Membrane filters are frequently associated with more-sensitive filtration processes as well. Certain devices have historically employed such filters to ensure that solutions passed through them are free of bacteria that could be harmful to the patient. In this situation, membranes are rated by their molecular weight cutoffs, rather than their pore size, and are used in conjunction with centrifugation or tangential-flow filtration to yield product that is uniform, highly controlled, and concentrated enough for sensitive assaying techniques. The pores that are present in these membranes are orders of magnitude smaller than even the tightest microfiltration units. Ultrafiltration allows researchers to concentrate biological solutions.
Dialysis can then offer further purification by removing salts and allowing for buffer exchange.
This helps ensure success, purity, and long life for their very sophisticated and expensive equipment. As all of these applications become increasingly sensitive and IVD and pharmaceutical manufacturers demand more from their processes, filtration will continue to be a critical technique. The uses of membranes, however, are not confined to filtration. Membranes offer a solid support for reagent application and delivery. The unique properties of a membrane to act as a solid phase for immunoassays and to carry reagents across its surfaces have made this material indispensable to the POC market.