HYDRODYNAMIC BEHAVIOR OF ANIMAL-CELL MICROCARRIER SUSPENSIONS IN SPLIT-CYLINDER AIRLIFT BIOREACTORS

Hydrodynamic characteristics of suspensions of microcarriers used for culturing anchorage dependent animal cells are reported in split-cylin der internal-loop airlift bioreactors. Cell culture media are simulate d using salt solutions that duplicate the ionic strengths of typical m edia. Effects of solids loading (0-30 kg . m(-3)), microcarrier partic le size (150-300 x 10(-6) m diameter) and density (1030-1050 kg . m(-3 )) on gas induced circulation of the slurry, mixing time, gas holdup a nd gas velocity requirements to attain complete suspension of solids a re discussed for two reactors with aspect ratios of 7.6 and 14.5, but equal riser-to-downcomer cross-sectional area ratios of 1.0, aerated a t low air flow rates (0-8 x 10(-6) m(3) . s(-1)) through a sintered gl ass sparger with 110 x 10(-6) m diameter pores. The study covers the r anges of solids concentrations, types, densities, particle sizes and a eration rates that are of relevance in animal cell culture application s. Airlift bioreactors displayed suitable hydrodynamic characteristics for potentially supporting anchorage dependent cell cultures on micro carriers at carrier loadings similar to those that are currently used in stirred tank bioreactors. The minimum gas flow rates and the induce d liquid circulation rates necessary to achieve and maintain suspensio n of the heaviest and the largest microcarriers were well within pract icable limits, limits which have been shown to be withstood by animal cells in non-anchorage dependent suspension culture in airlift bioreac tors. No floatation problems were encountered with the carriers, nor w as sedimentation a problem so long as the identified minimum suspensio n criteria were met. Chisti's liquid circulation equation, originally intended for two-phase flow, applied to the three-phase gas-liquid-mic rocarrier systems.