TECHNOLOGY FOCUS - POLYMERS - Preferred Membrane: The system may include a non-woven coarse filter layer in full contact with the membrane layer, and all parts (supporting layer, coarse filter layer (if any) and membrane layer) may contain polymer (I). All parts may also contain a reactive agent, preferably selected from nutrient media, cell cultures, phages, viruses, catalysts, fluorescent markers and/or colored markers. The system may contain electrodes and the membrane layer shows an open pore diameter of 10 nm to 100 microns.Preferred Polymers: Polyuronic acid polymers which are completely soluble in isotonic solution at room temperature, preferably homo- and co-polymers of glucuronic, galacturonic, mannuronic, hyaluronic and/or guluronic acid. These are derived from the corresponding alkali, alkaline earth, ammonium and/or aluminum salts.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Solutions: Isotonic solutions containing ascorbic, succinic, citric, salicylic and/or 5-sulfosalicylic acid (dihydrate), or (in buffered form) their derivatives, i.e. sodium or potassium L(+)-ascorbate, succinic anhydride, disodium succinate and its hexahydrate, citric acid monohydrate, tripotassium citrate monohydrate, ammonium iron(III) citrate, trisodium citrate dihydrate, and/or sodium or potassium salicylate. EXAMPLE - Commercial polypropylene (PP) non-woven fabric was conditioned to remove air bubbles, impregnated with 0.5-M aluminum polychloride solution, stretched on a finely-perforated plastic or stainless steel sieve plate and coated with a 0.5% solution of L-guluronic acid/D-mannuronic acid (equimolar) in a film thickness of 0.5 mm. After 20 seconds, the material was vigorously rinsed with water from below, flooded with water from above and tilted to remove the water. A coarse non-woven (B) consisting of aluminum alginate (see below; pre-impregnated with water) was laid over the undried membrane and covered with a plastic sheet, then the assembly was placed on a base with the sieve plate facing upwards. The sieve plate and PP non-woven were removed and the membrane (now on top) was covered with another water-impregnated non-woven, after which any air bubbles were removed by light application of a roller and round filters with a diameter of 5 cm were stamped out of the final sheet. These were kept under water or sterilized and welded into film for longer storage. The coarse non-woven (B) was produced by atomizing a guluronic/mannuronic acid solution (as above) and an aluminum polychloride solution in a 2-component nozzle to form fibres which were then sprayed with water, compressed to form a 3-mm thick fabric and dried.