Metabolic characterization of a CHO cell size increase phase in fed-batch cultures
Pan, Xiao ; Dalm, Ciska ; Wijffels, René H. ; Martens, Dirk E. - \ 2017
Applied Microbiology and Biotechnology 101 (2017)22. - ISSN 0175-7598 - p. 8101 - 8113.
Antibody production - Cell size increase - Chinese hamster ovary (CHO) cell - Fed-batch - Metabolic flux analysis - Phase transition
Normally, the growth profile of a CHO cell fed-batch process can be divided into two main phases based on changes in cell concentration, being an exponential growth phase and a stationary (non-growth) phase. In this study, an additional phase is observed during which the cell division comes to a halt but the cell growth continues in the form of an increase in cell size. The cell size increase (SI) phase occurs between the exponential proliferation phase (also called the number increase or NI phase) and the stationary phase. During the SI phase, the average volume and dry weight per cell increase threefold linearly with time. The average mAb specific productivity per cell increases linearly with the cell volume and therefore is on average two times higher in the SI phase than in the NI phase. The specific essential amino acids consumption rates per cell remain fairly constant between the NI and the SI phase, which agrees with the similar biomass production rate per cell between these two phases. Accumulation of fatty acids and formation of lipid droplets in the cells are observed during the SI phase, indicating that the fatty acids synthesis rate exceeds the demand for the synthesis of membrane lipids. A metabolic comparison between NI and SI phase shows that the cells with a larger size produce more mAb per unit of O2 and nutrient consumed, which can be used for further process optimization.
Phase transitions in polymer monolayers : Application of the Clapeyron equation to PEO in PPO-PEO Langmuir films
Deschênes, Louise ; Lyklema, J. ; Danis, Claude ; Saint-Germain, François - \ 2015
Advances in Colloid and Interface Science 222 (2015). - ISSN 0001-8686 - p. 199 - 214.
Clapeyron - Monolayers - PEO - Phase transition - PPO
In this paper we investigate the application of the two-dimensional Clapeyron law to polymer monolayers. This is a largely unexplored area of research. The main problems are (1) establishing if equilibrium is reached and (2) if so, identifying and defining phases as functions of the temperature. Once this is validated, the Clapeyron law allows us to obtain the entropy and enthalpy differences between two coexisting phases. In turn, this information can be used to obtain insight into the conformational properties of the films and changes therein. This approach has a wide potential for obtaining additional information on polymer adsorption at interfaces and the structure of their monolayer films. The 2D Clapeyron law was applied emphasizing polyethylene oxide (PEO) in polypropylene oxide (PPO)-PEO block copolymers, based on new well-defined data for their Langmuir films. Values for enthalpy per monomer of 0.12 and 0.23 kT were obtained for the phase transition of two different PEO chains (Neo of 2295 and 409, respectively). This enthalpy was estimated to correspond to 1.2 ± 0.4 kT per EO monomer present in train conformation at the air/water interface.