Control of dissolved oxygen concentration in mammalian cell culture using a computer-coupled masss flow controller

Abstract

An enhancement of the oxygen transfer rate in a 1 L bioreactor for mammalian cell culture by using a silicone rubber tubing as an oxygenator and the effects of the controlled dissolved oxygen(DO) concentraiton on the growth kinetics of Vero-6 cell were investigated. When the silicone membrane was used to supply oxygen to the culture broth, the oxygen transfer coefficients($K_La$) measured in deionized distilled water were markedly increased. Effect of surface aeration without the tubing aeration was very low under 1.0$hr^{-1}$ of $K_La$. The enhancing effects of agitation rates on $K_La$ were much more effective than aeration rates. The increase of $K_La$ with increasing tube length was observed as a results of the large surface area for oxygen supply. However, 2m of the tube length was adequate for a 1L vessel. The lager blade type of impeller was effective to enhance the $K_La$ values because of its high mixing intensity. In culture medium supplemented with 5\% serum, $K_La$ values reduecd to approximately 40\% probably due to the viscosity. Thus, oxygen enrichment in aeration and/or control of DO level were required for the adequate supply of oxygen to the cells. For this reason, a proportional control system of DO concentration in medium was developed by using a computer-coupled mass flow controller. The DO levels controlled by a microcomputer were very stable during the cultivation of Vero-6, while flow rates of air and/or oxygen enriched air were gradually changed depending on the DO concentration and the preset DO level. Growth of Vero-6 at the low level(10\%) of DO was retarded, probably due to the oxygen limitation which was obscrved intuitively from the result of the high production of organic acid. Vero-6 cell cultured at higher DO than 30\% could grow normally to the confluence on microcarriers.