Bioseparations, especially by hollow fibers

Downstream processing in biotechnology is best idealized as a four step process: removal of insolubles, isolation, purification, and polishing. The first and last steps are relatively easily achieved; the isolation and purification steps include most of the potential problems. While purification has often been presumed the most difficult, isolation may involve the greatest cost, presumably because it involves getting a small volume of concentrate from a large volume of feed. Both purification and isolation can sometimes use hollow fibers for extraction and chromatography.