Glass microspargers as effective frit spargers in single use bioreactors.

For multiple-use bench scale and larger bioreactors, sintered stainless steel frit spargers are commonly used as microspargers. For bench-scale single-use bioreactors (SUBs), existing microspargers are sintered plastics, such as polyethylene. However, though plastics are readily sterilized by irradiation making them convenient for single use, these designs overlook surface energy properties of the materials of construction. For these sintered plastic spargers, forces at the water-air-surface interface cause bubble coalescence, leading to lower effective mass transfer, higher gas flow rates, and differing pCO2 profiles in cell culture. Alternative materials of construction were evaluated based on contact angle information and bubble formation observations. Sintered glass was chosen over thermoplastic polymers for higher surface wettability as described in the glass/water contact angle, its history as a commonly sintered material, and availability at costs suitable for single use applications. Glass sintered spargers and traditional stainless steel frit spargers were compared by porosity, bubble size, and kL a studies. Mass transfer (kL a) and cell culture performance equal or greater than a standard 20 µm stainless steel microsparger mass transfer efficiency was achieved by a glass frit sparger, of international porosity standard "P40" according to ISO 4793-80, which corresponds to a range of 16-40 µm.

A practical approach in bioreactor scale-up and process transfer using a combination of constant P/V and vvm as the criterion.

Bioreactor scale-up is a critical step in the production of therapeutic proteins such as monoclonal antibodies (MAbs). With the scale-up criterion such as similar power input per volume or O2 volumetric mass transfer coefficient ( kLa), adequate oxygen supply and cell growth can be largely achieved. However, CO2 stripping in the growth phase is often inadequate. This could cascade down to increased base addition and osmolality, as well as residual lactate increase and compromised production and product quality. Here we describe a practical approach in bioreactor scale-up and process transfer, where bioreactor information may be limited. We evaluated the sparger kLa and kLaCO2 (CO2 volumetric mass transfer coefficient) from a range of bioreactor scales (3-2,000 L) with different spargers. Results demonstrated that kLa for oxygen is not an issue when scaling from small-scale to large-scale bioreactors at the same gas flow rate per reactor volume (vvm). Results also showed that sparging CO2 stripping, kLaCO2, is dominated by the gas throughput. As a result, a combination of a minimum constant vvm air or N2 flow with a similar specific power was used as the general scale-up criterion. An equation was developed to determine the minimum vvm required for removing CO2 produced from cell respiration. We demonstrated the effectiveness of using such scale-up criterion with five MAb projects exhibiting different cell growth and metabolic characteristics, scaled from 3 to 2,000 L bioreactors across four sites. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1146-1159, 2017.