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This article is the second of a 4 part series describing currently available apheresis devices and technologies. The sections will include: Part 1: Membrane Plasma Separator (published in Vol. 1); Part 2: Membrane Plasma Fractionator: Part 3: Leukocyte Filter; and Part 4: Adsorbent.

This article is the first of a 4 part series describing currently available apheresis devices and technologies. The sections will include: Part 1, Membrane plasma separator; Part 2, Membrane plasma fractionator; Part 3, Leukocyte filter; and Part 4, Adsorbent.

On-line membrane plasma fractionation techniques have made semiselective removal of pathological macromolecules practical. However, several problems such as cryogel formation exist when the procedure is performed at ambient temperature. Cryogel formation takes place when heparinized plasma is cooled below 35 degrees C and when it tends to occlude the pore structure of the secondary filter membrane resulting in a poor molecular cut off of the macromolecular filter. Thermofiltration is one of the on-line plasma fractionation techniques used when warming plasma from 37 to 42 degrees C to prevent cryogel formation. Thermofiltration enhanced the performance of the lipofilter (Kuraray 4A) and demonstrated better molecular cut off between low density lipoprotein (LDL) cholesterol and high density lipoprotein (HDL) cholesterol than double filtration plasmapheresis (DFPP). An improved lipofilter (Kuraray 5A) has been developed and has shown better molecular cut off between LDL cholesterol and HDL cholesterol than the 4A filter. However, cryogel formation still occurred even using the 5A filter during the DFPP procedure. Thermofiltration maintains the performance of the secondary filter by preventing cryogel formation. Further studies are required to evaluate the enhanced performance of the 5A filter by thermofiltration.