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 k_L a studies. Mass transfer (k_L 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.