HOLLOW FIBRE MICROFILTRATION

OVERVIEW

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LAST UPDATED 13 September 2004

SPECTRUM Hollow Fiber Microfiltration

Microfiltration is mostly the filtration of substances that range in size 0.1 µm to 10 µm. Often microfiltration is used to refer to the removal of microbes, such as in cold sterilization since bacteria, fungal spores, yeast and some viruses fall into this size range. Filters with a 0.2 µm or smaller pore size rating are frequently regarded as being able to sterilize solutions. Generally this is only approximately true and then only if the filter itself is sterilized before use. Filters with larger pore size ratings may be used to clarify samples without necessarily sterilizing them.

Filtration is similar to dialysis in that both use a membrane to effect a separation based on the size of particles or molecules. Filtration uses pressure to drive the material through the membrane; this differs from dialysis where osmotic pressure is used to drive the separation.

Because large pressures can be used to drive microfiltration separations, considerable concentration polarization can develop. In standard dead-ended separations (where the bulk fluid flow is toward the filter membrane) the concentration of retained species will increase most rapidly just behind the membrane. This leads to a decreasing flow as the retained material forms a barrier just behind the membrane. As the concentration of retained material just behind the membrane increases, its solubility limit may be reached. This will result in formation of a "gel" layer that further restricts the flow.

MEDICELL offers Spectrum's microfiltration products which are based on hollow fiber filters, bundles of small tubes (hollow fibers) of filter media. The use of many small tubes keeps the bulk flow moving along the surface of the membrane and not directly toward the filter surface. This lowers the concentration of retained material near the filter surface by continually washing it away and prevent the formation of a gel layer. Spectrum offers four ready-to-use microfilters for different applications:

• MediaKap® Hollow Fiber Media Filters for fast filtration of media.
• CultureGard™ Media Feed Protection Filter for Continuous Perfusion Cultures
• MiniKap® Point of Use Microfitration Filters for general use
• DynaGard® Syringe Filter Tips for HPLC applications and sterile filtration