(406d) Mechanisms of Pickering Foam Stabilization during Bioreactor Operation

Authors: 
Grismer, D. A., North Carolina State University
Ferguson, R., Biogen
Chang, K., Biogen
Osborne, D., Biogen
Velev, O. D., North Carolina State University
Pickering foams have garnered increasing attention because of their characteristically long decay times. However, their persistence can present a significant challenge when foam formation is undesired in the course of industrial processes such as bioreactor operation. In the later stages of cell culture proliferation in bioreactors, Pickering stabilization of the foam head occurs, causing the traditional remediation strategy of antifoam addition to be less effective. The correlation between foam stability and process age is strongly tied to the accumulation of biomass, specifically an increase in the number and the distribution of size and shape of biological particles. We present results and analysis of the stabilization effects and breakdown behavior of foams stabilized by these biological particles. Through the use of optical microscopy we observe the entrapment of cells in thin foam films and at Plateau borders. In order to elucidate the mechanisms of foam stabilization in this system, we study samples extracted at different time points in bioreactor cell culture processes each with corresponding differences in the cell concentration and viability as well as differences in the concentration of cell debris fragments and macromolecules. We compare data for interfacial adsorption, entrapment in the thin liquid films and Plateau borders, and accumulation in real bulk foams. We explore how each class of biological particles and surface-active agents contributes to foam formation and foam stabilization on their own and through interaction between the molecular and particle species. Additionally, we discuss the role that antifoam addition and deactivation has on the lifetime of these biological particle-based Pickering foams.