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Development of a Microgravity Cell Culture Platform for the Study of Bone Cell Metabolism Onboard the NASA Shuttle.    L. Misener, D. Sindrey, T. Smith, S. Pugh, D. Kusljic, P. Kwong.   Millenium Biologix Inc., Kingston, Ontario, Canada; Allelix Biopharmaceuticals Inc., Mississauga, Ontario, Canada.

The study of bone cell metabolism in space has been compromised by the lack of microgravity (µg) hardware that successfully addresses the biological requirements of bone cell cultures in this challenging environment. We have designed a unique cell culture platform (OSTEO^TM), utilizing Millenium's synthetic bone substrate (Osteologic^TM), which supports mineralization by osteoblasts (OB) and resorption by osteoclasts (OC) in µg. To address diverse experimental requirements, including the need for independent control of OB and OC environments, the system was designed to generate 192 data points from 12 independent bioreactors. In evaluating conditions influential in cell culture performance, the most important parameters affecting cell growth were: fluid dynamics, bio-compatible materials, sterility, gas exchange, temperature stability, and physical launch forces. Medical grade plastics were tested for biocompatibility with bone cell cultures. Hematoxylin/Eosin staining of cell monolayers and tetracycline labeling of mineralized matrix showed polystyrene as the most compatible material, followed by polysulfone and acrylic. Sterilization via hydrogen peroxide vapour was adopted to avoid the toxic residues left by ethylene oxide. BMS cells cultured, with and without 5% CO², in open slides and within the closed pathway system, revealed that normal growth and mineralization could be achieved with CO² dependent media without the need for CO² gassing. The culmination of this work has lead to the development of a proven system, operated by astronaut John Glenn on the NASA Shuttle STS-95 in October 1998, for the successful in vitro study of bone cell metabolism in µg conditions.