Cell-microcarrier adhesion to gas-liquid interfaces and foam

The interaction of microcarriers, both with and without cells attached, wit h gas bubbles was studied. These studies consisted of qualitative microscop ic observations of microcarriers with bubbles, quantitative measurements of microcarrier entrapment in foam, and quantitative measurements of the effe ct of bubble rupture at gas-medium interfaces. Ten different "protective ad ditives" were evaluated for their ability to change the dynamic surface ten sion of the culture media and to prevent microcarrier adhesion to air bubbl es during gas sparging and to prevent entrapment in the foam layer. These s tudies indicate that microcarriers, with and without cells, readily attach to gas-medium interfaces; yet unlike suspended cells, cells attached to mic rocarriers are not damaged by bubble ruptures at gas-medium interfaces. Onl y one surfactant was found to substantially prevent microcarrier entrapment in the foam layer; however, this surfactant was toxic to cells. No correla tion was observed between surface tension and the prevention of microcarrie r adhesion to gas-liquid interfaces. It is suggested that cell damage as a result of sparging in microcarrier cultures is the result of cells, attache d to microcarriers, attaching to rising bubbles and then detaching from the microcarrier as this combination rises through the medium. It is further s uggested that the hydrodynamic drag force of the rising microcarrier is suf ficiently high to remove the bubble-attached cell from the microcarrier.