(1) Field of the Invention
The invention relates to a filtration unit for the selective removal of target substances from a fluid such as blood or a blood component, and a method for manufacturing such a unit and a bag system comprising same.
It typically applies to the filtration of blood or a blood component to remove undesirable substances for transfusion, such as leukocytes, pathogens, prion proteins and/or substances used in pathogen inactivation and/or removal methods.
The blood or blood component, after the collection and separation thereof in the case of a component, is particularly intended to be transfused to a patient needing same. During transfusion, it is well known that leukocytes are undesirable in that they are liable to induce adverse and/or potentially dangerous reactions in the patient.
The same applies for certain substances such as the prion, the agent responsible for cases of transmissible subacute spongiform encephalopathy, particularly the Creutzfeld-Jacob disease variant in humans since recent studies have demonstrated a likely risk of prion transmission in blood transfusions.
To remove said undesirable substances, filtration units comprising a flexible outer casing containing a porous medium and provided with at least one inlet orifice and at least one outlet orifice wherebetween the fluid to be filtered flows in one direction are already known. The porous medium defines with the outer casing an inlet compartment for the fluid to be filtered and an outlet compartment for the filtrate.
In such units, illustrated for example by the document EP-A-526 678, the nozzles providing the inlet and outlet orifices are arranged symmetrically between two sheets forming the outer casing.
The document JP-3132307 describes a method used to seal a nozzle between two flexible sheets. According to this method, a stack consisting successively of a first flexible sheet, the nozzle and a second flexible sheet, is arranged between two identical moulds. A metal tube is inserted into the nozzle and a high-frequency dielectric current is sent into the mould to seal the nozzle with the sheets. As the two moulds holding the nozzle between the sheets are symmetrical, the seal is thus aligned on a diameter of the nozzle.
With such a method applied to the manufacture of filtration units, as described in the document WO-A1-01 56679, the flow of the fluid at the inlet and at the outlet of the filtration unit is not optimal. Indeed, due to the thickness thereof, the porous medium faces the opening of the inlet and outlet nozzle, impeding the circulation of the fluid in the filtration unit. In particular, the filling of the inlet compartment and draining of the outlet compartment are slowed down.
So that the inlet and/or outlet orifice opens directly into the inlet and/or outlet compartment without being impeded by the thickness of the porous medium, sealing a moulded part serving as a fluid inlet and/or outlet orifice on the surface of each of the flexible sheets has been envisaged. Such units are for example described in the document WO-A1-01 91880.
However, with such moulded parts, the wetting of the filtration medium is not optimised as the blood arrives perpendicular to the filtration medium. Furthermore, the sealing of said moulded parts on the surface of the sheets complicates the method for manufacturing filtration units and increases the cost thereof.