Patent Publication Number: US-2022226811-A1

Title: Vented Dual Port Centrifuge Tube

Description:
RELATED APPLICATION 
     This application claims the benefit of Provisional Application Ser. No. 63/139,934 filed Jan. 21, 2021. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a vented dual port centrifuge tube used to effectively separate and concentrate fluid biological products such as blood, stem cells, bone marrow aspirate and the like into constituent components, which may be conveniently and efficiently aspirated following centrifugation. The apparatus is particularly effective for sequestering platelet rich plasma and bone marrow aspirate for use in surgical, medical and veterinary procedures. 
     BACKGROUND OF THE INVENTION 
     Platelet-rich blood plasma is required for use in various medical procedures. This blood product is particularly effective due to its growth promoting features, which assist greatly in wound healing and bone regeneration. Presently, blood plasma with a high concentration of platelets is utilized for dental implants and other periodontal procedures, facial reconstruction, oral or maxillofacial surgery and chronic wound care. In order to obtain a required concentration of platelets, a blood sample normally must be centrifuged in order to separate the blood into its component blood products (i.e., plasma, red blood cells and platelets). The platelets, typically in a form of a white “buffy coat”, are then separated from the blood sample and sequestered in concentrated form through aspiration. Conventional aspiration techniques often fail to provide a satisfactory concentration of platelets. Cross-contamination between the constituent products is frequently encountered. In recent years there has been an increasing demand for improved, cost effective and easy to operate centrifuge tubes that facilitate the sequestration of platelets and provide for highly pure platelet production, while minimizing cross-contamination between blood components. 
     I have developed various centrifuge assemblies as disclosed in U.S. Pat. Nos. 6,835,353, 7,976,796, 10,300,481 and 10,537,888 to address the foregoing needs and concerns. These products have achieved superior results and proven to constitute a significant improvement over the prior art. I have also developed a dual piston centrifuge tube as disclosed in U.S. Pat. No. 10,987,672. This product especially reduces the risk of cross contamination of sequestered PRP by air and other blood components present in the tube. My dual piston device employs a simple and failure-resistant construction that enables PRP and other constituents of fluid biological products to be obtained in a quick, convenient and reliable manner for use in various surgical, medical and veterinary applications. 
     Notwithstanding the improved results achieved by the foregoing products, an ongoing need continues to exist for improved centrifuge tubes of this type. In particular, it is desirable to employ a construction that is constructed as simply as possible in order to reduce manufacturing complexity and the potential for product failure. In addition, the user should be able to operate the tube more conveniently and smoothly, and without encountering undue sticking or resistance caused by pressure imbalances produced in the tube during the sequestration process. This will better enable users to obtain high quality PRP, bone marrow aspirate and other desired biological constituents. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a simple, efficient and highly reliable centrifuge tube that allows blood, bone marrow aspirate and other fluid biological products to be effectively sequestered and concentrated into constituent components and conveniently aspirated following separation. 
     It is a further object of this invention to provide a dual port centrifuge tube featuring a simpler and less costly construction, and which is easier to use and less prone to product failure than existing centrifuge tubes. 
     It is a further object of this invention to provide a dual port centrifuge tube that is effectively, resists cross-contamination and yields a high quality biological fluid aspirate. 
     It is a further object of this invention to provide a vented dual port centrifuge tube employing a single piston and unique, highly efficient vent pipe construction that effectively equalizes air pressure imbalances in the tube and enables the piston to exhibit a smoother resistance-free movement, which facilitates and improves usage of the tube. 
     It is a further object of this invention to provide a dual port centrifuge tube which enables the manufacture of improved, highly concentrated and pure PRP in a relatively uncomplicated, quick, efficient, safe and effective manner. 
     It is a further object of this invention to provide a dual port centrifuge tube that enables blood product and other fluid biological products to be aspirated in a reliable and extremely safe manner. 
     It is a further object of this invention to provide a vented dual port centrifuge tube that permits a host of chemicals, bodily fluids, and other fluid biological products to be separated and individually aspirated with a low risk of cross contamination or airborne contamination. 
     It is a further object of this invention to provide a dual port centrifuge tube that is particularly effective for sequestering a high concentration of platelet-rich plasma for use in various medical, surgical and veterinary procedures. 
     It is a further object of this invention to provide a dual port centrifuge tube that may be used effectively and efficiently for separating and aspirating a wide range of biological products, including but limited to blood, stem cells, bone marrow aspirate, etc. 
     It is a further object of this invention to provide a uniquely vented centrifuge tube that eliminates the unbalanced operation commonly exhibited by known centrifuge tubes during centrifugation by reducing the amount of air trapped in the tube. 
     It is a further object of this invention to provide a dual port centrifuge tube featuring a configuration and construction that enables PRP and other biological fluids to be more effectively and completely recovered from the tube following centrifugation. 
     This invention results from a realization that a centrifuge tube for separating and aspirating constituent components of a fluid biological product may be significantly and efficiently simplified and yet provide extremely effective results by employing two opposing common inlet and outlet ports at respective ends of the tube, a single piston or diaphragm that is slidable through the tube and a unique flexible vent pipe interconnected between a capped upper end of the tube and the piston. When such a centrifuge tube is operated in accordance with this invention, it effectively equalizes or neutralizes pressure within the tube during injection and aspiration steps and therefore allows the user to perform such steps smoothly, easily and with less resistance or sticking exhibited by the piston. At the same time, the tube is constructed to produce a concentrated and high quality aspirate that may be employed in various surgical, medical and veterinary applications. 
     This invention features a dual port centrifuge tube assembly that includes an elongate tubular receptacle having an interior chamber and closed upper and lower portions. A liquid impermeable piston is mounted within the chamber and is slidable through the chamber while maintaining sealing engagement with an interior surface of the receptacle. A first common inlet and outlet port is formed in the upper portion of the receptacle for communicating with an upper region of the interior chamber above the piston. A second common inlet and outlet port is formed through the lower portion of the tubular receptacle for communicating with a lower region of the interior chamber below the piston. A vent is formed through the upper portion of the receptacle and a flexible vent pipe is communicably interconnected between the vent and the piston in communication with the lower region of the chamber. 
     In a preferred embodiment, the upper portion of the tubular receptacle includes an upper cap through which the vent and the first common inlet and outlet port extend. The vent is preferably spaced apart and distinct from the first common inlet and outlet port. The lower portion of the tubular receptacle may include a substantially flat base through which the second common inlet and outlet port is formed to communicate with the lower region of the chamber. The first common inlet and outlet port communicates with the upper region of the chamber above the piston. 
     The piston may include a body that is sealably and slidably interengaged with the interior sidewall of the tubular receptacle. A passageway may extend vertically through the piston body. The passageway, which is preferably formed centrally through the piston body, may be communicably interconnected between the vent pipe and the lower region of the receptacle chamber. The piston body may further include upper and lower circumferential flanges that are attached to and extend upwardly and downwardly respectively from the piston body. The lower circumferential flange will have a diametric channel formed therein. 
     The second common inlet and outlet port may include a tubular stem that extends into the lower region of the chamber. The stem may include an elbow having a distal end disposed proximate the circumferential flange of the piston and proximate an interior surface of a sidewall of the receptacle. 
     A base may be attached to and depend from the lower portion of the tubular receptacle. Preferably, the base has a cylindrical shape that conforms to the shape and diameter of the tubular receptacle. The base supports the tubular receptacle above an underlying surface and the second common inlet and outlet port may be surrounded by and centrally disposed within the base. 
     In the preferred version of the tube, blood or other biological fluid is introduced into the upper chamber region of the tubular receptacle through the first common inlet and outlet port. This drives the piston downwardly through the receptacle such that air in the lower region of the chamber beneath the piston is pushed upwardly through the passageway of the piston body and through the vent tube. Such air is expelled through the vent in the top of the tube, which equalizes pressure in the tube. When the piston is fully lowered, the diametric channel receives the tubular stem of the second port. The tubular receptacle is then centrifuged a first time to separate the biological fluid into a pair of layers representing respective constituent components (e.g., red blood cells—RBC, and plasma platelet suspension—PPS). The user then aspirates the top sequestered fluid layer (e.g., PPS) through the first common inlet and outlet port. That aspirated constituent is then introduced through the second common inlet and outlet port in the lower end of the receptacle to occupy a lower region of the receptacle chamber. Again, air within the lower region is displaced through the vent tube and vent to equalize pressure within the tube. The receptacle is then centrifuged a second time to separate the fluid constituents into the respective layers within the lower chamber region. In cases where PPS has been introduced into the lower chamber region, the second centrifugation may produce an upper layer of platelet poor plasma (PPP) and a lower buffy coat layer comprising PPS and platelet rich plasma PRP. Most of the upper layer produced within the lower chamber region is then aspirated to leave a remaining fluid within the lower region. The tube is then agitated to mix the remaining fluid (e.g., to mix any remaining PPP with buffy coat). This mixed product is then aspirated, which, in the case of blood sequestration, yields a high quality PRP product. 
     In an alternative embodiment, the second common inlet and outlet port may be offset from the center of the closed lower portion of the tubular receptacle. In such embodiments, a semi-cylindrical base is attached to and depends from the lower end portion of the tubular receptacle such that the second common inlet and outlet port is positioned radially to be at least partially outside of the semi-cylindrical base. This provides syringe access to the second common inlet and outlet port when the centrifuge tube is used as described below. 
     In the alternative embodiment of the invention, the second common inlet and outlet port may include a tubular channel that extends into the interior chamber of the receptacle below the piston. The channel may have a diagonal or slanted upper end to facilitate aspiration of PRP or other constituent fluids from the receptacle. The semi-cylindrical base may include a longitudinal slot formed in the base to facilitate user access to the second common inlet and outlet port. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features and advantages will occur from the following description of a preferred embodiment and the accompanying drawings, in which: 
         FIG. 1  is an elevational and cross-sectional front view of a preferred vented dual port centrifuge tube in accordance with this invention; 
         FIG. 2  is a simplified elevational side view of the tube of  FIG. 1 ; 
         FIG. 3  is a simplified elevational rear view of the preferred tube with a biological fluid, such as a blood sample, being introduced into the receptacle chamber above the piston; 
         FIG. 4  is a view similar to  FIG. 3 , which shows the tube after it is centrifuged a first time to separate the biological fluid into first and second constituent components, e.g., red blood cells and platelet plasma suspension (PPS); 
         FIG. 5  is a similar elevational view of the preferred tube wherein one of the separated constituents, e.g., PPS, is aspirated from the receptacle through the first common inlet and outlet port to raise the piston within the tubular receptacle; 
         FIG. 6  is a similar elevational view of the preferred tube that depicts the introduction of the previously aspirated component through the second common inlet and outlet port into a lower region of the receptacle chamber below the piston; 
         FIG. 7  is a similar elevational rear view of the preferred tube after it undergoes a second centrifugation to separate the constituent component in the lower chamber region into third and fourth constituent components, e.g., platelet poor plasma (PPP) and platelet rich buffy coat (PRB); 
         FIG. 8  is an elevational view of the tube similar to that shown in  FIGS. 3-7  and which depicts the third constituent component being aspirated from the receptacle through the second common inlet and outlet port; 
         FIG. 9  is a similar elevational view that depicts agitation of the tube to mix the third and fourth constituent components remaining in the receptacle to form a final fluid constituent product to be recovered, e.g., platelet rich plasma (PRP); 
         FIG. 10  is a view of the tube similar to that shown in  FIGS. 3-9 , which depicts the tube horizontally orientated for aspiration of PRP remaining in the receptacle; 
         FIG. 11  is an elevational front view of an alternative centrifuge tube in accordance with this invention with a blood sample received in the chamber of the tubular receptacle above the piston; 
         FIG. 12  is a similar view of the alternative tube after it has been centrifuged a first time to separate the blood sample into red blood cells and PPS; 
         FIG. 13  is a view similar to  FIGS. 11 and 12  that depicts the tube after the PPS has been aspirated from the receptacle and with the piston elevated and red blood cells being constrained within the upper chamber region of the receptacle above the piston; 
         FIG. 14  is a view similar to  FIGS. 11-13  and further depicting PPS being introduced into the lower region of the receptacle chamber beneath the piston; 
         FIG. 15  is a view similar to  FIGS. 11-14  after the tube has undergone a second centrifugation to separate the PPS into an upper layer of PPP and a lower layer of PRB; 
         FIG. 16  is a similar view of the alternative tube with the PPP drawn down to a level such that the total fluid remaining in the lower region of the receptacle chamber is less than 7 ml;, and 
         FIG. 17  is a similar view of the alternative tube after the remaining fluid components in the lower region of the receptacle chamber (e.g., PPP and PRB) have been mixed to produce a high quality PRP that is aspirated from the receptacle through the second common inlet and outlet port. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     There is shown in  FIGS. 1-2  a vented dual port centrifuge tube  10  that includes a tubular or cylindrical receptacle  12 . The receptacle is defined by an elongate cylindrical sidewall  13  that extends between closed upper and lower end portions. The closed upper end portion comprises a cap  14  ( FIG. 1 ) that may be either permanently or removably attached to sidewall  13 . The lower end portion includes a generally planar floor  16  that is unitarily connected to sidewall  13  and extends across the bottom of the receptacle. As best depicted in  FIG. 1 , cap  14  preferably includes an interior opening  18  that has a generally truncated conical shape and communicates with a first common inlet and outlet port  20  to facilitate introduction and aspiration of biological fluids into and out of receptacle  12 , as described more fully below. It should be noted that in certain embodiments, the configuration of the cap and cap opening may be simplified or otherwise modified. Indeed, in  FIGS. 2-10 , a simpler and generally planar cap  14   a  is disclosed. In such cases the port  20  may be communicably connected to the interior of receptacle  12  through a straight or otherwise alternatively shaped opening. It should be understood that in all versions of this invention, the cap or other upper end of tubular receptacle has an opening or passageway that defines or communicates with a syringe-engaging common inlet and outlet port for introducing and aspirating biological fluids into and out of the tubular receptacle  12  in accordance with this invention. Nonetheless, the particular configuration and construction of the upper end cap may be varied within the scope of this invention. 
     Receptacle  12  includes an interior chamber  22  that extends from floor  16  to cap  14 . This chamber accommodates blood, chemicals, stem cells, bone marrow aspirate or other biological fluids/products to be centrifuged and aspirated using tube  10  the tube is particularly effective for sequestering and recovering high quality platelet rich plasma (PRP). Nonetheless, it may be employed effectively for separating and recovering various other fluid biological constituents within the scope of this invention. 
     As used herein “centrifuge” and “tube” should be understood to comprise assorted shapes and sizes of vessels, receptacles and containers having an interior chamber for holding a biological product and capable of being centrifuged to aspirate the product into constituent components. The vented dual port, single piston centrifuge tube disclosed herein is not limited to just tubular and elongate configurations, although such configurations will typically be used in preferred embodiments of this invention. 
     A cylindrical skirt  24  is connected unitarily with and depends from floor  16  and/or sidewall  13  of tubular receptacle  12 . In alternative embodiments, skirt  24  may be separate from and releasably attached or affixed to the lower end of receptacle  12 . The cylindrical skirt acts as a base, which stably supports the tubular receptacle in an upright condition on a table or other flat or horizontal surface. In this way, the centrifuge tube does not require a separate rack or holder for support. Cylindrical skirt  24  also securely supports the device upright in a standard centrifuge machine when the tube is centrifuged in accordance with the orientation depicted in  FIGS. 4 and 7  as described more fully below. 
     Tubular receptacle  12  is typically composed of a durable plastic material such as polypropylene or other material suitable for medical or veterinary applications. The tube should be constructed to withstand the forces exerted by centrifuging. In certain applications, shatter-resistant glass may be employed. 
     A plurality of graduated volume markings, not shown herein, but see U.S. Pat. No. 7,976,796 (hereinafter &#39;796), may be formed at various selected intervals along the exterior sidewall  13  of tubular receptacle  12 . Such markings should be made at heights or intervals corresponding to commonly selected volumes of biological product that will be introduced into the tube. Such markings may be varied within the scope of this invention. 
     A vent  26  is formed through cap  14 ,  14   a  to communicably interconnect chamber  22  with the ambient air surrounding tube  10 . Vent  26  may be constructed analogously to the vents disclosed in U.S. Pat. No. &#39;796 and U.S. Pat. No. 10,300,481 (hereinafter &#39;481). In particular, vent  26  may comprise a vent plug that fits through a hole in the cap. The vent is communicably connected with an elongate, flexible vent pipe  28  in order to equalize and neutralize pressure in receptacle  12  during the operation of tube  10  as described below. Vent  26  may feature a through channel that accommodates a filter for trapping contaminants that are pulled into receptacle  12  with the ambient air during operation of the tube, again as described below. Once again, this filter construction may be of the type disclosed in the above-referenced patents. Vent pipe  28  is composed of a flexible yet strong plastic material such as silicone that permits the pipe to be reliably flexed or collapsed during operation of tube  10 . 
     In preferred versions of this invention, cap  14 ,  14   a  is permanently secured to the tubular receptacle. This may be accomplished by ultrasonic welding or other known methods. The upper end of the receptacle may also be formed by a cap or lid that is molded or otherwise formed unitarily with the cylindrical receptacle using techniques known to persons skilled in the art. Alternatively, the end cap may be releasably engaged with an open upper end of receptacle  12  in the manner for example shown in U.S. Pat. Nos. &#39;481 and 10,987,672 (hereinafter &#39;672). The cap may have a partially recessed upper surface as shown in  FIG. 1 , or a flat upper surface as depicted in the remaining figures. The truncated conical inlet  18  shown in  FIGS. 1 and 2  operates analogously to the corresponding opening or channel depicted in U.S. Pat. No. &#39;481 to facilitate introduction and aspiration of biological fluids into and out of the receptacle so that constituent components can be separated using the tube. 
     Vent  26  supports a tubular stem  27 ,  FIG. 1 , that is itself communicably interengaged with an upper end of flexible vent pipe  28 . The opposite lower end  36  of pipe  28  is communicably connected to a tubular fitting  38  that extends generally centrally through a liquid impermeable piston  30 , which piston is itself mounted for slidable reciprocating movement within chamber  22  of receptacle  12 . As described more fully below, this provides for a wholly unique and particularly effective manner for equalizing or neutralizing pressure within tube  10  during the centrifugation and fluid separation process. 
     As previously indicated, first common inlet/outlet port  20  is formed in an upper portion of receptacle  12 , preferably through cap  14 ,  14   a.  It should be understood that in alternative embodiments the first common inlet and outlet port may be formed elsewhere in the upper portion of the receptacle above piston  30 . More particularly first upper inlet/outlet port may comprise a conventional self-sealing construction and employ a standard luer port for releasably and securely interconnecting a hypodermic syringe to the port. Various forms of construction that may be used for the upper end cap  14  and the first common inlet/outlet port  28  are disclosed, for example, in U.S. Pat. No. 6,835,353 (hereinafter Patent No. &#39;353), U.S. Pat. Nos. &#39;481, &#39;796 and &#39;672, the disclosures of which are incorporated herein by reference. Preferably, caps  14 ,  14   a  are composed of polypropylene or other material similar to that formed in the tubular receptacle itself. The common inlet/outlet port may be communicably attached to the caps or alternatively molded together with the cap in a single manufacturing process. 
     As shown in  FIGS. 1 and 2 , piston  30  has a generally cylindrical peripheral shape conforming to the interior shape of sidewall  13 . The piston includes a body  31 ,  FIG. 1 , having upper and lower peripheral flanges  33  and  35  extending respectively upwardly and downwardly therefrom. Body  31  includes an annular peripheral groove  32 , best shown in  FIG. 2 , that accommodates an O-ring or alternative seal  34 , which sealingly and slidably interengages the interior surface of sidewall  13  of tubular receptacle  12 . This allows piston  30  to move longitudinally through chamber  22  during operation of tube  10 , as indicated by double headed arrow  36  in  FIG. 1 . Vent pipe  28  extends through an open upper compartment of piston  30  surrounded by flange  33  and the lower distal end  36  of pipe  28  communicably engages tubular fitting  38 . This fitting is formed centrally and communicably through piston body  31  and features an air passageway  37  that interconnects pipe  28  to an open lower piston compartment  42  surrounded by flange  35 . In this manner, the vent pipe  28  and interconnected vent  26  are communicably interconnected through open lower piston compartment  42  to a lower region of receptacle chamber  22  disposed beneath piston  30 . This provides a unique and very effective means to vent and neutralize pressure in the lower region of chamber  22  during operation of tube  10  as described more fully below. As best shown in  FIG. 2 , a channel  43  is formed diametrically across lower compartment  42  of piston  30 . 
     A lower, second common inlet and outlet port  44  is operatively and communicably connected to a lower region of chamber  22  beneath piston  30 . In particular, inlet/outlet port  44  includes a tubular conduit or stem section  46  that is formed through floor  16  of receptacle  12  and extends longitudinally into interior chamber  22 . Second inlet/outlet port  44  again includes a self-sealing valve port and luer-type interconnection analogous to previously described first port  20 . Port  44  is attached to the exterior surface of receptacle floor  16  within skirt  24  and is communicatively connected through floor  16  to conduit  46 , which extends upwardly from the floor of the receptacle. In alternative embodiments, conduit  46  may be formed separately from and connected to floor  16 . In still other embodiments, conduit  46  may comprise an integral and unitary part of port  44 . Conduit  46  itself is communicably joined to a tubular elbow  48 . As best shown in  FIG. 1 , the proximal end of elbow  48  interengages floor  16 . The distal end of elbow  48  is positioned proximate the interior sidewall surface of the receptacle chamber  22 . Elbow includes a generally vertical portion  52  and a horizontal portion  54 . As best shown in in  FIG. 2 , channel  43  formed diametrically through lower compartment  42  of piston  30  is generally aligned with the horizontal portion  54  of tubular elbow  48 . Accordingly, when piston  30  is in an elevated condition as shown in  FIG. 2 , the piston  30  and diametric channel  43  are raised above and clear of elbow  48 . When the piston is lowered within chamber  22 , as shown in  FIG. 1 , tubular elbow  48  fits neatly within channel  43  of piston  30 . This occurs during use and operation of tube  10  as described more fully below. Otherwise, the exterior connective portion of second common inlet and outlet port  44  supported below floor  16  is constructed and operates analogously to standard luer-type ports as referred to above and in the patents and applications referenced herein. 
     Prior to usage of tube  10 , sealing piston  30  is typically elevated at least somewhat within chamber  22  of receptacle  12 , although in some cases, it may be in the lowered condition shown in  FIG. 1 . Tube  10  is utilized to centrifuge a fluid biological product into its constituent components and then to aspirate one ore more of those components as shown in  FIGS. 3-10 . A preferred representative use for tube  10  is in the separation of a blood sample into constituent blood components. Typically, it is desirable to separate plasma and ultimately platelets, from red blood cells of a blood product in order to derive a highly concentrated platelet rich plasma (PRP) for use in various surgical, medical or veterinary applications. This process is performed using assembly  10  in the following manner. 
     Initially, the empty receptacle  12  is stood upright on its cylindrical base or skirt  24  upon an underlying table or platform. If a separate cover or closure is engaged with tube  10  or either of its ports  20 ,  44 , the cover/closure is removed. Blood product B,  FIG. 3 , is then introduced into the interior chamber  22  of receptacle  12 . Specifically, for example, a 60 ml or other sized hypodermic syringe containing the blood or other biological product is operably engaged with the first or upper self-sealing port  20  in a standard manner. See U.S. Pat. Nos. &#39;353, &#39;796 and &#39;481. The luer port  20  holds the dispensing tip of the syringe in place so that the hypodermic syringe is securely engaged with tube  10 . The syringe is then operated in a conventional manner to introduce blood product B to be separated through port  20  and into interior chamber  22  of receptacle  12 ,  FIG. 3 . As blood is introduced into upper region  60  of chamber  22 , the increasing volume of blood pushes piston  30  downwardly through receptacle  12 , as indicated by arrows  62 . Blood product is added to the receptacle by the syringe in this manner until a selected level of fluid is injected/introduced into the receptacle. Typically, piston  30  is pushed until it engages or is proximate to floor  16  of receptacle  12 . As previously described, tubular elbow  48  is enclosed by the descending piston  30  and specifically received in channel  43  (See  FIGS. 1 and 2 ). Critically, as piston  30  is driven downwardly through the receptacle, flexible vent pipe  28  expands from the coiled or collapsed condition shown in  FIG. 2  to the open and extended condition show in  FIG. 3 . As a result, the increased air pressure generated by piston  30  within the region of chamber  22  below piston  30  is effectively vented from the tube through pipe  28  and vent  26 . Air pressure within tube  10  is effectively neutralized or equalized so that a smooth and stick/resistance-free operation is achieved. Finally, when a selected or desired volume of blood has been added to the receptacle, injection is stopped and the injecting syringe is disengaged from port  20 . For human bloodwork, the selected volume of blood may be, for example, 50-60 mls. This volume is preferred because it typically yields approximately 7 mls of platelet rich plasma after the process is completed. 
     Tubular receptacle  12  is next placed in a centrifuge and counterbalanced by another tube placed in the centrifuge machine. Skirt  24  allows tube  10  to sit stably within the centrifuge. This helps the tube to remain properly balanced while it is being centrifuged. The tube is centrifuged for approximately 90 seconds (although this time as well as the speed of the centrifuge may be varied within the scope of this invention in a manner known to persons skilled in the art) and, as shown in  FIG. 4 , blood B is thereby separated within upper chamber region  60  into a top layer comprising largely platelet/plasma suspension (PPS) and a bottom layer (RBC) comprising primarily red blood cells. At this stage, typically at least 90% of the red blood cells in the blood product are separated from layer PPS and settle within layer RBC. Various known types of centrifuge machines may be employed for the initial centrifuging. A single round or multiple rounds of centrifuging may be utilized at this stage. After the first centrifuging stage is completed, tube  10  is removed from the centrifuge and again supported on its flat base or skirt  24 . Both layers PPS and RBC are held securely in the upper space  60  of chamber  22  above piston  30 . 
     A new syringe is next engaged with port  20  and operated as represented by arrow  66  in  FIG. 5  to aspirate the PPS from upper space  60  of chamber  22 . As indicated by arrow  70 , this draws ambient air inwardly through vent  24  and vent pipe  28  into lower region  72  of chamber  22  beneath rising piston  30 . This effectively counteracts and neutralizes the vacuum being drawn in lower chamber region  22  as the piston is pulled upwardly in response to the aspiration of PPS. Once again, pressure is equalized within the tube and there is much less potential for sticking of the piston and resistance to aspiration of the PPS. The aspiration operation is therefore smoother and facilitated. Aspiration continues in this manner until piston  30  generally reaches the boundary between the PPS and RBC layers. Aspiration is then discontinued and the aspiration syringe is disengaged from port  20 . The red blood cells RBC remain segregated and constrained in diminished space  60  between piston  30  and cap  14 . 
     The syringe holding the retrieved PPS is next engaged with second common inlet/outlet port  44  within skirt  24  according to  FIG. 6 . The syringe is operated to inject the sequestered PPS as indicated by arrow  74  through lower port  44  and connected elbow  48  into lower region  72  of chamber  22 . This substantially fills lower chamber region  72  with the retrieved PPS component. 
     When all of the PPS is reinjected into the lower chamber region  72  of receptacle  12 , the PPS syringe is disengaged from second inlet/outlet port  44  and receptacle  12  is again placed in a centrifuge machine. The tube is then further centrifuged for approximately 5 minutes, although this time may again be varied within the scope of the invention. For both centrifuging steps, centrifuge speeds and times may be adjusted in a manner that will be understood to those skilled in the art. As reflected in  FIG. 7 , the PPS injected into chamber region  72  is separated by the second centrifuging operation into an upper layer of platelet poor plasma (PPP) and a lower layer of platelet rich buffy coat (PRB). Tubular elbow  48  is constructed and positioned such that its distal end or tip  50  is held above the FRB layer and within the PPP layer. 
     As represented in  FIG. 8 , a new syringe is interengaged with second common inlet/outlet port  44  and operated, as indicated by arrow  76 , to aspirate PPP fluid from lower region  72  of chamber  22 . Typically, the syringe is aspirated from receptacle  12  until a total of approximately 7 ml of fluid, consisting of 6 ml PPP and 1 ml PRB remains in chamber  22  below piston  30 . These are typically the amounts remaining when an initial blood product volume of 50-60 mls is subjected to the two-stage centrifugation process in tube  10  as described above. Respective volumes may vary somewhat within the scope of this invention. As PPP is aspirated from tubular receptacle  12 , ambient air is again drawn into the chamber through vent  26  and vent pipe  28  in the manner indicated by arrows  80 . This again neutralizes pressure within lower region  72  of chamber  22  which facilitates aspiration of the PPP. 
     The syringe containing the aspirated PPP is next disengaged from port  44 . The platelets in the (e.g., 1 ml) platelet rich buffy coat layer PRB are then resuspended in the remaining (e.g., 6 ml) PPP layer contained in receptacle  12 . This is typically accomplished as shown in  FIG. 9  by swirling or otherwise gently agitating the tubular receptacle  12 , as shown by double-headed arrows  82 , so that the platelets of fluid layer PRB are effectively re-suspended into layer PPP. This produces a resulting volume of approximately  7  ml of pure and concentrated platelet rich plasma (PRP). 
     Following re-suspension of the buffy coat in the platelet poor plasma to produce the desired PRP, receptacle  12  is oriented horizontally in the manner shown in  FIG. 10 . This positions supportive skirt  24  and second inlet/outlet port  44  such that tubular elbow  48  is oriented with its distal end or tip  50  positioned within the PRP collected against the now lower interior surface of sidewall  13  of receptacle  12 . The user operatively connects a new syringe to the lower port  44  and aspirates the PRP, as indicated by arrow  88 , through port  44  via tubular elbow  48 . By positioning tip  50  of tubular elbow  48  very close to the interior surface of the sidewall  13 , virtually all of the PRP (approximately 7 mls) contained in the receptacle can be aspirated from receptacle  12 . This PRP has an extremely high platelet concentration and purity (approximately 80% or more). The aspirated PRP may then be utilized effectively for desired surgical, medical and veterinary applications. During the final aspiration step, the operation of the syringe is again facilitated because as PRP is withdrawn through elbow  48  and port  44 , ambient air is introduced into region  72  of chamber  22  through vent  26 , interconnected vent pipe  28  and tubular fitting  38  ( FIG. 1 ) formed through piston  30 . The pressure within the tube remains effectively equalized and neutralized. Resistance to movement of piston  30  is reduced and aspiration is facilitated. 
     An alternative vented dual port, single piston centrifuge tube  110  according to this invention is shown&#39;in  FIGS. 11-17 . The capacity, materials composing the tube and many if not most of the components comprising the tube are identical or analogous to those employed in the previously described embodiment. The most significant differences are described below. 
     Tube  110  includes a receptacle  112  featuring an upper portion that includes a cap  114  sealed or otherwise attached to an upper end of a cylindrical sidewall  113 . Cap  114  supports a first, upper inlet and outlet port  120  and a vent  126 . A vent pipe  128  is communicably connected to vent  126  in the manner previously described. Indeed, cap  114 , port  120 , vent  126  and vent pipe  128  are constructed in the manner previously described. 
     Receptacle  112  includes an interior chamber  122  that extends from cap  114  to a floor  116  at the lower end of receptacle  112 . Unlike the previously described embodiment, sidewall  113  of receptacle  112  includes an interior lip or ledge  115  above floor  116  and surrounding a smaller diameter lower portion  117  of chamber  122 . 
     A second common inlet and outlet port  144  is mounted to floor  116 . Port  144  again includes exterior components  145  that feature a self-sealing luer port connection, which will be understood to persons skilled in the art. Port  144  further includes an interior channel  148  that is communicably interconnected to luer port connection  145 . Tubular channel  148  is positioned within lower region  117  of receptacle chamber  122 . The distal tip  150  of channel  148  is angled as shown in  FIGS. 12-15 . This allows the tube  110  to function in the fluid sequestration process as described below. 
     A semi-cylindrical skirt  124 , which forms a base of tube  110 , is interconnected to and depends from the lower end of receptacle  112 . In contrast to the previously described embodiment, lower common inlet and outlet port  144  is offset from the center of the receptacle floor and is interconnected to floor  116  proximate sidewall  113  and at least partially outside of an arcuate slot formed in skirt  124 . Skirt  124  again forms a base that supports receptacle  112  in an upright condition as shown in  FIGS. 12-18 . This provides the user with unhindered access to port  144  so that during use of tube  110 , a syringe may be operably interconnected to port  145  for injecting fluids into and aspirating fluids from lower region  117  of chamber  122 . This process is described more fully below. 
     Sequestration of biological fluids into constituent components and recovery of such components is performed using tube  110  in a manner analogous to that previously described for tube  10  in  FIGS. 3-10 . Once again, the process will be described for the recovery of high quality PRP from a blood sample. However, it should be understood that tube  110  may likewise be used to separate other biological fluids into discrete constituent components in an analogous fashion. 
     A liquid impermeable piston  130  is again slidably mounted within chamber  122  of receptacle  112 . The piston may have a construction identical or similar to that of previously described piston  30 . In the version shown herein, the piston includes a circumferential seal or O-ring  134  that interengages the interior surface of sidewall  13  such that piston  130  is able to slide longitudinally through chamber  122  while maintaining a seal between the upper and lower regions of the receptacle chamber. An air passageway fitting  138  is formed centrally through the piston between upper and lower ends thereof. Air passageway fitting  138  is communicably connected to a lower end of vent pipe  128 . The air passageway fitting may be joined unitarily to the vent pipe as depicted in  FIGS. 11-17 . Alternatively, the vent pipe and air passageway fitting may comprise two separate pieces (see  FIG. 1 ) that are communicably joined by fitting one inside the other, for example. Other alternative means for communicably coupling the vent pipe and air passageway fitting (e.g., tubular couplers) are also encompassed by this invention. The lower end of fitting  138  communicates with a conical or tapered opening  139  of piston  30 . As a result, vent  126  is communicably linked to the lower region  117  of chamber  122 , the region between the piston and floor  116  of receptacle  112 . 
     As shown in  FIG. 11 , blood B is injected into the interior chamber of receptacle  112  through first port  120 . The introduced blood drives piston  130  downwardly through receptacle  112 . Typically, an upper region of chamber  122  fills with blood and piston  130  is pushed downwardly by the blood until the piston engages lip  115  of sidewall  113 . This limits downward movement of the piston and restricts further introduction of blood into the chamber. As piston  130  moves downwardly, air in the lower region of the chamber is vented to the atmosphere through opening  139  and air passageway fitting  138  in piston  130 , vent pipe  128  and vent  126 . Pressure within the tube and particularly air pressure in the chamber region below piston  130  is equalized and the piston is operated by the user easily and without undue resistance or sticking within the receptacle. This facilitates the introduction of blood into tube  110  considerably. 
     After 50-60 mls or other volume of blood is introduced into the upper region of chamber  122  the syringe is removed from port  120  and tube  110  is placed in a centrifuge machine, which is operated fora predetermined time and at a selected speed to separate blood B into constituent components. Skirt  124  stably balances the tube as it is centrifuged. As shown in  FIG. 12 , the first centrifugation separates the blood into a lower level of red blood cells (RBC) and an upper level of plasma platelet suspension (PPS). As previously described and as further illustrated in  FIG. 13 , a new syringe is attached to port  120  and aspirated to remove the PPS from tube  110 . Vent pipe  128  collapses and atmospheric air is permitted to enter the region of chamber  122  below piston  130 . This neutralizes pressure in the lower region of the chamber and facilitates aspiration of the PPS. 
     As depicted in  FIG. 14 , the PPS previously removed through port  120  is reintroduced into tube  110  through the lower second port  144 . In particular, the syringe containing the PPS is connected to exterior luer port connection  145  of port  144 . The syringe is operated to inject the PPS through luer connection  145  and channel  148  into receptacle chamber  122  including narrower diameter lower region  117 . Air within the region of the chamber between piston  130  and floor  116  is vented through the open bottom  139  and air passageway fitting  138 , as well as communicably connected vent pipe  128  and vent  126 . Pressure is thereby equalized within the chamber so that injection of the PPS is facilitated. 
     The PPS syringe is then disconnected from port  144  and tube  110  is centrifuged again for a predetermined time and at a selected speed. This separates the PPS in the lower region of chamber  122  as shown in  FIG. 15 . Specifically, an upper layer of PPP is formed above a lower layer of PRB. At this point, the upper end of angled channel  148  is disposed within the PPP layer. The user attaches a new aspirating syringe to port  144  and aspirates PPP from tube  110 , as indicated by arrow  190 . Typically, the PPP is drawn down until approximately 7 ml of total fluid (PRB PPP) remains in the chamber between piston  130  and floor  116 . See  FIG. 16 . Vent  126  and vent pipe  128  communicably interconnect the atmospheric/ambient air to the lower region of chamber  122  beneath piston  130 . This neutralizes pressure in the chamber and again facilitates aspiration of the PPP from the tube. 
     With approximately 7 ml of fluid remaining in the lower region of chamber  122 , the tube is swirled or agitated as previously described, to mix the PPP and PRB remaining in the tube. This produces a high quality platelet rich plasma (PRP), as shown in  FIG. 17 . A new aspirating syringe is attached to lower second port  144 . That syringe is operated to aspirate the PRP through channel  148  and self-sealing luer lock connection  145 , as indicated by arrow  192 . The recovered PRP may then be used for required medical and veterinary purposes. The unique vented construction employed by tube  110  again facilitates the final aspiration of PRP. 
     It should be further understood that the vented dual port, single piston centrifuge tube of this invention may employ additional and alternative assorted features and components as depicted in the above-referenced devices shown in U.S. Pat. Nos. &#39;353, &#39;796, &#39;481 and Application No. &#39;053. Moreover, various other modifications may be made within the scope of the invention. For example, the vent and/or one or both of the common inlet and outlet ports may be formed in the sidewall of the tubular receptacle. The terms “upper end”, “upper portion”, “lower end” and “lower portion” as used herein should be construed broadly to encompass portions of the sidewall of the tubular receptacle proximate the opposing longitudinal ends thereof. 
     Accordingly, the present invention provides for a vented, dual port, single piston centrifuge tube that is effective for producing a concentrated, pure and high quality PRP and which is operated easily and without undue or unwanted resistance or sticking. The unique venting system of the present invention, wherein a vent pipe is formed between a vent to the atmosphere and a lower region of the receptacle chamber situated below the piston, contributes significantly to this improved operation. In addition to producing high quality PRP, the tube may be employed analogously for separating other biological fluids into their constituent components and for aspirating these separated components from the fluids. The derived aspirates may be employed for a wide variety of surgical, medical and veterinary applications. 
     From the foregoing, it may be seen that this invention provides for a method and system for more effectively and efficiently concentrating blood platelets and other constituents and biological fluids for use in medical and other applications. While this detailed description has set forth particularly preferred embodiments of the apparatus of this invention, numerous modifications and variations of the structure of this invention, all within the scope of the invention, will readily occur to those skilled in the art. Accordingly, it is understood that this description is illustrative only of the principles of the invention and is not limitative thereof. 
     Although specific features of the invention are shown in some of the drawings and not others, this is for convenience only, as each feature may be combined with any and all of the other features in accordance with this invention.