Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Patent
1996-04-08
1999-06-22
Kim, John
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
21032175, 21032184, 210422, 210435, 210651, B01D 6114, B01D 6118, B01D 6308, A61M 134
Patent
active
059140429
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a device and method for separating blood cells from plasma or from another fluid in which cells are suspended.
An adult human contains about 5 liters of blood, of which red blood cells, also referred to as erythrocytes, account for about 45% of the volume, white cells about 1% and the balance being liquid blood plasma in which the cells are suspended. Blood also contains large numbers of platelets suspended in the plasma (their proportional volume is small). In view of the substantial therapeutic and monetary value of blood components, such as red blood cells, platelets and plasma, a variety of techniques have been developed to separate blood into its component fractions or to separate combinations of such components while ensuring maximum purity and recovery of each of the components.
Throughout this specification the term blood product will be used to refer to anticoagulated whole blood or suspensions of red blood cells (with or without other blood cell types) in a suitable fluid such as plasma or SAG-M (whose composition is detailed below).
In general, such separations have been achieved by centrifugation techniques. This requires, however, significant handling of the blood product, which can increase the risk of disease transmission. In addition, centrifuging also takes significant time.
An alternative to centrifugation for the separation of red blood cells, white blood cells and platelets from plasma or another fluid in which the cells are suspended is filtration. This can be achieved by flowing a blood product across a surface of a membrane whereupon plasma or another cell suspending fluid passes through the membrane under a pressure gradient generated across the membrane. This process is hereinafter referred to as cross-flow filtration. It has been found, however, that the filtration efficiency of such a membrane drops because the membrane pores become blocked with blood cells and cell fragment debris during filtration. Blocking cells and debris may not be effectively removed by cross-flow of the blood product across the surface of the membrane. As a result, the membranes previously used for such filtration have blocked before the haemocrit (the percentage of red blood cells in the suspending fluid) reaches a desired figure, for example 70% by volume.
In EP-A-464707, this problem is sought to be overcome by a shearing force induced at the membrane surface by forming the membrane as a cylinder and rotating it within a non-rotating outer cylinder whose walls are in close proximity to the rotating membrane. This process generates so-called "Taylor Vortices" which are intended to clear the membrane surface of clogging cells and debris and to provide increased trans-membrane pressure to increase plasma flow across the membrane.
A similar proposal for overcoming this problem is made by Beaudoin and Jaffrin in the article "Plasma Filtration in Couette Flow Membrane Devices" in the Journal "Artificial Organs" Volume 13 No. 1 1989 pages 43-51.
EP-A-0111423 endeavours to induce vortices in the flow using dimples formed on the surface of the membrane.
These approaches suffer from certain technical limitations. The proposal of EP-A-0111423 requires very precise alignment of the "dimples". Failure to achieve this will degrade the effectiveness of the device. The approaches of Beaudoin and Jaffrin and EP-A2-464707 require accurate alignment of the rotating and non-rotating cylinders and additionally require an electric motor to rotate the rotating cylinder which increases the expense and complexity of the device.
In all these proposals for plasma separation by filtration, it is essential that there is no or no significant lysis of erythrocytes in the blood product, since this releases haemoglobin. Since this is a protein, it can pass freely across the membrane with the other non-cellular components of the blood. Free haemoglobin (i.e. haemoglobin not contained within the erythrocyte cell membrane) is potentially undesirable, especially where the plasma is required for therapeutic purposes
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Ball Peter R.
Boulter Eileen M. A.
Hall Christopher C.
Kim John
Pall Corporation
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