Cell-microcarrier adhesion to gas-liquid interfaces and foam

The interaction of microcarriers, both with and without cells attached, with gas bubbles was studied. These studies consisted of qualitative microscopic observations of microcarriers with bubbles, quantitative measurements of microcarrier entrapment in foam, and quantitative measurements of the effect of bubble rupture at gas-medium interfaces. Ten different "protective additives" were evaluated for their ability to change the dynamic surface tension of the culture media and to prevent microcarrier adhesion to air bubbles during gas sparging and to prevent entrapment in the foam layer. These studies indicate that microcarriers, with and without cells, readily attach to gas-medium interfaces; yet unlike suspended cells, cells attached to microcarriers are not damaged by bubble ruptures at gas-medium interfaces. Only one surfactant was found to substantially prevent microcarrier entrapment in the foam layer; however, this surfactant was toxic to cells. No correlation was observed between surface tension and the prevention of microcarrier adhesion to gas-liquid interfaces. It is suggested that cell damage as a result of sparging in microcarrier cultures is the result of cells, attached to microcarriers, attaching to rising bubbles and then detaching from the microcarrier as this combination rises through the medium. It is further suggested that the hydrodynamic drag force of the rising microcarrier is sufficiently high to remove the bubble-attached cell from the microcarrier.