood vessels of the subject, around 32 ml/min. Thus total flow rate from the three output ports should be 32 ml/min according to one embodiment of the present invention. In one embodiment, the flow rate through each tube carrying fluid to and away from the rotor will be limited by mechanism employed to ensure that the entering and exit tubes remain kink-free as the rotor spins (several methods are currently used in aphaeresis systems). The rotor and method as described according to one embodiment of the present invention distinguishes itself from other clinical aphaeresis rotors by collecting all of the naturally occurring components of blood in a single flow path, separate from materials with buoyant densities higher than 1.2 g/ml. In the event these particles are designed to attach to a specific naturally occurring blood component, then that component will also be separated along with the particles from naturally occurring components of blood. Such particles are referred to as centrifugally retrievable target activated sub-micron particles, thus rTAP and have a density higher than the density of naturally occurring components of blood. Examples of cells, molecules, and ions that can be continuously retrieved with the proposed centrifugal device from the circulating blood include circulating tumor cells, ABO type red blood cells, macrophages, sickle cell hemoglobin, AOC, antigens, antibodies, drugs, toxins, and irons but are not limited thereto. 
         [0022]    A rotor according to one embodiment of the present invention would be able to separate continuously any particles in the flowing liquid through the rotor according to their densities when the system is exerting centrifugal force on the liquid. As the densities of targeted cells and molecules are sufficiently made higher by attaching to the retrievable high density sub-micron particles such as nanoparticles (referred to herein as high-density, retrievable sub-micron particles or rP), the target cells and molecules would establish their unique density profile of relative narrow range that can be separated with the proposed device. Retrieval of particle bound CTC, HbsS, AOC, by itself acting as high density sub-micron particles (see U.S. patent application publication US 2012/0164231 and US 2014/0008301) would offer significant benefit to the patient. The components bound to such particles will be referred to as targets and target activated rP will be referred to as rTAP, here after. 
         [0023]    Referring now to  FIG. 1 , an embodiment of the rotor is illustrated. The case of the centrifuge is not shown in  FIG. 1  to make the drawing simpler so the invention can be better understood. Rotor  24  comprises a circular rotor base  25  that is mounted on an axis  27  to a motor driven shaft (not shown). As shown in  FIG. 1  rotor base  25  is rotated in a counter clockwise direction for the rotor  24  configuration shown and described herein. The blood mixed with high density particles (rP or rTAP) enter at port  31  of the rotor consisting of elements  26   a  and  26   b  and their position on rotor base  25 , to create a density based gradient that separates RBC, of which light density plasma exits at port  29  and the high density particles (with or without targets depending on the desired outcome) exits from port  28 , while from a mixture of RBC and rTAP that is input to the centrifuge rotor at port  31 . Distances d 3 , d 4  and dr are shown in all of  FIGS. 1 ,  2  and  3  to better understand how the rotor is placed on the base. In one embodiment of the present invention the rotor has a width of each rotor element  26   a  and  26   b  of 0.5 cm, the height is 2 cm, and the length is 15 cm. In one embodiment of the present invention, the volume of the rotor will be only 15 ml. As mentioned the procedure is continuous, but actual separation of components take place within this 15 ml of fluid within the rotor when spinning. The dimensions can be changed responding to the demand, but the same principles of centrifugation apply. 
         [0024]    Rotor  24  is made up of two curved elements  26   a  and  26   b  that are joined together to form a total curved element of 180 degrees or less. The curvature of element  26   b  is slightly larger diameter than that of  26   a  generating slightly higher centrifugal force. The rotor is similar to that of a conventional aphaeresis instrument, but unlike the rotor of a conventional aphaeresis instrument the rotor of  FIG. 1  is 180 degrees of circular rotor on the base and the blood flow rate from the rotor to a receptacle such as a patient is as fast as 32 ml/min. In one embodiment, the rotor can operate at 2400 rpm of spin speed to allow the density gradient to be quickly established and maintained, since the distance between the highest (1.2) and the lowest (1.0) density will be quickly established. Even in the presence of a density as high as 1.9 g/ml, the rotor density gradient will be quickly established and maintained. The density gradient difference between the highest and lowest is still about 0.9 g/ml, but it is spread over the entire length of the rotor (15 cm) to permit subtle difference in density to be recognized with this rotor  24 . In one example, the complete blood enters from port  31  and because the rotor is off-centered from the axis of rotation, the high density components move towards the higher density, i.e. port  28 , while the low density components (e.g. blood components) move towards port  29 . Thus adjusting the relative flow rates of ports  28  and  29 , it would be possible to adjust the profile of density gradient over the entire range of the rotor. In practice, the whole blood enters port  31  under the controlled flow rate by a pump. The flow rates of ports  28  and  29  can also be adjusted with a pair of pumps and the net rates of both pumps define the out flow of blood from the port  30 , but the density of the particles at port  30  will be defined by the ratio of these two pumps. Thus, adjusting the rpm of the centrifuge, pumping rates at  31 ,  28  and  29 , it would be possible to what should be the density of particles, which come out from the port  30  at the known flow rate. In practice, however, the instrument will be usually adjusted so that only the high density retrievable particles and any attached materials should appear from port  28 . 
         [0025]      FIG. 2  is a top view of the novel centrifuge rotor  24  used in a centrifuge. As previously mentioned the different curvatures of rotor elements  26   a  and  26   b  and the offset of composite rotor element  26   a , 26   b  on rotor base  25  are best seen in  FIG. 2 . More particularly, rotor  26   a , 26   b  being belt shaped in the general shape of an ellipsoid with overlapping ends. With rotor  26   a , 26   b  being off centered on base  25  regions of high, medium and low centrifugal force are created depending on the distances from the axis of rotation  27 . Input  31  where the composite mixture of RBC and rTAP is input to the centrifuge rotor is offset from the junction of rotor elements  26   a  and  26   b  and is closer to rTAP output port  28  by a circumferential distance “dx” as shown. In one embodiment the distance d 3  is different from the distance d 4 . In one embodiment, the distance d 3  is less than d 4 . 
         [0026]      FIG. 3  is a linear graphical representation of the novel centrifuge rotor  24  of the centrifuge. This Figure shows how the distance between the face of composite rotor elements  26   a , 26   b  and the stretched form of the axis of rotation  27  of centrifuge rotor  24  changes. Thus, the magnitude of centrifugal force at different regions of centrifuge rotor  24  are depicted by the distance from the axis of rotation  27 , which is stretched and shown as the dotted line at the bottom of  FIG. 2 . The distances d 3 , d 4  and dr are shown in all of  FIGS. 1 ,  2  and  3  to better understand how the figures relate to each other. The degree of change in distance is basically linear and in some embodiments close to flat except where rotor element  26   a  meets rotor element  26   b.  This is due to the fact the curvature of element  26   a  is different than the curvature of element  26   b.  In alternative embodiments of the invention the rate of change in distance may be uniform, and in another alternative embodiment the rate of change may be non-linear. Distances d 3 , d 4  and dr between the face of rotor element  26   a , 26   b  and axis  27  are shown to link  FIG. 3  with  FIGS. 1 and 2 . The input port  31  and output ports  28 ,  29  and  30  and their relative position with respect to the linear depiction of rotor  24  is shown according to one embodiment. 
         [0027]    The whole blood including rTAP obtained from a person who is connected in a closed loop system with a density gradient centrifuge is input to the centrifuge rotor at input port  31 . The whole blood is separated from the rTAP because the density of the rTAPs is greater than the density of the whole blood and any of its individual components. The whole blood is output at output port  29  and port  30  and is returned to the person from whom the blood and rTAP were withdrawn or stored in a container for later use. The rTAP is released from output port  28  and disposed. In addition, at a particular location near where the rTAP exits the centrifuge via rTAP output port  28 , a small sample is removed from the density gradient centrifuge and exits the centrifuge at monitor output port  30 . The sample is input to a red blood cell sensor of a control circuit to be checked for the presence of any remaining red blood cells (RBC) with the rTAP about to exit the centrifuge rotor. If any RBC are detected control circuit adjusts the speed of the blood and retrievable particle pumps that are part of circuit shown in  FIG. 4  to permit the centrifuge rotor to fully separate any remaining RBC from the rTAP before the rTAP reaches monitor output port  30 . This feedback operation assures that only rTAP exit output port  28 . 
         [0028]    The centrifugal field generated in the density gradient centrifuge as novel centrifuge rotor  24  turns about its axis  27  ( FIGS. 1 and 2 ) creates a density gradient field that changes between output ports  28  and  29 . Depending on the shape of rotor elements  26   a  and  26   b,  how they are joined, and how they are positioned on rotor base  25  this density field may change uniformly or it may non-linearly. The result is that the lower density whole blood fraction is separated from the higher density rTAP fraction. In an alternative embodiment another output port may be added somewhere between output ports  28  and  29  to separate intermediate density fractions of blood. The separated whole blood and rTAP are withdrawn through their respective output ports as previously described. The whole blood collected may be subjected to further fractionation. For example, further fractionation may be used to separate platelets and white blood cells from the whole blood in a manner known in the art. 
         [0029]    The basic design of the centrifuge rotor  26   a , 26   b  is a belt shaped semicircular rotor placed slightly off-centered from the axis of rotation as shown in  FIGS. 1 and 2 .  FIG. 1  is a three dimensional view of the rotor  26   a , 26   b  on the spinning rotor base  25 , and  FIG. 2  is a top view of rotor  26   a , 26   b  on the spinning rotor base  25 . In  FIG. 3  the rotor  26   a , 26   b  is shown stretched out in a linear configuration to help show the location of the rotor on rotor base  25  with respect to axis of rotation  27 . 
         [0030]    With reference to  FIG. 3 , as the centrifugation begins the rTAP of the input mixture  31  remain at the wall of the furthest out rotor segment  26   b,  as it is the most dense material and moves towards the higher centrifugal field. This is to the right in  FIG. 3  and the output is indicated as output  28 . In  FIGS. 1 and 2  this is clockwise and the output is indicated as output  28 . All the blood components move toward the left in  FIG. 3  toward closer rotor segment  26   a  because their densities are smaller and they essentially float on top of the rTAP. In  FIGS. 1 and 2  this is counterclockwise and the blood components output is indicated as output  29 . 
         [0031]    More particularly, as the blood and rTAP continue to be injected into rotor  26   a,    26   b  at input  31  (shown in  FIGS. 1-3 ), the blood components move towards the lower centrifugal field while the rTAP move to the higher centrifugal field. The thickness of belt shaped rotor  24  is only 5 mm according to one embodiment. The separation of the rTAP and blood is carried out very quickly and form layers based are density of the particles. With separation being accomplished quickly it is possible maintain the rate of rTAP and blood inflow sufficiently fast to make the process “continuous-flow density separation”. As mentioned above the rTAP leave the rotor at output  28  at the end of highest centrifugal force, while the blood components move leave the rotor at output  29  at the end of lowest centrifugal force. The semicircular rotor has a small offset, bend and protrusion near the junction of segments  26   a  and  26   b  to make the separation of rTAP from the blood complete. In  FIGS. 1 ,  2  and  3  this is indicated by the number  40 , but offset  40  is best seen in  FIGS. 2 and 3 . More specifically, it is possible to enhance the change of centrifugal force by creating a protrusion at the site where distinctive separation of two layers is made, since their sedimentation coefficients are predominantly a function of (1−ρ/δ), the particulates will be positioned close to the outer wall of the rotor when the density equilibrium is established. 
         [0032]    Near at the exit port  28  of the rTAP, there is a monitor output port  30 , from which small samples are taken of the particles flowing toward its output  28  to test the purity of the rTAP. The purity of the rTAP might change slowly over time during centrifugal retrieval of the rTAP so the relative flow rates of pumps must be adjusted to maintain the purity of the rTAP output at its port  28 . Under a given revolution per minute of the rotor, to achieve the optimal removal of rTAP from the blood, using the notation in  FIG. 1 , the following flow conditions must be met according to one embodiment of the present invention. F31=F28+F29+F30 wherein F stands for flow rate. Each flow rate may be controlled by the corresponding monitor/pump, except the flow rate at tube  30  (RBC). The liquid flow rate of the blood entering into the rotor through tube  31 , will be set by the pump P31 at the desired flow rate. The RBC monitors will be mounted at both tubes  28  and  29 , so that there would be little RBC going through either tube by adjusting the flow rate controlled by the pump for each tube. In short, all blood components will be collected through only tube  30 , and the plasma through tube  29  and the highest density particles through tube  28 . 
         [0033]    According to one embodiment of the system and method of the present invention a rotor separates the components in the blood or fluid or solution according to their densities. Some of the components may be attached to high density sub-micron particles and thus they can be separated exclusively from all the blood components or the fluid or the solution. The process of separation can be done during continuous flow of the liquid through the device. The density separation is made possible with the rotor made of connecting at least two rectangular or other forms having a void within for receiving fluid or solution or blood and the forms are curved or circularly bent with two slightly different diameters of them each no longer than ¼ of the circle. The forms are mounted on the circular disc. The circular disc having a hole in the center to form a base of the rotor. A number of tubes connect to openings in the rotor such that the rotor connects fluid that flows via a tube to the rotor with one or more tubes that carry fluid that flows out of the rotor. The tubes may follow a path through the center whole and are configured so that the base will be able to continuously spin, along with the mounted rotor elements without interference from the one or more tubes. One of the tubes is connected through a port to the inner wall of the larger segment rotor and the blood or liquid will enter through the port by a pump, of which rate can be adjusted. The particles that enter the rotor will be separated according to their densities and pour out from the ports  28  and  29 . The rates of outflows will be regulated with two pumps, one pump for each port. From port  29  the lowest density matter (plasma) and port  28  the highest density matter such as rTAP bound with the target will flow out by the pumps. There is a third exit port  30  from which the particles next to the highest density particles, rTAP, such as RBC will exit. The separation will be done continuously with less than 100 ml of the samples in the rotor and feeding tubes. The entire amount of sample will be treated and collected after rising the rotor and feeding tubes. 
         [0034]    The novel density gradient separation technique taught and claimed herein may be used to separate other mixtures of substances having different densities. It may be used to separate and remove metastatic cancer cells from circulating blood. It may also be used for retrieval of low copy mammalian, bacterial or virus cells from blood. It may also be used to remove materials added to blood to enhance tissue and organ imaging. Depending on the application, the specific design requirement of these materials in terms of their size and composition may vary, but common to all of them are the properties summarized earlier, and the tailored ability for continuous retrieval from circulating fluids. 
         [0035]    While what has been described herein is the preferred embodiment of the invention it will be understood by those skilled in the art that numerous changes may be made without departing from the spirit and scope of the invention.