Centrifuge and centrifuge head for separating constituents of a liquid and a liner therefor

March 8, 1966 g. n. hein 3,239,136

CENTRIFUGE AND CENTRIFUGE HEAD FOR SEPARATING CONSTITUENTS OF A LIQUID AND A LINER THEREFOR

Filed May 7, 1962 4 Sheets-Sheet 1

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gn HEiN 3,239,136

CENTRIFUGE AND CENTRIFUGE HEAD FOR SEPARATING nnMCTTTlTKNTS OF A LIQUID AND A LINER

March 8, 1966

CONSTITUENTS OF A LIQUID AND Filed May 7, 1962

THEREFOR

Sheets-Sheet 2

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March 8, 1966 _G. _N. _Hein 3,239,136

CENTRIFUGE AND CENTRIFUGE HEAD FOR SEPARATING CONSTITUENTS OF A LIQUID AND A LINER THEREFOR

Filed May 7, 1962 4 Sheets-Sheet 3

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ATTOgMEYS

March 8, 1966 g. n. he in 3,239,136

CENTRIFUGE AND CENTRIFUGE HEAD FOR SEPARATING CONSTITUENTS OF A LIQUID AND A LINER THEREFOR

Filed May 7, 1962 4 Sheets-Sheet 4

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3,239,136

Patented Mar. 8, 1966

United States Patent Office

3,239,136

CENTRIFUGE AND CENTRIFUGE HEAD FOR SEPARATING CONSTITUENTS OF A LIQUID AND A LINER THEREFOR

George N. Hein, 331 Cheslsam Ave., San Carlos, Calif.

Filed May 7,1962, Ser. No. 192,709

Claims. (CI. 233—20)

This invention relates to a structurally and functionally improved apparatus and method for centrifuging liquid materials to separate them into their various constituents.

In the present world of technology and science the process of centrifugation, for certain applications may be extremely desirable.

One or more of the constituents, of definite specific gravity of a liquid may need to be removed or isolated in this manner, or, for that matter, the liquid may have to be broken down into all of its component parts of different weights to reach the ultimate desired. Notwithstanding the purpose, there are many avenues for improvement, in contemporary apparatus and techniques the need and demand for which obviously depend upon the application. In some cases, the apparatus and techniques employed are lacking in superior performance and accuracy or may be facing obsolescence. Sophistication in design and operation may⁷ also leave much to be desired.

While the present invention has general utility in the centrifugation field and is a significant and important contribution thereto, it does have particular application to the centrifugation of whole blood for providing cell free, substantially pure plasma. As an exemplary and illustrative specific embodiment, this disclosure will be devoted primarily to this area of blood separation. However, it should be abundantly clear that the invention does have a broad application in the field of liquid separation.

Heretofore, it has been proposed to obtain plasma from blood by the utilization of rather large, cumbersome and costly apparatus, as well as time-consuming and expensive techniques. For example, batch separation by centrifugation has ’been proposed wherein selected individual receptacles containing whole blood were suitably mounted in a centrifuge. Such apparatus, however, required a number of strategically located blood receptacles or counterweights before the centrifuging operation was initiated. Otherwise, the revolving head would not be properly balanced, thereby causing undesirable stresses and torques.

As a rule, the individual batches of blood, due to the particular parameters and characteristics of the apparatus, would be placed at an appreciable radial distance from the axis of rotation- of the centrifuge head. Quite understandably, the inertial forces required to be overcome resulted in an appreciable lapse of time before the centrifuge head would reach its selected running speed of rotation. Conversely⁷, when separation of the blood constituents was attained the deceleration time was also high, requiring, in a number of instances, the incorporation of braking devices.

Nevertheless cross-mixing of red cells with plasma occurred frequently thereby minimizing the accuracy of separation by such apparatus. On the other hand, if crossmixing in such apparatus was insured against, the percentage of pure plasma capable of being recovered was very small as compared to the quantity of whole blood utilized. Needless to say, the installation of such centrifuge apparatus was permanent and did not led itself to portability. If it were desirable to run coagulation and prothrombin time tests at the bedside of a patient, this would be virtually impossible.

The present invention not only overcomes the disadvantages of prior art centrifugation apparatus as typified in the above but, for the first time, as one of its objects, in troduces to the art a portable, miniature, compact and high-speed centrifuge specifically designed to provide for liquid separation in a minimum amount of time.

Another object is to providp for rapid separation of 5 liquid materials and wherein selected constituents are adapted to be isolated while, at the same time, being free from cross-mixing with one another.

Still another object is to provide for such liquid separation in which the isolated constituents are trapped and sealed from one another and wherein such separation takes place within a disposable bag having sealable zones for effecting constituent isolation.

It is an important object of this invention to provide for blood separation by centrifugation whereby cell-free, 15 pure plasma is obtained in a minimum amount of time, thereby eliminating the many variables due to prolonged processing of whole blood.

Another important object is to provide for the separation of whole blood into ready-to-use plasma by an im20 proved means and technique for centrifuging a single, in dividual blood sample, as distinct from batch separation, without being concerned with the balance of the centrifuge head.

A further object is to provide for accurate centrifuga25 tion, particularly of whole blood, wherein an optimum amount of pure plasma is attained rapidly without danger of detrimental or uncontrolled cross-mixing of the constituents by introducing an effective seal, after separation, between plasma and red cells.

A still further object is to provide an improved and efficient process for the centrifugation of whole blood by the employment of the foregoing apparatus and, at the same time, utilizing a disposable blood bag into which a blood sample may be readily introduced, separated into 35 its constituent parts which may then be trapped to provide pure plasma.

Other objects and advantages of the present invention are realized and contemplated by the following miniature, compact centrifuge having a minimum number of parts 40 and possessing characteristics of portability and high speed centrifugation. Thus, a centrifuge incorporating the teachings of the present invention includes a centrifuge head which, in its “cooked” or ready-to-use condition, is capable of receiving a disposable blood sample bag and 45 secure it in place during centrifugation. In this connection, a removable cap facilitates the positioning, securement and removal of the bag with respect to the head. At the same time, the cap, as well as the bag, are provided with aligned openings to permit the insertion of the 50 selected quantity of liquid to be separated. For purposes of discussion and as illustrative only, blood will be selected as this liquid.

The configuration of the bag is such that central chamber is provided within which the pure plasma will be ⁵⁵ eventually trapped, and an annular, circumferentially extending peripheral well communicating therewith. The volumetric capacity of the well is of such a proportion whereby, during centrifuging, all the red blood cells are accommodated plus a very small percentage of plasma, θθ The well is sufficiently large to permit the collection of all of the red cells, not withstanding the range of varying relative percentages of these constituents for the blood samples ordinarily contemplated. The primary intent of the centrifuge of the present invention, as applied to sep³³ aration of whole blood, is to provide pure plasma quickly and conveniently for test procedures to follow such as prothrombin time determinations. Therefore, remixing of the very small percentage of plasma and red blood cells in the peripheral well after centrifuging and following the entrapment of the major portion of plasma in the central chamber in a manner to be described shortly, is of no concern.

3,239,136

The centrifuge head is drivably coupled with the output shaft of a motor. This coupling output includes a quick disconnect locking assembly which serves a dual purpose. First of all, this assembly, which is fixed to the output shaft, enables the centrifuge head through a 5 mechanical frictional surface interengagement to turn with the output shaft without slipping. Secondly by the mere application of manual pressure, the locking means releases the head whereby it may be removed completely.

The centrifuge head includes a plunger on which the disposable bag is adapted to rest and which is spring biased towards the cap. At the same time the plunger is releasably latched in a bias condition by a pair of latch assemblies.

Thus, after the bag is mounted in the centrifuge head 15 and loaded with the selected blood sample, the motor is energized to initiate the period of rotation of the head, which may be manually controlled or automatically governed by a suitable timing means. As the head rotates, the blood constituents of higher specific gravity move 20 outwardly to replace, in the peripheral well of the bag, constituents of lower specific gravity. When the hydraulic pressure within the bag increases with increased induced centrifugal forces, the plunger will be forced downwardly away from the cap. At a given point of de- 25 pression, the plunger will be released by the latching means. After a given period of rotation at which the desired separation is attained, the motor is de-energized resulting in a deceleration of the head speed. The induced centrifugal forces will be correspondingly reduced ³³and the hydraulic pressure load on the plunger proportionately decreased. With this reduction in pressure, the plunger is free to move upwardly under the influence of its biased spring towards the cap. When this occurs, the adjacent walls of the bag will be sealed as the plunger ³³comes to rest against the cap. The sealed surfaces of the bag define an annular zone separating the main central chamber of the bag from its peripheral wall. This sealed relationship subsists after cessation of rotation whereby the lighter constituents, which in the instant embodiment is plasma, will be entrapped in the central chamber from the constituents of higher specific gravity contained in the peripheral well. The pure plasma may now be removed from the bag by merely employing conventional aspirating devices inserted through both coaxial 45 openings in the cap and bag.

In order to reload the centrifuge, the cap need only be removed and the bag replaced. Prior to the insertion of a fresh bag in the centrifuge head, the plunger is depressed to its “cocked” position at which the latching ³³means, once again, releasably lock the plunger against its biased spring. The cap is remounted to clasp the new cell securely in place in the centrifuge head after which the centrifuging operation, on a fresh blood sample, may be repeated. ⁰⁰

The following detailed description is to be taken in conjunction with the accompanying drawings illustrating a somewhat preferred embodiment of the present invention, it being understood, however, that the scope of the present invention is not necessarily limited thereby. ⁶⁰

FIG. 1 is a fragmentary side elevational view of the centrifuge embodying the teachings of the present invention;

FIG. 2 is a top plan view thereof;

FIG. 3 is an exploded elevational view of the components of the centrifuge with certain parts broken away and removed;

FIG. 4 is an enlarged fragmentary sectional view taken along the line 4—4 of FIG. 2 showing the centrifuge supporting a disposable bag containing the material to be ¹separated, which for illustrative purposes will be whole blood, prior to the initiation of centrifugation;

FIG. 5 is a similar view with further parts broken away and removed showing the level of the material in the 75 bag after commencement of operation, and, at the same time, the displacement of parts as centrifugation increases and accompanying centrifugal forces are produced;

FIG. 6 is also a similar view showing the entrapment of the heavier constituents, notably red blood cells, through the displacement of parts of the centrifuge, leaving pure blood plasma in the inner chamber of the bag;

FIG. 7 is an enlarged side elevational view in section of the locking assembly and the associated parts of the head assembly as the former is actuated to permit the removal of the latter;

FIG. 8 is an enlarged side elevational view of the disposable bag adapted for use with the centrifuge;

FIG. 9 is a perspective view on a reduced scale of the top disc of the bag;

FIG. 10 is a similar perspective view of the bottom disc of the bag; and

FIG. 11 is an enlarged cross-sectional view of the bag illustrating the displacement of the bottom disc wall in phantom for trapping the constituents of the contents of the bag having higher specific gravities.

The illustrated centrifuge includes a head assembly which may be permanently, or releasably, attached to motor 22. To render these parts operable, they should be mounted in a suitable casing which will also afford protection to the operator, in the event that some part should, fail, while rotating at high speed.

In accordance with the present invention, a portable, reduced-size centrifuge is proposed, not only for use in clinics and medical laboratories by trained as well as untrained technicians, but by physicians to the extent that blood separation can be performed at a patients bed side. Further applications in other liquid separation fields will also be apparent. This centrifuge can readily be lifted and carried with only one hand without any appreciable effort. The head assembly, for example, may be no more than approximately 1½ inches in diameter. Naturally, it will be understood that such parameters may be varied over wide limits. The speed capabilities of the motor employed ranges from about 15,000 to 20,000 r.p.m., averaging approximately 18,000 r.p.m.

The head assembly is formed with a compartment that serves to secure a disposable bag 26 in which the material to be separated is initially introduced, centrifuged, separated and its constituents trapped. Thus, the head assembly comprises a centrifuge body 28 supporting a plunger 30 which is adapted to be releasably latched thereto by a pair of identical latch assemblies 32. The plunger 30 is displaceable and under the bias of spring 34 acting against the body and the plunger through a spring cone 36. When unlatched, the displacement of the plunger 30 relative to the body 28 is limited by the screw 38. A cap 40 is additionally included and is removably secured to the body 28 to permit the disposable bag 26 to be anchored within the head assembly during centrifugation. On the other hand, the cap is readily removed from the body when the separated constituents of the blood have been utilized as intended and for permitting reloading of further bags for the selected samples to be centrifuged.

Reference is now made to the structural details of the body 28. In this connection, the body 28 is provided with a cavity 42 defined by a conical wall 44, base 46 and the somewhat thicker outer wall 48. A radial flange 50 extends inwardly from the conical wall 44 and is formed with a central bore 52 of sufficient diameter to receive the shank of the screw 38. The outer somewhat thicker wall is provided with a pair of diametrically opposed tapered bores 54 extending into inner reduced bores 56 communicating with the cavity 42. These bores serve to accommodate the latch assemblies 32 to be described in detail below. A circumferentially extending rim 58 projects upwardly from

3,239,136 taining face 102 from which extends inwardly, in concentric relation, a conical surface 104 which, in turn, extends into another conical surface also concentrically disposed but having a somewhat increased base angle. As 5 illustrated, the upper end of the cap 40 is recessed annularly, and at the same time, is provided with an axial opening 108 which permits the insertion of the material to be separated by the centrifuge. Thus, it will be observed that the cap 40 cooperates with the plunger 30 and jo body 28 to provide a main central cavity 110 and a communicating annular cavity 112 for the reception of corresponding parts of the bag 26 to be described in detail shortly.

As stated, a pair of latch assemblies 32 are employed 15 to releasably hold the plunger 30' in a cocked position against the bias of the spring 34 and, at the desired time, release the plunger to thereby initiate entrapment of certain of the separated constituents of the material in the bag 26. Although details of specific assemblies are dis20 closed herein, it should be understood, other comparable assemblies could be employed equally as well. Each assembly 32 includes a stud 114 having an enlarged head 116 both of which are adapted to be disposed in the associated opening 70 of the plunger 30; Under these cir25 cumstances, the head 116 will be adapted to latch with the lip 72 of the plunger 30. The stud 114 extends from a cylindrical cup 118 having a base 120 and cylindrical sidewalls 122 displaceable within bore 56 of body 28. A spring 124 projects outwardly from within the cup 118 30 having one of its ends bearing against the cup base 120¹. A plug 126 for the bore 56 includes external threads 128 engaged with threads 54. The other end of the spring 124 bears against this plug 126 and is maintained in coaxial relationship by means of the stud 13® extending 35 inwardly from the plug. The spring 124 is calibrated to exert sufficient force to maintain the stud 114 within the opening 70 and with enlarged head 116 is latched position with the lip 72. However, when a desired and predetermined magnitude of centrifugal force is attained, and 40 the head 116 and lip 72 are unlatched, the biased spring is adapted to be overcome by the radial thrust of the mass acting thereon, thereby permitting the retraction of the head 116 from the opening 70. Accordingly, the plunger 30 will now be free to shift upwardly under the 45 influence of the spring 34.

In order to create the centrifugal forces for constituent separation it is preferred that centrifugal head 20' be rotated by motor 22. To this end, the head 20 is drivably connected to the motor shaft 132 by locking assem50 bly 24 which, as will be fully explored, also permits complete disengagement and removal of the head. Accordingly, cone 134 is pressure fitted on the terminal end of the shaft 132 and seats the head body 28 by engaging the inner face of the conical wall 44. The cone presents an 55 annular radial flange 136 intermediate its ends. A cage of cylindrical figuration 138 is secured to the periphery of this flange 136 and is provided with apertures 140 at spaced intervals which for purposes of balance during centrifuging may be located at 120 degree intervals. Balls 60 142, having a diameter larger than that of the apertures 140 of the cage 138, are nevertheless adapted to project through the associated aperture so that the flange 136 and the inner face of the conical portion 64 may be simultaneously engaged thereby. Under these circumstances, 65 the head 20 will be adapted to be locked to the cone 134, and consequently the shaft 132.

The present invention contemplates a quick disconnect coupling of the head 20. A coupling of this nature may include a locking member 144, having a conically tapered 70 side face 146 which is adapted to cam against balls 142 and maintained them in locking position. In addition, the locking member 144 includes a sleeve 148 which surrounds a base 150 of the conical member 134, and is adapted to slide thereon. A cavity 152 is provided for 75 locking member 144 exteriorly of the sleeve 148 and is ⁵ the outer wall 48 and is formed with external threads 60 mating with corresponding threads of cap 40. A lower circumferentially extending wall 62 is provided with a conical extension 64 to be releasably locked by locking assembly 24.

As stated, plunger 30 is adapted to be displaceable with respect to body 28 in order to permit trapping of the bag constituents during the centrifuge operation. Under such circumstances, plunger 30 includes a cylindrical body portion 66 in sliding engagement with the inner face of the thickened outer wall portion 48 of the body 28. A radial flange 68 extends outwardly from the cylindrical body portion 66, and, in turn, is in proximity with the inner face of the rim 58 of the body 28. The cylindrical body portion 66 is provided with an annular groove 70 which receives displaceable projecting portions of the assemblies 32. The exterior lip 72 is adapted to engage with these portions in completing the intended latching function. The piston 30 further includes an upper head portion 74 extending over the top of the cylindrical body portion 66. Head portion 74 is predominantly conically shaped having inclined face 76 and an arcuate apex 78. The outer circumferentially extending periphery of the head portion 74 includes an annular surface portion 80 at a divergent angle with respect to the conical surface 76. This annular portion defines with the outer circumferentially extending wall surface 82, an annular corner lip 84 which cooperates in providing the sealing zone in trapping the separated constituents of the liquid within the bag 26 during centrifugation. As will be observed, the wall portion 82 together with the flange 68 and inner face of the lip 58 form an annular cavity for receiving the peripheral well of the bag 26. A concentric cylindrical boss 86 projects from the interior of the head portion 74 and is formed with internal threads 88 for mating with the threads of the screw 38, which serves as a stop for limiting the permissible vertical movement of the plunger 30.

The plunger 30 is biased longitudinally away from pie body 28 by means of spring 34. One end of the spring 34 engages with the base 46 of the body 28; and the other end bears against the spring cone 36. In this connection, the cone 36 includes annular spring retaining flange 90 extending downwardly and interiorly of the upper end of the spring 34. The apex end of cone 36 on the other hand, is provided with an axial opening 92. This end is accordingly permitted to rest in the arcuate comer of the head portion 74 and boss 86 of the plunger 30. Thus, the spring pressure will be exerted on the plunger 30 through the interposed spring cone 36.

When the latches 32 are retracted to release the plunger 30, upward movement of the plunger under the influence of the spring 34 is limited by the screw 38. As mentioned in the foregoing, this screw 38 engages with the internal threads 88 of the plunger boss 86. The head 96 of the screw is disposed on the other side of the radial flange 50 of the body 28, and, consequently, is adapted to engage therewith in limiting the upward longitudinal displacement of the plunger 30 relative to the body 28.

The bag 26 is secured in position when mounted in the centrifuge by means of the cap 40. This cap is preferably formed from a transparent material in order that the contents of the bag 26 which may also be transparent can be advantageously observed through the centrifugation process. Any one of a number of materials can be utilized in fabricating the cap. Lucite, however, has been found to perform satisfactorily under the contemplated conditions. The cap 40 includes an annular flange 98 having internal threads 100 which mesh with the threads 60 of the rim 58 of the body 28. The inner surfaces of the cap 40 conform with the contours of the associated parts of the bag 26. In this regard, while progressing radially inwardly the interior will include an annular re3,239,136 adapted to seal one end of the spring 154. A ring 156, secured to the lower terminal end of the stem 150 of the cone 134, is formed with a circular slot 158 for receiving the other end of the spring 154 and maintain it in a compressed state. A radial flange 160 extends outwardly from the base of the locking member 144 and facilitates gripping of this member so that it may be depressed against the bias of the spring 154 to permit the ball 142 to be shifted inwardly to clear the conical portion 64 of the head body 28 to permit the removal of the entire head assembly 20.

It will be apparent, that with the parts in the position shown in FIG. 4, the head assembly 20' will have its conical wall 44 firmly seated on the cone 134 so that the head will turn with the motor shaft 132. However, depression of the locking member 144 relative to the base 150 and the cone 134, as for example, by applying pressure against the radial flange 160, will shift the parts to the position depicted in FIG. 7. The balls 142 under these circumstances will shift inwardly towards the center to a position at which they clear the conical extensions 64. Accordingly, the head 20 need only be grasped and lifted to clear the locking assembly 24.

Conversely, if it is desired to remount the head 20', the member 144 is depressed against the bias of spring 154 to shift the balls 142 inwardly to thereby permit the conical extension 64 to freely ensleeve the ring 138 with the conical wall 44 firmly seated in place on the cone 134. At this time, the locking member 144 may be released whereupon the spring 154 will shift the locking member 144 and particularly its sleeve 148 upwardly along the stem 150. Under these circumstances, the centrifugal head 120 will be locked in place against unintentional detachment.

The bag 26 is preferably formed of an organic plastic material which renders it economically feasible commercially to permit only-one-time use of the bag and its eventual disposal. The volumetric capacity of the bag need only be a little over 3 ml. The bag is comprised of an upper disc 162 and a lower disc 164 which may be formed separately and then bonded together adjacent their peripheries along the zone 166. The upper disc 162, under these circumstances, is preferably of a somewhat rigid nature as compared to the lower disc 164, which, on the other hand, is substantially flexible for reasons that will become evident shortly. The peripheral zone 166 when placed in the centrifuge head 20 is adapted to be clamped between the rim 58 and the cap face 102 when the cap is screwed tightly on the head body 28.

The upper disc 162 is adapted to conform in configuration with the interior surfaces 102, 104 and 106 of the cap 40. Thus, the upper disc 162 will include a substantially planar peripheral annular wall 168 from which extends inwardly a conical wall 170 which in turn extends into a second conical wall 172 possessing an increased base angle. At its upper end the disc 162 defines a substantially coaxial circular opening 174 which permits the introduction of the material to be separated and at the same time eventual removal of constituents of lesser specific gravity.

The lower disc 164 possesses a shape generally conforming to that of the top of the plunger 30. In this connection, a conical wall 176 is present and includes a central and accurately shaped apex 178. Its base extends into a substantially divergent annulus 180 terminating in rounded corner 182. The outer peripheral edge of the lower disc 164 includes a pair of slightly converging downwardly projecting side walls 184 and 186 joined to one another by an integral bottom wall 188. The lower disc includes a peripheral annular wall 190 which is sealed to the wall 186 of an upper disc 162 along peripheral zone 166. In view of the flexibility of the lower disc 164, it is adapted to flex upwardly such that the rounded annular corner 182 will firmly engage the upper disc 162 along zones of the conical wall 170 in sealing relationship to permit entrapment of separated constituents of the contents of the bag during centrifugation. Under the circumstances, the corner 182 divides the interior of the bag into an inner chamber 192 and outer annular well 194. As will become apparent shortly, the constituents of the material to be separated of a higher specific gravity will eventually be disposed primarily in the well 194 whereas the constituents of lower specific gravity will be contained in the main chamber 192.

In using a centrifuge incorporating the teachings of the present invention, the cap 40 is initially detached from the head body 28 by unscrewing it relative to the body lip 58. The piston 30 is then depressed to its cocked position and releasably locked by latch assemblies 32 as depicted in FIG. 4. Whereupon disposable bag 26 will be placed upon piston 30 and the cap 40 reapplied so that the periphery of the bag 26, as defined by the annuli 168 and 190 in the respective upper and lower discs 162 and 164, is clamped between the face 102 of the cap 40 and the lip 58. While the present invention may be advantageously employed in the centrifugation of various solutions, as stated, it is particularly significant in connection with separating constituents of blood. In this connection, the centrifuge is employed advantageously in providing pure plasma quickly and conveniently for testing, as for example, in prothrombin or coagulation time determinations.

With this in mind, a measured quantity of whole blood would be introduced into the disposable bag 26 through the openings 108 and 174 of the cap 40 and bag 26, respectively. Centrifugation would, under these circumstances, have the effect of separating whole blood into pure plasma and red blood cells which would collect in the well 194 of the bag, because of their higher specific gravity. The lower specific gravity constituent, notably plasma, would collect closer to the axis of rotation and occupy the chamber 192. The measured quantities of blood ordinarily contained by the bag 26 will be in the neighborhood of approximately 2 ml.

Thus, after loading the positioned bag 26 the motor 22 is energized. The head 20 will immediately begin its period of rotation. As the head 20 rotates, constituents of the blood possessing higher specific gravities will move radially outwardly and replace those of lower specific gravity. Accordingly, the heavier red blood cells will accumulate in the cavity 194 whereas the plasma will predominate the inner bag chamber 192. The volumetric capacity of the well is designed to result in collection of all red blood cells plus small percentages of plasma. The well is therefore sufficiently large to accommodate the range of varying relative percentages of red blood cells for a 2 ml. volume of sample. Since the primary intent of the bag when filled with whole blood is to provide pure plasma quickly and conveniently for test procedures to follow, there is no appreciable concern over remixing of plasma and red cells in the peripheral well after centrifuging.

When the pressures exerted by the separated blood as induced by centrifugal force, increase on the walls of the bag 26, they will be transmitted to the plunger head 74. A point will be reached due to the calibration of the spring 34, whereupon the piston 30 will move downwardly. Eventually, at a given point of depression of the plunger, the head 116 of each latching assembly 32 will no longer be latched by the lip 72 thereby permitting the head to be thrust radially outwardly against the bias of spring 124 as shown in FIG. 5. The side walls of the plunger 30 will now be cleared by the latching assemblies 32. With the head 116 fully retracted, the piston 30 is free to move upwardly under the bias of spring 34 except for the hydraulic pressure load counterbalancing the effect of this spring.

After a given period of rotation, the motor 22 is deenergized resulting in a deceleration and reduction of the rotational speed of the head 20. The centrifugal forces

3,239,13b are correspondingly reduced, and consequently, the hydraulic load on the plunger 30 previously maintaining it in a depressed position. With this reduction in pressure, the piston 30 is forced upwardly by the spring 34, with the lip 72 bypassing the still extended head 116 of the latch assembly 32. The plunger head portion 74 will accordingly raise the bag’s lower disk 164 and cause the rounded corner 182 into firm engagement with the wall 170 of the upper disk 162. Under such circumstances, an annular sealed zone is created separating the main central chamber 192 from the peripheral well 194. The heavier constituents, namely the red cells, will be isolated from the lighter plasma occupying the main chamber 192. This sealed relationship will continue after the head rotation has stopped. It has been found, that the complete centrifugation cycle takes between 15 to 20 seconds for satisfactory results to be realized. In order to assure the collection of pure plasma, a relatively small percentage of the plasma will be trapped in the well 194. The pure plasma may now be applied, particularly for test purposes, by merely removing the desired quantities from the main chamber by the employment of conventional aspirating devices inserted through coaxial openings 108 and 174. Such devices may include syringes, pipettes and the like.

When it is desired to reload the centrifuge in order to perform another separation, the cap 40 need only be removed and a fresh bag 26 mounted in place on the plunger 30. Prior to the placement! of this bag 26 the plunger 30 is depressed to its cocked position. In this connection, the head 116 of the latch assemblies 32 will be forced radially inwardly under the influence of their associated springs 124 to latch with the corresponding plunger lips 72. The cap 40 is then returned to its bag clamping position on the body 28. A new sample of liquid material to be separated by centrifugation may subsequently be deposited in the bag 26 and the above centrifuge cycle repeated.

Thus, it should be readily apparent to those skilled in the art, that a relatively light-weight, miniature centrifuge is contributed to the art by .the present invention, facilitating rapid separation of samples of liquid materials and collection of their constituents within a minimum amount of time. The size and structural characteristic of the centrifuge permit portability and enables the centrifugation operation to be performed at any desired location. In the case of blood separation, in order to secure pure plasma quickly, the centrifuge may be conveniently utilized at a patient’s bedside. The centrifuge is of such a nature that it can be carried in an ordinary physician’s bag to such locations. Needless to say the percentage of plasma recoverable for unit sample of whole blood is significant and comparatively high. Obviously, the disadvantages inherent in .prior art batch separation techniques have thusly been most effectively obviated by the teachings of the present invention.

As will be apreciated, whole blood includes white blood cells and platelets in addition to plasma and red blood cells. The white and red blood cells together with the platelets are heavier than plasma and are formed elements which are carried by the plasma. With this in mind, the instant disclosure has merely mentioned plasma and the red cells for simplicity. It should be realized, however, that in obtaining pure plasma by centrifugation all of the heavier particles are separated. Therefore, the designation of red blood cells as used herein is intended to include the white blood cells and platelets as well.

Thus, among others, the several aforenoted objects and advantages among others are most effectively attained. Although only a single preferred embodiment of the invention has been disclosed and described in detail herein, it should be understood, that the present invention is in no sense limited thereby, and its scope is to be determined by that of the appended claims.