Liquid purification or separation – Casing divided by membrane into sections having inlet – Cylindrical membrane
Reexamination Certificate
2001-10-29
2004-08-10
Walker, W. L. (Department: 1723)
Liquid purification or separation
Casing divided by membrane into sections having inlet
Cylindrical membrane
C210S321790, C210S500230, C210S646000, C422S044000
Reexamination Certificate
active
06773591
ABSTRACT:
The present invention relates to a bundle of hollow fibres for a device for treating blood or plasma by extracorporeal circulation, and to a process for producing a bundle of hollow fibres constituting the semi-permeable membrane of the device.
Membrane devices for treating blood or plasma by extracorporeal circulation are used in many different medical or paramedical applications, such as treating renal insufficiency by dialysis or haemofiltration, plasmapheresis and apheresis for therapeutic and non-therapeutic purposes, oxygenating blood, immunopurification, etc.
In general, semi-permeable membranes can be classified by their hydraulic permeability into low flux membranes, medium flux membranes and high flux membranes.
Hydraulic permeability describes the quantity of water that can be ultrafiltered through a semi-permeable membrane with a given active surface area, at a given transmembrane pressure over a given time period. Simultaneously with the water ultrafiltration, salts and toxins traverse the semi-permeable membrane. Eliminating the different solutes depends on a property of the membrane known as the rejection rate or transmittance (transmittance=1 or rejection rate=0 for solutes traversing the membrane with no change in concentration, rejection rate=100% and transmittance=0 for completely cleared solutes). The transmittance of a particular molecule is defined as the ratio of the concentration of the molecule in ultrafiltered water (ultrafiltrate) to its mean concentration in the unfiltered fraction of the blood.
With high flux semi-permeable membranes, i.e., with a hydraulic permeability of at least 31×10
−12
m
3
/s.Pa.m
2
(15 ml/h.mmHg.m
2
), the quantity of water extracted from the blood must be regulated using a water extraction controller. Devices provided with a high flux membrane run the risk of reverse filtration or back filtration, which consists of migration of a portion of the dialysis solution into the blood.
The dialysis solution, which has an electrolytic composition that is close to that of a normal extracellular liquid, is usually a non-sterile aqueous solution. Before use, the dialysis solution is normally free of solutes to be eliminated from the blood, but can contain foreign substances or pyrogenic substances, for example as a result of microbial contamination. Dialysis solution is not intended for injection into the blood and thus does not have the quality of an injectable liquid. With back filtration, then, there is then a risk of causing foreign or pyrogenic substances to enter the blood with the dialysis solution.
As is known, back filtration can be minimised by using semi-permeable low flux membranes with a hydraulic permeability of less than 12.5×10
−12
m
3
/s.Pa.m
2
(6 ml/h.mmHg.m
2
), or medium flux semi-permeable membranes with a permeability of between about 12.5 and about 31×10
−12
m
3
/s.Pa.m
2
(between about 6 and about 15 ml/h.mmHg.m
2
). However, the reduction in hydraulic permeability is generally accompanied by a reduction in transmittance, i.e., a reduction in the fraction of certain molecules that pass by convection through the pores of the membrane and which are intended to be eliminated from the blood.
Thus, one aim of the invention is to provide a device for treating blood or plasma by extracorporeal circulation, comprising a semi-permeable membrane with a reduced overall hydraulic permeability to limit the risks of reverse filtration, while retaining satisfactory transmittances, in particular those for toxins and proteins.
A further aim of the invention is to provide a device for treating blood or plasma by extracorporeal circulation comprising a semi-permeable membrane, the characteristics (hydraulic permeability, transmittances) of which can be adjusted independently of each other to a certain extent such that the hydraulic permeability of the membrane is low flux, medium flux or high flux, while the transmittances, in particular as regards toxins and proteins, are maintained at satisfactory values.
In a first aspect of the invention, these aims are achieved by a bundle of hollow fibres intended to constitute the semi-permeable membrane of a device for treating blood or plasma by extracorporeal circulation, in which:
the distribution of the hollow fibres in the bundle is heterogeneous; and
the internal diameter and wall thickness of the hollow fibres located in the zones most dense in hollow fibres are respectively greater than the internal diameter and wall thickness of the hollow fibres located in the least dense zones.
Preferably, the internal diameter and wall thickness of the hollow fibres located in the zones least dense in hollow fibres are respectively a minimum of 180 microns and 40 microns.
In a variation of the invention:
the heterogeneity of the distribution of the hollow fibres in the bundle corresponds to a higher density of hollow fibres around at least a portion of the periphery of the bundle compared with a density of hollow fibres at the centre of the bundle; and
the internal diameter and wall thickness of the hollow fibres located at the periphery of the bundle are respectively greater than the internal diameter and wall thickness of the hollow fibres located at the centre of the bundle.
In a second aspect of the present invention, the above aims are achieved by a bundle of hollow fibres intended to constitute the semi-permeable membrane of a device for treating blood or plasma by extracorporeal circulation, in which:
the hydraulic permeability of the hollow fibres in the bundle is heterogeneous; and
the ratio of the highest hydraulic permeability measured on some hollow fibres of the bundle to the lowest hydraulic permeability measured on other hollow fibres of the same bundle is at least about 5.
In a variation of the invention, the heterogeneity of the hydraulic permeability in the bundle corresponds to a higher hydraulic permeability around at least a portion of the periphery of the bundle compared with a hydraulic permeability of the bundle fibres, such that the ratio of the highest hydraulic permeability measured at the periphery of the bundle to the lowest hydraulic permeability measured at the centre of the bundle is at least about 5.
In a further variation of the invention, the heterogeneity of the hydraulic permeability is associated with a heterogeneity of the distribution of the hollow fibres in the bundle, the hydraulic permeability being higher in the zones most dense in hollow fibres and lower in the zones least dense in hollow fibres.
Advantageously, the internal diameter and wall thickness of the hollow fibres located in the zones most dense in hollow fibres are respectively greater than the internal diameter and wall thickness of the hollow fibres located in the zones least dense in hollow fibres. Advantageously again, the internal diameter and wall thickness of the hollow fibres located in the zones least dense in hollow fibres are respectively a minimum of 180 microns and 40 microns.
In one embodiment of the invention, the overall hydraulic permeability of the bundle of hollow fibres is in the range 10×10
−12
to 312×10
−12
m
3
/s.Pa.m
2
(5 to 150 ml/h.mmHg.m
2
), the lowest hydraulic permeability measured at the centre of the bundle is less than 17×10
−12
m
3
/s.Pa.m
2
(8 ml/h.mmHg.m
2
) and the highest hydraulic permeability measured at the periphery of the bundle is more than 42×10
−12
m
3
/s.Pa.m
2
(20 ml/h.mmHg.m
2
).
In a further embodiment, the overall hydraulic permeability of the bundle of hollow fibres is in the range 42×10
−12
to 146×10
−12
m
3
/s.Pa.m
2
(20 to 70 ml/h.mmHg.m2), the lowest hydraulic permeability measured at the centre of the bundle is less than 17×10
−12
m
3
/s.Pa.m
2
(8 ml/h.mmHg.m
2
), the highest hydraulic permeability measured at the periphery of the bundle is more than 83×10
−12
m
3
/s.Pa.m
2
(40 ml/h.mmHg.m
2
) and the ratio of the highest hydraulic permeability measured at
Boivin Didier
Farjaud Jean
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Hospal Industrie
Menon Krishnan S
Walker W. L.
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