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The present invention relates to a device for centrifugation
of a liquid comprising a stationary portion, a processing
chamber rotatably mounted with respect to said stationary
portion for rotation about a predetermined axis, a
multi-chanel flexible tubing one end of which being fixed
with respect to said stationary portion substantially along
said predetermined axis, with the other end of said flexible
tubing being attached substantially on said axis in rotationally
locked engagement to the processing chamber and a
supporting means to prevent any substantial elongation of
said tubing due to the centrifugal forces to which it is
submitted during rotation of said processing chamber and to
keep the tubing with a shape having radii of curvature large
enough for improving the rotation of the tubing around its
longitudinal axis. This invention also relates to a centrifugation
member.
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Such a liquid centrifuging device comprising a rotor
assembly for receiving liquid to be processed by centrifugation
has already been disclosed e.g. in US 4'113'173. Liquid
communication is maintained with the rotor assembly during
rotation of the latter by means of a flexible umbilical duct
element which extends from the rotor assembly to a location
external to the apparatus by way of a passageway provided in
the support shaft of the rotor assembly and a guide sleeve
carried on and rotatably mounted to the rotor drive assembly.
The rotor assembly is rotatably driven in the same
direction as the rotor drive assembly with a speed ratio of
2:1 to prevent the umbilical duct element from becoming
completely twisted during the operation of the apparatus. A
guide sleeve is provided on the rotor drive assembly to
support the umbilical duct element during operation. The
tubing forming the multi-chanel flexible tubing is submitted
to various stresses. The first one is an alternate bending
due to the fact that one extremity of the tubing is fixed,
whereas the other extremity is solid with and coaxial to the
rotor assembly. It has already been proposed, particularly
in WO 00/61295, a low diameter rotor assembly which is able
to spin at approximately 5'000 t/min, so that the tubing is
submitted to a very high frequency repeated bending stresses.
These repeated bending stresses extending on the whole
liquid processing, lasting possibly up to several hours. In
order to prevent over heating and early destruction of said
tubing, the latter has to be extruded in a soft plastic material.
However, the drawback of a soft plastic material is
to render the tubing less resistant to torque reaction, and
thus to substantially diminishe its capacity to transmit a
torque able to overcome the friction forces with the supporting
surfaces intended to prevent any substantial elongation
of said tubing due to the centrifugal forces to which it is
submitted during rotation of said processing chamber. The
tubing will thus present a torque reaction more important as
it made from a softer plastic material, possibly completely
collapsing the multi-chanel inside said tubing.
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The second stress is due to the centrifugal force exerted
on the tubing, proportional to the square of its rotational
speed. At 2'500 t./min, centripetal acceleration to
which the tubing is submitted is equal to approximately 350
times terrestrial gravitation. This heavy acceleration requires
the utilisation of a support element for sustaining
the tubing while rotating, so that it doesn't elongate until
breaking, or that it doesn't adopt an unfavourable shape for
its duty of alternate bending (e.g. as having locally too
small curvature radius).
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However, it is known that the friction coefficient of a
soft plastic material against any rigid material can only be
high. This implicates that friction of the soft plastic
tubing against the support element would cause a substantial
heating, and finally an early material injury.
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It is important to point out that the two problems are
intimately bounded. In fact, when the system is set in rotation,
the heavy increase of the centrifugal force on the
tubing induces an increase of the friction torque between
the tubing and its support element proportional to the
variation of the centrifugal force. This friction torque is
contrary to the alternate bending work of the tubing and
therefore creates a torque reaction on the tubing. The more
the plastic material of the tubing is soft the more the
torque reaction of this tubing will increase.
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The important friction torque between the tubing and
its support element induces also a notable heating of the
tubing, softening the plastic material from which it is
formed (lowering the Shore's hardness) and, finally, implicates
a more and more elevated torque reaction of the tubing
up to the complete collapse of the multi-chanel inside the
tubing, or even the breaking of the tubing.
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It has already been proposed in US 4'299'256 a flexible
coextruded tubing having an outer portion of polyvinyl chloride
plastic containing a minor amount of intimately mixed
silicone oil and having an inner portion of plastic free of
silicone in order to improve the frictional resistance of
tubing, while at the same time the interior of the tubing
remains unchanged.
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Such a coextruded plastic tubing is relatively expensive
to produce and allows neither to increase enough the torque
resistance of the tubing, nor to regularize the radius
of curvature of the tubing where it does not rest against a
supporting surface, thus allowing elevated constraints to be
locally exerted on the tubing. Furthermore it does not prevent
the attrition of the tubing.
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It has also already been proposed in US 4'710'161 to
surround such a plastic tubing which is rotatably held on a
bearing carried on and rotatably mounted to a rotor drive
assembly by a coil spring, the both ends of which are respectively
fixed to a centrifugal rotor assembly and to said
bearing at the portion thereof fixed to said tubing. Such a
coil spring is intended to transmit the torque from the centrifugal
rotor assembly to said bearing in order to substantially
cancel relative angular movement between said tubing
and said bearing, so that there is practically no friction
between tubing and bearing. The coil spring according to
this reference is not solid with the tubing and does not
rest against a supporting surface of the tubing.
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The aim of the present invention is to make it possible
to provide means able to reduce the friction torque between
the tubing and a supporting surface and, in the same time to
reinforce the tubing with respect to the centrifugal force
which exerts on it during the centrifugal processing, without
increasing the bending strengh of this tubing.
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To this end, one object of the invention is a centrifugal
liquid processing apparatus according to claim 1.
Another object of this invention is a centrifugation member
according to claim 10.
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The advantage of the coil spring sheathing the tubing
and solid with it on its whole length, according to the
present invention is on the one hand, to avoid the friction
between the soft plastic material of the tubing and the hard
material of the supporting surface of this tubing as well as
to reduce the friction area with this supporting surface and
on the other hand, to uniformly reinforce the tubing all
along its length, thus substantially reducing the risk of
localised constraints exerted on the tubing during centrifugal
processing. Another advantage of the invention is that
the tubing is guided by supporting means. These supporting
means allows to keep the related angular position and the
radius of the tubing unchanged during the rotation of the
rotor assembly, so that this rotor assembly may be poised
with a very high precision. This feature is essential for a
high speed rotor assembly.The appended drawing illustrates,
schematically and by way of example, one embodiment of the
centrifugal processing apparatus which is the subject of the
present invention.
- Figure 1 shows a sectional elevated view of this embodiment;
- Figure 2 shows a partial section view along line II-II
of Figure 1;
- Figure 3 shows a sectional enlarged view of the tubing
of Figure 1.
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The centrifugation device illustrated in Figure 1 is
substantially similar to that disclosed in WO 00/61294 and
is intended especially for blood apheresis and includes a
centrifugation rotor having the shape of a disk 1 comprising
a central tubular element 1a, mounted so as to pivot in two
sets of ball bearings, B1, B2. This centrifugation rotor 1,
carries a disposable centrifugation cup 2 in which is formed
a ring-shaped processing chamber 3 connected to a tubular
housing 10 formed coaxially to the rotation axis of the cup
2 by a plurality of radial channels 4, 5, 6, 7 shown in
Figure 2, provided through the bottom of the cup 2. Such a
disposable cup 2 is known and it is not necessary to disclose
it more for understanding the present invention, more
especially as it is already completely disclosed in the
above-mentionned WO 00/61294 to which it is possible to
refer.
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The disposable cup 2 is connected in a non-mobile way
to the centrifugation rotor 1 in the manner described below.
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The bottom of the cup 2 includes a coupling element
consisting of a cylindrical shank 11, that has a groove 11a
with a semi-cylindrical cross-section, adjacent to a truncated
end 11b. This coupling shank 11 engages with a coupling
ring 12 of a coupling tube 13, which are housed in the tubular
1a of the centrifugation rotor 1.
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The coupling tube 13 includes a coupling device, which,
in this embodiment, consist of a ball ring 16, located at
the inner end of the axial passage formed by the ring 12,
connected to the tubular part 1a of the rotor 1. A tubular
piston 17 is mounted so as to slide in the tubular part 1a.
Its upper end is terminated by a funnel-shaped surface 17a.
This tubular piston 17 is pressed axially against the inner
end of the ring by a coil spring 18, which is pressed
between one end of the tubular part 1a of the rotor 1, and a
bearing surface of the tubular piston 17. This axial pressure
in the direction of the ring 12 and the funnel shape 17a
have the effect of exerting centripetal forces on the ball
ring 16, which press them into the groove 11a of the
coupling shank 11 of the disposable cup.
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In order to prevent that these balls enter in the axial
opening of the ring 12, during removal of the coupling shank
11, a second piston 14 is mounted so as to slide inside the
tubular piston 17 and a second coiled spring 19 pushes it
axially against the end of the coupling shank 11.
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The outer end of the tubular piston 17 is connected to
a grasping element 20 to permit axial traction to be applied
opposite to the pressure of the spring 18, in order to permit
the balls 16 to move outward. The piston 14, subject to
the axial pressure of the spring 19 can then eject the cup 2
upward and simultaneously hold the balls 16 apart.
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The ball bearings B1, B2 of the tubular part 1a of the
rotor are mounted in a support element 21 attached to a plate
22, which is attached in turn to an upper disk 26, by two
verical hollow supports 15. A drive shaft 23 is mounted
inside one of these hollow supports 15 so as to pivot by
means of two ball bearings 24, 25 attached respectively to
the plate 22 and to an upper disk 26, located above the cup
2. This upper disk 26 is attached to a drive shaft 27 of a
motor 28, coaxial with the axis of rotation of the rotor 1.
An end of the shaft 23 extends above the disk 26 and is
attached to a satellite gear 29 in mesh with a fixed gear 30
coaxial to the axis of the rotor 1. The ratio between the
diameters of the satellite gear 29 and the fixed gear 30 is
1:1, so that if the rotation velocity of the plate 26 is ω,
that of the shaft 23 about its axis is 2ω. The lower end of
this shaft 23 carries a gear-wheel 31, connected by toothed
belt 32 to a gear-wheel 33 of the same diameter as the gear-wheel
31, so that the rotor 1 is driven at velocity 2ω.
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The radial channels 4, 5, 6, 7 provided through the
bottom of the cup 2 are connected to four conduits, 4a, 5a,
6a and 7a respectively (Figure 3), which are arranged in
parallel in a single flexible tubing 9. In the disclosed
embodiment, there are four radial channels 4, 5, 6, 7 connected
to four conduits 4a, 5a, 6a, 7a. However, obviously,
the invention is not limited to such a number of channels
and conduits. The cross-sections of the conduits 4a and 6a
having the larger section areas are elliptical, the major
axes of these ellipses being tangent to at least one circle
that is concentric to the longitudinal axis of tubing 9.
This orientation of the elliptical sections of conduits 4a,
6a facilitates the rotation of the tubing about its
longitudinal axis.
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The flexible tubing 9 forms an open loop, one end 9a of
which is attached and held in the tubular housing 10 whereas
the other end 9b is attached and held in a tubular adaptation
housing 10', substantially similar to the housing 10
supporting the first end of this tubing 9 and fixed and
coaxial to the axis of rotation of the rotor 1. These two
ends 9a, 9b are preferably glued in the housings 10, 10'.
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Between these two ends 9a, 9b attached to the housings
10, 10', the flexible tubing is sheathed by a coil spring 35
which is solid with this tubing on its whole length. To this
end, the coil spring may be avantageously glued around the
tubing. The gluing material must, in any case, not substantially
lowering the flexibility of the tubing. According to
an embodiment of the invention, if the tubing is manufactured
with a sufficiently flexible PVC to allow alternate bending
constraints, preferably with a PVC with rigidity in the
range of 50 to 75 ShA, moreover the disposal of such a
material being made easy. The gluing material may avantageously
be a cyanolit type adhesive material.
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The internal diameter of coil spring 35 must be slightly
larger than the external diameter of the tubing 9 in
order to prevent pre-constraints, detrimental to the bending
work of the tubing. According to a prefered embodiment of
the invention, the tubing has a diameter of 6,0 mm whereas
the coil spring has an internal diameter of 6,1 mm.
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The winding direction of the coil spring 35 has to be
the same than the rotation direction of the centrifugation
rotor 1.
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Avantageously, the coil spring 35 is made of stainless
steel so that it is simple and cheap to manufacture, and the
disposal of such a material is made easy. It could be also
made of hard plastic material such as hard PVC, PC or PMMA.
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The dimensions of coil spring 35 must be selected in
order to remain as light as possible so as to exert on the
tubing a centrifugal force as low as possible. The better
experimental results have been obtained with a wire section
diameter of the coil spring comprised between 0,1 to 0,6 mm,
preferably a diameter of 0,4 mm, with a coil pitch comprised
between 1 to 5 mm, avantageously a coil pitch of 2 mm for a
tubing diameter comprised between 3 and 12 mm. These dimensions
allows sufficent support of tubing 9 and prevent any
bead formation between adjacent coils.
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A support 36, provided with a curved guiding channel 37
having a semi-circular cross-section for receiving the flexible
tubing 9 sheathed by the coil spring 35, is attached
under the upper disk 26. This support 36 is made in a material
having a low friction coefficient and a low attrition
rate with the material of the coil spring 35. Avantageously,
it is made in Vaflon® (Dixon Resine) which is a PTFE and
polymer mixture, or in UltraCOMP® (Parker Hannifin) which is
an injection moulding thermoplastic or an equivalent platic
material. Preferably, the radius or radii of curvature of
curved guiding channel 37 will not be lower than 25 mm for
improving the rotation of the tubing 9 around its longitudinal
axis.
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The coil spring 35 sheathing the tubing 9 is able to
reduce the friction torque between the tubing 9 and the guiding
channel 37, thus maintaining the temperature of the tubing
as well as that of the liquid (particularly the blood)
flowing through it, lower than 38°, in order to prevent all
blood injury (particularly blood hemolysis).
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The coil spring is also able to rigidify the tubing 9
against the torque reaction in order to prevent any risk of
complete or partial collapse of the conduits 4a, 5a, 6a, 7a
inside the tubing 9.
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The coil spring sheathed tubing according to the present
invention is more particularly useful in the case of a
liquid centrifuging apparatus disclosed in WO 00/61295, since
such a coil spring sheathed tubing allows to substantially
increase the rotational speed of the centrifuging rotor
1. The centrifugal force being proportional to the centrifugal
radius and to the square of the rotational speed of the
centrifugation cup 2, it may be observed that if the rotational
speed of this cup 2 is doubled while its diameter is
reduced by half the separation power remains unchanged.
Accordingly, the present invention allows to obtain a very
compact liquid centrifuging device having very low overall
dimensions.