stated, the cell concentration in the foam will depend on the attachment of cells to
bubbles, the cell concentration, the amount of liquid transferred to the foam and the
drainage of liquid from the foam relative to the drainage of cells. The combination of cell
attachment to bubbles and drainage of cells from the foam layer is studied in foam-
fractionation studies. In these studies a foam layer formed by blowing air through a cell
suspension is captured and the cell concentration in this captured foam is determined.
Michaels et al. (1995b) and Wen and Tan (1999) did this kind of study in the presence of
different additives. Michaels et al. (1995b) measured the following parameters: A cell
separation factor being the cell concentration in the foam (Cfoam) divided by the cell
concentration in the bulk (Cbulk):
(22)
Cbulk is the average cell concentration in the bulk at the start and end of a foaming
experiment.
Fractional fluid transfer FL:
(23)
Since fluid transfer and cell adsorption may assumed to be related to the total surface
area, both parameters may be corrected for the total surface area:
(24)
(25)
where NF is the ratio of the Sauter mean bubble diameter in a particular medium to the
one in a serum-free medium.
The viabilities in the foam and bulk were quantified using the following normalised
viabilities:
(26)Of final interest is the fraction of cells removed through the foam corrected for the total
surface area, b:
(27)Finally, the foaming height and the half time for foam reduction may address the stability
of the foam. Results are shown in Table 15.5 and Table 15.7 and can be summarised as
follows:
Multiphase bioreactor design 480