Off-Gas-Based Soft Sensor for Real-Time Monitoring of Biomass and Metabolism in Chinese Hamster Ovary Cell Continuous Processes in Single-Use Bioreactors

Abstract

In mammalian cell culture, especially in pharmaceutical manufacturing and research, biomass and metabolic monitoring are mandatory for various cell culture process steps to develop and, finally, control bioprocesses. As a common measure for biomass, the viable cell density (VCD) or the viable cell volume (VCV) is widely used. This study highlights, for the first time, the advantages of using VCV instead of VCD as a biomass depiction in combination with an oxygen-uptake- rate (OUR)-based soft sensor for real-time biomass estimation and process control in single-use bioreactor (SUBs) continuous processes with Chinese hamster ovary (CHO) cell lines. We investigated a series of 14 technically similar continuous SUB processes, where the same process conditions but different expressing CHO cell lines were used, with respect to biomass growth and oxygen demand to calibrate our model. In addition, we analyzed the key metabolism of the CHO cells in SUB perfusion processes by exometabolomic approaches, highlighting the importance of cell-specific substrate and metabolite consumption and production rate qS analysis to identify distinct metabolic phases. Cell-specific rates for classical mammalian cell culture key substrates and metabolites in CHO perfusion processes showed a good correlation to qOUR, yet, unexpectedly, not for qGluc. Here, we present the soft-sensoring methodology we developed for qPyr to allow for the real-time approximation of cellular metabolism and usage for subsequent, in-depth process monitoring, characterization and optimization.

Current challenges and recent advances on the path towards continuous biomanufacturing

“…For example, an in-line gas probe in combination with a multilinear regression model was utilized as a soft sensor for biomass estimation in perfusion bioreactors. 129 Also, a soft sensor based on a combination of multi-wavelength fluorescence spectroscopy and a hybrid model demonstrated good performance in estimation of cell concentration, titer, glucose and ammonia. 130 However, it should be noted that several challenges are associated with 131 (2) a need to minimize sampling due to the risk of compromising the sterile barrier (e.g., biomass estimation in continuous aseptic closed systems) or (3) it has demonstrated higher robustness to process fluctuations and background compared to already existing physical sensors (e.g., capacitance probe).…”

“…Data‐driven and hybrid models are the predominant model types employed for soft sensors. For example, an in‐line gas probe in combination with a multilinear regression model was utilized as a soft sensor for biomass estimation in perfusion bioreactors 129 . Also, a soft sensor based on a combination of multi‐wavelength fluorescence spectroscopy and a hybrid model demonstrated good performance in estimation of cell concentration, titer, glucose and ammonia 130 .…”

Special Issue: Mathematical Modeling and Control of Bioprocesses

“…Sari [10] considers one-step and two-step models of anaerobic digestion together with a large class of growth functions encountered in applications, and studies their operating diagrams as a function of the dilution rate and inlet concentration, so as to define the best operating conditions for biogas production. In [11], Wallocha and Popp present an off-gas-based software sensor for real-time biomass estimation in continuous single-use bioreactors with CHO cell lines. They discuss the interest of considering viable cell volume concentration (instead of the density) as cell size or volume can have a direct impact on oxygen demand.…”