WO1998018509A1

WO1998018509A1 - A method and apparatus for improving device platelet compatibility

Info

Publication number: WO1998018509A1
Application number: PCT/US1997/019191
Authority: WO
Inventors: Bruce W. Gibbs
Original assignee: Cobe Laboratories, Inc.
Priority date: 1996-10-28
Filing date: 1997-10-23
Publication date: 1998-05-07

Abstract

An apparatus and method are provided for reducing platelet clumping in a concentrated platelet solution. A pump (32) is provided by having a tubing loop (54) of a surface modified polymer, to pump the concentrated platelet solution. Clumping is reduced in the concentrated platelet solution following transport through the pump tubing loop (54).

Description

TITLE

A Method and Apparatus for Improving Device Platelet Compatibility .

FIELD OF INVENTION

The present invention relates to extracorporeal tubing sets for use during blood processing including harvesting of blood components. More particularly, the present invention relates to a peristaltic pump tubing loop disposed in the pump raceway, formed from a polymeric material having a surface modifying additive for reducing clumping in concentrated platelet solutions following transport of the concentrated platelet solution through the peristaltic pump tubing loop.

BACKGROUND OF THE INVENTION

During typical apheresis procedures, whole blood is removed from a donor, anticoagulant is added to the blood to prevent coagulation, the whole blood is fractionated into various blood components, the desired blood components are harvested and the remaining blood components returned to the donor. Whole blood or particular blood components may also be harvested from a plurality of donors and pooled together. Pooled whole blood may be further fractionated into various blood components. Often platelets are the blood component being harvested.

Platelets are harvested during an apheresis procedure at high concentrations. It has been observed, however, that clumps are present in concentrated platelets solutions after the solution has been pumped through a tubing loop of a peristaltic pump. In contrast, this clumping is not observed, or is not detectable, in whole blood when the whole blood is pumped through the tubing loop of peristaltic pumps throughout the blood processing system. Therefore it appears that the concentrated platelet solution is more susceptible to the formation of clumps. Furthermore, while these observed clumps tend to mimic the appearance of thrombi or activated platelet aggregates, they do not exhibit the characteristics. For example, the observed platelet clumps occur in the absence of thrombin and in such concentrated platelet solutions in the absence of activated platelet aggregates.

It is known that artificial surfaces, particularly during extracorporeal circulation, may interact with whole blood to result in the formation of thrombi. Such artificial surfaces are often referred to as thrombogenic .

The presence of thrombin in extracorporeal blood is often indicative of blood coagulation and the formation of thrombi. An active thrombin molecule is formed when prothrombin is cleaved to thrombin, resulting in an active thrombin molecule and a 1.2 kilodalton protein fragment. Detection of this 1.2 kilodalton fragment correlates with the presence of active thrombin in the tested blood sample and the formation of thrombi. Clumping in concentrated platelet solutions during plateletpheresis has been observed in the absence of this 1.2 kilodalton fragment.

It is also known that artificial surfaces may interact with whole blood to result in the formation of activated platelet aggregates. Platelet activation and aggregation comprises a complex series of reactions and stages. One indicator of platelet activation is the detection of the GMP-140 protein that is typically present on the internal membranes of platelets. The GMP-140 protein is generally not detectable on intact platelets. When activated platelets undergo release, the GMP-140 protein appears on the external platelet surface where it can be assayed and detected. Clumping in concentrated platelet solutions has been observed even where elevated GMP-140 levels were not detected.

Clumping present in concentrated platelet solutions where there is detection of only normal amounts or not elevated amounts of the 1.2 kilodalton fragment or the GMP-140 protein has been observed to be reversible. Such clumps in concentrated platelet solutions are considered reversible because they disappear without filtration, enzymatic, chemical or thermal intervention.

Reversible clumping in concentrated platelet solutions, however, remains problematic. Such clumping may indicate a form of blood trauma. Further, such clumping is problematic because it mimics the appearance of thrombi or activated irreversible platelet aggregates. Thrombi and activated platelet clumps are not reversible and filtration, thermal, or enzymatic reactions are required to remove them after formation.

A technician may, therefore, mistake the reversible platelet clumps for thrombi or activated platelet aggregates. In response to this mistake, the technician may filter the harvested platelets to remove the supposed thrombi or activated platelet aggregates, thereby reducing the number of platelets ultimately harvested in a given procedure. Further, a technician, mistaking the reversible platelet clumps for thrombi or aggregated platelets, may increase the concentration at which anticoagulant is delivered to the extracorporeal tubing set in an attempt to prevent the supposed blood coagulation. Increasing the concentration at which anticoagulant is delivered to the extracorporeal tubing set ultimately reduces the amount of blood that may be processed during a given apheresis procedure and, therefore, the number of platelets that may be harvested. Therefore it is desirable to prevent reversible clumping in a concentrated platelet solution. It is known to construct or coat medical devices that contact whole blood with polymeric materials having surface modifying additives, such as siloxane containing additives, as set forth in the article "Surface Modifying Additives for Improved Device-Blood Compatibility" ASAIO JOURNAL, July-September 1994, Vol. 40, No. 3. The prior art, however, does not suggest or teach a method for preventing reversible clumping in biological solutions having concentrated platelets rather than whole blood. It is, therefore, desirable to provide a means for preventing or reducing clumping in concentrated platelet solutions, especially when such solutions are transported through the tubing loop of a peristaltic pump.

SUMMARY OF THE INVENTION

A significant aspect of the present invention is a method and apparatus for preventing reversible clumping in concentrated platelet solutions during plateletpheresis procedures . Another important aspect of the present invention is a method and apparatus for preventing clumping of concentrated platelet solutions when such solutions are transported through the tubing loop of a peristaltic pump.

In accordance with these aspects of the invention, an improved peristaltic pump design for the platelet collection pump is provided. The present invention provides a tubing loop for the raceway of a peristaltic pump comprising a base polymer that includes a surface modifying additive. It is preferred that the surface modifying additive comprise a block copolymer of polycaprolactone and polysiloxane . Also provided is a method for reducing reversible clumping.

Other objects of this invention will appear from the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG.l illustrates the flow path for a hypothetical apheresis procedure that includes fractionating the blood into its components including a high platelet content component .

FIG. 2 is a top cut away of the rotor assembly of the present invention having a single spring loading each roller element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The flow paths for a hypothetical blood apheresis procedure, which includes plateletpheresis, are shown in FIG.l. The flow paths in FIG.l are not intended to depict any actual apheresis procedure, but instead are intended to be exemplary of the possible flow paths used for a variety of possible procedures that include harvesting platelets. Actual procedures may not include all the flow paths shown in FIG.l, but rather a subset of the depicted flow paths and may include additional flow paths (not shown) . Further, FIG. 1 illustrates a dual needle procedure. It will be recognized by those skilled in the art that the present invention may be used with a single needle procedure as well. Further, the present invention may be used where whole blood is removed from a donor and stored for later separation into blood components. Fig. 1 is schematic and it is understood that the flow paths pass through the tubing loops of the various pumps . Whole blood is removed from a donor into and through an inlet line 12. An anticoagulant, such as citrate based ACD-A, is pumped from an anticoagulant reservoir 14 by an anticoagulant pump 16 through an anticoagulant line 18 into the inlet line 12 of an extracorporeal tubing set 20. The extracorporeal tubing set 20 may be formed out of any of the conventional polymeric materials, well known to those skilled in the art, typically used for the construction of medical tubing sets. For example, polyvinyl chloride ("PVC") may be used to form the extracorporeal tubing set. The whole blood with added anticoagulant is pumped by an inlet pump 22 to a separator system 24, also referred to as a blood processor, for separating the whole blood into fractionated components. The separator system 24 may be a centrifuge of the continuous flow type, such as the centrifuge used with the COBE SPECTRA^® brand apheresis system manufactured by COBE BCT, Inc. The separator system 24 may also be any other system capable of separating blood into its components such as other types of continuous and batch centrifuge systems and membrane separation systems. The separator system 24 may include a batch processor used in a laboratory or manufacturing setting where individual or batched units have been collected and stored for later processing. The present invention may also be adaptable to other extracorporeal circulation systems or medical devices that contact concentrated platelet solutions. The separator system 24 fractionates the whole blood into a variety of blood components such as plasma, platelets, white blood cells, red blood cells or any combination of them. The plasma is drawn off by a plasma pump 26 to a collect line 28 and into a collect bag 30. Platelets are drawn off by a platelet pump 32 to a collect line 34 and into a platelet collect bag 36. A return line 41 returns to the donor any components that are not collected. In fluid communication with the return line 41 there may be a replacement line 38 although it is understood that a replacement fluid may also not be used. A replacement fluid pump 40 pumps replacement fluid if used, such as sterile saline or blood plasma, from a replacement fluid reservoir 42 into the replacement fluid line 38. The outlet end of the return line 41 enters the donor. The flow through the various pumps is monitored and controlled using a microprocessor based controller 42 connected to the various peristaltic pumps by conventional electrical interconnects 44, 46, 48, 50, and 52. The pumps are any conventional peristaltic pump well known to those skilled in the art.

Platelets are generally present in the whole blood of a typical, healthy donor at a concentration of around 200,000 to 400,000 platelets per cubic microliter. During plateletpheresis, the separator system 24 will typically fractionate and concentrate the platelets from whole blood into a concentrated platelet solution comprising platelets and blood plasma. This concentrated platelet solution may range from 400,000 to 20,000,000 platelets per microliter with an incorporated amount of anticoagulant. The platelet pump 32 draws the concentrated platelet solution through the platelet collect line 34 into the platelet collect bag 36. The present invention prevents the clumping that is often observed in conventional extracorporeal tubing sets in the platelet collect line 34 of concentrated platelet solution following transport of the solution through the platelet pump 32. Referring next to FIG. 2, a cut away of the rotor assembly 56 of the platelet pump 32 is shown. The portion of the platelet collect line 34 that passes through the platelet pump 32 is the tubing loop 54. The platelet pump 32 is any conventional peristaltic pump well known by those skilled in the art, including those having spring loaded roller elements. The tubing loop may be solvent bonded into sockets in a mounting cassette as is well known if needed.

The present invention prevents clumping in concentrated platelet solutions often observed after such solutions are pumped through the tubing loop 54 of the platelet pump 32 by forming the tubing loop 54 out of a base polymer having a surface modifying additive. The base polymer, of tubing loop 54, may comprise polyurethane, polyurea, polyvinylchloride, polyamide, epoxy resin, phenoxy resin, polyester, polyester-polyether copolymer, acrylonitrile-butadiene-styrene resin, styrene- acrylonitrile resin, polycarbonate, styrene-maleic anhydride copolymer, polymethyl methacrylate, or polyolefin .

It is preferred that the surface modifying additive of the present invention comprise the linear block copolymer polycaprolactone and polysiloxane. Compositions of this surface modifying additive are commercially available from Thoratec Laboratories Corporation (Berkeley, California) . The nominal molecular weights (number average) of the polysiloxane blocks suitable for use herein range from about 1000 to about 5000, while the nominal molecular weights of the caprolactone blocks range from about 1000 to about 10,000.

It is contemplated that other surface modifying additive materials could be used with the base polymer to reduce clumping in concentrated platelet solution. Suitable surface modifying materials would be those that would form with the base polymer. It is necessary to use a surface modified polymer that does not increase the formation of thrombin, or increase the formation of activated platelet aggregates. It is also necessary that the surface modified polymer prevent reversible clumping in the concentrated platelet solution without other adverse effects.

To prepare the surface modified polymers of the present invention, the base polymer may be melt blended using the polycaprolactone-polysiloxane as an additive copolymer. Polycaprolactone-polysiloxane may also be added to the monomeric materials from which the base polymer will be formed. When the base polymer is polymerized a physical mixture of the polycaprolactone- polysiloxane and the base polymer will form. Polycaprolactone-polysiloxane may also be used as a prepolymer, and thereby be chemically incorporated into the base polymer. Synthesis of linear block copolymer polycaprolactone-polysiloxane surface modifying additives designated SMA and corresponding surface modified polymers, are described in U.S. Patents 4,663,413 (1987), 4,963,595 (1990), and 5,235,003 (1993) to Ward et al., the disclosures of which are incorporated herein by reference. The block copolymer polycaprolactone-polysiloxane or the selected surface modifying additive may also be coated onto the base polymer as set forth in commonly owned patent application U.S. Serial No. 08/473,723 to the same assignee. The disclosure of U.S. Serial No. 08/473,723 is herein incorporated by reference. The coating can be applied by any convenient technique for coating materials or articles as set forth in the above identified patent application.

PVC, polyvinylchloride, tubing comprising 1% SMA 422, SMA 422 having a nominal configuration of 2000-2000-2000 of polycaprolactone-polysiloxane-polycaprolactone, is one tubing suitable for forming the tubing loop 54 of the present invention. This tubing, Plastron 5120-68 tubing having 1% SMA, is commercially available from Plastron (City of Industry, California, U.S.A.) under the name

Plastron 808. It is understood that other configurations of polycaprolactone-polysiloxane-polycaprolactone could be used.

To further reduce platelet clumping, the spring loaded rotor assembly 56 may be modified to reduce the force used to occlude the tubing loop 54. This force is applied when the roller elements 58, 60 press the tubing loop 54 against the wall of the peristaltic pump raceway 62. By occlusion force is meant the force inserted on the tubing by the roller set such that it collapses the tubing; that is, the force necessary to collapse the tubing such that there can be no back flow. Typically, an occlusion force of about 12 pounds has been used to occlude a tubing loop in the raceway of a peristaltic pump, where the tubing loop is composed of PVC (sold as Natvar 610) having approximately 0.287 cm internal diameter and approximately 0.094 cm wall thickness without any SMA. Similarly, an occlusion force of about 15 pounds has been used to achieve occlusion, as described above, for PVC tubing, in a tubing loop composed of Plastron 5120-68 PVC tubing having 1% SMA (Plastron 808) with approximately 0.287 cm internal diameter and 0.094 cm wall thickness. PVC tubing (Natvar 610) occluded by an occlusion force of about 12 pounds and PVC tubing having 1% SMA (Plastron 808) occluded by an occlusion force of about 15 pounds will be defined as being occluded by the standard force for occlusion or the typically used force for the particular tubing.

The standard force for occlusion is typically achieved by attaching two compressive springs (not shown) , to each roller element of the peristaltic pump. The compressive springs force the roller elements towards the raceway wall thereby fully occluding the tubing loop with the standard force for occlusion.

The second preferred embodiment of the present invention uses a single compressive spring 64, 66 attached to each roller element 58, 60 (as shown in figure 2) to occlude the tubing loop 54. This optimizes the force for occlusion. That is, the force applied is the optimal force or approximately the minimum force required to occlude the tubing. The optimal force allows for tolerances due to variances in raceway, spring, rotor parts, roller and tubing. The use of a single spring is in contrast to the use of two-compressive springs by prior pumps for each roller element. The rotor assembly 56 and attachment of compressive springs 64, 66 to roller elements 58, 60 are conventionally designed as is well known by those skilled in the art. The single spring for each roller can be adjusted to provide sufficient force to occlude the tubing. It is also understood that other modifications could be made to the pump to achieve the optimal force.

For PVC tubing comprising 1% SMA (Plastron 808), the optimal occlusion force using the single spring is about 7 to 8 pounds . The use of the minimum or optimal force for occlusion reduces trauma to the platelets and clumping associated with the trauma.

The benefits of the instant invention will now be further described with respect to the various comparison tests set forth below.

Tubing Comparison Tests

Platelets were collected from a single donor at approximately 3 million platelets per μl during an apheresis procedure using the COBE SPECTRA^® brand apheresis system manufactured by COBE BCT, Inc. A syringe pump was inserted in the tubing of the COBE SPECTRA^® apheresis system at a point before the tubing loop of the platelet collect pump to collect the concentrated platelets . The concentrated platelet solution was then pumped through the tubing loops of three parallel peristaltic pumps. The first parallel peristaltic pump (Pump 1) comprised conventional PVC (Natvar 610) tubing occluded with the standard force for occlusion. The second parallel pump (Pump 2) comprised 1% SMA (Plastron 808) tubing occluded with the standard force for occlusion.

The third parallel pump comprised 1% SMA (Plastron 808) tubing occluded with approximately the optimal determined force for occlusion. All the tubing tested had approximately 0.287 cm internal diameter and a 0.094 cm wall thickness.

This optimal force for occlusion for the Plastron 808 (about 7 to 8 pounds of force) was achieved through the use of a single spring on each roller of the pump.

The three parallel pumps were connected together to a main tube from which three separate tubes extending therefrom. Each of the three separate tubes passed through a different one of the parallel pumps. The concentrated platelet solution was delivered simultaneously to each parallel pump by introducing the concentrated solution as a single bolus into the main connector tube. The concentrated platelet solution was processed through each pump at a rate of 2 milliliters/minute and 10 milliliters of post-pump concentrated platelet solution was collected into a separate syringe for each pump. The post-pump solutions were allowed to rest undisturbed for 1 to 5 minutes to allow the post-pump clumps to accumulate at the bottom of the syringe.

The post-pump solutions were visually observed for clumping and videotaped for detailed visual inspection. Clumping observed in the platelet solution from the first peristaltic pump (Pump 1) was pronounced. Clumping observed in the platelet solution of the second pump (Pump 2) was less than that observed in the first pump. Clumping in the solution of the third pump (Pump 3) was barely detectable.

The clumps were then quantified by measuring the platelet concentration of the clear fluid on the top 2 milliliter (the supernatant) , and the concentration of the remaining milliliter solution after the clumps were resuspended. The sample of the supernatant indicates the nonclumped platelets. This concentration multiplied by 10 is the total nonclumped platelets. The platelet number of the adjusted supernatant was subtracted from the number obtained for the resuspended sample to obtain the number clumped. This number divided by the total of all platelets is the percentage clumped. The total number of all platelets is the number of platelets in the 2 milliliters supernatant sample plus the quantity in the 8 milliliter resuspended sample. The total minus the nonclumped platelets gives the number of clumped platelets. The results are shown in Table 1.

Table 1

The results show a decrease in clumping for the Pump 2, Plastron 808 (1% SMA) tubing pump, and negligible clumping for the optimally occluded Plastron 808 (1% SMA) tubing, single spring, pump.

Platelet Activation Tests

GMP-140 protein is an indicator of platelet activation. When platelets are activated, the GMP-140 protein is released and can be detected and assayed.

Samples of the platelet solution were taken as set forth in the Tubing Comparison Tests as set forth above. The concentrated platelet solution was again pumped through the tubing loops of three parallel peristaltic pumps. Samples were taken before each platelet solution passed through each peristaltic pump and after pumping. Both sample solutions were then measured, using a flow cytometer for the GMP-140 protein. The amount of GMP-140 detected before pumping was compared to the amount after pumping. A post-pump amount/pre-pump amount ratio percent was obtained. The pump configurations for Table 2 are a pump one (1) configuration of PVC Natvar 610 at a 12 pound force for occlusion; a pump two (2) configuration having a tubing loop of Plastron 808 (1% SMA) set at a 15 pound force for occlusion; and a pump three (3) configuration having a tubing loop of Plastron 808 (1% SMA) at a reduced 7 to 8 pound force for occlusion. All three tubing loops had approximately 0.287 cm internal diameter and 0.094 cm wall thickness. Table 2 below shows the results for the different pump configurations. Table 2

The value above indicated less GMP-140 protein and correspondingly less platelet activity for the tubing loops using Plastron 808 (1% SMA), (Pumps 2 and 3). Therefore the use of 1% SMA does not adversely increase platelet activity.

Thrombin Tests

The post pump or after pump samples of platelet solution identified above were also tested for the presence of a 1.2 kilodalton protein fragment that is cleaved from prothrombin when thrombin is formed. The pump configurations were as given for the detection of the GMP-140 protein above. An ELISA (enzyme linked sorbent) assay was run on each sample to detect the 1.2 kilodalton fragment. The results of the assay for each of the respective pump configurations identified above are given in Table 3.

Table 3

The table shows that the three pump configurations had virtually indistinguishable levels of PF 1.2 which were within normal blood levels of less than 3 nanomolar/liter for PF 1.2. Therefore use of 1% SMA or an optimal force for occlusion does not appear to increase the presence of thrombin in an adverse manner.

Dual Spring vs. Single Spring Tests

The same method for gathering samples and determining platelet concentrations as set forth above concerning the Tubing Comparison Tests was used to compare the dual spring and single spring pump operation. The Plastron 808 (1% SMA) tubing was used for both pumps. The single spring pump configuration was the Plastron 808 (1% SMA) tubing occluded with an optimal force of approximately 8 pounds. The double spring pump configuration was the Plastron 808 (1% SMA) tubing occluded with a standard force of approximately 15 pounds. Both tubings had 0.287 cm internal diameter and 0.094 cm wall thickness. The percent of clumping using each peristaltic pump configuration was determined and the results are set forth in Table 4 below for four different collection runs.

Table 4

The results show that the percentage clumping was consistently lower for the single spring, (8 pound force for occlusion) peristaltic pump. It is believed that the improved results are due to reduced trauma on the blood component or platelets from the reduced force.

It is clear that using a surface modifying additive in the tubing loop of a peristaltic pump can be advantageously used to control clumping including reversible clumping. Optimizing the force used for the occlusion of the tubing appears to further reduce clumping by reducing trauma on the platelets. Furthermore, use of surface modifying additive or the optimized force does not appear to increase the amount of GMP-140 or PF 1.2 in the solution . Although the present invention has been described with reference to preferred embodiments, it is contemplated that numerous modifications and variations can be made and still come within the scope of the invention. No limitation with respect to the specific embodiments disclosed herein is intended or should be inferred.

Claims

I CLAIM:

1. In apparatus for processing platelets, the apparatus passing a concentrated platelet solution, the improvement comprising a pump for pumping the concentrated platelet solution, comprising: a tubing loop for carrying the concentrated platelet solution; the tubing loop further comprising a surface modified polymer.

2. The pump of claim 1, wherein the surface modified polymer comprises a base polymer and a linear block copolymer blended with the base polymer.

3. The pump of claim 2, wherein the block copolymer comprises polycaprolactone-polysiloxane.

4. The pump of claim 3, wherein the base polymer is selected from polyurethane, polyurea, polyvinylchoride, polyamide, epoxy resin, phenoxy resin, polyester, polyester-polyether copolymer, acrylonitrile-butadiene- styrene resin, styrene-acrylonitrile resin, polycarbonate, styrene-maleic anhydride copolymer, polymethyel methacrylate, or polyolefin.

5. The pump of Claim 1 further comprising at least one roller element, said at least one roller element capable of occluding the tubing loop by application of a predetermined force.

6. The pump of claim 5, wherein the predetermined force for occlusion is optimized to reduce platelet trauma .

7. The pump of Claim 5 wherein the roller element further comprises a single spring for applying the predetermined force to the roller element.

8. The pump of claim 7 wherein the predetermined force is approximately the minimum force required to occlude the tubing loop.

9. The pump of Claim 1 wherein the tubing loop further comprises a base polymer and a block copolymer coated on the base polymer.

10. The pump of claim 1, wherein the concentrated platelet solution comprises a concentration of platelets ranging from about 400,000 to 20,000,000 per microliters of fluid.

11. A process for reducing blood component reactions in blood processing comprising: receiving blood; transporting the blood to a blood processor; fractionating the blood in the blood processor into at least two components wherein at least one of said components comprises platelets; providing a pump; providing a tubing loop in the pump wherein the tubing loop comprises a surface modified polymer; pumping the component comprising platelets through the tubing loop wherein the surface modified polymer of the tubing loop reduces clumping of the platelets pumped therethrough.

12. The process of Claim 11 wherein the platelet component pumped through the tubing loop is platelets in a concentrated platelet solution higher than physiological concentrations .

13. The process of Claim 11 wherein the surface modified polymer comprises a base polymeric material and a surface modifying additive comprising a block copolymer.

14. The process of Claim 11 further comprising occluding the tubing loop in the pump by applying a minimum force optimal for the tubing loop.

15. A method of reducing reversible platelet clumping in a concentrated platelet solution comprising: providing a pump for pumping the concentrated platelet solution; providing a tubing loop in the pump; forming the tubing loop in the pump out of a base polymer and a surface modifying additive; pumping the concentrated platelet solution through the tubing loop of the pump for collection wherein the surface modifying additive reduces clumping of the platelets in the concentrated platelet solution.

16. The method of Claim 15 further comprising occluding the tubing loop of the pump with a minimum force optimal for the tubing loop.

17. The method of Claim 16 wherein the force is less than the standard force typically applied to the tubing loop.

18. The method of Claim 16 further comprising providing at least one roller in the raceway of the pump; and providing the force for occlusion of the tubing loop through the roller.

19. The method of Claim 18 further comprising providing a spring on at least one roller wherein the spring provides force for occlusion to the roller.

20. A method of reducing platelet trauma in a concentrated platelet solution comprising: providing a pump having a tubing loop of tubing; pumping the concentrated platelet solution with the pump for collection; passing the concentrated platelet solution through the tubing of the tubing loop; and occluding the tubing of the tubing loop with a minimum force less than the standard force typically applied to the tubing to pump the concentrated platelet solution and reduce platelet trauma.