A unit element forming a membrane comprising a semi-permeable material able toseparate in two compartments a filtration device for extracorporeal treatmentof fluid. The material is negatively charged and the element has a firstinternal face for direct contact with fluid under treatment and a secondexternal face for contact with filtrate. The second face has a surface treatedby a substance comprising at least a cationic polymer, or by a mixture ofpolymers of which at least one polymer is cationic. The unit element can alsohave a first face treated as the second face. The invention refers also to asemipermeable membrane comprising the unit elements, and to a filtrationdevice comprising two compartments separated by such a semipermeable membrane,as well as to processes for manufacturing above components and devices.
